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INTRODUCTION TOMILLING AND PARBOILING

presentation on :-

- :Subject: -

AGRICULTURAL PROCESSING

PRESENTED BY:-

Kaushal. V. Gadariya (PAGEN-097-2012)

Baria Dipak (PAGEN-091-2012)

Dave Dhruv (PAGEN-094-2012)

Chovatiya Chintan(PAGEN-093-2012)

MILLING

Milling refers to the size reduction and separationoperations used for processing of food grains intoedible form.

PRINCIPLES OF SIZE REDUCTIONS

Followings are some laws of energy required to sizereduction : -

- Rittinger's law

- Kick's law

- Bond's law

RITTINGER’S LAW

• It is states that the work required in crushing isproportional to the new surface created.

• Rittinger’s assumed that size reduction is essentially ashearing procedure.

• Therefore, energy requirement is proportional to thesquare of the common linear dimension .

• The value of n = 2

Where,E is energy requirement for size reductionXp is length of productXf is length of feed

SIZE REDUCTION METHODS

The size of agriculture products may be reducedby several ways, but mainly the following fourmethods are used in size reduction machines.

1.Compression or crushing.

2.Impact.

3.Shearing.

4.Cutting.

SIZE REDUCTION PROCEDURES

Crushing :-

In crushing the particle produced after crushingare irregular in shape & size.

The type of material and method of forceapplication affects the characteristics of newsurfaces and particles.

Food grain flour, grits and meal, ground feed forlivestock are made by crushing process.

Crushing is also used to extract oil from oilseedsand juice from sugarcane.

CRUSHING ULTRAFINE MILL

Impact:-

When a material is subjected to sudden blowof force in excess of its strength, it fails, like acracking of nut with the help of a hammer. Forexample Hammer mill.

Shearing:-

-It is a process of size reduction whichcombines cutting and crushing. The shearing unitsconsist of a knife and a bar.

Cutting:-

In this method size reduction isaccomplished by forcing a sharp and thin knifethough the material. The size of vegetables andfruits are reduced by cutting.

SIZE REDUCTION MACHINARYSize reducing devices are grouped as follows:-

SIZE REDUCTION MACHINARY

GRINDER

FINE DRINDER

CUTTING MACHINES

CRUSHER

WHEAT FLOUR MILL

HAMMER MILL

Crushers : -

- These type of reducing machines squeeze or press thematerial until it brakes.

- Crushers are mostly used to break large pieces ofsolid materials into small lumps.

- Crushers are used in industrial operations, like minesetc.

- Use of crushers in agricultural operations is limited.The crushers in use are,1.Jaw crushers. 2. Gyratory crushers. 3. Crushing rolls.

Grinders:-

- The grinders are used to mill the grains intopowder.

- The grinder comprises a variety of sizereduction machines like attrition mills, hammermills, impactors and rolling compression mills.

Cutting machines: -

- Size reduction of fruits and vegetables aremostly performed by cutting operation.

- To make thin slices of fruits and vegetablesknife cutter are used.

- Few types of knife cutters have been developedfor cutting slices / chips of potatoes, banana etc.

SIZE REDUCTION MACHINES

OPERATION AND PERFORMANCE

To achieve good results from any size reducing machinesthe followings should be given due care,

Feed should be of proper size and feeding rate should beuniform.

Hard or unbreakable material is not allowed to enter themill.

After grinding the product is removed as soon aspossible.

There should be some arrangement to remove the heatgenerated during milling operation.

OIL EXPRESSION

Expression is the process of mechanicallypressing liquid out of liquid containing solids.

Screw presses, roll presses and mill, collapsibleplate and frame filler presses, disk mill are someof examples of a wide range of equipment usedfor expression of liquid.

FIG: OLIVE OIL PRESS

MECHANICAL EXPRESSIONDEVICES

Hydraulic press: -

- It considered of a series of horizontalcorrugated iron plates.

- These plates are separated by 4 to 14 remoldedoil seed cakes.

- Pressing is completed in two stages.- In the first stage, the oil samples are pressed at

approximately 5MPa for 15 to 20 minutes.- Afterward a pressure of 28MPa is applied for 5

to 10 minutes to complete the expression process.- The output of the press varied depending on the

sizes seed being pressed.

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Screw press: -

- In screw press, the press has a horizontal mainshaft.- The screw assembly is formed integrally with thisshaft.- This screw rotates within a cage of barrel.- Barrel is made of case hardened, tool steel bars orthis may be made out of assembly of rings.- Spacers are used between the lining bars or ringsto allow drainage of the oil as the pressure on thefeed material is increased.

FIG: SCHAMETIC VIEW OF HYDRAULIC PRESS

OIL EXTRACTION

Extraction is the process of separating a liquidfrom a liquid-solid system with the use ofsolvent.

Extraction may also be said as a process toextract oil from oil bearing material throughprocess of diffusion with the help of low boilingpoint solvent.

This process gives a higher recovery of oil and adrier cake then expression.

OIL EXTRACTION METHOD

Extraction methods include: -

Traditional methods:-

- Oil is extracted from, for example, freshcoconut, olive, palm fruit Shea nut by separatingthe flesh and boiling it in water.

- Salt can be added to break any emulsion whichis commonly formed and the oil is skimmed fromthe surface. In palm oil processing the fruit is firstheated in a digester.

• Manual methods:-

- Oil can be extracted by pressing softer oilseedsand nuts, such as ground nuts and Shea nuts,whereas harder, more fibrous materials such ascopra and sunflower seed can be processed usingghanis.

- Pulped or ground material is loaded into amanual or hydraulic press to squeeze out the oil-water emulsion.

MECHANIZED EXTRACTION Ghani (kolhus):-

- The Ghani consists of a large mortar and pestle, the

mortar being fixed in the ground and the pestle being

moved within the mortar by animal traction (donkey or

mule) or a motor.

- Oilseeds are placed in the mortar and the pestle grinds

the material to remove the oil.

- The oil runs out of a hole in the bottom of the mortar and

the cake is scooped out by hand.

- This method is slow and requires two animals, replacing

the tired one with another after about 3-4 hours of work.

ANIMAL DRAWN KOLHUS

Expeller :-- The basic steps involved in processing

oilseeds by expeller are shown in the flow diagrambelow.

PARBOILING

It is a pre milling treatment given to paddy prior to itsmilling to achieve maximum recovery of head rice and tominimize breakage.

In this process paddy is soaked and the wet paddy isheated and dried.

During soaking of paddy water penetrates into starchgranules and result in swelling of grains.

In heating, the energy weakens the granule structure andmore surface becomes available water absorption andresult in irreversible granule swelling.

This phenomenon is called gelatinization of starch.

The main objectives of parboiling are –

1. to increase the total and head rice yield ofpaddy.

2. to prevent the loss of nutrients during milling.

3. to salvage wet or damaged paddy.

4. to mill the rice according to requirement ofconsumers.

ADVANTAGES OF PARBOILING

The milling yield increases and the quality isimproved.

The milled rice becomes translucent and shining.

Shelling of parboiled rice is easier.

Bran of parboiled rice has more oil.

Parboiled rice retains more proteins, vitamins andminerals.

Parboiled rice is more digestible and less solids areleft behind in the cooking water.

DISADVANTAGES OF PARBOILING

Parboiling process needs extra capital investment.

Parboiling adds to the cost of drying.

More power is required for polishing of parboiled rice.The process becomes difficult and lowers the capacity ofpolisher.

Parboiled rice takes more time to cook than raw rice andmay have characteristics off flavor which may not beliked by raw rice eaters.

The heat treatment during parboiling destroys somenatural anti-oxidants.

SOAKING STEAMING DRYING

Parboiling of paddy is carried out in three steps,

PARBOILING OF PADDY

Soaking of paddy is carried out by dipping in water.Dipping in water at ambient temperature takes longtime (72 h) for soaking, making paddy susceptible todevelopment of micotoxins.

Hence, soaking at elevated temperature of water isconsidered better. The soaking duration varies withwater temperature.

1.Soaking of paddy: -

S. No. Temperature, °C Time, h

1 Water heated to 50°C and allowed to come to

ambient temperature

24

2 Water heated to 75°C and allowed to come to

ambient temperature

12

3 Maintained at 60°C 8

4 Maintained at 65°C 6

5 Maintained at 70°C 4

6 Maintained at 72°C 3.5

7 Steam at 0.5 atm. pressure 0.4

The following time-temperature combination is considered optimum

for soaking:

Time-temperature combination for soaking of paddy:

2. Steaming of paddy: -

PARBOILING OF PADDY

Steaming is carried out to gelatinize starch. Generally, saturated steam at a pressure of 1-5kg/cm2 is used for steaming of soaked paddy. Duration of steaming depends upon quantity ofpaddy. For small batch, 2-3 min whereas for largebatch (6-8 tones), 25-30 min of steaming isrequired.

3. Drying of paddy: -

Drying of parboiled paddy from 45-50% (db) to 14-16% (db) needs to be done for proper milling andstorage.

Sun drying of paddy is generally practiced. For uniform drying, it is important that paddy is spread

in 2-3 cm thickness layer and stirred at an interval ofhalf hour.

It is also important that paddy is dried in two passesinstead of continuous drying. In first pass, paddymoisture content should be brought down to 18-20%and rest in second pass.

Parboiling tank is filled with clean water and heated to

about 85°C.

Paddy is dumped into hot water in tank for soaking. the

temperature of paddy-water mixture comes down to 70°C

which is maintained for 3-3.5 h.

After soaking, water is drained from tank and then

exposed to steam at a pressure of 4 kg/cm2 until husk

starts splitting. Steamed paddy is dried in multiple passes. During parboiling, the water requirement is about 1.25

times the weight of paddy and requirement of steam is

about 200 kg/ton of paddy.

CFTRI PARBOILING METHOD

Thanks for your attention

Have a good day………….