Previous Year Questions(Solved) | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

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   1. Que 1:  Write short note on salient Points to be Kept in Mind While Collecting and Transporting Raw Milk (CSE, 1981):
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   3. Collection:
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   • Milk collection should be swift, with reception expedited within 3 to 4 hours, especially for large volumes.
   • Timely collection prevents milk deterioration, reduces labor and operation costs.
   • Incoming milk quality significantly influences the final product; it should be clean, sweet, and free from contaminants.
   • Contamination with antibiotics, pesticides, and other chemicals is undesirable; abnormal milk should be rejected.
   • Acid development indicates bacterial count and reduces heat stability; such milk should not be accepted.
   • Grading based on organoleptic tests (odor, taste, appearance, acidity, sediment) is essential.
   • Water adulteration should be checked using a lactometer and Gerber's test.
   • Accurate samples must be collected for bacteriological and chemical examinations.

3. Transport:

   • Choose appropriate transport modes; for short distances, use head load, shoulder sling, pack animals, bullock carts, bicycles, or cycle rickshaws.
   • Larger quantities and longer distances may require lorries, rail or road-tankers.
   • Within a 50 km radius, lorries can transport milk in ordinary cans; for a 100 km radius, chilling centers are needed.
   • Prefer insulated milk tankers over cans for large quantities to minimize surface contamination and temperature issues.
   • Restrict transport between collection centers and milk producers; use insulated milk tankers for transport to the plant.
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   2. Que2 : What do you understand by Pasteurization of Milk. Give different methods of Pasteurization.(CSE, 1981):

5. Definition:

   • Pasteurization involves heating every particle of milk to specific temperatures for designated durations to ensure safety and improve keeping quality.

6. Methods:

   • In-the-Bottle Pasteurization:

     • Bottles held at 63.66°C for 30 minutes; not commonly used due to slow heat transfer and risks of bottle breakage.

   • Batch/Holding Pasteurization (LTLT):

     • Milk heated to 63°C for 30 minutes and promptly cooled; three types - water-jacket, water-spray, and coil-vat.

   • High Temperature-Short Time (HTST) Pasteurization:

     • Heated to 161°F for 15 seconds; plate heat exchanger widely used.
     • Advantages: Quick treatment, lower initial cost, easily cleaned.
     • Disadvantages: Not suitable for small quantities, gasket maintenance, milk stone accumulation.

   • Vacuum Pasteurization (Vacreation):

     • Pasteurization under reduced pressure using direct steam.
     • Designed for cream pasteurization; removes volatile flavors.

   • Stassination:

     • Tubular exchanger with three concentric tubes; heats milk to 74°C for 7 seconds.

   • Ultra-High Temperature Pasteurization:

     • Temperatures of 130-150°C for a fraction of a second; requires immediate aseptic packaging.

   • Uperization:

     • Heated to 150°C for a fraction of a second with preheating steps; offers long keeping quality.

Que 3:  Define Clarification, Homogenization, Pasteurization, and Sterilization of milk. Briefly narrate the principles involved in HTST and Holder methods of pasteurization. What is the acceptable Indian Standard Plate Count (per ml) for pasteurized milk at the plant in its final container? (CSE, 1990)

Ans: Clarification of milk is the process by which the suspended foreign particles in milk are removed by a process of centrifugal sedimentation. This is done to improve the appearance of milk by removing visible foreign matter that is unsightly and may cause consumer complaints.

Homogenization of milk is the process by which the fat globules in milk are broken up to such an extent that after 48 hours of quiescent storage, no visible cream separation occurs in the milk, and the fat percentage of the top 100 ml of milk in a quart bottle or proportionate volumes in containers of other sizes does not differ by more than 10 per cent from the fat percentage of the remaining milk, as determined after thorough mixing. In efficiently homogenized milk, the fat globules are subdivided to 2 microns or less in diameter.

Pasteurization of milk: The term 'pasteurization' as applied to market milk today refers to the process of heating every particle of milk to at least 63°C (145°F) for 30 minutes or 72°C (161°F) for 15 seconds (or to any temperature-time combination which is equally efficient) in approved and properly operated equipment. The term pasteurization has been derived from the name of Louis Pasteur of France, who between 1860-64 demonstrated that heating wine at temperatures between 122 and 140°F (50 to 60°C) killed spoilage organisms and helped preserve wine. Pasteurization of milk is attributed to Dr. Soxlet of Germany when he applied this principle of Pasteur to milk in 1886.

Sterilization of milk: The term sterilization, when used in association with milk, means heating milk continuously to a temperature of 115°C for 15 minutes or 145°C for 3 seconds or an equivalent time-temperature combination to ensure preservation at room temperature for a period of not less than 15 days from the date of manufacture. Sterilized milk shall show the absence of albumen by a negative Turbidity Test. Sterilized milk shall be sold only in the container in which the milk was sterilized.

Principles involved in HTST and Holder Method of Pasteurization: HTST (Plate) Pasteurization: This is a continuous process for large-scale handling. It allows for much greater regeneration than would be possible with any other process.

Procedure and Principles Involved: The milk from the raw milk storage tank enters into the balancing tank, which is provided with a float-controlled valve for gravity flow. The float regulates the milk flow into the balancing tank. From the balancing tank, the raw milk is pumped by a timing pump into the first compartment of the pasteurizer called the generator. Here, preheating of the raw milk takes place by counterflow of hot milk on the other side of the plate. The preheated milk coming out of the regenerator enters the filter. Preheating becomes essential if the incoming milk is cold; otherwise, the flow of milk is hampered. As the temperature of milk increases, the viscosity decreases, and more efficient filtration results. Filtration/clarification is done to improve the appearance of milk by removing visible foreign matter, which is unsightly and may cause consumer complaints. Both filtration and clarification tend to decrease the depth of the cream layer that will form on milk, and this becomes more pronounced as the processing temperature increases. Filtration does not improve the keeping quality of milk. Milk coming out of the filter enters into the heating section of the pasteurizer, where it is heated to the required temperature. This is accomplished by a plate heat exchanger that consists of a series of assembled plates. The milk flowing on one side of the plate is heated by the hot water flowing on the other side in the opposite direction. Then the milk goes to the holding section, where it is held for the required time. From the holding section, milk goes through a flow division valve. If the milk is not heated to the required temperature, the FDV diverts the milk to the balancing tank. If the heating of milk is proper, it re-enters the regenerating section of the plate exchanger to heat the incoming raw (cold) milk at the same time it is partially cooled. Further cooling is done by the chilled water in the cooling section of the plate exchanger, where again the milk will be flowing on one side of the plate, and the chilled water with counter-current flows on the other side. The chilled milk goes to either the packaging section or the pasteurized milk storage tank. The pressure of raw milk is lower than the pressure of pasteurized milk, so there is no chance for any possible contamination of pasteurized milk with raw milk. For the same reason, the heating and cooling media are circulated at a lower pressure than that of raw milk. The advantages of HTST pasteurization are: 1. Being a continuous process, there is no wastage of time, and milk can be bottled within a few minutes of entering the plant, thus permitting more efficient use of labor for packaging and distribution. 2. This type of equipment occupies only a fraction of the floor space required for the Vat (Batch) method. A 4.5 square meter area will suffice for handling 10,000 liters of milk per hour. 3. A proportionately lower initial cost of equipment for a large volume of operations. 4. Maximum use of regenerative heating and cooling with lowered costs for heating and refrigeration. 5. The equipment is easily cleaned, and the sanitized system adapts itself to CIP (Clean in Place) cleaning. 6. The possibility of outside contamination is eliminated because of the closed system. 7. Difficulties due to bacterial growth of thermophilic bacteria are eliminated. 8. Automatic precision controls ensure positive pasteurization.

Holder Method of Pasteurization: This is a low-temperature long-time process where milk is heated to 63°C/145°F for 30 minutes and promptly cooled to 5°C or below. In this system, heating is done indirectly, the heat moves through a metal wall into the product for heating and out of the product for cooling. The pasteurizers are of three types: (i) water-jacketed vat, (ii) spray type, and (iii) coil vat type.

The advantages in the above are flexibility in use, in that other fluid products like flavored milk, ice cream, etc., may be handled.

The acceptable Indian Standard Plate Count/ml (per ml) for pasteurized milk at the plant in its final container is it should not exceed 30,000 per ml.

Que 4. What are the problems in the collection and transportation of raw milk from rural to urban areas in India? How can these be overcome? (CSE, 1991)

Production of milk is generally confined to rural areas, while demand is mostly urban in nature. Hence, milk has to be collected and transported from production points in the milk shed areas to processing and distribution points in the cities.

This is done through cooperative organizations formed by individual or collective milk supply societies. This suits the producers best because it secures a fair price for the producer as no profit-making middlemen are involved. Milk is also procured or collected by contractors, but in such cases, there is less return to the producers. Milk is also procured and supplied by individual producers. This is possible only for those situated near processing dairies. The allocation of definite milk sheds to individual dairies for the purpose of developing the same is advisable.

Other aspects to be considered in collection are:

(i) to preserve the quality of raw milk supplies; and

(ii) to provide easy transport to the processing dairies.

The quality of raw milk is preserved by establishing milk collection-cum-chilling centers. The items of equipment such as milk weigh tank/pan and weighing scale, drop tank, can washer, milk pump, surface/plate cooler should be suitably cleaned. There should be a refrigeration unit as well as a cool room of suitable capacity.

On arrival, the milk should be graded for acceptance or rejection, weighed, sampled for testing, cooled, and stored at low temperature until dispatch to the processing dairy. Milk contains some microorganisms when drawn from the udder; their numbers increase during subsequent handling. This increase in numbers will result in the deterioration of the quality of milk. This is prevented by prompt cooling to a low temperature. This can be done by in-can or can immersion method or in surface coolers or in-tank or bulk tanker coolers or in-milk chilling centers.

Transport of Raw Milk:

The road condition in any country poses a problem for the transport of milk. There are several methods of transport for milk in India. For small loads and short distances, head load, shoulder sling, animal forage (horses and donkeys), bullock cart, and tonga are used. For long-distance city milk plants, milk is transported by motor trucks, rails, and road tankers. If the milk is to be collected within a radius of 50 km, lorries can be used for bringing the milk in ordinary milk cans. If the distance is more than 50 km, collection-cum-chilling centers will have to be provided. Depending on the quality, milk can be transported either by road tankers or by lorries carrying thermocans. If the distance is beyond 50 km, thermocans become necessary. If the milk is to be transported from a place 300 km or beyond to a central dairy, it has to be pasteurized and sent by road or rail tanker in thermocans in lorries or train. Large quantities are always transported by road or rail tankers to be economical.

The spoilage of milk when transported in road tankers is less compared to transport in thermocans in lorries because of the low ratio of surface area to volume of milk in the former. Further, the temperature of milk in road tankers is lower, and so bacterial count is low. Hence, for long-distance transfer of milk, the road tanker is the best in spite of the heavy investment since the transfer cost is minimum, and there is no spoilage of milk because of less contamination, better refrigeration, and bacterial quality are assured. A rail tanker will involve additional expenditure on railway siding and also a road tanker for collecting milk from the rail tanker. Further, if the milk is transported by rail, it also involves additional labor in transport of milk to the railway station, delay in booking and collection at the receiving end and transport to the central dairy.

The use of cans is nowadays restricted to and from the collection centers and the milk producers. Thus, road transport is recommended over short distances as it is cheaper than rail, less time-consuming, while rail transport is recommended over long distances and when large quantities of milk are to be handled at a time.

Que5: Discuss the processes involved in the manufacture of butter in a factory.

(CSE 1987)

On receiving, the milk in the dairy plant is graded, sampled, weighed, and tested. Then

it is preheated to increase the efficiency of the cream separation. The cream is separated by centrifugal

methods and the same is neutralized by adding the required amount of lime and soda. Subsequent

to the neutralization of cream, the cream is standardized, pasteurized, cooled, aged, ripened,

churned, washed, settled, and worked and finally packed and stored.

Standardization of cream: This consists of adjustment of the fat level in the cream to

the desired percentage by the addition of the calculated amount of skim milk. The purpose is to

obtain the lowest fat loss in buttermilk during churning.

Pasteurization of cream: The standardized cream is then pasteurized by any one of

the following methods: (1) Holder pasteurization, (2) HTST (plate) pasteurization, and (3) vacuum

pasteurization. Holder method is used for small-scale pasteurization while HTST (Plate)

pasteurization is followed for large-scale handling. Plate pasteurizer is better suited for freshly

separated sweet cream than neutralized cream. The maximum temperature in HTST is 95-100°C

(203-212 F) for 15-16 seconds.

Cooling and aging of cream: After pasteurization, the cream is cooled and then aged

to make churning possible. Cream will not churn until the butter-fat in the fat globules has

at least partially solidified. If it is improperly solidified, the butter will have a weak body. The

optimum cooling and aging under Indian conditions are 5-10°C (41 to 50°F) for at least 2 to 4

hours. 15-16 hours overnight cooling is preferable.

Ripening of cream: This refers to the fermentation of cream with the help of desirable

starter cultures. The objective of ripening is to produce butter with pleasing flavor and aroma

and to obtain exhaustive churning with low fat loss in buttermilk. The butter-starter culture

containing lactic acid producers like Streptococcus lactis and/or Streptococcus cremoris

together with aroma (diacetyl) producers is added to the standardized, pasteurized, and cooled

(20-22°C/68-72 F) cream at 0.5 to 2.0 per cent. After it is thoroughly mixed, the cream is incubated

at 21°C (70°F) for 15-16 hours.

Churning: This consists of agitation at a suitable temperature until the fat globules

adhere, forming larger and larger masses until a relatively complete separation of fat and serum

occurs. The churning operation consists of (a) preparing the churn, (b) filling cream into the

churn and (c) addition of butter color.

The churn should be properly sanitized and cooled. The amount of cream to be filled

should be slightly below the rated capacity. A standard butter color of vegetable origin like

annatto or carotene or mineral origin like coal-tar dyes varying between 1 and 250 ml per

100 kg is to be added to the cream.

Operating the churn: After initially rotating the churn for 5 to 10 minutes, the liberated

gas is removed, once or twice by opening churn vent. Then the cream sample is drawn for the

fat test. During churning there is invariably a rise in temperature from 1 to 30°C. Sometimes

water (breakwater) is added to reduce the temperature of the churn contents. The addition of

breakwater can be avoided by providing an air-conditioned butter making room and/or chilled

water spray over the butter churn.

Washing: The next operation is washing. This is done to remove all loose buttermilk

adhering to the butter grains so as to reduce the curd content of the butter thereby improving

its keeping quality, to correct defects in the firmness of butter and to decrease the intensity of

certain off-flavors. The procedure in washing consists of first draining the buttermilk. Then

chilled water equal to the amount of buttermilk drained is added at a temperature 1 to 20°C

lower than the churn temperature. After a few revolutions, the wash water is drained out.

Salting and working: This refers to the addition of salt to butter to improve the keeping

quality, to enhance taste and to increase overrun. Common salt is added at the rate of 2 to 2.5

per cent of butter fat. Salting can be done by: (1) Dry salting when the desired amount of dry

salt is sprinkled over the butter during working: (2) Wet salting when the calculated amount of

salt is wetted in the least amount of potable water and then sprinkled over the butter, (3) Brine

salting when the salt is added in the form of a saturated solution of brine.

Working: This refers to the kneading of butter to completely dissolve, uniformly distribute

and properly incorporate the salt and to bring the butter grains together into a compact mass

for convenient handling and packing. During working, the moisture in butter is reduced to

droplets of microscopic size. The working should be continued until the butter has a compact

body, a closely knit grain, a tough waxy texture and even distribution of salt and moisture. There

should be no free moisture on the sample drawn by a butter drier. The legal limit of moisture

content in butter in most countries is 16 per cent although it is 80 per cent fat in India.

Packaging of butter. The butter is removed from the churn either manually or by gravity

or, by mechanical means. Bulk or wholesale packs are done in developed countries in

boxes/tuba/casks (New Zealand 66 lb; US 63 lb; Europe 50 kg). The packaging material is wood

or timber-like white pine to which is given a paraffin lining. Retail packs are of 1, 2, 4, 8 or 16 kg

or 25, 50, 100, 250, 500 gm packs. Vegetable parchment paper cellophane or aluminum foil

laminates are used as packing material. Tin plated cans are used in tropical countries.

Storage of butter: Butter is stored at temperatures ranging from - 23°C to 29°C

(-10°F to -20°F) commercially. There is invariably some flavor deterioration on storage. There

is a slight loss of weight on storage caused by the evaporation of moisture from the butter pat

Moisture-proof/grease-proof wrappers cause less shrinkage. Lower the temperature of storage

lower is the shrinkage. The keeping quality of butter is reduced by higher temperature of storage.

Exposure to light lowers keeping quality. Sweet/unsalted butter has a better keeping quality

than salted butter. Butter should be kept in a dry cool place not directly exposed to sunlight.

The temperature during the entire period of distribution should be between -16°C and -29°C

(0 to 20°F), It may be sold in retail trade from a deep freeze or refrigerated butter box.