PasteurizationDr. Mohammad Ashraf Paul

Division of Livestock Products TechnologyFaculty of Veterinary Sciences & Animal

Husbandry ,SKUAST-K Alusteng, Ganderbal Kashmir

• PasteurizationHistory Term pasteurization coined after the name of louis

Pasteur of France, who in 1860-64 demonstrated that heating wine at a temp. between 122-140oF (50-600C) killed the spoilage organisms and helped in its preservation.

Although louis Pasteur pioneered studies on heat-treatment for preservation, pasteurization of milk was first attributed to Dr. Soxhlet of Germany in 1886.

Definition Pasteurization refers to the process of

heating every particle of milk to at least 630C (1450 F) for 30 m, or 720C (1610 F ) for 15 sec. or to any temp-time combination which is equally efficient, in approved and properly operated equipment. After pasteurization, the milk is immediately cooled to 50C(410F) or below.

Objecta. To render milk safe for human consumption by

destruction of cent % Pathogenic organisms.

b. To improve keeping quality-by destruction of almost all spoilage organisms (85-99%)

Objections:a. may be used to mask low quality milkb. Encourages slackening of efforts for clean milk

productionc. It diminishes significantly the nutritive valued. It reduces the cream line/cream volumee. Pasteurized milk does not clot with rennetf. Careless pasteurization gives a false sense of security.g. Fails to destroy bacterial toxinsh. In India, pasteurization is of little use as the milk is

invariably boiled before use.

Standards for pasteurization

A. Bacterial destruction– Cent percent for pathogens– Index /target organism– Most heat resistant – Mycobacterium tuberculosis

– Coxiella burnetti ,Listeria monocytogensB. Cream line reduction– Cream line (Quality) reduces with increase in time temp combinations

C. Phosphatase inactivation– Complete destruction of phosphatase enzyme

Thus the standards for pasteurization are such as to ensure:

Complete destruction of pathogens

Negative phosphates test.

Least damage to cream line.

Pasteurization requirements

Considerations @ 30 minutes

@ 15 seconds

To Kill T.B germs 58.900C 700C

To inactivate phosphatatase

61.10C 71.10C

Optimum Cream line 62.20C 72.20C

Pasteurization Requirement

62.80C(63.0)

71.70C(72.0)

Salient remarksa. Although considered as a health measure it is

actually a commercial expedient.b. Pasteurization is neither panacea nor fool proof Process & equipment ( Methods/types)

1. In - the - bottle pasteurization 2. Batch/ holding (LTLT)a. Water jacked vat.b. Water spray type.c. Coil vat type

3. Continuous processesI. Vacuum Pasteurization (Vacreation )II. Stassanization.III. Flash pasteurization IV. Electric pasteurization V. Uperization VI. HTST pasteurizationVII. UHT pasteurization

1. In- the- bottle pasteurization Filled bottles tightly sealed with special caps held at 63- 660C (145-1500F)/ 30min. Bottles pass thru cold water spray of decreasing temp. Advantages: prevents possibility PP contamination. Disadvantages: very slow heat transfer Risk of bottle breakage oversized bottles have to be used to allow for milk expansion

during heating Special types of water tight caps have to be used. Method is outdated- however in the bottle sterilization is

prevalent

LTLT Method/Batch method

• Low Temperature Long Time

• Milk heated to 63 o C for 30 minutes

• Heating is indirect

• Heat moves through a metal wall

• flexibility in use multipurpose or multi process vat.

Water jacketed Vat/Process vat

• Double walled vessel• Steam or hot water circulates for heating

• Water for cooling• Outer wall is insulated to reduce heat loss

• Heat exchange through the inner wall to milk

• Difference between temp of heating medium and milk ΔT is kept minimum

• Milk is agitated by slowly moving paddles/propellers

Water Spray type

• A film of water is sprayed from a perforated pipe over the surface of the tank holding the product

• Milk is agitated

• Rapidly moving continuous film of water provides rapid heat transfer

Coil vat type

• Heating /cooling medium is pumped

through a coil

• Coil placed either vertical or

horizontal

• Coil is immersed inside the

product

• Coil is turned through the

product

• Turning agitates the product

• Coils difficult to

clean(Disadvantage)

General remark (holding/batch pasteurization)

i. Vat heating / cooling is rather slow and involves too much agitation, causing churning and impairment of creaming properties

ii. Operation can be efficiently carried out by plate or tubular heat exchanger

iii.With the installation of multiple vats a continuous flow of milk can be obtained, however this may encourage growth of thermopillic organisms over long periods.

Vacuum Pasteurization (vacreation):

Developed in new Zealand by M/s Murray Deodorizers Pvt. Ltd primarily for pasteurization of cream for butter manufacture.

Now used for milk . Under low pressure/ vacuum product

is pasteurized which helps to remove off odors.

Steam has to be of very good quality as it comes in direct contact with the product

3 chambers of SS.

Stassanization

Term coined after Henry stassano of France

Used extensively in Denmark, Italy, France etc.

Tubular heat exchangers based equipment

Three concentric tube structure Milk passed thru a pipe (0.6-0.8 mm

dia.) Heated up to – 740C /7secs Cooled promptly

Flash pasteurization

Milk in thin film forced between two heated surfaces

One of such units, the Danish heater

system consists of a large cylinder with a jacket.

Steam in the central cylinder heats

water between cylinder and jacket.

Milk is pumped into bottom of the unit then moved by centrifugal force to the walls of the tank where it is heated. The products then leaves through a pipe at the top end of the tank liner

No particular holding time is required as the product is heated up to 850C

Process of regeneration can be used by passing the out going warm milk thru a heat exchanger so that heat is passed to incoming milk.

UPERIZATIONo Term derived from ultra pasteurizationo First developed in Switzerland o Milk directly heated with steam to 1500C for a

faction of . Process Raw milk clarified chilled & stored

In the first phase milk fore warmed (500C)

Deaeration chamber -removes dissolved O2 & volatile off flavors

II phase preheating (80-900C) in the same chamber

Product Pumped to uperization chamber

Heated to 1500C for 1/3 -3/4th of a second

Expansion chamber ( maintained at atmospheric pressure) – removes moisture/ steam

Entrainment chamber-removes extra moisture & if some milk comes with moisture it can

be regained

Advantages

• Long keeping quality• Removes of off odour efficiently• Appreciable homogenization effect is achieved.

• Reduction in the acidity of products • Efficient destruction of micro- organisms

• Effect on nutritive value & flavor- comparable with HTST

CautionSteam has to be high quality- free from boiler components. Dry saturated steam & not exhaust steam

HTST System First developed by A.P.V. co. (Aluminum plate & vessel co. England in 1922.

Used where larger volumes of milk are to be handled- 720C/ 15 sees cooling 50C or below

Advantages ~Quick and adequate heat transfer with rigid quality control over both raw and finished products

~Less floor space required ~Lower initial costs ~Simultaneous packaging is possible ~Easy cleaning & sanitization

~Lower operating costs

- Capacity can be increased at nominal cost.

- Reduced milk losses.- Growth of thermopiles is not a problem unlike batch process.

- Process after interruption can be quickly restarted.

- Automatic precision controls ensure positive pasteurization

Disadvantages• Not well adapted for small scale production

• Gaskets need a constant attention for damage and cleanliness

• Margins of safety in product sanitary control are so narrow, that automatic control

• Functions of Important components

Float-controlled balance tank (FCBT): maintains a constant level of raw milk for feeding the raw milk pump.

Receives sub-temp milk diverted by FDV.

Pump: A rotary positive pump between

regenerator and heater (USA) or a centrifugal pump with a flow control device after FCBT (UK & Europe)

Plates: Plate heat exchanger (Para flow) is

commonly used.

Plates used for heating, cololing,holding, Regeneration

Rubber gaskets vulcanized to Plates Corrugations for turbulent flow

Regeneration heating: The raw (cold) milk is Partially and

indirectly heated by out going warm milk, (Milk-to-milk regeneration)-adds to economy of HTST method as less heat is required for the milk to reach the required temp.

Filter: Placed after pre-heater or regenerative

heating, cylindrical ,40-90 mesh cloth. Two filters are used but one at a time-permits continuous operation.

If one gets out of older, we can switch on the other.

Holding:• Plates or tubes-holds at 720C/15 sec. Flow diversion valve (FDV): Pasteurized→ directed forward Under pasteurized→ diverted back for

proper heat treatment to FCBT. FDV: Controlled by a device called –safety

thermal limit recoder(STLR) operated by air pressure working against strong spring.

Temp→ air pressure →value shuts safe immediately

Pump stop: Substitute for FDV under pasteurized milk→ pump stop →

stops pump motionRegeneration (cooling): Pasteurized outgoing milk is

partially and indirectly cooled by the incoming cold milk (Milk to milk regeneration

Control Panel: consists of: ~Control instruments ~FDV-mechanisms ~ holding system

All centralized in a moisture proof panel. Lower part of panel forms an air insulated chamber which carries the holding tube.

Hot Water Set : Circulates hot water though the

machinery wherever it is required and maintains correct milk temp within very fine limits.

Automatic control device: i. Steam pressure controller - acts

as a reducing valve in the steam line to give a constant steam pressure and constant temperature

ii.Water temperature controller - regulates the amount of steam entering the hot water circulating system.

iii.Milk temp recorder –thermograph.

Pressure in the system: Pasteurized milk -15 psi Raw milk-14 psi Heating/cooling medium-12-13 psi

Holding time test: flow time of the fastest

moving particle of milk at a prescribed temperature though the holding section.

Methods of testing holding time: i. Electrical conductivity (salt soln) ii.Dye injection methodsiii.Electronic timer method.