AP630 Improved fruit quality using new handling technology

John Lopresti Agriculture Victoria

AP630

This report is published by the Horticultural Research and Development Corporation to pass on information concerning horticultural research and development undertaken for the apple and pear industry.

The research contained in this report was funded by the Horticultural Research and Development Corporation with the financial support of Global Plastic Systems Pty Ltd.

All expressions of opinion are not to be regarded as expressing the opinion of the Horticultural Research and Development Corporation or any authority of the Australian Government.

The Corporation and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this report and readers should rely upon their own enquiries in making decisions concerning their own interests.

Cover price: $20.00 HRDC ISBN 1 86423 737 6

Published and distributed by: Horticultural Research & Development Corporation Level 6 7 Merriwa Street Gordon NSW 2072 Telephone: (02) 9418 2200 Fax: (02) 9418 1352 E-Mail: hrdc@hrdc.gov.au

© Copyright 1997

WJ HRD\C

HORTICULTURAL RESEARCH & DEVELOPMENT CORPORATION

Partnership in horticulture

Contents

1. INDUSTRY SUMMARY 1

2. TECHNICAL SUMMARY 2

3. INTRODUCTION 3

4. BULK HANDLING METHODS 4

4.1 Field bin handling 5 4.2 Storage in bins 5 4.3 Bin emptying 6 4.4 Distribution using bulk bins 6 4.5 Empty bin storage 7

5. BULK PRODUCE HANDLING OPTIONS 8

5.1 Bulk bin design requirements 8 5.2 Wooden field bins 8

5.2.1 Wood characteristics 9 5.3 Plastic field bins 10

5.3.1 HDPE characteristics 11

6. FIELD BINS, HANDLING AND QUALITY 12

12 12 12 12 13 14 14 14 15 15 17 18 19 20

7. DISTRIBUTION AND HANDLING OF FIELD BINS 22

8. ECONOMIC CONSIDERATIONS 23

8.1 Economic models 23 8.2 Potential economic benefits 24

8.2.1 Initial purchase cost 25 8.2.2 Depreciation and salvage value 25 8.2.3 Maintenance costs 25 8.2.4 Chemical, handling and cooling costs 25 8.2.5 Crop losses 26

6.1 Scope of study 6.2 Handling and maintenance issues

6.2.1 Stacking strength 6.2.2 Durability and service life 6.2.3 Damage and maintenance 6.2.4 Ease of handling 6.2.5 Storage 6.2.6 Safety aspects

6.3 Fruit and vegetable quality issues 6.3.1 Precooling and storage 6.3.2 Humidity and moisture loss 6.3.3 Produce damage 6.3.4 Hygiene and rot development 6.3.5 Other considerations

8.3 Economic analysis: apples 8.3.1 Scope of evaluation 8.3.2 Procedure 8.3.3 Pome fruit operation 8.3.4 Results

RECOMMENDATIONS

9.1 Extension/adoption by industry 9.2 Directions for future research

9.3 Financial/commercial benefits of adoption of

ACKNOWLEDGEMENT

LITERATURE CITED

APPENDICES 12.1 Economic evaluation equations 12.2 Batlow technical workshop paper

1, Industry summary

Utilising improved technology in postharvest handling systems can lead to horticultural produce having better quality and freshness at the retail level. It can also reduce product wastage leading to greater market opportunities and increased profitability for growers and packers. Plastic field bins for horticultural use have been available in Europe for more than twenty years and in Australia for the last five years. In general their higher purchase cost compared to softwood bins has deterred industry from using them. There is evidence to suggest that benefits derived from using plastic bins over the longer term may compensate for their higher initial cost.

Analysis of published literature on plastic bin use and consultation with industry have demonstrated that there are a number of benefits in using plastic bins and disadvantages associated with handling produce in wood bins. Although wood bins have been the standard for many years they do not have all the features necessary to ensure optimum fruit quality and handling efficiency. They absorb moisture, are more easily damaged and have minimal ventilation area. This review determined that plastic bins are closer to the ideal bulk container for fruit and vegetable handling. They are durable, have comparable stacking strength to wood bins and require significantly less maintenance than their wood counterparts. Overseas experience suggests that they have a useful life of two to four times that of wood bins.

A number of studies have shown that handling in plastic bins reduces abrasion damage to fruit during transport, increases cooling rate of produce in storage and can minimise rot development due to pathogens adhering to bin surfaces. There is also evidence to suggest that use of plastic bins will reduce the amount of postharvest chemical used per bin of fruit because plastic does not absorb solution during drenching.

An economic evaluation of apple handling in wood and plastic bins was performed in the United States where some of these benefits were quantified in dollar terms and the long-term average annual cost for both bin types calculated. Using plastic and wood bin cost estimates based on a literature review and grower consultation, an economic model for an average apple production operation in Australia was derived. When costs relating to maintenance, fruit losses, chemical use and cooling were taken into account it was found that the difference in average annual cost between plastic and softwood bins became insignificant over a service life of 18-20 years at current bin prices. Further research and cost data are required to accurately evaluate the potential cost savings of plastic bins for the pome fruit and other horticultural industries that use bulk bins.

Significance of the issues raised in this report will vary depending on the particular industry and on each grower's situation. Plastic bin technology is already established and models are available that have been specifically designed for use in horticulture. Distribution of this review by the industry partner and through grower associations will allow growers and packers to better judge whether they will benefit financially from this new handling technology. This information is also likely to provide an incentive for innovative growers to trial plastic bins in their postharvest operation over a number of seasons to compare bins and determine the potential cost savings for themselves.

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2. Technical summary

A critical assessment of published literature established that very few studies have been performed comparing wood and plastic field bins in terms of handling, maintenance and their affect on the quality of fruit and vegetables. Much of the evidence is anecdotal and supplied by growers who have experience in handling produce in plastic bins. Wood bins used in Australia are generally constructed from softwood panels nailed to triangular corner posts. Ventilation and drainage is provided by spacing the side and base panels about 1 cm apart. When used as part of a bulk container, wood has limitations such as its porosity, rough surface, water absorbing characteristics and low thermal conductivity. Volume changes due to water uptake and drying lead to internal stresses and eventual warpage of softwood panels. Plastic bins are constructed from non-absorbent, UV stabilised, high density polyethylene and have a larger vented area. They are as durable as wood bins and have a higher-strength-to-weight ratio. Overseas experience has demonstrated that four-way forklift entry, positive interlock stacking and deeper fork openings allow quicker handling of produce. Their lighter weight and smoother surface can make them more difficult to handle.

A few studies have compared the affect of wood and. plastic bins on fruit quality and operating costs. A number of other reports provide evidence that plastic bins have benefits that lead to substantial cost savings. Significant quality improvements from use of plastic bins are likely to be achieved for produce that is stored medium to long-term such as pome fruit, onions and potatoes, or for produce that is susceptible to abrasion damage such as citrus. Benefits are also likely for produce with a short shelf-life that needs to be handled quickly and cooled rapidly e.g. stone fruit and sweet corn.

Storage trials with apples has demonstrated that initial cooling is 2 to 3 times faster in plastic bins than in plywood ones. It has also been found that humidity levels are higher in cool stores containing fruit in plastic bins and that moisture loss from apples is less when they are stored in this manner. Assessment of apples after long distance transport in both types of bin showed that abrasion damage was up to 5 times higher on fruit carried in hardwood bins. Significant abrasion damage due to handling in wood bins has also been detected in Valencia oranges and papaya fruit. Wooden surfaces of fruit bins are an important source of decay pathogens for fruit and vegetables. Studies have found that removal of fungi from porous bin surfaces is difficult and that sodium hypochlorite, a common postharvest disinfectant, is more effective on plastic surfaces than wood. Research has also demonstrated that up to 9 litres of chemical solution during drenching can be lost for every bin of fruit due to the absorption of solution by the wood bin. This leads to dilution of drenches and dips and the need to top them up, thereby increasing the amount of chemical used.

Estimates in operating costs using wood and plastic bins in an average Australian apple orchard showed that wood bins were approximately $6 more expensive than plastic ones due to increased maintenance, chemical usage, disinfestation, cooling and waste. An economic model was established based on these estimates and demonstrated that the average annual operating costs of plastic bins fell below those of wood bins after about 18 years of service.

Further work is required to quantify benefits of plastic bins in dollar terms. Accurate economic models are required for the major horticultural industries that will allow estimation of differences in annual cost when using wood and plastic bins over their respective service life.

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$, Introduction

Containers are a basic and vital element in the distribution of horticultural produce. Properly designed containers can reduce wastage and improve the quality and freshness of produce reaching the consumer. In practice, growers usually seek a trade-off between the cost of packaging and the likely increase in return which may be achieved for higher quality produce (Sayers & Sneddon, 1986). Wooden bins have been the standard in the tree fruit, potato and vegetable industries for many years where they are used in harvesting, packhouse, storage and transport operations. Although they have high strength and are relatively inexpensive they can also be inherently damaging to delicate produce and have the potential to harbour pathogenic fungi and pests. Other problems associated with the use of wood bins include high moisture retention, poor storage space utilisation and high labour costs during maintenance. The Australian industry is very aware of the need to reduce waste and increase product quality. One possible approach in achieving these objectives is the use of new hardware such as plastic bulk bins in the postharvest handling chain. With increasingly strict domestic and export market requirements comes the need to place a greater emphasis on reducing quality loss during postharvest handling and distribution. The pome fruit, stone fruit, fresh tomato and other industries currently using field bins need to consider utilising the most suitable handling equipment so that they can successfully compete with other producers.

This project aims to provide industry with comprehensive guidelines regarding the adoption of plastic bin technology based on a critical review of information concerning their use. This will be achieved by:

(1) critically analysing and assessing information published in industry journals and scientific literature, and gathered from plastic bin suppliers; (2) consultation with relevant industry sectors regarding plastic bin technology; (3) comparison of advantages and disadvantages in using plastic and wood bins in terms of quality and handling; (4) determining if changes in procedures and equipment are required to allow integration of plastic bins into current handling systems; (5) economic evaluation of long-term use of plastic and wood bins in Australia.

Dissemination of this information will increase industry awareness of the potential for plastic bins to improve quality and will also enable individual growers and packers to make an informed decision about the suitability of this technology for their own operation.

The scope of this project is limited to the analysis of bulk field bin usage in postharvest handling of fruit and vegetables. The focus will be on crops where information is readily available such as pome fruit, stone fruit and citrus. It is intended that this report be relevant to some of the largest horticultural industries in Australia, including pome fruit, citrus, stone fruit, potato and tomato. Where possible, differences in quality obtained using different bin types have been quantified but in some instances this has been limited by the number of studies completed and published. Only the general features of plastic bins are considered in this report and no comparisons are made between the various models currently marketed. An economic evaluation has only been performed for field bin use in the pome fruit industry due to a lack of appropriate data concerning handling costs and wastage in other sectors.

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4. Bulk handling methods

Since the 1970's bulk bins of 200-500 kg capacity have been used in Australia during harvesting, handling and storage of many fruits and vegetables. These have almost totally replaced 10-30 kg capacity wooden field or Tug' boxes. Bulk bins are much more economical than field boxes, both in terms of crop carried per unit volume and durability, and also give better protection to the product (Devine, 1981; Peleg, 1985; O'Brien, 1964; Steer, 1970). Other benefits include reduced labour costs, improved product quality and savings in costs of containers, transportation and storage space (Smith, 1976; Blandini, 1982). Bin handling also has the advantage of being adaptable to manual or mechanical harvesting, and facilitates the movement of large quantities of produce using trailers and forklifts. The general movement and use of bulk bins in postharvest handling operations have been described for the apple and citrus industries (Figure 1 and 2).

General bin handling process - Apples

Bin

storage

o Transport to

orchard

Bin

unloading

Bin

disinfestation

Bin

disposal

Bin fill

Bin pick-up

N. Transport

/(trailer or truck)

No

Bin

replacement

Receival

(packing shed)

Bin inspection

& maintenance

o Bin tip or

water flume

Empty bin

Transport to

drench/dip tan

Bulk drench

or dipping

Fruit storage

in CA (bulk bin

General bin handling process - Citrus

Figure 1. General movement of field bins Figure 2. General movement of field in the postharvest handling of pome fruit. in the postharvest handling of citrus.

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4.1 Field bin handling

Most fresh market fruits are harvested by hand into buckets or bags, which are then emptied into field bins for subsequent handling (Mitchell, 1992a). Many vegetable crops are harvested directly into bulk bins in the field while some crops such as processing tomatoes are mechanically harvested into field bins. Potatoes and onions are usually transported from the field in bulk trucks or bins and may be cured in bulk bins or curing rooms.

A combination of methods is used to transport bins to and from the field depending on the distances between the field or orchard and packhouse and the space available between plantings or rows of trees. Empty bins can be loaded onto flat-bed trucks or tractor-drawn trailer platforms using fork lift equipment. If trailers are used then bins can be taken directly to where harvesting is taking place and in most cases do not have to be unloaded off the trailer. This avoids unnecessary risk of soil contaminating bins that can lead to fruit infection.

Fork lift attachments, mounted on general purpose tractors' three-point hitches and operated by the tractors' hydraulic system, are more economical for handling bins in the field or orchard, enabling the tractor to perform other tasks when not transporting bins to the packhouse or loading them onto trucks (Peleg, 1985). Large forklifts that can carry up to 3 full bins are commonly used in the citrus industry as well as five-bin trailers with straddle carrier systems that are capable of loading and unloading field bins hydraulically from ground level (Alsoboh & Moore, 1996).

It is generally better to transport a large load slowly than a relatively light load more quickly. Front and rear fork lift attachments on a tractor can be used for direct transport from the field or for loading trailers or trucks. Where the distance between the field and packhouse or store does not exceed 500 metres the bins may be carried directly on the tractor forks (Devine, 1981). Many of the larger fruit growers are using specialist equipment such as bin trailers that can carry up to 12 bins per trip.

After full bins are unloaded, empty bins from a pool are loaded onto flat trucks or tractor-towed trailers, for return to the orchard or field for another haul.

4.2 Storage in bins

When bulk bins are used instead of field boxes, the volume of fruit it is possible to put into a store rises by at least 15% (Devine, 1981). Freshly harvested produce in bulk bins is commonly unloaded and handled in the packhouse using fork lift equipment. Full bins are usually stacked to await either: (1) Precooling before crop is fed onto the packing line; (2) Accumulation of enough produce to begin packing operations; (3) Interim storage in cool rooms which can be from several days to several weeks depending on market requirements; (4) Long term storage in controlled-environment stores e.g. potatoes and onions, or in CA stores e.g. pome fruit.

Several cooling methods are available for use with horticultural crops. Those most commonly used for produce in field bins are room cooling, forced-air cooling and hydrocooling. Postharvest chemical application to fruit using dump tanks or drenches is usually performed in field bins before transport to the packingline, cool room or CA store. Vegetables may also be disinfested by similar systems using sodium hypochlorite.

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4.3 Bin emptying

From interim storage or long term CA storage, produce is fed onto the packing line by either of two methods: (1) Wet feeding (or hydrohandling) immerses full bins into a tank of water where the crop gently floats out of the bin thereby minimising damage; (2) Dry feeding involves tipping bins directly onto a conveyor belt for transfer to the packing house process (Devine, 1981). The former method is primarily suitable for bruise sensitive fruit such as apples and avocados, and for many fragile vegetables. In comparsion dry feeding can be used for less sensitive produce such as citrus, pears or some stone fruits which should not be wetted (Peleg, 1985).

Older hydrohandling systems are manually operated and submerge one bulk bin at a time (Pflug & Dewey, 1960; Clarke, 1996). Modern hydrohandling systems utilise automatically controlled hydraulic bin submerging equipment (Mitchell, 1992a; Dewey et al, 1972). In this process a forklift is used to feed full bulk bins stacked one or two high onto a roller conveyor. The cycle of grasping a full bin, bin submersion as it travels along a conveyor, empty bin removal after the fruit has floated away and empty bin expulsion is completely automatic. Control is by microswitches which sense the position of the bin in the cycle and microprocessor logic control of the appropriate hydraulic cylinders (Stout et al, 1966; Peleg, 1985). Pumps circulate the dump-tank water to move the free-floating fruit toward the processing line. Usually, dry feeding systems use a simple hydraulically operated bulk bin tipping mechanism. Full bins are fed onto a roller conveyor and either manually or automatically tipped onto electronically-controlled delivery belts that can adjust crop flow to the sorting line (Mitchell, 1992a). Dry dumps are normally designed so that the bin is covered with a padded lid, then inverted, and fruit is delivered through a controlled opening in the lid (O'Brien et al, 1983). Other systems simply tip the fruit quickly out of unlidded bins. Potatoes and onions may be tipped directly out of bins into a feed hopper using a forklift for inversion.

4.4 Distribution using bulk bins

Sometimes full bulk bins are transported long distances by truck from the field or storage area to a packing house when a number of growers use a large cooperative packing house. Occasionally bulk bins are used as shipping containers for fruits and vegetables going to terminal market warehouses to be sold in smaller units or to be repackaged in consumer packs. A survey of Australian apple growers found that wood bins represented 9% of packaging used for distribution in domestic and export markets (Meyers Strategy Group, 1995).

Bulk bins may be refilled with fruit before bulk transport to market or after presorting and presizing for CA storage. Many vegetables are filled into bins manually while less sensitive crops such as citrus are filled from fruit accumulators at the end of the packing line. Automatic bin fillers that gently lower fruit into bulk bins using vertical conveyors are generally used for apples.

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4.5 Empty bin storage

At the end of harvest season, or once they have been emptied after cold or CA storage, bins are usually inspected for damage and either maintenance or disposal are carried out if necessary. Many growers also disinfest their bulk bins using pressure washing in conjunction with disinfectants or hot water. The frequency and extent to which individual growers go through this process depends on factors such as crop type and the level of wastage due to rots and spoilage incurred.

Empty bins are stored out of season either in cold stores that are not in use or stacked in the open on soil or a concrete slab. They are often stacked up to ten high in a tight pattern to minimise the storage space required. In some cases an overhead roof is constructed over the storage yard to protect bins from the weather although this is generally not justified economically (Devine, 1981).

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5. Bulk produce handling options

5.1 Bulk bin design requirements

Bulk bins must be designed and manufactured to meet a wide range of requirements which can be summarised as follows:

(1) allowance for easy and efficient handling; (2) sufficient mechanical strength to protect crop during handling, transport and while stacked; (3) meet handling requirements in terms of shape, size and weight; (4) material of construction must be impervious to foreign matter and not contaminate the crop; (5) allow maximum ventilation area for cooling; (6) have sufficient drainage area; (7) and be designed to minimise quality loss in crop.

5.2 Wooden field bins

Pallet-based wood bins are the most common type of bulk container used in Australian horticultural industries. These are mostly manufactured from softwoods such as plantation pine (e.g. Pinus radiata) which is sourced from saw mills or timber processors such as CSR Softwoods P/L, Mount Gambier. Field bins may be constructed by these companies or by others, including growers. Many older bins still in use are constructed from hardwood such as Eucalyptus spp. and have metal reinforcing along each outside edge to strengthen the bin. This bin type is commonly used by citrus growers. Plywood bins are a more expensive option and aren't generally used in Australia but are common in other countries such as the United States. It is estimated that over 750,000 bins are required to store Australia's annual apple crop, while the citrus industry uses about 500,000 bins. Most growers own or use under 3,000 bins per season. At present the abundant supply of pine makes field bins inexpensive but in the medium to long term this may not necessarily be the case. Although they are the standard in the pome fruit industry, only 12.6% of growers rated wood bins as "very good packaging' (Meyers Strategy Group, 1995), demonstrating some disenchantment with this type of bulk container.

The majority of bins used in Australia have a square foot print (base) but in some regions such as Batlow, rectangular bins are the standard. This allows nesting of empty bins inside one another and reduces transport costs. Bin base dimensions are usually standardised according to prevailing vehicle dimensions. Standard pallets in Australia have dimensions of 46" x 46" (1160 mm) and bin sizes may range from 1000 mm to 1200 mm per side. Bin depth is determined by the type of crop handled. Citrus, potatoes and other root vegetables may be packed up to 70 cm high; pears, apples and tomatoes filled to a depth of 60 cm while stone fruits are usually not filled over 40 cm i.e. half-bins are used. A standard bin usually has an overall height of approximately 80 cm with a maximum filling depth of 60-70 cm. Bin volumes can vary significantly but are usually in the range of 650-800 litres. This means that a standard bin can hold around 500 kg of fruit.

Wood bins are usually constructed from softwood side panels (approximately 17 mm thick) that are nailed to triangular corner posts. The base is similarly made up of panels nailed at

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right angles to three thick base blocks that run the length of the bin. Corner posts provide improved stacking strength and prevent pinching of fruits in the corners of the bin.

In many instances the internal side and base panels are planed smooth and board edges rounded off to prevent damage to fruit. These precautions are often taken when bins are used to harvest and handle stone fruit. The use of metal brackets and corner braces is usually avoided in the construction of new soft wood bins. Galvanised nails are generally used in their construction.

Adequate ventilation and water drainage are provided by spacing the side and base panels about 1 cm apart. Devine (1981) suggests that ventilation apertures equivalent to 4-6% of the basal area are adequate to allow satisfactory cooling of pome fruit. Separate plastic liners are sometimes installed inside bins to minimise abrasion damage to fruit during transport but they can cause problems where side venting is required for cooling, or where water dumping is practiced (Mitchell, 1992b). Bin weight can vary but is generally 60-80 kg for a standard size bin. Water take-up during packhouse operations can increase the net weight by as much as 8%.

5.2.1 Wood characteristics

The behaviour and durability of wood bins is determined by the material of construction which is usually softwood or hardwood rough-sawn timber. An understanding of the structure and characteristics of wood is required to appreciate it's benefits and limitations when used in the postharvest handling chain. Wood is botanical in origin and so there is both consistency and variety in it's structure. The microscopic structure is complex and consists of fibres made up of cellulose. The directional properties of wood are attributable to these fibres. Wood is porous and hydroscopic, absorbing water in its pores and adsorbing it on the fibres in its cell walls, where it induces volume changes. These volume changes are not uniform and often lead to internal stresses and to warpage. Up to a certain point an increased moisture content can increase thermal conductivity and lower the strength and elasticity of wood. Knot holes are common in sawn timber and may have a pronounced effect on the strength of the board depending on their location. Wood strength is affected by moisture content but not by temperature. It has high strength in the direction in which fibres are aligned (longitudinal strength). This strength in tension is usually 20 times the radial and tangential strength. The thermal conductivity of wood is low compared to other materials including high density polyethylene but this is a disadvantage when cooling produce as it slows the process.

Under favourable conditions, such as a dry environment, wood can retain its characteristics for many years. The conditions encountered during postharvest operations, such as water drenching, hydrocooling and bin storage in the open, are usually far from ideal and can affect the durability of wood field bins. When the surface of unprotected dry wood becomes wet, it swells and introduces compressive stresses in the surface layer. With subsequent drying, the wood in this surface layer contracts, opening up microcracks. Repeated wetting and dryings accentuate this cracking into deep checking with eventual loss of surface fibres. Weathering by ultraviolet radiation from of sunlight leads to breakdown of cellulose in the surface fibres and to loss of mechanical properties such as strength. In some instances wood decay may occur due to biological action of fungi on the cellulose, particularly if the moisture content of the wood remains saturated i.e. above a moisture content of 30%, for an extended period of time (Van Vlack, 1982).

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5.3 Plastic field bins

Plastic bulk bins have been used in Europe for over 20 years for harvesting and handling of fruit and vegetables (Coster, 1973; Knoll, 1974; Engel, 1975). Bins imported from overseas have been available in Australia for over five years and recent increased interest in the use of plastic field bins has also lead to their local manufacture. Virtually all plastic bins for horticultural use are manufactured from recyclable, UV stabilised, food grade high density polyethylene (HDPE). Manufacturers are rapidly introducing new models that have a number of designs and incorporate features not found in wood bins. These differences can include:

• Various wall and base designs • Different dimensions, height and internal capacities • Larger ventilation and drainage area • Two-way or four-way forklift entrance • Rigid, collapsible bin or knock-down containers • Label plates, card holders and ID tags • Non-skid feet • Tapered side walls

Bins designed for horticultural use are usually manufactured using high pressure injection moulding techniques. This process involves the uniform injection of hot plastic by either screw or hydraulic plunger into a closed die which is a split mould that contains the negative contours of the product to be made. Injection moulded bins can be designed to incorporate intricate features and characteristics but the tooling is expensive and custom moulding can only be justified if a considerable quantity of containers is involved (Sayers & Sneddon, 1986). In general plastic bins are rigid moulded containers constructed with double wall corners and centre posts. Side walls are also strengthened by a number of ribs running horizontally just below the top of the bins (Figure 3). Most models allow for four-way forklift entry and positive interlock stacking. Collapsible and knock-down bins are also available such as the AgBin 4848 (Perstorp Xytec, Inc.) which can reduce space used during out-of-season storage and transport by up to 60% f Plastic containers that collapse easily', 1995). Half-bins are also available for use with stone fruit. Ventilation and drainage holes ranging from 6-10mm are usually incorporated into the side walls and bin base. General plastic field bin specifications are listed in Table 1.

Figure 3. Design features of a plastic field bin (Perstorp Plastic Systems P/L).

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Table 1. General plastic field bin specifications and tolerances .

Material: High density polyethylene; UV stabilised, 100% recyclable, inert & non-absorbent

Operating temperature: -40°C to 60°C

Weight: 30-45 kg

Approvals: FDA & USDA (in the USA), AQIS

Maximum static load: 3,500 - 6,000 kg i.e. 6 to 12 full bins in storage

Forklift entry: 140-155mm

Volume: 680 - 750 litres Specifications will vary within these ranges depending on bin design.

5.3.1 HDPE characteristics

High density polyethylene (HDPE) is a crystalline thermosetting plastic that has acceptable heat tolerance, a high strength-to-weight ratio and good impact resistance (Sayers & Sneddon, 1986). Carbon fillers and UV stabilisers provide resistance to weathering and sunlight. It's thermal conductivity is approximately five times that of pine and it is inert and resistant to most chemicals including hypochlorites when they are used below 60°C (Krisher & Siebert, 1987). The behaviour of HDPE is highly dependent on operating temperature. At low temperatures the material is relatively brittle, rigid and hard, and at high impact loading behaves elastically. High temperatures e.g. greater than 100°C, can lead to softening, and sustained loading at these temperatures can lead to permanent deformation (Van Vlack, 1982). Postharvest operations such as handling and storage are in all but the most extreme cases performed within the service temperature of HDPE.

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6, Field bins, handling and produce quality.

6.1 Scope of study

In this section a critical assessment will be conducted on the benefits of using plastic bins in the postharvest handling of horticultural produce. This assessment will focus on issues such as ease of handling, maintenance requirements and maintaining crop quality. The analysis will be based on interviews with growers and bin suppliers, and on a review of published information including industry articles, research papers and other relevant material. Anecdotal evidence from growers who have experience with plastic bins will also be referred to where appropriate. Information regarding use of plastic bins in horticultural industries is relatively scarce and mainly focuses on pome fruit and citrus.

6.2 Handling and maintenance issues

6.2.1 Stacking strength

Static loading of bulk bins originates primarily from top to bottom stacking forces when containers are stored on top of each other. High stacking is desirable for maximum utilisation of storage and transportation space. Moulded plastic bins have a higher strength-to-weight ratio than wood bins. They are aproximately 50% lighter but can support a static load comparable to wood bins. Unlike wood bins their stacking strength is dependent on temperature but in cold storage (i.e. below 7°C) they are designed to stack 9 to 12 high filled with 500 kg of fruit. This is equivalent to a maximum static loading in CA storage of approximately 6,000 kg. This compares favourably with a stack number of 6-10 bins which can safely be achieved using standard wood bins. At ambient temperatures the maximum stack height is 6-8 high (Anon.,1997a; Anon., 1997b; Anon., 1996).

6.2.2 Durability and service life

Bulk bins for produce harvesting are usually subjected to extremely rough handling. They may be filled on uneven ground, carried over bumpy terrain, rolled off trucks, bumped against each other and immersed in water or drenched during packhouse operations (Peleg, 1985). Structural strength and durability is extremely important in ensuring crop protection and overall longevity of bulk bins. These are functions of construction material and bin design. Some concerns have been raised about the durability of plastic bins in comparison to wood bins. European grower experience suggests that the useful life of plastic bins may be as high as 15-20 years whereas most wood bins are likely to last for 5-8 years ('Stacking up the savings', 1995). This will depend on the industry involved and the amount of cycling i.e. movement of bins from orchard to packhouse or processor, which can be as high as 50 times per year in the citrus and stone fruit industries (Waelti, 1992).

Although wood bins have relatively high stacking strength their durability is compromised by variation in moisture content and structure in the timber from which they are constructed. Knot holes, cracks and nail joints are weak points in a bin and these reduce its overall durability. Timber boards vary in dimension at right-angles to the line of the grain according to moisture content of the timber. For a width of boards totalling 525 mm nailed to corner posts 525 mm long, the increase in board width can be as much as 10 mm whereas the posts remain the same length. When bins are stacked in this condition, loads are transmitted through the side boards and not the corner posts until they either crack or the nail joints fail (Devine,

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1981). Softwood timber used in bins is prone to splitting, warping and splintering with age, particularly if stored in the open. Timber expands and contracts with prolonged use due to moisture and temperature changes which may also loosen nails and thereby weaken the structural integrity of the bin (Van Vlack, 1982). Water retention caused by drenching and dumping operations over a number of years increases the potential for this deterioration.

In the past plastic bins were fragile, often cracking, deforming or failing in the field or during storage due to inadequecies in the materials used to manufacture them (Knoll, 1974). Current models are specifically designed for agricultural purposes and under normal circumstances would be expected to have comparable or better durability than wood bins. In theory, plastic bin structural strength is unaffected by sunlight or rain. Most models are UV stabilised and HDPE is an inert, impervious material that does not absorb water. A plastic bin is a moulded, one-piece unit so stresses due to thermal expansion and contraction are spread fairly evenly throughout the bin and structural integrity should remain intact (Van Vlack, 1982). Although 20 year old bins are still used in Europe it has not been verified whether their structural strength has remained unchanged over this period. Experience there indicates that most of these bins are in good condition even though many were constructed from structural foam which has less strength than the HDPE used at present (Waelti, 1995).

6.2.3 Damage and maintenance

The incidence and severity of damage to wood bins will vary with the number of times they are used every season and the horticultural industry in which they are utilised. For example, bins in the citrus and processing tomato industries are in use for a large part of the year, the many movements from the field increasing the likelihood of them requiring some form of maintenance or even replacement at the end of the season. The majority of wood bins will require some maintenance during their service life. Major repairs usually include replacement of broken, cracked or warped side or base boards, and refixing of loose boards. It is difficult to determine the number of wood bins in the fruit and vegetable industry that need repair annually as it will vary widely among growers and crops. It is likely that this figure will range between 5-15% ('Bin survey', 1997). Factors such as rough handling e.g. impacts with other bins or forklift tines, outdoor storage and greater bin age are likely to increase the number of units that need repair.

Overseas experience suggests that plastic bins are more durable and have good impact strength (Cox, 1995). Unlike wood bins the most likely type of damage they will experience is abrasion, puncturing or deformation due to, for example, impacts from forklifts during handling. In severe cases cracking may occur that can sometimes be repaired by heat welding. Impact transmission is more evenly distributed in plastic bins than in wood bins due to their construction and uniform structure of the HDPE. Damage to plastic bins is generally quite minor so that in many instances they will not require maintenance and fruit quality will not be affected. In comparison fractures and splintering of wood bins is much more likely to damage produce and to be a safety hazard. The costs of maintaining field bins will be discussed in chapter eight. Growers in the USA have found that about 3 in 1000 plastic bins need annual replacement (Cox, 1995). In Australia wood bin replacement per annum can be as high as 100 in 1000 for processors and anywhere below this figure for growers and packers (Mills, 1997).

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6.2.4 Ease of handling

Another advantage of plastic bin use is increased efficiency in crop handling. Overseas experience has demonstrated that four-way forklift entry, positive interlock stacking and deeper fork openings on bins allow quicker handling of fruit in the packhouse (Acuff, 1995; "Stacking up the savings', 1995). Positive base-to-top interlocks allow quicker stacking of bins into secure, self-supporting columns. This feature combined with the consistent shape of plastic bins, due to straight side walls, has been found to allow easier loading of trucks and more rapid filling of CA rooms. The large number of drainage holes in plastic bins also leads to quicker throughput of full bins in water dumps because they can be immersed and drained more rapidly than their wooden counterparts. This is because plastic bins have approximately 25% more openings.

Due to their lighter weight and tendency to be more slippery (due to a smoother surface), full plastic bins can be more difficult to handle on forklifts and trucks. Operators may need training to become accustomed to plastic bins. It has been suggested that rubber sleeves, welded cross beads or a tacky coating on forks will prevent slipping during forklift handling. Full plastic bins stacked four high can be carried, on flat-bed trucks due to both positive interlocking and their lighter weight, but it has been found that better tie-down may be needed to avoid bin shifting (Chase, 1995). Another problem noted by some United States growers is that wood and plastic bins cannot be stacked together. Gradual change over from wood to plastic may also be difficult as handling equipment may require retooling to accommodate plastic bins (Warner, 1993).

6.2.5 Storage

In storage plastic bins can be stacked more accurately and higher than wood bins due to positive interlocking (Batlow grower, 1996). To an extent plastic bins can also solve the problem of dead air space left between wood bins in storage. It has been calculated that tighter stacking of plastic bins can increase available floor space by about 16% (Staples, 1994). This is based on a gap reduction between bins of 20 cm. Closer stacking is possible due to the better ventilation achieved through the side walls and floor of plastic bins. Vegetable packers have noted that improved air flow during curing meant that onions dried in about 8 hours rather than the 12 to 24 hours required in wood bins ("Stacking up the savings', 1995).

It has been noted by some growers that plastic bins hold less fruit than wood bins with the same external dimensions (Dodds, 1996). This may be due to a number of factors. Side panels of plastic bin walls can be up to 2-3 times thicker than wood side boards (50-80 mm as compared to 20-25 mm) which reduces internal volume. Thicker walls are required to allow for positive interlocking of stacked bins and to increase structural strength. Bin wall design may also contribute to a marginally reduced internal capacity.

6.2.6 Safety aspects

With respect to occupational health and safety of workers, plastic bins have several advantages over wood bins. Most importantly plastic bins are much more secure when stacked. However, the lighter weight of these bins also means that more care needs to be taken when moving them by forklift ("Wood vs plastic bins: Making a choice', 1995). Slower speeds will reduce the possibility of accidents. The likelihood of worker injury due to contact with broken timber boards, rusty nails, splinters, sharp corners or metal reinforcing is eliminated

14

when plastic bins are used. Distortion of softwood bins after prolonged use can make them unsafe to stack ('Box design - plywood versus softwood, 1996).

6.3 Fruit and vegetable quality issues

Although plastic bins have been used in Europe for over 20 years little published information is available comparing the quality of fruit and vegetables when handled in wood and plastic. The horticultural sector generally acknowledges that using plastic bins is likely to improve produce quality ('Bin survey', 1997). Crop quality will depend on the interaction between the type of bulk container used and the produce handled. Factors such as the type of transport used and storage environment are also important. More specifically the type of bin used will influence the amount of moisture loss from produce, precooling rate, and losses due to fruit damage and rot development. Significant quality improvements resulting from use of plastic bins are likely to be achieved for produce that is stored long-term e.g. pome fruit, onions and potatoes. Benefits are also likely for produce with a short-shelf life that must be handled quickly and cooled rapidly such as stone fruit and sweet corn.

6.3.1 Precooling and storage

Good cooling and temperature management practices are critical in lowering the rate of physiological deterioration of fruit and vegetables. Many crops benefit from prompt, thorough cooling which limits decay, moisture loss and ensures maximum storage life (Mitchell, 1992b). Precooling and cool storage are separate operations that have vastly different requirements. In air-cooling systems, the refrigeration capacity and airflow rates needed are much greater during cooling than during storage. High relative humidity, essential in avoiding excessive water loss during long-term storage, is of lesser importance during rapid air cooling. The type of field bin used is probably more important during precooling as it may affect the cooling rate, air circulation and temperature uniformity in the load. Cooling fruit in such containers requires a system that facilitates good coolant penetration through the fruit mass (Mitchell, 1989).

Fast initial cooling may be carried out using room cooling, forced-air cooling, hydrocooling and vacuum cooling depending on the commodity and capital investment. Room and forced-air cooling are the most commonly used systems. Studies on apples have demonstrated that for most varieties rapid cooling is beneficial in preserving texture, firmness and juiciness (Blanpied & Smock, 1982). It has not been established whether faster cooling leads to economically significant quality loss in apples after long term CA storage. But it has been found that a delay of 24 hours at 21°C after harvest will take 7-10 days off the potential storage life of apples at 0°C (Schomer, 1965). The large dimensions and low ventilation area of wood pallet bins (i.e. 4-6% of basal area) (Divine, 1981) result in much of the product being remote from the top or side of airflow surfaces. This allows little opportunity for cold air to penetrate into the bin in normal room cooling operations (Mitchell, 1992b), which means that the majority of cooling in wood bins is through the slow process of heat conduction from the produce to the bin surface (Bazan et al, 1989).

Two seasons of Golden Delicious storage has demonstrated that initial cooling is 2-3 times faster in plastic bins than plywood ones but quality ratings at out-turn were similar for fruit stored in both types of bin (Chase, 1995). Temperature recorders were put into the centers of six bins in specific locations in two identical rooms, one with wood bins and the other with

15

plastic bins. Half-cooling time for the two rooms was determined after the recorders were retrieved at the end of the storage season (Figure 4) (Waelti, 1996).

30

25

20

15

10

Half-cooling time (hours) % weight loss

Bin type • Plywood bin • Plastic bin SFruit in softwood bin •Fruit in plastic bin

2.5

1.5

0.5

92/93 season 93/94 season Air storage

Figure 4. Comparison of half-cooling times for Golden Delicious apples CA stored in plastic and plywood bins (Waelti, 1996) {Left). Comparison of weight loss in 'Aroma' apples stored in plastic and softwood bins in air for 6 weeks at 2-3 °C (Ericsson & Tahir, 1996) (Right).

Softwood bins have a slightly larger ventilation area than their plywood counterparts and so these results are only a guide and further research is required to confirm these findings under local conditions. Plastic bins generally have a larger ventilation area than wood bins i.e. approximately 25% greater, and more air circulates through the bin and fruit. Tight stacking enhances the cooling process further by forcing the air to circulate through the fruit and not just over the bin surface. This isn't usually possible with wood bins as they may vary in construction so that vents and forklift openings do not match when they are stacked (Kasmire, 1992). Variations in size may also lead to some spaces between bins being partially blocked, leading to dead air zones, with resultant higher temperatures (Patchen, 1971; Ryall & Lipton, 1959). One side effect of tightly stacking plastic bins is possible higher initial moisture loss from produce. In most cases this is not a problem as faster cooling results in reduced total moisture loss over the whole storage period (Blacker, 1989). Return air may be warmer when bins are tightly stacked, and there may be more frost build-up because of the moisture picked up by the air as it moves through the bin ("Wood or plastic ?: Its just not a matter of price', 1995).

Bin venting and stacking requirements are critical for effective forced-air cooling of produce as cold air must be able to pass through all parts of the container. The standard size and construction of plastic bins enhances field heat removal by enabling accurate stacking of bins so that vertical vent slots and forklift openings match (Mitchell et al, 1972). The major advantage of hydrocooling produce in plastic bins rather than wood ones comes from quicker

16

cooling and faster throughput which is possible when bins are stacked two to three high due to more efficient flow of cold water through the stack (Pflug et al, 1970).

6.3.2 Humidity and moisture loss

The humidity of air in storage rooms directly affects the keeping quality of products held in them. If humidity is too low wilting and shrivelling are likely to occur in most fruit and vegetables. Some products can show visual signs of moisture loss after loss of just 3 to 5% of their initial weight. Weight loss is cumulative from time of harvest until consumption, therefore even limited water loss during storage can result in clearly apparent shrivel, particularly in pome fruit, stone fruit and some vegetables (Mitchell, 1992b). For example, if weight loss exceeds 2.5% in pears and 3.5% in apples the fruit develops a wrinkled appearance, is less crisp, and invariably sells at a discount price (Little & Holmes, 1997). High humidity is also beneficial for wound healing and periderm formation during curing of certain crops. High relative humidities are recommended (85-95% RH) during cool storage and curing for most crops (Hardenburg et al, 1986).

It is generally agreed that wood bins in cool storage absorb moisture from the air and thus reduce the relative humidity in the store (Divine, 1981). For example, it is estimated that during long term C A storage of pome fruit, each bin can absorb up to 6 kg of water from the air and fruit (Little & Holmes, 1997). Only one published study is available comparing humidity levels in cool rooms. Golden Delicious were stored in long term CA in plastic and plywood bins and it was found that relative humidity levels were up to 5% lower in the plywood bin rooms, especially during the initial cooling period (Waelti, 1996). A similar or even greater reduction in relative humidity may be likely using softwood bins as they can be expected to absorb more moisture than plywood bins. Weighing of bins in and out of storage indicated that fruit in plastic bins lost 22% less moisture than that in plywood bins but the results were not significantly different (Waelti, 1996). Weight loss in "Aroma' apples stored in wood bins for 6 weeks in air at 2-3°C was found to be 2.5% as compared to 1.7% for fruit stored in plastic bins; a 30% difference (Figure 4) (Ericsson & Tahir, 1996). Plastic bins can also be useful for storage of cabbage as it wilts quickly if held at below 90% RH (Parsons et al, 1960). Their use will prevent moisture absorption from the crop and air, and replace the need for plastic liners that are commonly used in wood bins.

Produce in dry bins after harvest may be dipped or drenched in a postharvest chemical, or hydrocooled using cold water. In some cases growers use the water absorbed by wood bins during these operations to raise the relative humidity in cool rooms. This also prevents absorption of water from fruit by dry boxes (Pieniazek, 1942). This is a haphazard method of maintaining high humidities for medium to long-term storage because once the bin's free moisture has been released, water absorption from the fruit and air will again be a problem. Little and Holmes (1997) also suggest that for apples a high initial relative humidity during cooling is not crucial and that it is important to maintain the relative humidity at 80% during storage. When using plastic bins, some water droplets will remain on the bin surface after dipping and will be taken up by the air in storage so that the relative humidity may still be adequate. Other systems can also be used to maintain high humidities when using plastic bins including mechanical humidifiers, fog spray nozzles and flooding of room floors with water.

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6.3.3 Produce damage

Research has shown that the construction, condition and type of wood finish on field bins can have an effect on produce quality. The most common type of damage in bulk bins is abrasion or vibration bruising when fruit moves or vibrates against rough surfaces or other fruit during transport (Mitchell, 1992a). Damage levels encountered will depend on road surface, type of suspension on trailer or truck and condition of bin surfaces. Poorly maintained bins that rattle and vibrate during transport and that are made from rough-sawn timber can cause bruising and abrasion on fruit (Maindonald & Finch, 1986; O'Brien et al, 1980; Burton et al, 1989; Pang et al, 1995). Armstrong et al, (1992) found that plywood bulk bins generally caused less bruise damage to apples than did hardwood bins. Plastic bins, plywood bins, and sanded or plastic-lined wood bins have smoother internal surfaces than sawn hardwood or softwood. Frequent washing, water dumping or hydrocooling can further increase the surface roughness of wood bins and subsequently increase abrasion damage (Mitchell & Kader, 1989). Sargent et al, (1987) also found that transport in wood bins from the orchard to the packing line could increase bruising. This occurred due to the springing of boards in the base of bins exacerbated by fork lifting with short tines.

Grower experience in the USA suggests that smooth plastic bin surfaces reduce abrasion damage during fruit transport from the orchard. Less damage has been observed after pome and stone fruit has been handled in plastic as compared to wood bins but this has not been quantified (Cox, 1995; Warner, 1993). It has been determined that during harvesting operations using wood bins more than 30% of Valencia oranges were damaged at bin sides and 50% at the bin bottom layer as a result of direct contact between fruit and internal surfaces (Alsoboh & Moore, 1996). This could lead to increased moisture loss from the damaged fruit surface and increased fruit decay during storage. In another study mechanical injury during handling of papaya fruit was found to be caused by abrasion and puncturing of the fruit against the sides of field bins. Fruit taken from the centre of bins had no skin injury. It was concluded that the use of plastic liners could significantly reduce abrasion damage (Quintana & Paull, 1993). Early crop potatoes have immature skin that is easily abraded. Severe skin loss may lead to rot development in storage (Rose & Cook, 1949). In this case the handling of potatoes in plastic bins would significantly reduce this type of damage and thus the potential for crop loss.

The level of bruising and abrasion in Golden Delicious apples transported by semi-trailer using plastic and hardwood bins has been studied in the USA by Timm et al, (1995). This apple variety was selected because bruises and abrasions are easy to see. Two hardwood bins and four plastic bins were used in the transport tests in conjunction with two different suspension type semi-trailers. The load configuration for each semi-trailer consisted of two rows of 13 bins stacked two high for a total of 52 bins. The results indicated that higher apple quality could be maintained if fruit was road transported in plastic bins and on semi-trailers equipped with air-cushion suspension. Damage incurred during each test was measured according to USDA Apple Grades based only upon mechanical injury (abrasion, bruising, cut and puncture). The premium grade is known as U.S. Extra Fancy. Overall quality of fruit positioned on the side of all bins was much lower compared to fruit in the middle. The percentage of undamaged fruit was significantly effected by suspension type, bin type and trip distance. Bruise damage was similar for each of the bins (ranging from 7 to 15%) when transported for 1.5 hours along a road in "poor' condition. Abrasion damage was significantly higher for the fruit transported on steel spring suspension and in hardwood bins. Abrasion damage in hardwood bins averaged 65% as compared to 12% in plastic bins. In the air

18

suspension tests the abrasion damage ranged from 0.6 to 5% for all bin types. Figure 5 shows the percentage of undamaged fruit (US Extra Fancy grade) under various trial conditions.

no % premium grade fruit

Bin type •Wood bin •Plastic bin

80

60

40

20

n

WM • 80

60

40

20

n

~ ~ ~ ^ ^ l ^^H 1 1 __

80

60

40

20

n

^̂ H — ~^^H 1 1 --

Spring/45 mins. Spring/90 mins. Air/45 mins. Air/90 mins.

Suspension type and trip time

Spring = spring suspension Air = air cushion suspension 45, 90 mins. = trip distance

Figure 5. Comparison of percentage of premium grade fruit remaining in plastic and hardwood bins after road transport on air cushion and spring suspension semi trailers (Timm etal, 1995).

The results from these tests indicate the advantage of plastic bins and air-cushion suspension transport. The benefits of using plastic bins are more apparent when transporting with spring suspension semi-trailers. Another study by Ericsson and Tahir (1996) found that apples handled in plastic bins during picking, transporting to the packhouse and storage had significantly less bruising damage than those handled in wood bins. Using bruise weight percentage (BWP) as an accurate indicator of bruising they determined that plastic bins caused 13.5%, 41.1% and 34% less BWP in the three handling steps respectively. Bruising was more apparent on the fruit in the top layers of the bins than in the bottom layers. The type of bruising encountered i.e. impact, vibration or compression, was not specified in the report.

6.3.4 Hygiene and rot development

Wooden surfaces of fruit bins are an important source of decay pathogens for fruit and vegetables (Spotts et al.„ 1988; Sonoda et al, 1981). Pathogens from bins contaminate drenches, water flotation systems, dump tanks and hydrocoolers which in turn facilitates the spread of inoculum (Holmes, 1993). This is a particularly important issue in handling of highly susceptible crops such as pears, stone fruit and fresh-market tomatoes. The porous nature of wood surfaces means that they are easily contaminated and relatively difficult to disinfest. Manual pressure washing of wood bins with steam or water and disinfectant is a common disinfestation method. Pressures in excess of 1500 psi are usually required and it may take up to 5 minutes to thoroughly wash individual bins (Lopresti et al, 1995). As the pressure washer nozzle needs to be close to the bin surface for effective pathogen removal, scuffing of the wood

19

fibres may lead to a rougher internal surface after drying. Food safety studies have demonstrated that wooden boards inoculated with a mixture of bacteria and then disinfected still retained relatively high bacterial counts after cleaning. Studies on planed samples showed penetration of bacteria into the wood within the structural xylem fibres and vegetative elements (Abrishami et al, 1994). Bacteria that adhered to plastic surfaces were more easily removed by low-temperature washing than were cells that adhered to wood surfaces.

Plastic bins are considered to be more hygienic, easier and quicker to clean than wood bins due to the impervious nature of HDPE and a smooth finish (Warner, 1993; Acuff, 1995; Chase, 1995; Cox, 1995). To date, this claim has not been fully verified but a few sanitation studies have demonstrated that this is very likely to be the case. Several disinfestation methods have been tested on small pieces of wood and plastic inoculated with P. expansum and Alternaria alternata (Spotts & Cervantes, 1994). Steam was the most effective treatment for killing spores of both fungi on wood and plastic surfaces. Most chemical treatments were of similar effectiveness on plastic and wood. However sodium hypochlorite, a common disinfectant in the fruit and vegetable industry, was more effective on P. expansum spores on plastic than on wood. When P. expansum spores on wood and plastic were treated with 100 mg/L sodium hypochlorite solution for 10 minutes, 97% of spores on the plastic were killed compared to 70% on wood. Chlorine is highly reactive with organic matter and loses its efficacy very rapidly (Jolley & Carpenter, 1983). This may explain why sodium hypochlorite more effectively reached spores on smooth plastic than on rough wood. In many cases bulk bins are only partially sanitised during water dumping or drenching of fruit with a disinfectant solution. This is not a very effective method as chlorine in the recycled water is likely to react with wood bin surfaces and thus become inactivated (Bliss, 1997). It has also been demonstrated that without removal of the organic matter and debris from bin surfaces, chlorine cannot penetrate and kill pathogens (Holmes, 1993).

6.3.5 Other considerations

There may also be other advantages in the increased ventilation area available in plastic bins during fruit storage. Postharvest chemicals applied by drenching or dipping can cause skin injury on fruit under extreme conditions including a slow drying time i.e. greater than 24 hours. Factors that increase drying time and the risk of skin injury include plastic lining of wood bins e.g. used for pears and Golden Delicious apples to prevent shrivel, and retention of moisture at the point of fruit to fruit contact (Little, 1985). Additional air movement inside plastic bins should shorten the drying time thus preventing possible fruit-skin injury and touch burn where fruit contacts one another. The use of forced-air cooling in conjunction with plastic bins is likely to enhance the drying process and prevent this type of injury occurring. Better ventilation through apples stored in plastic bins may also increase the rate of removal of potentially harmful volatiles that can increase the incidence of physiological disorders in storage (Tindale, 1970).

It has also been shown that during DPA dipping of pome fruit in wood bins approximately 6 litres of solution is removed with each bin of dry apples (Little & Holmes, 1997). In addition there is a 10%-20% dilution (reduction in concentration) of the DPA concentration after 100 bins are treated by immersion which is caused by uptake of the chemical by the fruit and wood bins. Skin injury in the form of touch burn increases and scald control becomes marginally less effective, as throughput increases from 50 to 100 bins. Addition of extra chemical is thus required due to reduced DPA concentration, organic matter accumulation and reduced volume of the dip in the tank. It was found that after 7 months cold storage, scald

20

incidence and skin injury on Granny Smith was 2% and 7% respectively when 100 bins of fruit had been dipped without addition of DPA solution. Kenna (1985) estimated that 9 litres of fungicide solution may be lost for each bin of stone fruit dipped and that extra fungicide must be added as a double-strength mixture to maintain the correct concentration. As plastic bins do not absorb moisture it is likely that this fruit injury would be avoided because they prevent dilution of the dip. In general, the use of plastic bins is also likely to impact on potato quality as ventilation and relative humidity are important parameters during bin storage (Hardenburg et al, 1986). Good ventilation is required to dry wet potatoes and rapidly cool them down to desired storage temperature. Very humid air (95% RH or higher) is required during cooling and curing to prevent moisture loss and stimulate suberisation and wound healing (Rastovski & van Es, 1987). This is likely to be more achievable in a shorter time using bins made from plastic rather than softwood.

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7. Distribution and handling of field bins

Briefly considered in this section are other possible benefits of using plastic bulk bins in horticulture. As wood bins absorb moisture during handling and storage this will increase their weight resulting in a possible loss of product capacity on trucks during transport (Anon., 1997a). Due to their lighter weight and interlock stacking plastic bins provide optimum stability and volume utilisation in transit (Sayers & Sneddon, 1986). Plastic field bins used to distribute produce to cooperatives or markets can also be clearly labelled with the owners identification e.g. by using hot foil stamping (Anon., 1997b). This can reduce the possibility of bin losses during distribution due to pilferage. From a marketing viewpoint, bulk plastic containers can be used to enhance sales appeal by improving the presentation of the product which currently may be displayed in wood bins (Sayer & Sneddon, 1986).

Plastic bin hire is another option that is not readily available with wood bins. For example, in the citrus industry most wood bins are owned by packhouses and sent to growers during the harvest season with no direct charge. Hiring plastic bins to growers could improve the efficiency of bin usage and allow implementation of a monitoring system that can track the movement of bins and allow growers to acquire bins on an 'as required basis' (Alsoboh, 1996). Sayer and Sneddon (1986) have listed the practical benefits of hiring plastic bins. These include:

• A grower's bin requirements can be seasonal, and they may only require them for only a certain period of the year. By hiring, a grower has access to the precise number of bins they require and avoids idle bins and shortages.

• Hiring as needed avoids the capital investment required for purchase. • Hiring is an operating expense and thus has tax advantages while purchase of bins is a

capital expenditure, depreciable over a number of years (depreciation can be high for wood bins).

• With a fee-per-use bin exchange the grower only faces the risk of loss or damage while the bin is under their direct control.

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8, Economic considerations

At present the higher initial cost of plastic bins is preventing many growers from investing in this new handling technology. Due to the difficulty in obtaining industry cost data, very few economic analyses comparing the long-term cost of plastic and wood bins have been published. Any analysis should, if possible, quantify the benefits and disadvantages associated with both bin types and their cost. No comprehensive study of the Australian situation has been performed. At present it is difficult to quantify many of the benefits of plastic bins in dollar terms. In comparing the true operating cost of each bin type a number of factors need consideration including initial purchase cost, service life, interest rates, salvage value, maintenance cost, freight costs, depreciation, fruit loss cost, and chemical, storage and cooling costs (Waelti, 1992). In the following section handling and quality benefits obtained from handling produce in plastic bins are considered in financial terms and where possible costs are estimated from information currently available. The focus is mainly on pome fruit handling as cost data concerning other crops is scarce.

8.1 Economic models

An economic analysis comparing plastic and wood bins was conducted in the USA in 1995 (Waelti, 1995). It is informative to note some of the conclusions reached in this study even though the cost structure differs from the Australian situation. An annual cost method was used as a non-uniform series of payments was involved. Long-term costs were calculated using a range of purchase prices and interest rates. Estimates of service life, maintenance cost and salvage value were also used. Other operating costs and increased returns from better quality fruit were not included in the calculations as they could not be determined.

The study found that the average annual cost of wood bins is highly influenced by their service life because it is relatively short. Repair and disposal expenses also significantly influenced average annual cost of wood bins. It was determined that the difference in annual costs between wood and plastic bins becomes marginal under low interest conditions and after a 15-25 year period if the price difference between the two bins remains at $AUS 40-50. For example, annual costs were found to be similar for a wood bin with a useful life of 10 years and a plastic bin with a service life of 16 years. An increase in interest rate had a greater effect on the annual cost of plastic bins than on wood bin costs because a larger initial investment is necessary for plastic bins. Figure 6 demonstrates the decrease in average annual cost with increasing bin service life based on a purchase price of $65 for wood bins and $105 for plastic bins.

When applying this result to the Australian situation the likely differences in labour and repair costs must be considered. Average repair and disposal costs are likely to be greater in Australia due to higher labour costs and smaller economies of scale achieved by growers and packhouses as compared to their US counterparts. Maintenance costs are also expected to increase for wood bins made from softwood rather than high quality plywood. This may also shorten the service life of wood bins (Waelti, 1995). In most horticultural industries wood bins are unlikely to have a service life of more than 10 years without major repairs. The current disparity in initial purchase price between bins may be greater in Australia i.e. $55 rather than $40, but this will ultimately depend on the quantity purchased.

23

10 Average annual cost ($ per year)

8

8 12 16 20

Years of use

24 28

Figure 6. Estimated average annual cost of wood and plastic bins. Salvage value used for plastic bins was 33% of initial cost. Average repair and disposal cost for wood bins was estimated at $ AUS1.00 per bin per year (annual cost in 1995 AUS dollars), (Waelti, 1995).

8.2 Potential economic benefits

Although there are many horticultural industries with the potential to benefit from plastic bins, growers that produce crops listed in Table 2 are likely to achieve significant economic gains from their use. Also shown is a subjective assessment of what type of benefits are likely for each crop handled.

Table 2. Summary of the areas where use of plastic bins is likely to produce a significant economic benefit for growers and packers.

Crop Cost saving1 Crop Handling2 Chemical Storage3 Cooling Crop loss4

Apples Pears Stone fruit Citrus Potatoes Onions Tomatoes Other vegetables5

* * * * * * *

* *

* * * *

Depreciation and maintenance costs will be lower for plastic bins regardless of crop. Includes reduced labour costs during bin disinfestation, topping up of dip tanks and handling

of bins. Includes savings in storage space and curing time for potatoes and onions. Due to mechanical damage and rot development Includes sweet corn, cabbage and broccoli.

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8.2.1 Initial purchase cost

At present plastic bins generally cost between $120-140 each but purchase price is usually lower than $130 per bin when large quantities are purchased i.e.200 or more. Softwood bin purchase price usually varies between $50-60. It has been noted that traditional packaging materials such as timber are no longer readily available at very low cost in Australia. The cost of timber and steel has been increasing at a far higher rate than that of moulding-quality plastics (Sayers & Sneddon, 1986). Over the next decade the price differential between bin types is likely to decrease due to market forces, greater plastic bin production volumes and reduced availability of quality timber as has occurred in the United States (Cox, 1995). Bin hire is also an option that isn't available with wood bins. It has been estimated that over a thirty-five week period each wood bin can cost up to $3.00/week to use (Anon., 1997a). Operating costs of this magnitude would make plastic bin hire a viable option.

8.2.2 Depreciation and salvage value

Wood bins have a relatively short service life which means their value depreciates at a faster rate than plastic bins. Plastic bins are recyclable and have a salvage value, the cost of which is difficult to determine but a conservative estimate is 15% of initial purchase price. A figure of 10% is commonly used for farm machinery which is sold as scrap at the end of its service life (Baimretal., 1955).

8.2.3 Maintenance costs

A number of costs are incurred in repairing wood bins. These include labour, materials, inspection, sorting and disposal costs. Costs for plastic bins are expected to be low (Waelti, 1995). The actual maintenance cost will vary depending on the number of bins that need repair each season which is a function of the handling method, crop volume and storage conditions. In most cases this cost is expressed as labour and materials required per bin repaired per annum. In general, unskilled labour on relatively low wages is used in the US to repair wood bins. In Australia labour costs are likely to be higher. Bin repair costs are very difficult to determine due to lack of grower records and difficulty in determining the time required for repairs. It is estimated that major bin repair may cost $6-12 per bin repaired per annum. This figure includes inspection and sorting costs. The higher costs in this range are likely to be incurred by citrus packers and tomato processors. Maintaining pome fruit bins will be less costly due to the likelihood of fewer major repairs as they are used less frequently. Costs for disposal of old and broken wood bins are often not known. Burning bins in the open air is not allowed in most cases so some expense is incurred in disposing of them i.e. landfill or incinerator. It will be assumed that this cost is included in the maintenance figure for wood bins.

8.2.4 Chemical, handling and cooling costs

It is likely that a significant reduction in postharvest fungicide, disinfectant and DPA usage will result from using plastic bins. Wood bins absorb moisture and chemical during drenching or dumping leading to chemical wastage and the requirement for 'topping-up' of chemical solutions. One pome fruit grower has estimated that by using plastic bins postharvest chemical costs have been reduced by one third (Batlow grower, 1996). Sodium hypochlorite efficacy in hydrocoolers and drenches may be affected by wood bin surfaces and organic matter. Again

25

the use of plastic bins may reduce the requirement to constantly add chemical to maintain appropriate disinfectant levels.

Some potential will exist to reduce the cost of disinfesting fruit bins to remove pathogens that can contaminate postharvest handling equipment. This is likely to be due to the reduced labour, disinfectant and water costs incurred when pressure washing plastic bins rather than wood ones. It has been estimated that five minutes is required to manually wash a wood bin thoroughly (Lopresti et al, 1995). The washing time required for plastic bins is likely to be shorter by at least 50% due to their smooth surface and no crevices inside which a build up of pathogens can occur. Washing each bin surface will also be quicker due to the ease with which they can be lifted and rotated.

Plastic bins can be stacked as high or higher than wood bins. Furthermore, the ability to tightly stack them is likely to reduce storage space required (and subsequently storage cost) by 10-15%. This is particularly important for growers who hire CA storage space from a larger packer or cooperative. Freight costs may also be substantially reduced during long-distance transport as positive interlocking and lighter weight of plastic bins allows more fruit to be carried per load i.e. up to four bins can be stacked on a truck.

Initial cooling in CA using plastic bins may result in reduced electricity costs due to the shorter time for which full refrigeration capacity is required. Little & Holmes (1997) have calculated that the energy needed to cool apples during summer over a three day period can be 20 times as much as is needed for winter-spring storage. Plastic bins have been shown to reduce half-cooling time substantially, and consequently for pome fruit there should be associated reductions in energy consumed during storage. Cooling costs for other crops such as stone fruit may also be reduced depending on the whether or not conventional cooling is used.

8.2.5 Crop losses

It has been demonstrated that less abrasion damage occurs in plastic compared to wood bins during bulk apple transport. Whether the losses during packout are significantly reduced by using plastic bins can only be determined by individual growers under their own handling procedures. A combination of rough orchard roads, steel spring suspension on trailers, long trip times and highways in poor condition can cause significant fruit losses. It is likely that under these conditions significantly more abrasion damage will occur in wood bins, particularly if they are poorly maintained, than in plastic bins. Timm et al, (1995) estimated that there were substantial economic benefits in using plastic bins during transport on semi­trailers. Due to an increase in premium quality apples they calculated a $AUS 7.60 benefit per bin when using plastic bins and steel-spring suspension trucks. The benefit was reduced to $AUS 2.10 when they were used in conjunction with air-cushion suspension. The economic benefits of using plastic versus wood bins during transport is dependent on many factors including utilisation of the fruit, varietal differences in resistance to bruise and abrasion damage, fruit price and transport distances.

Estimates based on data from Holmes (1993) and production figures in the Meyers Strategy Group (1995) report demonstrate that losses in the apple industry due to abrasion, scratches and punctures that occur between harvest and packing are around $3.5 million annually (based on 1994/95 production). Alsoboh & Moore (1996) found that about 6% of Valencia oranges in every wood bin are downgraded due to mechanical damage caused by bins in poor

26

condition. It was estimated that the citrus industry annually loses of about 38,000 tonnes or $9.5 million dollars. This figure is likely to include fruit losses due to decay and olleocelosis initiated by abrasion and puncture damage.

No data is available on stone fruit damage in wood bins but it is expected to be less than for other fruits due to the general use of sanded wood bins and plastic liners in field containers. Although this will substantially reduce abrasion damage it does increase the cost of wood bins and handling fruit.

8.3 Economic analysis: apples

Growers and packers in the pome fruit industry may benefit significantly from using plastic bins in their handling operations. It has been determined that 71% of grower/packer operating costs are made up of labour, chemicals, maintenance and depreciation (Meyers Strategy Group, 1995). Savings are likely in each of these categories by replacing wood bins with plastic. An economic evaluation of the Australian situation similar to that performed by Waelti (1995) in the US is useful in determining if plastic bin use is economically justified. The evaluation presented here will focus on.the apple industry as there is sufficient data available to estimate the majority of costs. This study will also outline the methodology that can be used to analyse the citrus, stone fruit and vegetable industries.

8.3.1 Scope of evaluation

The economic comparison of wood and plastic bins will focus on a general apple production operation as outlined in Figure 1. Partial budgeting will be used to compare wood and plastic bin operating costs. This means that only the changes in input and outputs associated with each method of handling fruit will be accounted for. For example, average operating cost will not include bin transport from orchard to the packhouse as this will be the same for each type of bin. Cost savings, if any, associated with faster handling of plastic bins due to easier stacking cannot be determined. Similarly any higher returns due to faster cooling of fruit e.g. due to decreased moisture loss, are not included in the analysis. Maintenance costs for wood bins do not include average annual cost of replacement bins. Assumptions and cost estimates are based on data obtained from growers, published literature and bin suppliers. From the data available, conservative cost estimates will be used in the evaluation and realistically the average operating cost figures are likely to be within +/- 30% of the true value.

8.3.2 Procedure

Although this economic comparison uses an annual cost method similar to that of Waelti (1995), other factors such as chemical, fruit loss, utilities and handling costs are included. This approach is appropriate when non-uniform series of payments of costs are involved. The time value of money is accounted for by using the concept of "present value'. This approach brings the value of future costs to a common point in time i.e. the present, by taking into account the interest earning capability of money (Bell, 1984). Once the total present value is calculated it is averaged over the various service life periods using appropriate capital recovery factors (Waelti, 1995). Bainer et al, (1955) outlined a procedure for estimating the cost of owning and operating farm machinery. A straight-line depreciation schedule was suggested. Appropriate calculations used to estimate operating costs are detailed in Appendix 12.1.

27

8.3.3 Pome fruit operation

The economic evaluation presented here will be based on an average-sized apple growing and packing operation where the grower owns their own cooling and CA facilities. All bins go through the handling process as described in Figure 1. The following assumptions and economic data apply.

Average yield: No. of bins: Cooling facilities: Drench tank: Electricity cost: Temperature pulldown: Freight costs: Storage hire: Interest rates: Salvage value: Discount rate:

750 tonnes/year (all fruit cooled and stored in bins) 1500 Conventional CA 1200 litres $0.10 per kWhour (average tariff)

3 days n/a n/a 10% per year 15% of plastic bin purchase price 6% per year i.e. potential interest rate on investment

Operating costs (per year):

Wood bins Purchase prices: Maintenance costs:

Service life: Disinfestation costs:

Drenching cost:

Fruit losses:

Cooling cost:

Plastic bins Purchase price: Maintenance cost:

Service life: Disinfestation costs: Drenching cost:

Fruit losses:

Cooling cost:

$40, $50 & $60 (current purchase price range)

$2.00/bin (includes materials, handling, labour and disposal costs; cost averaged over all bins in use; expected to be low for apple handling)

4, 8, 12 & 16 years $3.50/bin (all bins are manually pressure washed; includes labour, water &

chemical costs) $7.00/bin (includes chemicals, Rovral® plus Benlate® and DPA &

water and labour during topping-up) $3.50/bin (losses are fruit downgraded to juicing & includes mechanical

damage due to transport in bins but not due to rot development that may be associated with use of wood bins; estimate based on study by Holmes (1993))

$2.20/bin (energy consumption data from Little & Holmes (1997))

$110, $120 & $130 (current purchase price range)

$0.50/bin (maintenance costs for plastic bins are not available at present but are expected to be only a small fraction of those of wood bins (Waelti, 1995))

8, 12, 16, 20 and 24 years $2.50/bin $5.50/bin (based on data from Little & Holmes (1997) and Holmes (1993); savings

in chemical and water per 100 bins) $1.20/bin (based on study by Timm et al (1995) which showed that abrasion

damage was up to 3-5 times less in plastic bins) $1.50/bin (assuming cooling time decreased by one third)

28

8.3.4 Results

Based on the estimated operating costs for an average apple growing and packing operation the economic evaluation of plastic versus softwood bin use demonstrates that the difference in average annual cost between wood and plastic bins becomes insignificant over a long service life at current bin purchase prices (Figure 7). In general, most wood bins used for pome fruit handling would have a relatively long service life of about 12-15 years. The cost model demonstrates that a plastic bin would need to be in service for over 18 years to make its use economically viable. A higher interest rate such as 12% instead of 10%, will increase the annual cost of plastic bins at a greater rate than that of wood. In this analysis, higher interest rates would marginally increase costs requiring a plastic bin service life of over 20 years to justify its purchase. Overseas experience suggests that this is possible using current plastic bin models specifically designed for agricultural purposes.

Average annual cost (1997 $/year)

28 r

—o— $50 Soft wood bin • •••<>••• $130 Plastic bin

16 " \ . \ \ ^ o.

12 " X^''.;.;;

8 - '.'.-.•.•,.,,,......

4

4 6 8 10 12 14 16 18 20 22 24

Service life

Figure 7. Estimated average annual cost of softwood and plastic bins for various years of use. Interest rate used is 10% per annum and costs are in 1997 dollars.

Waelti (1995) observed that initial purchase price and interest rates were major items affecting long-term bin costs. By taking into account most of the operating costs that can vary with type of bin, it was found that in the Australian model no single factor had a major influence on average annual cost. For example, a decrease in the maintenance cost of wood bins would not affect the annual cost significantly. The financial advantages of using plastic bins for apple handling would only become marginal over a long service life if the cost of operations such as bin disinfestation, maintenance and drenching were significantly reduced. This type of economic evaluation would also be useful in determining the annual bin costs incurred in other horticultural sectors such as citrus and stone fruit. Table 2 suggests similar operating costs as in pome fruit production will have to be taken into account. In the case of citrus, service life is likely to be shorter for wood bins and maintenance costs higher due to frequent use every season. This indicates that the economic advantages to be gained by using plastic bins in the citrus industry may be greater than those for pome fruit.

29

9* Recommendations

9.1 Extension/adoption by industry

The major horticultural industries in Australia, including pome fruit, citrus, stone fruit and potatoes, are likely to benefit from the use of plastic field bins. The many advantages of their use have been summarised in this report and if growers/packers consider operating costs averaged over many years of service the potential for plastic bins to reduce their production costs are clear. Implementation of project findings is likely to lead to reduced waste, increased product quality and greater profitability for growers. Most growers and packers have knowledge of the availability of this handling technology and some have already invested in it. It is likely that wide distribution of the information contained here will clarify the situation for many growers, particularly in the fruit industry, and put them in a better position to judge whether plastic bins are the future in produce handling.

The results of this study have been progressively provided to the industry partner (Perstorp Plastic Systems P/L) and dissemination of results has occurred through contact with bin manufacturers and growers, and through articles in various industry publications. Specifically, extension activities have included: • Articles in Good Fruit and Vegetables (Jan., 1997) and in Northern Victoria Fruit Grower

(Feb., 1997); • Plastic bin presentation at the Batlow Fruit Cooperative Technical Workshop '97 (Sept.,

1997); • Plastic bin paper published in Batlow Technical Workshop '97 proceedings (See Appendix

12.2); • Future article presenting major project findings in Good Fruit and Vegetables (Jan., 1998).

The industry partner will also be using their own sales network to distribute the information contained in this report.

9.2 Directions for future research

Completion of this project has highlighted a lack of detailed cost information in many horticultural industries which is required for an accurate economic evaluation of the benefits in using plastic bins. Future research should focus on:

• Further work to determine improvements in fruit quality, hygiene and postharvest chemical quantities used in relation to plastic bins;

• Quantify the true operating costs of field bins through industry surveys, and handling and storage trials in conjunction with growers;

• Development of accurate economic models for the major horticultural industries to enable estimation of annual average costs when using wood and plastic bins.

9.3 Financial/commercial benefits of adoption of research findings

The pome fruit, citrus, stone fruit, potato and tomato industries, when combined, make up a large proportion of the gross value of horticultural production in Australia. These industries will be the main beneficiaries of this new handling technology. Available information already demonstrates that use of plastic bins is likely to reduce production costs and significantly reduce crop losses, particularly in pome fruit and citrus production.

30

10. Acknowledgment

I wish to thank Perstorp Plastic Systems P/L and the Horticultural Research and Development Corporation for funding of this project.

11, literature cited

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Blacker K.J. (1989). 'Humidity', in Fresh Produce Manual, 2nd ed., Aust. United Fresh Fruit & Veg. Assoc. Ltd., 45-62.

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"Box design - plywood versus softwood (1996). Annual Review, Sutton Bridge Experimental Unit, 12-13.

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Devine E.S. (1981). Bulk handling of apples and pears. Booklet 2355, Ministry of Agriculture, Fisheries and Food, 16pp.

Dewey D.H., B.A. Stout & J.F. Herrick Jnr (1972). Evaluation of a hydrohandling system for sorting and sizing apples for storage pallet boxes. USDA Marketing Res. Rep No. 948.

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Hardenburg R.E., A.E. Watada & C.Y. Wang (ed.) (1986). The commercial storage of fruits, vegetables and nursery stocks. USDA Agric. Handbook No. 66.

Holmes R.J. (1993). Diseases causing Post-harvest crop Loss in Apples and Pears: Epidemiology and Control. Phd thesis, Sept., School of Agriculture, La Trobe Uni., Australia.

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Little C.R. (1985). Avoiding problems in post-harvest dipping of apples and pears. Agnote No. 211/56,No\.

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Mitchell F.G. (1992a). "Preparation for fresh market', in Postharvest technology of horticultural crops. Special Publication 3311, 2nd ed., Cooperative Extension, Univ. California, 31-38.

Mitchell F.G. (1992b). "Cooling horticultural commodities', in Postharvest technology of horticultural crops. Special Publication 3311, 2nd ed., Cooperative Extension, Univ. California, 31-38.

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33

Parsons C.S., L.P. McColloch & R.C. Wright (1960). Cabbage, celery, lettuce and tomatoes: Laboratory tests of storage methods. U.S. Dept. Agr. Market Res. Report 402, 30p.

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34

Sports R.A. & L.A. Cervantes (1994). Contamination of harvest bins with pear decay fungi and evaluation of disinfestants on plastic and wood bin material. Sixth Intern. Symposium on Pear Growing, Intern. Soc. Hort. Sci., No. 367, June 1994, 419-425.

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12, Appendices

12.1 Economic evaluation equations

Average annual interest = Pxi/2x(n+l/n) Bainer et al, (1955).

where P = Purchase price i = interest rate/100 n = service life

Present value, P0 = Sn(l+i)"n Bell (1984).

where Sn = future cash flow at the end of n periods i - discount rate/100

n = service life

12.2 Batlow technical workshop paper

Use of plastic bulk bins in the tree fruit industry

John Lopresti Institute for Horticultural Development

Agriculture Victoria

1. Introduction Wood bins have been the standard in the Australian tree fruit industry for many years where they are utilised in harvesting, packhouse, storage and transport operations. However, plastic bulk bins have been used in Europe for over 20 years. Imported bins have been available in Australia for about five years and recent interest in use of these bins has lead to their local manufacture. This has substantially reduced their purchase cost and made them a possible alternative to wood bins.

The purpose of this paper is to briefly compare wood and plastic bulk bins with respect to handling, fruit quality and operating costs, with the aim of raising grower awareness of the issues that need consideration when choosing the appropriate bin type for handling operations. Much of the information concerning plastic bin usage is based on grower experiences in Europe and the United States. Where possible published research is used to quantify differences between bin types.

2. Bulk bin design Bulk bins for use in the fruit industry must be designed to meet certain requirements. These include ease of handling, sufficient mechanical strength, ventilation, drainage, and correct shape, size and weight. They should also protect produce from mechanical damage and not contaminate the crop.

Pallet-based wood bins are the most common type of bulk container used in Australian horticultural industries. New bins are mostly manufactured from softwoods such as plantation pine (e.g. Pinus radiata) which is sourced from saw mills or timber processors. Many older bins still in use are constructed from hardwood and have metal reinforcing along each outside edge to strengthen the bin. The majority of bins used in Australia have a square foot print (i.e. base) but in some areas such as the Batlow region, rectangular bins are the standard. Bin base dimensions are usually standardized according to prevailing vehicle dimensions. Standard pallets in Australia have dimensions of 46" by 46" (1160 mm sq.) and bin dimensions may range from 1000 mm to 1200 mm. Bin depth is

36

determined by the produce type handled and can range from 40-70 cm. Pome fruit is usually filled to a depth of 60 cm.

Virtually all plastic bins for horticultural use are manufactured from recyclable, UV stabilised, food grade, high density polyethylene (HDPE). Plastic bins are available from various manufacturers and models can vary in terms of side wall and base design, external dimensions, internal capacity and number of ventilation and drainage holes. Bins designed for horticultural use are manufactured using structural foam or injection moulding techniques. In general plastic bins are rigid, moulded containers constructed with double wall corners and centre posts. Side walls are also strengthened by a number of ribs running horizontally just below the top of the bins. Most models allow for four-way forklift entry and positive interlock stacking. Collapsible and knock-down bins are also available. Ventilation and drainage holes are usually incorporated into the side walls and bin base. Due to differences between models, each plastic bin type should be evaluated on its own merits. The weight of plastic bulk bins varies between 35 to 45 kg compared with 70 to 80 kg for wood bins.

3. Comparison of wood and plastic bins

3.1 Handling issues Stacking strength One-piece moulded plastic bins have a higher strength-to-weight ratio than wood bins as they are lighter yet can support a static load comparable to wood bins. They are designed to stack 10 to 12 high filled with 500 kg of fruit in CA storage (i.e. below 7°C) and 6 high at ambient temperature ' . This is equivalent to a maximum static loading of approximately 5,500 kg. This compares favourably with a stack number of 6-8 bins which is generally achieved using standard wood bins.

Durability Bulk bins for produce harvesting are usually subjected to rough handling. They are often filled on uneven ground, carried over bumpy terrain, rolled off trucks, bumped against each other and immersed in water or drenched during packhouse operations. Durability is extremely important in ensuring crop protection and overall longevity of bulk bins. Some concerns have been raised about the durability of plastic bins in comparison to wood bins. European grower experience suggests that the useful life of plastic bins may be as high as 15-20 years whereas most wood bins are likely to last for 5-8 years .

Softwood timber used in bins is prone to splitting, warping, cracking and splintering with age, particularly if stored in the open. Timber expands and contracts with prolonged use due to moisture and temperature changes which may loosen nails and weaken the structural integrity of the bin . In theory plastic bin structural strength is unaffected by sunlight or rain. Most models are UV stabilised and HDPE is an inert, impervious material that does not absorb water. As plastic bins are a moulded, one-piece unit, stresses due to thermal expansion and contraction are spread fairly evenly throughout the bin and so it's structural integrity should remain intact4. Although 20 year old bins are still used in Europe it has not been verified whether their structural strength has remained unchanged over this period. Experience there indicates that most of these bins are in good condition even though they were constructed from structural foam which has less strength than HDPE used at present .

Damage and maintenance Most wood bins require some maintenance during their service life. Major repair usually entails replacement of broken, cracked or warped side or base boards, and refixing of loose boards. It is difficult to determine the number of wood bins in the fruit industry that need repair annually but growers that handle bins roughly or store them outdoors are likely to have to repair some bins. Overseas experience suggests that plastic bins are more durable and have good impact strength . Unlike wood bins the most likely type of damage they will experience is puncturing or deformation due to, for example, impacts from forklifts during handling. In severe cases cracking may occur that can sometimes be repaired by heat welding. Growers in the USA have found that about 3 in 1000

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plastic bins need annual replacement5. Damage to plastic bins is generally quite minor so that in many instances it may be possible to continue using them without major repair with fruit quality being unaffected. In comparison fractures and splintering of wood bins is much more likely to damage apples.

Ease of handling The major advantage of plastic bins is superior handling efficiency compared to wood bins. Overseas experience has demonstrated that four-way forklift entry, positive interlock stacking and deeper fork openings on bins allow quicker handling of fruit in the packhouse . Positive base-to-top interlocks allow quicker stacking of bins into secure, self-supporting columns. This feature combined with the consistent shape of plastic bins (i.e. straight side walls) has been found to allow easier loading of trucks and more rapid filling of CA rooms. The large number of drainage holes in plastic bins has also lead to quicker throughput of full bins through water dumps as they can be immersed and then drained more rapidly than their counterparts.

Due to their lighter weight and tendency to be more slippery, full plastic bins can be more difficult to handle on forklifts and trucks. Operators may need training to become accustomed to plastic bins. It has been suggested that rubber sleeves, welded cross beads or a tacky coating on forks will prevent slipping during forklift handling3. Full plastic bins stacked four high can be carried on flat-bed trucks due to positive interlocking and their lighter weight, but it has been determined that better tie-down may be needed to avoid bin shifting7. Another problem noted by some growers in the USA is that use of wood and plastic bins cannot be integrated as they cannot be stacked together. A gradual change over from wood to plastic may also be difficult as handling equipment may require retooling to

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accommodate plastic bins .

Storage In storage plastic bins can be stacked more accurately and higher than wood bins due to positive interlocking9. To an extent plastic bins can also solve the problem of dead air space left between wood bins in storage. It has been calculated that tighter stacking of plastic bins can increase available floor space by about 16% . This is based on a gap reduction between bins of 20 cm. Better ventilation achieved through the side walls and floor of plastic bins allows this stacking arrangement. It has been noted by some growers that plastic bins hold less fruit than wood bins with the same external dimensions9. This may be due to the fact that side walls of plastic bins can be up to 2-3 times thicker than wood side boards (50-80 mm as compared to 20-25 mm) which reduces internal volume. Thicker walls are required to allow for positive interlocking of stacked bins and to increase structural strength.

Safety aspects In terms of occupational health and safety of workers, plastic bins have several advantages over wood bins. The main benefit is that plastic bins are much more secure when stacked due to positive interlocking ' . However, the lighter weight of these bins also means that more care needs to be taken when moving them by forklift14. Slower speeds may reduce the occurrance of accidents. The likelihood of worker injury due to contact with broken timber boards, rusty nails, splinters, sharp corners or metal reinforcing is eliminated when plastic bins are used.

3.2 Fruit quality issues Although plastic bins have been used in Europe for over 20 years little published information is available comparing pome fruit quality handled in wood and plastic bins. The main factors that influence final fruit quality and that may depend on the type of bin used during postharvest handling and storage include moisture loss, cooling rate, fruit damage and hygiene.

Humidity and moisture loss It is generally agreed that wood bins in CA storage absorb moisture from the air and thus reduce the relative humidity in the store . It has been estimated that during long term storage they may absorb up to 6 kg of water from the air and fruit . Only one published study is available comparing humidity levels in CA rooms when storing Golden Delicious in plastic and plywood bins . It was determined

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that relative humidity levels were up to 5% less in the plywood bin rooms, especially during the initial cooling period. A similar or even greater reduction in relative humidity may be likely using softwood bins as they can be expected to absorb more moisture than plywood bins. Weighing of bins in and out of storage indicated a 22% reduction in fruit weight loss in plastic bins compared to plywood bins but the results were not significantly different11. Weight loss in "Aroma' apples stored in wood bins for 6 weeks at 2-3°C was found to be 2.5% as compared to 1.7% for fruit stored in

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plastic bins; a 30% difference .

Cooling rate For most apple varieties rapid cooling is beneficial in preserving texture, firmness and juiciness . It has not been established whether faster cooling leads to economically significant quality loss in apples after long term CA storage. The large dimensions and low ventilation area of wood pallet bins (i.e. 4-6% of basal area) result in much of the product being remote from the top or side of airflow surfaces. This allows little opportunity for cold air to penetrate into the bin in normal room cooling operations . Two seasons of Golden Delicious storage has demonstrated that initial cooling is 2-3 times faster in plastic bins than plywood ones but quality ratings were similar for fruit stored in both types of bin7.

Softwood bins used in Australia have more ventilation area than their plywood counterparts and so differences in cooling rate may not be as pronounced and further research is required. Plastic bins generally have a much larger ventilation area (i.e. up to 600 ventilation slots) and more air flow passes through the bin and fruit. Tight stacking enhances the cooling process further but this may lead to higher initial moisture loss in plastic bins. In most cases this is not a problem as faster cooling results in reduced total moisture loss over the whole storage period . Return air may be warmer when bins are tightly stacked, and there may be more frost build-up because of the moisture picked up by the air as it moves through the bin .

Fruit damage The commonest type of damage in bulk bins is abrasion or vibration bruising when fruit moves or vibrates against rough surfaces or other fruit during transport . Damage levels encountered will depend on road surface, type of suspension on trailer or truck and condition of bin surfaces. Poorly maintained bins that rattle and vibrate during transport and that are made from rough-sawn timber can cause bruising and abrasion on fruit19. Plastic bins, plywood bins, and sanded or plastic-lined wood bins generally have smoother internal surfaces than sawn hard or soft wood. Grower experience in the USA suggests that smooth plastic bin surfaces reduce abrasion damage during fruit transport from the orchard. Less damage has been observed after pome and stone fruit has been handled in plastic as compared to wood bins but this has not been quantified ' . It has been determined that during harvesting operations in Australia more than 30% of oranges next to side walls inside wood bins may be damaged as a result of direct contact between fruit and internal surfaces °.

A study was conducted in the USA to compare the level of bruising and abrasion in Golden Delicious transported using plastic and hardwood bins . The results indicated that higher apple quality could be maintained if fruit was road transported in plastic bins and on semi-trailers equipped with air-cushion suspension. Overall quality of fruit positioned on the side of all bins was much lower compared to fruit in the middle. The percentage of undamaged fruit was significantly affected by suspension type, bin type and trip distance. Bruise damage was similar for each of the bins (ranging from 7 to 15%) when transported for 1.5 hours along a road in 'poor' condition. Abrasion damage was significantly higher for the fruit transported on steel spring suspension and in hardwood bins. Abrasion damage in hardwood bins averaged 65% as compared to 12% in plastic bins. In the air suspension tests the abrasion damage ranged from 0.6 to 5%.

Hygiene Wooden surfaces of fruit bins are ah important source of decay pathogens for pome fruit. Pathogens from bins contaminate DPA drenches and water flotation systems which in turn facilitate the spread of

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inoculum . The porous nature of wood surfaces means that they are easily contaminated and relatively difficult to disinfest. Manual pressure washing of wood bins with steam or water and disinfectant is a common disinfestation method. Pressures in excess of 1500 psi are usually required and it may take up to 5 minutes to thoroughly wash individual bins24. As the pressure washer nozzle needs to be close to the bin surface for effective pathogen removal, scuffing of the wood fibres may lead to a rougher internal surface after drying. Food safety studies have demonstrated that wooden boards innoculated with a mixture of bacteria and then disinfected still retained relatively high bacterial counts after cleaning. Studies on planed samples showed penetration of bacteria into the wood within the structural xylem fibres and vegetative elements .

Plastic bins are considered to be more hygienic, easier and quicker to clean than wood bins due the impervious nature of HDPE and their smooth surface3'5'6'8,18. To date, few studies on sanitation have verified this claim. Several disinfestation methods have been tested on small pieces of wood and plastic innoculated with P. expansum and Alternaria alternate?3. Steam was the most effective treatment for killing spores of both fungi on wood and plastic surfaces. Most chemical treatments were of similar effectiveness on plastic and wood. However sodium hypochlorite, a common disinfectant in the fruit industry, was more effective on P. expansum spores on plastic than on wood. Chlorine is highly reactive with organic matter and loses its efficacy very rapidly 6. This may explain why sodium hypochlorite more effectively reached spores on smooth plastic than on rough wood. In many cases bulk bins are only sanitised during water dumping or drenching of fruit with a disinfectant solution. This might not be very effective as chlorine in the recycled water is likely to react with wood bin surfaces and thus become inactivated9.

3.3 Economic comparisons At present the higher initial cost of plastic bins is preventing many growers from investing in this new handling technology. Due to the difficulty in obtaining industry cost data, very few economic analyses of the long-term cost of plastic and wood bins have been published. No detailed study of the Australian situation has been performed. At present it is difficult to quantify many of the advantages and disadvantages of plastic bins in dollar terms. In comparing the true operating cost of each bin type a number of factors need consideration including initial purchase cost, service life, interest rates, salvage value, maintenance cost, freight costs, depreciation, fruit damage cost, and chemical, storage and cooling costs .

An economic analysis comparing plastic and wood bins was conducted in the USA in 1995 . It is informative to note some of the conclusions reached in this study even though the cost structure differs from the Australian situation. An annual cost method was used as a non-uniform series of payments was involved. Long-term costs were calculated using a range of purchase prices and interest rates. Estimates of service life, maintenance cost and salvage value were also used. Other operating costs and increased returns from better quality fruit were not included in the calculations as they could not be determined. The study found that the average annual cost of wood bins is highly influenced by their service life because it is relatively short. The difference in annual costs between wood and plastic bins become marginal under low inflation and interest conditions over a 20-25 year period if the price difference between the two bins remains in a $AUS40-50 range. Increases and decreases in interest rate have a greater affect on annual cost of plastic bins than wood bins because a larger investment is necessary for plastic bins.

A practical economic model must include all costs to be useful to growers. Although it is difficult to estimate cost differences it is likely that important savings can be achieved using plastic bins because:

• At present plastic bins cost $100-150 but price varies depending on number purchased. Bin hire is also an option that isn't available with wood bins.

• A number of costs are incurred in repairing wood bins. These include labour, materials, inspection, sorting and disposal costs. The repair costs for plastic bins are expected to be low . They are also recyclable and have a salvage value.

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• It is likely that a significant reduction in postharvest fungicide usage will result from using plastic bins . Wood bins absorb moisture and chemical during drenching or dumping leading to chemical wastage.

• It has been demonstrated that significantly less abrasion damage occurs in plastic compared to wood bins during bulk apple transport21. Whether the losses during packout are significantly reduced by using plastic bins can only be determined by the grower under their own handling procedures. A combination of rough orchard roads, steel spring suspension on trailers, long trip time and highways in poor condition can cause substantial fruit damage. It is likely that under these conditions significantly more abrasion damage will occur in wood bins, particularly if they are poorly maintained, than in plastic bins.

• Plastic bins can be stacked as high or higher than wood bins resulting in equivalent or reduced storage costs. This is particularly important for growers who hire CA storage space from a larger packer or cooperative. Freight costs may also be reduced as positive interlocking and lighter weight of plastic bins allows more fruit to be carried per unit load. Up to four bins can be stacked on a truck but these may have to be secured to prevent shifting. Initial cooling in CA using plastic bins may result in reduced electricity costs due to the shorter time for which full refrigeration capacity is required.

4. Conclusions

Greater emphasis on quality assurance and higher expectations from consumers means that growers need to implement the best practices to ensure cleaner and better quality fruit. Wood bins have been the standard for many years but they do not meet all the design requirements to ensure optimum fruit quality and handling efficiency. Plastic bins are closer to the ideal bulk container for fruit handling and to an extent its advantages have been demonstrated from overseas grower experiences and a few research trials.

The importance of the issues raised here will vary depending on each grower's situation and the perceived costs and benefits of using plastic bins. In general the higher purchase price of plastic bins has deterred industry from using them but when all other factors are taken into account, they are a viable option over the longer term. Further information and research is required to determine true operating costs when using bulk bins in Australia. This can only be obtained if growers trial plastic bins, and costs and fruit quality differences compared to wood bins are recorded over a number of seasons. These innovative growers will then be in the best position to judge whether plastic bins are the future for the fruit industry.

5. Citations

Perstorp Xytec Inc., 1995. Macro Plastics Inc., 1996. The Grower, Jan. 1995. Van Vlack, Materials for Engineering (Addison-Wesley), 1982. Country folks grower, June 1995. Fruit Grower, June 1995. The Grower, Jan. 1995. Perstorp Plastic Systems Pty. Ltd., 1994. Pers. comm., 1997.

w Booklet 2355, Ministry of Agric, Fisheries & Food, 1981. 1 ' Waelti, FY 94 Briefing report, 1996. 12Blanpied,MS7/zesw, 1955. 13

Kader et al, Postharvest technology of horticultural crops, 1985. Packer/Shipper, June 1995. Fresh produce manual, AUF, 1989. Waelti, Plastic bins - How do they compare with plywood bins ?, 1995.

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Good Fruit Grower, May 1995. 18

Good Fruit Grower, March 1993. 19Maindonald & Finch, NZJ. of Technology, 1986.

Al Soboh, Citrus harvest notes 4, 1996. 21 Timm et al,ASAE Paper No.95-6169, 1995. 22 Holmes, Phd thesis, 1993. 23 Spotts & Cervantes, ISHS, No. 367, 1994.

Lopresti et al, Progress report, IHD, 1995. 25 Abrishimi et al, J. Food Safety, 1994.

Jolley & Carpenter, Environmental Impact and Health Effects, 1983. Waelti, Tree Fruit Postharvest Journal, 1992.

Acknowledgements The funding contributed by Perstorp Plastic Systems Pty. Ltd. and HRDC has been essential in the compilation of this paper.

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