Dairy Processing

• Domestication of animals for milk goes back to 6000 – 8000 BC.

• Milk is consumed as a fluid or used as a raw material to various types of dairy products – butter, cheese, ice cream etc.

• Number of dairy products is very high.

• The tropical countries have not been traditional milk consumers, whereas the more northern regions of the world, Europe (especially Scandinavia) and North America, have traditionally consumed far more milk and milk products in their diet than tropical people.

United States 77,470

India 38,500

Germany 28,180

France 23,970

Brazil 23,300

China 18,850

New Zealand (2004) 14,500

United Kingdom 14,400

Poland 12,700

Netherlands 10,630

Italy 10,400

Australia (2004) 10,700

Mexico 9900

Canada 7540

Cow milk production ('000 tonnes) in selected countries in the world (2005).

• Milk - is defined as a lactal secretion of mammals practically free from

• colostrum - yellowish colour, salty liquid has a very high serum protein content.

• Within 72 hours, the composition of colostrum returns to that of fresh milk.

• Milk nourishes young mammals provides immunological protection

• Composition of milk varies from mammal to mammal.

Composition of Milk from Different Mammalian Species (per 100 g fresh milk).

  Protein (g) Fat (g) Carbohydrate (g) Energy (kcal)

Cow 3.2 3.7 4.6 66

Human 1.1 4.2 7.0 72

Water Buffalo 4.1 9.0 4.8 118

Goat 2.9 3.8 4.7 67

Donkey 1.9 0.6 6.1 38

Elephant 4.0 5.0 5.3 85

Monkey, rhesus 1.6 4.0 7.0 73

Mouse 9.0 13.1 3.0 171

Whale 10.9 42.3 1.3 443

Seal 10.2 49.4 0.1 502

• Milk components vary not only in amounts but also in exact composition except lactose e.g fatty acid of goat milk – melting points, flavor characteristics, allergic reactions are different from cows milk.

• This has to be considered in milk processing.

• Composition of cow’s milk itself varies on many factors – breed, animal to animal, age, stage of lactation, season of the year, feed, time of milking, period of time between milkings, physiological condition etc.

• Because of this variability only a approximate composition for milk can be given.

Gross composition of milk of various breeds, g/100g.

 Body Wt.

(kg)Milk Yield

(kg)Fat (%) Protein (%)

Lactose (%)

Ash (%)Total

Solids (%)

Holstein 640 7360 3.54 3.29 4.68 0.72 12.16

Brown Swiss

640 6100 3.99 3.64 4.94 0.74 13.08

Ayrshire 520 5760 3.95 3.48 4.60 0.72 12.77

Guernsey 500 5270 4.72 3.75 4.71 0.76 14.04

Jersey 430 5060 5.13 3.98 4.83 0.77 14.42

Shorthorn 530 5370 4.00 3.32 4.89 0.73 12.9

Holstein

Brown Swiss

Ayrshire

Guernsey

Jersey

Shorthorn

Approximate Composition of Milk• water (range of 85.5% - 88.7%) • 3.9 % milkfat (range of 2.4% - 5.5%) • 8.8% solids-not-fat (range of 7.9 - 10.0%):

– protein 3.25% (3/4 casein) – lactose 4.6% – minerals 0.65% - Ca, P, citrate, Mg, K, Na, Zn, Cl,

Fe, Cu, sulfate, bicarbonate, many others – acids 0.18% - citrate, formate, acetate, lactate,

oxalate – enzymes - peroxidase, catalase, phosphatase,

lipase – gases - oxygen, nitrogen – vitamins - A, C, D, thiamine, riboflavin, others

Milk ComponentsWater• Provides the medium for the other components.• Hydrate salts and lactose.• There tow types – free, bound.Fat• Increase palatability and the smoothness of

products - lubrication. • The main milk lipids are triglycerides (98 -

99%).• 95% of milk fat exist as fat globules – Diameter

0.1 to 15 μm – covered by a membrane – 8-10 nm.

• Fat globule membrane is composed of phospholipids (1-2%), and proteins.

• In the core less polar sterols, caratenoids, and trace amount of free fatty acids are found.

• Fat soluble vitamins (A, D, E, K) are also found in the fatty portion of milk.

• Butter flavor is due to short chain fatty acids.

• If fresh milk is left undisturbed at the room temperature creaming takes place.

• This process is speed up at lower temperature by IgM.

• Therefore dairy processors rarely obtain milk of uniform composition.

• The following terms are used to describe milk fractions:

Plasma = milk - fat (skim milk)

Serum = plasma - casein micelles (whey)

solids-not-fat (SNF) = proteins, lactose, minerals, acids, enzymes, vitamins

Total Milk Solids = fat + SNF

• By observing under different magnifications milk can be described as:

an oil-in-water emulsion with the fat globules dispersed in the continuous serum phase

a colloid suspension of casein micelles, globular proteins and lipoprotein partilcles

a solution of lactose, soluble proteins, minerals, vitamins other components.

Milk Proteins

• The Major protein in milk is casein (80%).

• Rest of the 20 % is composed of lactalbumin and lactoglobulin – whey proteins.

Total protein – 3.5%

Casein 2.9% whey protein 0.6%

• Alpha s1, alpha s2 , beta, kappa

• In addition to protein N milk has non protein N (NPN).

• All caseins are low soluble at pH 4.6

• All these types of proteins polymerize to form casein submicelle.

• Caseins are conjugated proteins – phosphate groups esterify with serine residues.

• Phosphate groups are important to the structure of the casein micelle.

• Calcium bound to individual caseins is proportional to the phosphate content.

• Most, of the casein proteins exist in a colloidal particle known as the casein micelle.

• the micelle also contains citrate, minor ions, lipase and plasmin enzymes, and entrapped milk serum.

• There are several models which have been suggested for describing the structure of casein micelles.

• Although the casein micelle is fairly stable, there are four major ways in which aggregation can be induced:

- chymosin - rennet or other proteolytic enzymes as in cheese manufacturing

- acid

- heat

- age gelation

Chymosin coagulation – • Rennet is a natural complex of enzymes

produced in the stomach of mammalians to digest the mother's milk - rennin or chymosin.

• Casein can be precipitated by adding rennet at 400C.

• Ca assists the precipitation process.• Chymosin is active in acidic media.• Alpha and beta caseins are hydrophobic

proteins that are readily precipitated by calcium- milk calcium is enough for that.

• Kappa casein is not calcium-precipitable. • When in micelles Kappa casein prevents

precipitation of alpha and beta caseins – keep them soluble.

• Chymosin cuts and inactivates kappa casein, converting it into para-kappa-casein and a smaller protein called macropeptide.

• Para-kappa-casein does not have the ability to stabilize the micellar structure and the calcium-insoluble caseins precipitate, forming a curd.

• Originally rennet was obtained from calves, goat and sheeps – vegetable rennets- microbial rennets (Rhizomucor miehei)- genetically engineered rennet.

Acid coagulation• Acidification causes the casein micelles to

destabilize or aggregate.• the acidity of the medium increases the

solubility of minerals so that organic calcium and phosphorus contained in the micelle gradually become soluble in the aqueous phase - Acid curd is more fragile than rennet curd .

• Casein micelles disintegrate and casein precipitates.

• Acid coagulation can be achieved naturally with the starter culture, or artificially with the addition of gluconodeltalactone.

Heat

• At temperatures above the boiling point casein micelles will irreversibly aggregate.

Age Gelation

• Shelf-stable, sterilized dairy products, such as concentrated milk and UHT milk products.

• After weeks to months storage of these products, there is a sudden sharp increase in viscosity accompanied by visible gelation and irreversible aggregation of the micelles into long chains forming a three-dimensional network.

• The actual cause and mechanism is not yet clear, however, some theories exist: proteolytic breakdown of the casein, chemical reactions, formation of kappa-casein-ß -lactoglobulin complexes.

Uses of Casein

• Casein is used in many industries other than the food industry.

• Coating paper – dissolve in an alkaline slon. – pigments – brushes or rollers – adding fomaldyhyde the mixture can be made waterproof- playing cards, wall pappers.

• As a glue in wood works – Ca(results Ca caseinate) , alkaline slon. - Ca caseinate becomes water insoluble after drying.

• In the textile industry – colour fixing, water proofing, softening.

• In the leather industry – glossy appearance.

Whey Proteins

• The proteins appearing in the supernatant of milk after precipitation at pH 4.6 are collectively called whey proteins.

• More water soluble – does not aggregate upon renneting or acidification.

• Can be denatured by applying heat.

• Denaturation increases their water holding capacity.

• The principle fractions are ß -lactoglobulin, alpha-lactalbumin, bovine serum albumin (BSA), and immunoglobulins (Ig).

• Highest BV – recommend for pregnant mothers – bodybuilders other athletes.

• Comes mainly in three forms – concentrate, isolate and hydrolysate.

• Concentrate-29%-89% protein by weight – low level of fat and lactose.

• Isolate – removing fat and lactose.

ß –lactoglobulin:• Can be removed after precipitating caseins –

acetic acid and NaAc.• Then pH is increased 6.8 – 7.2 and use MgSO4

– the precipitate is removed.

alpha-lactalbumin:• Remove casein and lactoglobulin – reduce pH

to 4 add MgSO4 - Purification

Lactose

• 70% of whey solids.

• Hydrolyze - increases the sweetness – depresses the freezing point.

• Ferment to lactic acid.

• Lactose intolerance.

• Crystallization – sandiness.

Enzymes• Raw milk contains variety of enzymes

AmylaseCatalaseLactase-(through bacterial synthesis)LactoperoxidaseLipasePhosphatase

• Bacterial lipases are more heat resistant. Even UHT treatment does not destroy all.

Phosphatase Test

• Alkaline phosphotase (alkaline phospho monoesterase) – milk enzyme – thermo-labile enzyme - inactivation temperature is slightly above pasteurization temperature.

Phenol phosphoric acid compounds

(disodium phenyl phosphate)

Alkaline phosphotase

Phenol

Organic compounds (2,6 dichloroquinonechlorimide)

Deep blue colour

Anti-Microbial Systems in Raw Milk

• lysozyme - lactoferrin - lactoperoxidase – lacto peroxidase system

hydrogen peroxide + thiocyanate + raw milk hydrogen peroxide/enzyme

bacteriostatic compounds (gram –ve)

Vitamins in Milk

Minerals• All 22 minerals considered to be essential to

human diet are present in milk. • Total content is less than 1%.• Minerals are found solubeised in milk serum or

in casein compounds. • The amounts of minerals is not constant.• Na content increases towards the end of the

lactation period and in the case of udder diseases while the content of other minerals correspondently decrease.

Mineral Content per litre---------------------------------------------------------------------------------Sodium (mg) 350-900Potassium (mg) 1100-1700Chloride (mg) 900-1100Calcium (mg) 1100-1300Magnesium (mg) 90-140Phosphorus (mg) 900-1000Iron (ug) 300-600Zinc (ug) 2000-6000Copper (ug) 100-600Manganese (ug) 20-50Iodine (ug) 260Fluoride (ug) 30-220Selenium (ug) 5-67Cobalt (ug) 0.5-1.3Chromium (ug) 8-13Molybdenum (ug) 18-120Nickel (ug) 0-50Silicon (ug) 750-7000Vanadium (ug) tr-310Tin (ug) 40-500Arsenic (ug) 20-60

Other Constituents • Somatic cells • white blood cells• Number is low in the milk of healthy cows.• Normally lesser than 200,000 cells/ml.• Upto 400,000 cells/ml can be accepted.

Gases• When milk is just out of the udder it contain

about 5-6% gases by volume.• The can increase up to about 10%.• Gas can be in the form of dissolved, dispersed

and bound.

Physical PropertiesDensity:• Depends upon the ratio between solid and

liquid.• Depends on the temperature.• Used for - converting mass into volume and

vice versa. - estimate the solids content.• The density of milk varies within the range of

1027 to 1033 kg m-3 at 20° C.• In milk instead of the density often specific

gravity is measured by using a lactometer

Equipment used for determination of milk density

Sample Milk temperature OC

Lactometer reading

Correction True reading

1 17 30.6 ºL - 0.6 ºL 30.0 ºL

2 20 30.0 ºL Nil 30.0 ºL

3 23 29.4 ºL + 0.6 ºL 30.0 ºL

•For each ºC above the calibration temperature add 0.2ºL; for each ºC below calibration

temperature subtract 0.2 ºL from the recorded lactometer reading.

A correction should be made on the lactometer reading if the reading is taken at a temperature other than its calibration temperature.

• Total Solids can be estimated from the corrected lactometer reading (L).

•Once TS is found, SNF can be estimated

Viscosity:• Rate of creaming, rates of mass and heat transfer, the

flow conditions.• Depends on - Temperature, pH.• Agitation increases viscosity – partial coalescence of

fat globules (churning) – cold agglutinated fat globules may dispersed if milk is agitated vigorously – viscosity decreases.

Freezing Point:• -0.512 to -0.550° C average -0.522° C • Used to determine added water, lactose content in

milk, water activity of cheese, estimate whey powder contents skim milk powder.

• Correct interpretation - most significant variables are the nutritional status, access to water -Under feeding and consumption of large amounts of water causes increased freezing points.

pH:

• 6.5 to 6.7 at 250C.

• Titratable acidity

• components in milk provide a buffering action - caseins and phosphate.

Mastitis and Antibiotics:

• Udder infection by bacteria and/or yeast.

• Lactose decreases - SNF decreases – Na and Cl increase.

• Increase bacterial count – human pathogens - increase in somatic cells.

• Antibiotics -antibiotic residues - fermented milks – allergies – development of resistant mutants.

• Withholding-times from milking. Amoxcillin 60 hrs.Cloxacillin 48 hrs.Erythromicin 36 hrs.Novobiocin 72 hrs.Penicillin 84 hrs.Sulfadimethozine 60 hrs.Sulfabromomethozine 96 hrs.Sulfaethoxypyridozine 72 hrs

Milk Grading

• Primary senses are very important in the sensory evaluation of dairy products: sight, taste, smell, touch and sound.

• Mouth allows to get such reactions as coolness, warmth, sweetness, astringency, etc.

• Odoriferous material such as 1part of mercaptain can be detected in 20 billion parts of air.

• To be detected by smell, a substance must dissolve at body temperature and be soluble in fat solvents.

• Senses become fatigue – washing the mouth.• Temperature should be between 15.5-21° C –

volatize

Flavor Defects of MilkRancidity:• Oxidative or hydrolytic rancidity.• Hydrolytic rancidity is caused by the action of

lipase - indigenous or microbial.• active at the fat/water interface - ineffective

unless the fat globule membrane is damaged or weakened.

• Agitation, and/or foaming, pumping and homogenization.

• Pasteurization is done just before or after the homogenization.

• Late lactation, mastitis, hay and grain ratio in diets and low yielding cows are more susceptible.

• Lipolysis can be detected by measuring the acid degree value

Oxidation:• Milk fat oxidation is catalysed by copper and

certain other metals with oxygen and air. • Dry feed, late lactation, added copper or other

metals, lack of vit E (tocopherol) or selenium (natural antioxidant) in the diet all lead to spontaneous oxidation.

• UV-rays from sunlight or flourescent lighting catalyze oxidation of unprotected milk.

• oxidation activates riboflavin which is responsible for catalyzing the conversion of methionine to methanal.

• Off flavor disappear in the storage of few days.

Cooked

• High temperature applications act on certain proteins and cause burned flavor– whey proteins.

• Defect is obvious immediately after the heat treatment but dissipates in 1-2 days.

Transmitted flavours:

• Cows transmit bad flavors through milk or milk absorbs.

• Some feed – cows are removed from feed 2 – 4 hours before milking.

• Some flavors are picked up by the cows through breathing.

• These flavors are volatile and can be driven off by vacuum de-aeration.

Microbial:

• Bacteria, yeast and fungi cause flavor defects.

Acidic/sour – lactic acid bacteria.

fruity flavors - Pseudomonas fragi - apsychrotroph.

Milking

• Milk releasing is controlled by the pituitary hormone oxytocin –released as a response to external stimuli - increases the pressure of the udder- let down reflex

• Effect of oxytocin starts about 1 min after the stimuli and fades away within 5-8 min.

1.Hand milking – churns, pail

2. Machine milking – system consist of a vacuum pump, vacuum vessel (collecting pail), a pulsater applies vacuum and atmospheric pressure alternatively, teatcups connected to hoses, vacuum pump and pulsater

Massage phase Suction phase

• In medium and large scale diaries the machine milking system is directly connected to the collecting tank -CIP.

tropical regions - refrigeration, immediate consumption of warm milk after milking, boiling milk, conversion into more stable products such as fermented milks.

After milking• Usually cooled – 40C.• In the farm spray coolers or immersion coolers

are used. • In farms of which milk production is less than

5000 L tanks attached cooling equipments are used – large farms use tanks with attached heat exchangers.

• Usually transported in bulk tank trucks within 2-3 days to the processing plant-during the transportation the temp. could increase.

• Before withdrawing samples mixing should be done.

Milk Reception • Several inspection tests are done for controlling the

quality – fat, SNF, sediments, bacteriological quality, flavor, adulteration –test for udder cells (Coulter counter etc), antibiotic residues, pesticide residues Acidity, Alcohol test - acidity 21% (75% alcohol), COB.

• Next step is determining the quantity

volume – use flow meters and register air as well. Can be improved by combining with air eliminator.

• Weight – can be taken in two ways.

-Weighbridge

-Using special weighing tank a weighing cell attached with the feet

• Milk received is stored after cooling to 40C in horizontal tanks or in silos – vertical tanks of which capacity is 20,000-150000 L .

• To prevent the agitation and damage of fat globules silos are filled from the bottom.

• Some times milk is sent through a course filter to get rid of particles ≤ 0.5 mm

Clarification: (removal of solids from a liquid)

• Purpose is removal of body cells, sediments, bacterial cells etc.

• Milk is passed through a centrifugal clarifier.

• Milk is distributed as thin layers over revolving set of conical shaped discs.

• Discs increase the area available for sedimentation

Vg = Floating or Sedimentation Velocity d = diameter of the particle or the dropletsP1 = density of the continuous phasePp = Density of the particle or dropletn = viscosity of the continuous phase

Stoke’s LowSince, fat globules clusterize floating velocity increases

• Centrifugal separation is used in the diary industry

Clarification

Skimming

Standardizing

whey separation

bactofuge treatment

separation of serum phase from anhydrous milk fat (butter production)

Clarifier

Cream separation:

Gravity Separation

• Creaming takes place when fresh milk is kept undisturbed for about 30 to 40 min.

•The skim milk usually contains about 0.5 to 0.6% butterfat.

Centrifugal Separation• Gravity separation is slow and inefficient.• CS is more effective - 0.1% fat.• 120 discs stacked together at a 45 to 60 degree angle

and separated by a 0.4 to 2.0 mm.

Standardization of milk:• Bringing the final fat and SNF content of milk to the

desired level. • Perarson’s square is used.

Homogenization:• Mechanical treatment of the fat globules in milk

brought about by passing milk under high pressure through a tiny orifice.

• Decrease in the mean diameter of the fat globules, a decrease in the size distribution of the fat globules and an increase in density of the globules

• In conventional homogenizing milk flows at a rate of 20,000 l/hr. at 14 MPa (2100 psig).

• Homogenization comes before or after pasteurization.

Thermal Treatments of Milk•There are many different types of thermaltreatments used in the dairy industry. Main aim of all of them is preserving the product from microbial spoilage and pathogens.However in some applications heat is

manipulated to improve the physical and chemical quality of the products e.g. precipitating whey proteins in the yoghurt production in order to prevent whey separation

(synerisis), improving the stability of proteins at strong heat treatment used in the latter part of the condensed milk production.

•Heat treatments used are divided into basic categories considering the time temperature combination as follows

Thermisation

• Relatively milder heat treatment carried out if there is delay in the utilization of milk.

• Increasing the temperature of milk to

– 63 – 650C for about 15 seconds-

• This treatment does not destroy, the enzyme phosphatase.

• After thermisation milk must be chilled for preventing the possible growth of spore-formers.

Pasteurization:

• Theoretically the process aims at the destruction of most heat resistant pathogen that could be in the dairy product (food product) concerned.

• Methods used are categorized considering the time temperature combinations used as

Low temperature long time (LTLT)

High temperature short time (HTST) or considering the nature of the process as

Batch

Continuous

Batch method (LTLT): • Jacketed vats, are often used. Water or steam

is circulated in the jacket. Some vessels can be seen surrounded with coils of water or steam.

• Agitator, thermometer and lid are attached with the vessel.

• Time-temperature combination depends on the mix being pasteurized e.g frozen dairy dessert mix at least 69° C for not less than 30 min or at least 80° C for not less than 25 sec.

Continuous Methods:

• Save time, energy and space.

• There are basically three different types heat exchangers used for continuous heat tretment.

1. plate heat exchanger – a stack of corrugated stainless steel plates clamped together in a frame. When they are clamped it is done so that separate chambers are resulted.

2. Tubular Heat Exchangers

• No contact points as in PHE. Therefore THEs can be used for particulate foods as well.

• Can be run longer than PHE between two cleaning.

• The heat transfer efficiency is lower than PHE.

• Basic structure can be considered as two concentric metal tubes.

• Available in two fundamentally different types• Multi/ mono channel

• Multi/mono tube

• Header in each end act as a distributor and a collector

• The service medium is provided to the outermost channel.

• Monochannel – one annular product channel enclosed between two concentric channels for the service medium

Multi/mono tube• The product flows through a set of parallel

tubes and the service medium in between.

3. Scraped Surface Heat Exchangers

• Pasteurized milk is packaged in paper cartons, plastic jugs, or other types of packages.

Other Pasteurized Milk ProductsVitamin D milkNaturally occurs in milk – varies with cow’s feed –lack in the children diet –

UV 7-dehydrocholesterol Vit D – limited.Vit D is generally added before pasturisazion.

Low-sodium milk• High blood pressure – low sodium diets.

• Produced by sending milk through an ion exchange resin – replace sodium with potassium – 3-10mg/100ml- untreated 50mg/100ml.

Soft-curd milk:• Curd hardness depends on the amount of

casein and calcium and other factors.• Various treatments are used – removal of Ca,

treating with enzymes.Low-lactose milk:• Lactose intolerance – milk is treated with

lactase in the course of processing – adding lactase given, by the consumer.

• Pasteurization does not destroy almost all microorganisms in raw milk. Thermophillic microorganisms of which many of them could be spore-formers can survive pasteurization.

• Therefore, in order to increase the self-life pasteurized product they must immediately be refrigerated.

• Even then the self-life is limited to a short period time which depends solely on the initial microbiological quality of the raw milk used and hygiene of the production process.

• The self-life of ordinary pasteurized milk is about 8-10 days at 5-70C.

• Some manufactures use ultrapasteurization in order to extend the self life of pasteurized products further (to produce extended self-life (ESL) products).

• The typical time temperature combination of the ultrapasteurization is 125-1300C for 2-4 sec.

Sterilized Milk

• In the production of sterilized milk and other dairy products they are subjected stronger heat treatment for achieving the state commercial sterility .

• Therefore the products exhibit excellent keeping quality at the ambient temperature.

• There are many advantages of sterilized milk over pasteurized milk.

- possibility of delivering to larger, geographically wider markets

- elimination of he return of unsold product- reducing the storage and transport cost due to ambient storage etc..

Raw Materials:• Row milk which is either soured, with high serum

content or without correct salt balance can not be used since such milk can cause processing problems.

• These conditions can simply be found out by performing the alcohol precipitation test.

• Due to the high temperatures used, sterilized milk can chemically change resulting colour compounds (browning) and/or flavours (cooked, caramel).

• Two methods are used for producing sterilized milk

1. In-container sterilization

2. Ultra High Temperature sterilization (UHT)

1. In-container Sterilization

• The product is filled into containers which can withstand sterilization temperature (e.g. 110-1200C for 15-40 min.).

• There are two basic methods

a). Batch processing

b). Continuous processing

a). Batch Processing

• Milk is first preheated to a temperature around 800C and then filled into containers.

• This is followed by the capping of the containers.

• For retorting containers in batch systems the retorts can be operated by three different methods as .

- Stack of creates in a static pressure vessel

- Cages that can be rotated in a static pressure vessel.

- In rotary autoclave

b). Continuous Processing

• Preferred to be used if the number of units produced is grater than 10,000 per day.

• In the system there has be an effective pressure locking system since the product is continuously moved from a low pressure/low temperature region to a high pressure/high temperature region and back.

• There are two systems used

Hydrostatic vertical sterilizer/tower

Horizontal rotary valve-sealed sterilizer

Hydrostatic Vertical Sterilizer/Tower

• A pressure vessel of which pressure and thereby the temperature is controlled by the height of water columns either side of the central sterilizing chamber.

• The water column act as pressure locks as well.

• Into the central sterilizing chamber high pressure steam is introduced.

• The water in the inlet side is heated while the water in the outlet side is cooled.

• Therefore the product temperature changes gradually without heat shock.

Horizontal rotary valve-sealed sterilizer

• Filled containers are fed in to the pressure vessel through a rotary valve.

• Containers circulate in the sterilizing zone of the vessel at 132-1400C for 10-12 min.

• Overall cycling time is about 30-35 min.

• Capacity of the system is usually about 12000 units/hour.

2). Ultra High Temperature sterilization (UHT)

• In container sterilization needs much time, energy and space than the UHT treatment.

• Since the product remains in the in-container sterilization for a considerably long period of time at a high temperature the product quality goes down – undesirable colors and flavors develop and some nutrients are lost.

• To overcome this problem the UHT treatment has been introduced in which the product is heated to a higher temperature for relatively a shorter period of time.

• Milk is sterilized before filling into pre-sterilized containers in a sterile environment aseptic packaging - Used for many foods product that can be handled as a fluid.

• Heated to a temperature above 1300C.• Two principal methods Direct Heating

Indirect HeatingDirect Heating – • heating medium (steam) directly come into

contact with the product – high heat transfer – lesser holding time.

• There are two methods – injection, infusion

Injection –

• High pressure steam is injected directly into pre heated milk using a special injector.

• Then the product is flashed- cooled in a vacuum to remove the amount of condensed steam.

Infusion – milk is pumped through a nozzle into a chamber of HP steam.

Indirect Heating System:

• The heating medium and the product are not in contact – plate, tubular, scraped surface.

• In practical situations, in sterilized milk production plants, different types of heat exchanger are used combinely for a better effect.

Evaporation• Concentration of liquids by evaporating the

solvent-usually in food systems the solvent evaporated is water.

• In concentration the liquid state remains in contrast to drying in which liquids become solids

• In the food industry evaporation is used to- reduce the cost of drying- induce crystallization - reduce cost of transportation and storage.

- reduce aW and thereby for microbiological safety

- recover by products from wastes

• When water is evaporating, since the latent heat of evaporation of water is high considerably high amount of energy should be spent on.

• Further, the evaporation efficiency can be increased by introducing the concentrating liquid on to the evaporation surface as a thin film.

• Two of these factors should be taken onto consideration in designing evaporators.

• For recovering energy multiple effect evaporators, thermocompressors and mechanical compressors are used

• In the dairy processing evaporation is done mainly in the concentration of raw milk (in the yoghurt production, in milk powder production dry matter content is brought up form 9-13% to 40-50%) and in the production of condensed and sweeten condensed milk.

• Most simple evaporator that can used for evaporating milk may be a evaporation pan.

• But in the dairy industry three types of evaporators are widely used.

- Circulation evaporators- Falling film evaporators- Rising film evaporators

Circulation Evaporators

• Used for achieving low degree of concentration e.g. in the yoghurt production

• The process simultaneously deaerate and rids of off flavors.

• Usually the product is heated to a temperature lower than 1000C and introduce in to a vacuum chamber as a thin film.

• From the film of milk water evaporates leaving concentrated milk in the bottom of the evaporator

Falling film evaporators

• Milk is made to flow as a thin film under the gravity.

Rising film evaporators

• Milk is allowed to rise along a tall narrow tubes

• During this period water evaporate

Evaporated Milk:

• After standardization preheat water is evaporated homogenize cool

re-standardize fill and seal the cans

sterilize.

• Concentrated 2:1 or 3:1.

• Sterilized by retorting (1180C for 15min) – characteristic caramelized cooked colour and flavor.

• UHT – no cooked colour and flavor

Sweetened Condensed milk:

• Not sterilized.

• Pasteurized milk condensed add

sugar (63%).

• Much is used in the production of bakery products, ice cream and confectioneries.

Milk Powder• Milk powder is used

- recombined milk- bakery industry – volume, softness,

and freshness - pastry dough –

crisper- bread and

pastries- chocolate, ice cream

- animal feed- as a sbstitute of mother’s milk in infant foods

• Milk is persevered by reducing the water content – skimmilk – 3 years, whole milk 6 months.

• In drying water removal is higher in contrast to condensation – The liquid state change to solid state.

• There are different drying methods used in the food processing e.g freeze drying, roller drying, spray drying

Roller Drying or Drum Drying

• Milk is distributed on to steam-heated drum and evaporated water is drawn off by a flow of air.

• Intense heat treatment – the product becomes hygroscopic.

• According to the feeding system drum dryers are divided in to two

trough-fed roller dryer

spray-fed roller dryer

Trough-fed roller dryer

Spray-fed roller dryer

Spray Drying• Can be used for drying any material that can be

atomized e.g liquids, low viscous pastes and purees

• A two stage process - Pretreated milk is evaporated – DM

content 45-55%- Final drying in a heated tower or a

chamber with heated air • Microbial counts in reconstituted milk should be

less than 3000 – 5000 / liter, according to many of the standard,

• If thermopilic microorganisms are present in raw milk, the count could go up during the concentrating - Bactofuge®. Microfilteration

Pre-treatement

• Standardized milk for DSM is pasteurized at least for inactivation of phosphotase

• In the production of DWM pasturisation aims at the inactivation of both pathogens and lipase.

Spray Dried Milk Powder:

• Clarification standardization heat treatment evaporation spray drying

Evaporation less air, viscosity , particle , saves energy

Atomising

• Braking (liqid) milk into fine droplets so that surface area increases significantly

1 liter = 12 billion particles = 30 m2 = 700

• Properties of the dried product depend on the design of the atomiser.

Spray nozzles

Rotating disc –5000 – 25,000 rpm

Basic Components of a Spray Drying system

- Pre- concentration step

- High pressure pump

- Heating chamber (+ and associated dryer)

- Atomizing device

- A source of heated air with a blower

- Secondary collection vessel/s (for removing the dried food from the air stream

• There are several different drying installations

Single-stage drying –

- Most simple drying installation

- Moisture removal completes in the drying chamber itself

Two-stage drying -

• Removing last traces of water is very difficult – the outlet temperature has to be kept at higher temperature.

• This would bring the product quality down

• To overcome this problem after-drying stage is incorporated – fluidized bed

• When the product leaves the drying chamber its moisture content is 2-3% lower than the expected final moisture content.

• The fluid bed attached dries and cools the product

Three-stage drying

Second drying stage is found in the base of the drying chamber itself.

Third stage in which final drying and cooling take place is outside the drying chamber

Production of Instant Milk Powder

• Milk powder particles must be agglomerated and enlarged in size – become pours.

• The powder must be first dried so that most of free, capillary water and water in pores evaporates.

• Then particles are humidified - become sticky –agglomerate

• Dried milk powder is packed in different types and sizes of packages.

• Milk fat could oxidize during the storage. This can be minimized by

special pre-treatment

adding antioxidants

filling under inert gas

Ice Cream

• In the production of many of different ice cream varieties dairy ingredients are used – as whole milk, cream, frozen cream, butter, butter oil (99% butter fat), condensed milk products, dried milk etc.

• General Ingredients – milk fat, MSNF, sugar (sucrose, dextrose and dextrose fructose mixture), stabilizers (gums- gelatin, gum guar, gum karaya, carboxymethyl cellulose) emulsifiers (earlier egg yalk was used now, mono and triglycerides and polysorbate 80 are used) flavoring agents, water, air.

• Ice creams are categorized in to four different basic groups according to their ingredients.

• Frozen ingredients without air is called the ice cream mix.

• Exact composition is decided according to the market.

e.g average ice cream – 12% milk fat,11%MSNF, 15% sugar, 0.2% stabilizers, 0.2% emulsifiers and trace of vanilla – total solid 38.4% - flavoring (fruits, nuts, chocolate). milk ice - 4% milk fat,12%MSNF, 13.5% sugar, 0.2% stabilizers, 0.2% emulsifiers and trace of vanilla –33.5% total solid.

• Standards specify the minimum amounts of fat, MSNF and other ingredient a particular ice cream variety should contains.

• Ice crams are produced by incorporating air into the mix– whipped product – the prevent becoming too dense, too hard, too cold.

• Increase of volume cased by air is called overrun – usually 70% - 100%.

(vol. of ice cream – volume of mix) X 100

overrun% =

volume of mix

Functions of the ingredientsMilk fat/Fat – rich flavor, smoothness, calories,

body.MSNF – flavor, body, texture ( MSNF OR)Sugars – sweeten, lower freeing point, a cheapest source of solids.Stabilizers – form gels with water, improve

body, texture, delay melting and prevent leaking water, prevent formation of large ice crystals – drier product.Emulsifiers – lecithin – disperse fat globules, prevent churning, help OR, make dry and stiffFlavors – give variety

• Some manufactures replace some or all of fat with vegetable fats - coconut oil, sun flower oil, rapeseed oil, soybean oil

• In the selection of non dairy fats their liquid fat to solid fat ratio at the freezing stage should be taken into consideration.

• Increasing MSNF by adding skim milk, sweetened condensed milk etc can increase the lactose content in the product so that lactose crystallizes upon freezing giving a sandy texture

Flow Chart of Ice Cream Production Process

The Production Process

• Mix calculation according to the chosen formula is the first step.

• Then ingredients are measured and blended

• For mixing dry ingredient well with liquids high speed blenders are used

• To improve the solubility of ingredients the liquids in the mix are preheated e.g. 430C, .

• mixing liquid ingredients with solids

•Pasteurization (71/820C for 30/25 min/s)•Homogenization –two stage, improves body

and the texture, better air stability, resistance to melting

• Cooling 4.4 – 5 0C•Aging 3-24hr at 4.4-5 0C or lower (fat

solidify, stabi. and proteins swell and combine with water, viscosity ) – smoother, slow melting

•Flavor and colors are added•Freezing – bringing temperature down to -

5.50C, incorporate air – batch or continuous freezers- continuous multicylinder freezers, only about 50% of water is frozen.

• Freezing is done using either batch freezers or continuous freezers

• Batch freezing takes ≈ 10-15 min.

continuous freezing ≈ 30 seconds

Continues freezers are similar to scarped surface heat exchangers. But asthe service medium a refrigerant isCirculated e.g. ammonia, freon

• Frozen ice cream which still remains as a semisolid slurry is filled into cups, cones, other containers or molds (novelty products). Extruders with dies of various shapes and sizes are used for giving special shapes and blending of different types of ice creams

• Particulate materials such as nuts, fruits, candy cookies are added to the frozen slurry.

• Hardening – After addition of particulates ice creams are frozen in blast freezers at -30° to -40° C – become stiff - most of remaining water freezes in blast freezers

• Ice creams without subjecting to hardening are called soft serves.

• These are bought from venders for immediate consumption.

Ice Cream Novelty/Impulse Products

• These are ice creams produced usually as single-serving products for immediate consumption.

• They come in different sizes, shapes, colors, flavors and in packing etc e.g. popsicles, ice creams with sticks.

Production of Popsicles and Ice Creams with Sticks

• Water ice or soft ice cream is first filled into suitable mold kept in a cold bath of calcium chloride.

• When the product in the mold is partially hardened stick is inserted.

• Completely harden product is released from the mold by holding from the stick and defrosting the surface.

• Then the mold is cleaned by moving through a bath of cleaning liquid

• Novelties with or without out sticks that can not be felled out by the stick and of fancy shapes such as cubes, cylinders are produced by using extruders and knives.

•

Cultured Milk Products• Cultured milk products e.g yoghurt, ymer, kefir,

cultured butter milk etc. are produced by using microbial fermentation

• Lactic acid bacteria and yeast are often employed in the production.

• MO convert part of milk lactose into lactic acid.• Lactic acid (low pH) becomes inhibitory to most

of microorganisms except some yeasts and other fungi

• In the production culture organisms are provided with best conditions

Destroying competing microorganismsKeeping under optimum temperature

• Once the correct flavor and aroma have developed by the MO, the product is cooled.

• Texture, consistency and appearance depend very much on the conditions used in pretreatment.

• The pretreatment of milk for cultured dairy products smellier to many other dairy products.

Yoghurt• Most popular cultured dairy product• Consistency (viscous liquid, softer gel, frozen),

aroma and flavor vary from region to region • Typically classified as – set type, stirred type,

drinking type, frozen type, concentrated• Milk used for cultured dairy products is obtained

from selected supplies and should be free from antibiotics, bacteriophages, residues of CIP cleaning and sterilizing. Composition of Yoghurt Fat

• Fat content may be 0 – 10%.

• Usually kept in the range 0.5 -3.5%

Dry Matter• FAO/WHO recommended minimum is 8%• High proportion of casein and whey result firmer

coagulum• Adjusted by – Evaporation (10 – 20% of the

milk volume), addition of SKMP, addition milk concentrate,

Additives

Sugar, Sweeteners

• Sugar – sucrose, glucose in combination with fruits – diabetic patients: aspartame

Stabilizers

• Prevents whey separation

• Amounts depend on the type

• Correctly produced natural yoghurt needs no stabilizers

• Usually pectin, gelatin, starch are used in the range of 0.1 – 0.5 %.

Cultures• Customized cultures are produced for specific

flavors and viscosity e.g High viscosity low acetaldehyde and fairly high pH – low viscosity medium acetaldehyde content.

• Handling and propagating of cultures under strict hygienic conditions is important – concentrated freeze dried and frozen cultures are available.

• In the designing of plants the sensitivity of coagulum to mechanical stresses (the coagulum is very sensitive to mechanical stresses. Once broken it can not be recreated) must be taken into consideration

Pretreatment• Weather it is set yoghurt or stirred yoghurt the

pretreatment is similar. Usual pretreatment operations are

Evaporation – 10-20% water is evaporated usually for increasing the solid content- small scale

processors use evaporation pans- large scale processors use circulation evaporators or, falling film evaporators

HomogenizationPasteurization – at 850C for 30 min or 950C

for 10 min

Cooling – temperature of the mix is reduced to the optimum temperature (430C) of the culture organisms

• There are many different types of yoghurts.

• But all can be divided into two basic categories as set stile yoghurts and stirred style yoghurts.

• In the production set yoghurt, the pretreated mix with the culture is first filled into containers and then incubated – without braking or disturbing the developing coagulum.

• In the production of stirred type yoghurts incubation is carried out in a special tank then the coagulum is broken before filling.

Set Yoghurt Production Process

Stirred Yoghurt Production Process

• Drinking yogurts are stirred products of which the total solid content is less than 11%.

• In the production the fermented product is homogenized in order to reduce the viscosity to the required level.

• Homogenized product can be directly filled into containers.

• If the product is heat treated (pasteurization or UHT) the self life can be prolonged.

Heat treatment of yoghurt

•In order to prolong the self life some producers heat treat (72-75 0C) their products

Starter bacteria are inactivated

Inactivation of contaminants

•In some countries heat treatment has been prohibited

Frozen Yoghurt

• Produced either adding yoghurt into the ice cream mix or further processing of fermented yoghurt mix.

• Frozen yoghurt is available in soft-served or hard frozen types.

• Mix contains stabilizers and emulsifiers

• Mix is de-aerated and homogenized at 700C

• Pasteurized at 900C for 5 min.

• Incubated at 430C. Because of the high carbohydrate content in the mix incubation period is longer (e.g 7-8 hr) than that of normal yoghurt.

• Incubation is stopped when right pH has been reached.

• At the next stage of the production process fermented mix is frozen as it is done in the ice cream production.

Butter• Produced by using milk fat• Usually divided into two main categories

1. Sweet cream butter2. Cultured or sour cream butter-produced

by souring milk with microorganisms• According to salt content they can also be

divided as UnsaltedSalted Extra-salted

• In the large-scale productions both batch and continuous processes are used

Composition

Fat 80%

Moisture 16-18%

• The moisture content varies according to the amount of salt added.

• Butter is a water-in-oil emulsion rich in vitamin A and D

• In the butter production the water content is dispersed well so that the product becomes dry

• Natural color depends on the amount of cartotenoids present in cream –buffalo milk does not contain carotenoids.

Butter production Process

• Cream used may be separated by the producer from whole milk or obtained from an outside supplier

• Then cream must be pasteurized at 950C or above for destroying microorganisms and enzymes.

• The pasteurization results anti-oxygenic sulphhydryl compounds

• If the cream has undesirable aroma vacuum deaeration is important before pasteurization -usually this is done for preheated milk at the stage of pasteurization.

• In the sour/cultured butter production cultures are added next – culture organisms develop flavor and acidity – the process is called ripening-during the ripening process the temperature is controlled

• Mixed cultures of Streptococcus cremoris, S.lactis and Leuconostoc spp. are used.

• Aging-cream is subjected to special temperature program according to the composition of cream for achieving the correct crystalline structure of fat and the consistancy of the final product – 12-15hr.

• Temperature of aged cream is brought up for the next stage (churning) by sending through a heat exchanger

• Cream is then vigorously agitated – churned.• At the churning, fat globules break and

coalesce into butter grains.• At this stage cream can be seen fractioned into

two - butter grains and the liquid fraction, butter milk

• Churning is continued until the size of butter grains come to the required size, then churning is stopped and butter milk is drained off.

• In continuous butter making butter milk is continuously removed

• Earlier processors washed butter after churning for removal of residual butter milk and solids but now this is not practiced.

• Butter should be further worked after draining butter milk for a continuous fat phase and finely dispersed water phase in it.

• Salt is spread over the mass of butter grain (batch processing) or added as slurry in the continuous processing.

• Salted butter must be worked for uniform distribution of salt.

• The working affects color, aroma, taste and the keeping quality.

• The finished product is packed and send to the cold room storage.

• In the traditional batch churning cream of which fat percentage is 25-35% used.

Continuous Butter Making Process

• Milk pretreated in the conventional way is introduced from the ripening or aging tank to the section (1) where cream is beaten and churned – the section consists of a variable speed motor and beaters.

• Then the butter grains formed and butter milk resulted are sent to the first working/separation section (2) where butter milk is removed.

• Since butter is moved from the separation section to the next by using a screw conveyer first working starts at this section.

• The shape of the separation section is conical. Therefore, when butter passes the section more butter milk is squeezed out. Squeezing of butter milk is enhanced by the perforated plate which separates the next section from separation section.

• Then the butter enters into the second working section which is usually operated by a separate motor. At the end of the second working section salt may be added.

• The third working section of the machine has been connected to a vacuum pump.

• The vacuum pump reduces the air content of butter to the air content of conventional butter.

• The final working section consist of several small sections. Each section has been separated from each other by a perforated plated with different size and shapes of pores.

• In each small section there is an impeller. Their shapes could be different from each other.

• If the moisture content of butter is lower than the required level water is added to the first small section.

• The final product is ejected from a nozzle which is ready to be packed.

Continuous Butter Production

Cheese

• Cheese has been producing in many cultures traditionally for years

• It is a concentrated product in which fat and protein contents are nearly 10 times higher than normal milk.

• Therefore a good source of nutrients – staple diet in some countries-good method of milk preservation without refrigeration

• Most common step in the production is curdling cow’s milk, milk of other mammals, their cream, partly SM or butter milk by using rennin or acid from lactic acid bacteria.

• But, in producing some cheeses whey solids, vegetable fats and proteins are used, instead.

• Whether the curd is further treated with heat, pressure, salt and ripening (leaving the curd under suitable conditions the culture organisms and/or enzymes act and developing quality) or not, depends on the type of cheese produced.

• There are many different types of cheeses in the world. Number of different names given for different cheeses exceeds 800.

• They are categorized into many basic groups considering

moisture content- extra hard, hard, soft etc

fat Content – high fat, full fat, medium fat, low fat, skimmed milk

curing or ripening – cured, ripened

• About 18 different varieties of cheeses can be recognized according to the differences in the production processes used– brick, Camembert, Cheddar, cottage, cream, Edam, Gouda, hand, Limburger, Neufchatel, Parmesan, Provolone, Romano, Roquefort, sapsago, Swiss, Trappist and whey cheese.

• The production of cheese is considered as an art rather than a science because, the quality very much depends on the milk used and the type of microorganisms that can not be controlled everywhere in the world equally.

The Production Process• Milk used should be, free from antibiotic

residues and of good microbiological quality.• First few steps of the production are as same

as in the production of most of other dairy products up to standardization.

• If milk is to be kept without taking into processing for a long period of time thermisation is important - 63-65° C for 15 to 16 sec. – do not destroy all microbes.

• Milk used for cheese production is not usually hormogenised – increases the surface area of fat globule and casein adsorption – This, results soft, weak curd at renneting (addition of the enzyme rennin in order to coagulate milk in the cheese production) and increases hydrolytic rancidity.

• But in the production of Blue and Feta cheese milk is homogenized for enhancing lipase activity.

• Number of additives are added into cheese milk.

Calcium chloride – facilitate renneting and reduces the amount of rennet required.

Nitrates (Sodium or pottassium nitrate)- undesirable effects of some microorganisms e.g: Clostridium tyrobutyricum and coloiforms in some cheeses

Colours- Natural color of milk is due to carotenoid which varies season to season. Therefore keep the color of cheeses uniform colours are added- Annato, Beta-carotene and paprika

hydrogen peroxide – some times as an alternative to pasteurization hydrogen peroxide is used

lipases- to bring up the lipase content which goes at the pasteurization down. This supports for proper flavor development-kid goat lipases

Pasteurization

• If cheese is ripened more than a month according to FAO, milk pasteurization is not necessary.

• In the processing of some cheeses like Parmesan, Grana milk is not heated above 400C-but this increases the risk of microbial spoilage and spreading pathogens.

• Therefore, often manufactures pasteurize milk at the expense quality.

• As an alternative to pasteurization (for preventing the growth undesirable microorganisms) chemicals (sodium/potassium

nitrate) are used.

• But in some countries using these chemicals are also prohibited.

• If so available alternative for reducing the microbial load in milk is mechanical methods e.g Bactofugation®, microfiltration

Ripening the milk- Inoculating lactic acid bacteria (LAB) which lower the pH, assist coagulation, promotes syneresis, help to prevent spoilage and pathogenic bacteria from growing, contribute to cheese texture, flavor and keeping quality,

• LAB produce growth factors which encourages the growth of non-starter organisms, and provide lipases and proteases necessary for flavor development during curing.

• The temperature must be adjusted according to the type of cheese produced and culture organisms before introducing ripening cultures into the vat of heat treated or unheattreated milk, e.g. in the cheddar cheese production Streptococcus lactis at 310C, in the cottage cheese production S.lactis and Leuconostoc citrovorum at 220C

• Various types of equipments can be fixed on to drive motor.

• Then milk is incubated for certain period of time under the temperature. Within this period acidity develops for the next step - rennet coagulation e.g. for cheddar cheese 30 min., for cottage cheese 14 hr.

• At the end of this period rennin (most active enzyme in the complex of enzyme usually obtained from the forth stomach of calves: rennin is also called chymosin; the commercial preparation is called rennet) is added.

• Rennet like enzymes obtained from microorganisms and rennin obtained from

Genetically modified microorganisms are now available for cheese manufactures.

• The rennin added and the acidity developed by this time combinely contribute, to coagulate casein which traps considerable amount of fat, some lactose, water and minerals, in to a curd.

• Curd is formed under controlled conditions-In which temperature, acidity, rennin concentrations are controlled. This gives curd of the desired moisture content and texture for subsequent processing.

Curd Treatment –One of another parameter which makes one type cheese different from another is curd treatment

• Once curd has reached to the desired firmness- the curd is cut into small pieces with a knife or a wire knife.

• This facilitates whey separation by increasing the surface area and shortening the distance whey should travel to reach out.

cooking – At this stage the temperature of the curd whey mixture is increased. The final moisture content of the curd depends on the cooking temperature and duration –If the fermentable lactose content in the milk or curd is higher it results more lactic acid and thereby low moisture content in milk/curd.

• Whey is removed when the pH and moisture is correct – from the top or bottom.

• In the production of some varieties of cheese the curd is kept in a mold and pressed for further removal of whey.

• Mold used may be of different size and shape. They are called hoops.

• In the production of some cheeses like Colby, Gouda and Brine brick the curd is washed.

• This increases the moisture content and reduces the lactose content which lowers the final acidity. This also results decreases in the firmness and increases in the openness of the texture.

• Curd handling from this point on is very specific for each cheese variety e.g Salting may be achieved through brine as with Gouda, surface salt as with Feta, or vat salt as with Cheddar.

Cheese Ripening • Except for fresh cheese, the curd is ripened, or

matured, at various temperatures and for different periods of time until the characteristic flavor, body and texture profile is achieved.

• This final stage varies from weeks to years according to the cheese variety.

• During ripening, degradation of lactose, proteins and fat are carried out by ripening agents.

The ripening agents in cheese are:

bacteria and enzymes of the milk lactic culture rennet lipases added moulds or yeasts environmental contaminants

Cheddar Cheese Production

• Popular in the UK, USA and Canada

• Streptococcus lactis is added at the level of 1% to the pasteurized milk at 310C.

• If it is needed colors a added at this stage.

• After about 30 min when the acidity is about

0.2 % (calculated as lactic acid) rennet is added.

• Stirring is stopped for allowing the curd formation (for about another 30 min.).

• Then the curd is cut into cubes of which a side is 0.25-0.5 in.

• Cooking – 38 0C for 45 min while agitating.

• Agitation is stopped and whey is drained off from the vat.

• The curd is allowed to mat for about 15 min.  

• After draining of whey curd is allowed to mat during which the pieces of curd fuse to rubbery mat.

• The process of matting and subsequent handling is called cheddaring.

• Cheddering involves cutting the matted curd into blocks and turning the blocks at 15 min intervals and piling the blocks on one another two or three deep.

• This continues until the whey coming, out of the blocks records the 0.5-0.6% acid.

• Then slabs are milled into small pieces and salt is added.

• Salted curd is placed in hoops fitted with cheesecloth and then in a hydraulic press.

• After overnight pressing , cheese is removed from the hoops and placed in a cold room at 160C and 60% RH for 3-4 days

• This causes mild drying on the surface. Mold growth possible on the surface of the cheese is prevented by vacuum packing or dipping in hot paraffin.

• Boxed cheese is ripened at 20C and 85% RH at least for 60 days. Some are ripened 12 months or longer.

Cottage Cheese Production

• A low fat soft cheese.

• Coagulation is done with lactic acid not with rennin.

• Curd is not pressed, therefore found in particulate form.

• Pasteurized skimmed milk is used

• Cheese is not aged or ripened.

• Culture (S.lactis and Leuconostoc citrovorum) is used at about 1% of milk.

• Fermentation is carried out for 14 hr

• Coagulum is cut into cubes

• Cubes are cooked at 500C for 90 min while agitating.

• Then whey is drained and curd is washed with water.

• Now the curd may be salted for preserving and improving the flavor.

• Sometimes 2 or 4% cream is added if so the product is called creamed cottage cheese.

• No further processing. The self-life is short. Kept under refrigeration.

Swiss Cheese Production

• A variety of hard cheese.

• Characterized by the large holes and the nutty flavor due to Propionibacterium shermani in the culture.

• The starter culture contains Lactobacillus bulgaricus and Streptococcus thermophilus in addition to above.

• Raw milk is used. After the initial lactic acid fermentation rennet is used.

• Then curd is cut into very small pieces. This is followed by the cooking of whey/curd mix at 530C for about 1hr.

• Curd after the cooking is taken into a cheese cloth and hoisted from the kettle.

• Entire curd from the kettle is placed in a hoop and pressed for one day.

• Then on the following day the curd is placed in a tank of brine at 100C. This continued about three days.

• Cheese from the brine tank is transferred to a ripening room at 210C and 85% RH. This continues about 5 weeks.

• Eyes are formed at this stage and curd become rounded.

• Then cheese is transferred to a more colder ripening room, 70C. The cheese is ripened in the room from 4-12 months.

Processed Cheese

• Processed cheese is produced by mixing or grinding different varieties of cheese together.

• Since cheese of different qualities can be mixed the product with very attractive qualities can be produced.

• Usually the mixed is heated to 710C for melting and emulsifiers such as sodium citrate, disodium phosphate are added for preventing fat separation.

• Melted cheese then add into cartoon and allowed to set.