Manufacture of dairy products

Definitions
 As per FSSAI (2011), Butter means the fatty product
derived exclusively from milk of cow and/or buffalo or
its products principally in the form of water-in-oil type
of an emulsion.
 Product may be with or without added common salt
and starter cultures of harmless lactic acid and/or
flavour producing bacteria.
 Table butter shall be obtained from pasteurised milk
and/or other milk products which have undergone
adequate heat treatment to ensure microbial safety.

 It shall be free from animal body fat, vegetable oil and
fat, mineral oil and added flavour.
 It shall have pleasant taste and flavour free from off
flavour and rancidity.
 It may contain food additives permitted in these
Regulations
 It shall conform to the microbiological requirements
of the regulation.
 It shall conform to the microbiological requirements
of the regulation.

FSSAI standards for butter
Product Moisture Milk Fat Milk solids
not fat
Common
salt
Table Butter 16.0% (w/w,
max.)
80.0% (w/w,
min.)
1.5% (w/w,
max.)
3.0% (w/w,
max.)
Desi
/cooking
butter
--- 76.0% (w/w,
min.)
--- ---

Permitted food additives in butter as
per FSSR
Additive Quantity
Colours (natural: singly or in combination)
Curcumin 100 ppm max
Beta carotene 100 ppm max
Carotene (natural extract) 100 ppm max
Annatto extract on bixin/nor bixin basis (50:50) 20 pm max
Beta apo-8 carotenal 35 ppm max
Methyl ester of beta apo-8 carotenoic acid 35 ppm max
Acidity regulators
Sodium and calcium hydroxide 2000 ppm max

Microbiological requirements of
pasteurized butter
Microbiological
parameters
Sampling plan Count
Total plate count m 10,000/g
M 50,000/g
Coliform count m 10/g
M 50/g
E.coli M Absent/g
Salmonella M Absent/g
Staphylococcus aureus m 10/g
M 50/g
Yeast and mould count m 20/g
M 50/g
Listeria monocytogenes M Absent/g

BIS standards for pasteurized butter
Characteristic Table butter White
butter
Milk fat, per cent by mass (min.) 80 82
Moisture, per cent by mass (max) 16 16
Acidity (as lactic acid), per cent by mass (max) .15 .06
Curd, per cent by mass (max) 1 1.5
Common salt, per cent by mass,(max) 2.5 ---
Coliforms, per ml, (max) 5 5
Yeast and mould count, per ml, (max) 20 20

CODEX STANDARDS OF BUTTER
 Butter is a fatty product derived exclusively from milk
and/or products obtained from milk, principally in the
form of an emulsion of the type water-in-oil.
 Butter should be made from milk and/or products
obtained from milk.
 Permitted ingredients
 Sodium chloride and food grade salt
 Starter cultures of harmless lactic acid and/or flavour
producing bacteria
 Potable water.

 Composition
• Minimum milk fat content 80% m/m
• Maximum water content 16% m/m
• Maximum milk solids-not-fat content 2% m/m
• The products should comply with any microbiological
criteria established in accordance with the Principles
for the Establishment and Application of
Microbiological Criteria for Foods (CAC/GL 21-1997).

Composition of butter
Constituents Quantity (% w/w)
Fat 80-83
Moisture 15.5-16
Salt 0-3
Curd 1-1.5

CLASSIFICATION OF BUTTER
 Based on acidity of cream used for butter making:
• Sweet cream butter : made from non-acidified cream;
having pH of ≥6.4
• Mildly acidified butter: made from partially acidified
sweet cream, having pH in the range of 5.2 to 6.3.
• Sour cream butter: made from ripened cream which
has more than 0.2% acidity, having pH ≤ 5.1.

 Based on salt content :
 Salted butter: Butter to which salt has been added. It is
added to improve flavour and keeping quality of
butter.
 Unsalted butter: This type of butter contains no salt. It
is usually prepared for manufacturing other products
such as ghee and butter oil

 Based on end use (as followed by BIS):
 Table Butter: made from pasteurized cream obtained from
cow or buffalo milk or a combination thereof with or
without ripening with the use of standard lactic culture,
addition of common salt, annatto or carotene as colouring
matter and di-acetyl as flavouring agent.
 White Butter: made from pasteurized cream obtained from
cow or buffalo milk or a combination thereof without
ripening and without addition of any preservative
including common salt, any added colouring matter or any
added flavouring agent.

 Based on the manufacturing practice (as followed by
FSSAI):
• Pasteurized cream butter/ Pasteurized Table butter: This is
made usually from pasteurized sweet cream. Such butter
usually has a milder flavour than that made from similar
cream not pasteurized.
• Desi butter: The butter obtained by traditional process of
churning dahi or malai as practiced at domestic levels.

Cream preparation for Butter
Manufacturing

Neutralization of cream
 Sour cream must be neutralized to make butter of
good keeping quality.
 By neutralization of cream acidity of cream is reduced.
 Churning of High acid cream may cause high fat loss
which can be prevented by neutralization.
 In pasteurization of sour cream, the casein curdles, by
entrapping fat globules, as the bulk of curd goes in
butter milk, causing high fat loss.

Objectives of neutralization
 To reduce the acidity in cream to a point (0.14 -0.16%)
which permits pasteurization without risk of curdling,
to produce butter which keeps well in cold storage
 To avoid excess loss of fat which result from the
churning cream i.e. excessively sour.
 To guard against undesirable flavors which may result
when a cream of high acid which is subjected for
pasteurization at higher temperatures.
 To improve the keeping quality of butter from high
acid cream. Salted-acid-butter develops a fish flavor
during commercial storage at -23 to -29°C.

Factors affecting neutralization
 Accurate neutralization of sour cream is important to
get a desired quality product.
a. Accuracy in sampling.
b. Accuracy in testing.
c. Accuracy in estimation of amounts of cream and
neutralizer.
d. Careful weighing the quantity of neutralizer.
e. Thorough mixing of neutralizer in cream prior to
pasteurization.

Method of neutralization of cream
 There are five essential steps to follow for cream
neutralization. These are:
1. Adoption of definite standard of churning acidity
2. Correct estimation of acidity
3. Calculating the amount of neutralizer to be added
4. Adding neutralizer in the correct manner
5. Checking results by re-testing acidity

Adoption of a definite standard of churning
acidity
 Acidity of cream at churning time controls the flavour and
keeping quality of the butter.
 Therefore, it is important to decide that at what acidity the
cream shall be churned.
 Churning acidity should be kept upto that maximum acidity
where absence chemical deterioration of butter (fishy flavour)
with age can be ensured.
 For cream of average richness (about 30%), fishy flavor can be
prevented by keeping the churning acidity to 0.3% maximum.
 The safe maximum limit of churning acidity varies with the
richness of the cream.

Correct Estimation of Acidity
 Representative sample should be taken.
 Weight of cream should be accurately measured as the final
amount of neutralizer will be dependent on the weight of
cream.
 Effect of CO2 on acidity should be taken care especially in
high acid cream (acidly> 0.65%)

Calculating the amount of neutralizer to be
added
 Q𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑛𝑒𝑢𝑡𝑟𝑎𝑙𝑖𝑧𝑒𝑟 𝑔 = % 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑎𝑐𝑖𝑑𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑢𝑟 𝑐𝑟𝑒𝑎𝑚 −

Adding neutralizer in the correct manner
 Neutralizer should be dissolved or emulsified in clean
water, diluted to approx. 20 times its weight with water.
 The solution must be distributed quickly & uniformly
throughout the entire batch of cream and mixed
thoroughly with cream.
 For efficient mixing, neutralizer is usually sprayed onto the
surface of well agitated cream.
 While the neutralizer is added, the cream should be
agitated vigorously and continuously.
 Agitation of cream is preferable for 5-10 min after
neutralization.
 Temperature at the time of neutralization should be 30oC.

Checking Results of Neutralization by Re-
testing for Acidity
 Acidity should not be checked immediately after
neutralization because of the following reasons:
 In case of lime and Magnesia neutralizers, the
neutralizing action is slow. It completes after
pasteurization & cooling.
 In case of soda neutralizers, CO2 is liberated and this
reacts acid toward the phenolphthalein indicator.
After pasteurization, expulsion of CO2 is largely
accomplished. Therefore, testing acidity after
pasteurization would give correct results

Type of Neutralizers
 Neutralizers in order to accomplish the purpose, for
which they are used in the creamery, must have
alkaline properties.
 They must be alkalis, alkaline earths or their
substances.
 The neutralizers used for reducing acidity in cream
belong to either one or the other of two groups
namely.
 Lime Neutralizers
 Soda Neutralizers

 Lime neutralizers:
 The principal constituent of the majority of lime
neutralizers is calcium.
 Many of the lime neutralizers available for cream
neutralization also contain some magnesium.
 The various commercial lime neutralizers differ from
one another chiefly with respect to the proportion of
calcium and magnesium they contain.

Cont..
 They are conveniently placed in three groups, as follows:
 Low magnesium limes: Containing 5% or less of
magnesium. A well Known brand of creamery lime
belonging to this group is peerless lime.
a. Medium magnesium limes: Containing about 30-35%
magnesium. To this group belong such brands as Kelly
Island lime, Neutra-Lac and Neutra-Lime.
b. High magnesium limes: Containing about 45 to 55%
magnesium. All wood lime is an outstanding
representative of this group. All magnesium limes in the
form of magnesium oxide and magnesium carbonate are
also available. They are artificially prepared limes

 Soda neutralizers:
 Soda neutralizers commonly used in the creamery are:
 Bicarbonate of soda or baking soda
 Sodium carbonate or soda ash
 Mixtures off baking soda and soda ash, such as
Sodium sesquicarbonate, Neutralene and Wyandotte

Standardization of Cream
 Adjustment of fat to desired level .
 Done by adding calculated quantity of skim milk or
butter milk.
 Desired level of fat in cream for butter making is 33 to
40 per cent.
 Standardization to both higher and lower level leads to
higher fat loss in butter milk.

Pasteurization of Cream
 Adjustment every particle of cream to a temperature not
less that 71°C and holding it at that temperature for at least
20 min or any suitable temperature-time combination
using properly operated equipment.
 A number of equipment can be employed for this purpose.
 More severe heat treatment of cream should be avoided
 Pasteurization of cream for making ripened cream butter is
commonly carried out at higher temperature than for sweet
cream butter e.g. 90-95ºC for 15 or 105-110ºC with no
holding.

Ripening of Cream
 Process of fermentation of cream with the help of suitable
starter culture.
 Can be eliminated if sweet-cream butter is desired.
 Main object of cream ripening is to produce butter with
higher di-acetyl content.
 Starter culture consisting of a mixture of both acid
producing (Streptococcus lactis, S.cremories) and flavour
producing (S.diacetylactis, Leuconostoc citrovorum and/or
Leuc. dextranicum) organisms is added.
 Amount of starter added usually ranges between 0.5-2.0
per cent of the weight of the cream

 After thoroughly mixed, the cream is incubated at about 21°C till
desired an acidity is reached.
 Cream is subsequently cooled to 5-10°C to arrest further acid
development.
 Biosynthesis of diacetyl is not sufficient above pH 5.2.
 Stopping fermentation of cream by cooling at pH 5.1-5.3, results in a
milder flavour; whereas continuing fermentation upto pH 4.5-4.7
results in higher levels of both diacetyl and lactic acid, giving more
pronounced flavour

Starter culture
 Mixture of both acid producing organisms (Lactococcus lactis, L.
cremoris) and flavour producing organisms (S. lactis subsp.
diacetylactis, Leuconostoc citrovorum and/or Leuconostoc
dextranicum) is used.
 Starter culture is added at the rate of 0.5 to 2.0% of the weight of
cream and incubated at about 21oC till desired acidity is reached.
 Usually it takes 15-16 hrs

Cooling and Ageing
 Processes which prepare the cream for subsequent
operation of churning.
 When cream leaves the pasteurizer, the fat in the
globule is in liquid form.
 When cream is cooled, fat crystallization starts, cream
will not churn unless the butter fat is at least partially
crystallized.
 If solidification of fat is not sufficient, the fat losses in
butter are high.

 The temperature to which cream is cooled is chosen is
such a way that the butter produced is of optimum
consistency and cream churns to butter in a
responsible time of about 35-45 minutes.
 Churning at too high temperature may give butter with
‘greasy‘ body which may work up too quickly and
become sticky.
 Generally cooling temperature in summer should be 7-
9°C and that of in winter 10-13°C.

CHURNING OF CREAM
 The sequence of events that occur during churning is as
follows:
 Churning is initiated by agitation of cream causing
incorporation of numerous air bubbles into the cream.
 With incorporation of air there is increase in the volume of
cream and air plasma interface.
 Surface active (such as frictional, impact, concussion etc.)
causes partial disruption of fat globule membrane
 The fat film, thus formed, serve as a foam depressant
causing the air bubble to burst.
 The liquid fat also serves as cementing material causing fat
globules to clump together and eventually butter grains are
formed which floats in plasma i.e. butter milk.

Initial Working:
 Working of butter is essentially a kneading process in
which butter granules are formed into a compact mass.
 During this operation, any excess moisture or
buttermilk is removed.
 However, the emulsion (w/o) at this stage is not fully
stable.

Salting of Butter
 In conventional process, butter may be salted by adding
salt to butter churn after initial working of butter.
 Salt to be added must be high quality e.g. IS 1845:1961, with
low level of lead, iron and copper.
 It should be 99.5 to 99.8% sodium chloride and microbial
count should be less than 10/g.
 Salt sets up osmotic gradient which draws water from the
butter grains. This can lead butter to be leaky. Salted butter
should therefore, must be thoroughly worked.
 Salt may be added either in dry form or as saturated brine
solution.

Adjustment of Moisture
 After the addition of salt, the moisture content in
butter is adjusted by adding calculated amount of
additional water.
 In most countries, maximum limits of 16% is placed on
the level of moisture.
 Starter distillates, if required, may also be added at this
stage to enhance the flavour of resultant butter, if
cream has not been cultured.

Final Working of Butter:
 The objective is to incorporate moisture and uniformly
distribute added moisture and salt in butter.
 During this process remaining fat globules also break
up and form a continuous phase, and moisture is
finally distributed to retard bacterial growth in butter.
 Moisture droplet size normally ranges from 1 to 15
micron and there are approximately 10 billion droplets
per gram of butter.
 Air content of conventional butter range from 3-7% by
volume with an average of 4 ml/100 while that of
vacuum worked butter it is about 1 ml/100g.

 The product obtained from cow or buffalo milk or a
combination thereof or from standardized milk by
partial removal of water.
 May contain calcium chloride, citric acid and sodium
citrate, sodium salts of ortho-phosphoric acid and
poly-phosphoric acid not exceeding by 0.3% by weight
of the finished product.
 Shall contain not less than 8% milk fat and 26% milk
solids.

Composition of evaporated milk
Component Percentage
Moisture 69
Total solids 31
Fat 9
Milk SNF 22
Protein 8.3
Lactose 12.2
Ash 1.5
Total milk Solids 31

Standards
Characteri
stics
requirements
Evaporated
milk
Evaporated
partly
skimmed milk
Evaporated
skim milk
Evaporated
high fat milk
Total milk
solids (min)
26 20 20 27
Fat % by
mass
Not < 8 Not > 8
& Not < 1
Not > 1 Not < 15
Milk
protein in
milk SNF
(min)
34 34 34 34

Manufacture
Receiving milk
↓
Filtration / clarification
↓
Standardization
↓
Fore warming / pre heating
↓
Evaporation
↓
Homogenisation first stage (2000 psi)
↓
Second stage (500 psi)
↓
Cooling

Cont..
↓
Pilot sterilization test (117ºC, 15 mins)
↓
Packaging
↓
Sterilization (116-118ºC, 15 mins)
↓
Cooling
↓
Shaking
↓
Storage

 Filtration/clarification : to remove the visible foreign
matter at a temperature of 35-40ºC, and then cooled.
 Standardization
 Standardization of the raw milk is carried out in 3 stages,
 For desired fat/SNF ratio, (usually 1:2.44, done in raw milk)
 Desired ratio of added sugar to the total milk solids (done
prior to condensing)
 To adjust the concentration of the finished product to the
required total solids content (after finishing the batch, i.e,
prior to homogenization).

 Fore warming/Pre-heating:
 Done for making the finished product free from
microorganisms and enzymes.
 To ensure uninterrupted boiling in pan
 To control age thickening in the finished product.
 The time temperature combination varies over 82-
93°C for 5-15 minutes or 115 –118°C for no hold.
 Tubular heat-exchangers are commonly used.

 Evaporation:
 Means the concentration of milk or liquid products.
 Milk is passed through steam heated tubes under
vacuum
 Correct concentration of solids – density 1.07
 No sugar is added here and normally a continuous
operation takes place.
 It is customary to slightly over-condense the milk to
facilitate standardization later.

 Homogenization:
 After evaporation and before cooling, the evaporated
milk is thoroughly homogenized to obtain a uniform
fat emulsion and reduce separation of fat to a
minimum during storage.
 The temperature is usually 49 °C as the product is
removed from the last part of the evaporator.
 Two-stage homogenization is generally recommended,
2000 psi in the first stage and 500-psi in the second
stage.
 After which the samples are cooled to 7 °C and stored.

 Pilot sterilization test:
 Purpose is to determine the amount of chemical stabilizers (tri
sodium citrate or di sodium phosphate) to be added to any given
batch of evaporated milk for the most satisfactory heat stability.
 The amount of stabilizers to be added to any batch is determined
by trial.
 The sample cans containing measured amount of stabilizer
solution and a fixed quantity of evaporated milk are sterilized at
117 °C for 15 minutes and then cooled rapidly to 24 °C
 As soon as they have been cooled the cans are opened, examined
for smoothness and colour and tested for viscosity.

 According to Mojonnier and Troy, a viscosity of 150ºR on
the Mojonnier-Doolittle viscosimeter represents the
correct viscosity of evaporated milk as it comes out of the
sterilizer.
 If the viscosity tests for pilot sterilized can show that no
stability correction is necessary, the batch is ready to be
filled into the cans.
 However if the tests show otherwise, stability corrections
becomes necessary.
 Based on the pilot sterilization test, the calculated quantity
of stabilizer should be added to the evaporated milk in the
form of a solution using just enough water to dissolve it.

 Packaging
 The cans are now mechanically filled with volumetric
fillers, the types of one used for this purpose are the
sanitary can, the can with a solder seal, and the vent
hole can.
 The temperature of evaporated milk when filling the
cans should be neither high nor low, but around 5 ºC; a
higher temperature cause foaming; while a lower
temperature increases the tendency towards ‘flipping’.
 The cans should be filled as nearly full as possible.

 Sterilization:
 Immediately after sealing and before sterilization, each can is tested for
any leakage using leak checker /detector, where the cans pass
submerged in a hot-water bath.
 In case of leaky cans, air bubbles rise to the top: these cans are removed
for repair.
 The filled and sealed cans, which have passed the test for leaks, are
ready for sterilization.
 The purpose of sterilization is to destroy all germ life and enzymes
present, thereby preserving the product permanently.
 During sterilization, the temperature is raised to 116-118 ºC and held at
this temperature for 15 minutes.
 If the cans cannot be sterilized within an hour or two, they should be
then held under refrigeration.

 Batch method :
This consists of a water steam boiler-like, horizontal steam
drum, with hollow interior having a revolving frame, in
which the cans are loaded.
The sterilizer rotates at 6-12 rpm, with uniform distribution
of heat.
 Continuous method:
Here the cans are progressively heated to a few degrees
below the boiling point, and finally enter the sterilizing
area proper.
Later cooling process starts with the cans gradually moving
through progressively less hot-water chambers and finally
through cold water.

 Cooling
 Immediately after holding time is over, the evaporated
milk is cooled within 15 minutes to 27-32ºC.
 Rapid and uniform cooling is important.
 Bulging of the cans can be avoided by using cold water
and in continuous system, cooler operates at 10 psi.
 Shaking
 done to break mechanically, any curd, which might
have formed during the process of sterilization to a
homogenous smooth consistency.

 Storage
 Though evaporated milk can be stored at room
temperatures, a storage temperature of 5-16 ºC is
generally used, which helps to keep the product
acceptable even up to 2 years.
 Inversion of cans once in 3-6 months during storage
will help to minimize fat separation

 Milks obtained by evaporating part of water of whole
milk, or fully or partly skimmed milk, with or without
the addition of sugar.
 The term ‘condensed milk’ is commonly used when
referring to “full cream sweetened condensed milk”.
 Skimmed milk products are known as “sweetened
condensed skim milk” and “unsweetened condensed
skim milk”.
 The ratio of concentration of milk solids is about 1:2.5
for full cream products and 1:3 for sweetened
condensed skim milk.

 According to the PFA (1976) the various condensed milks have
been specified as follows:
 Unsweetened condensed milk (evaporated milk) : the
product obtained from cow or buffalo milk or a combination
therefore, or from standardized milk, by the partial removal of
water.
 It may contain added calcium chloride, citric acid and sodium
citrate, sodium salts of ortho-phosphoric acid and poly-
phosphoric acid not exceeding 0.3 per cent by weight of the
finished product. Such addition need not be declared on the
label.
 Unsweetened condensed milk should contain not less than 8.0
per cent milk fat, and not less than 26 per cent milk solids.

 Sweetened condensed milk : the product obtained from
cow or buffalo milk or a combination thereof, or from
standardized milk, by the partial removal of water and after
addition of cane sugar.
 It may contain added refined lactose, calcium chloride,
citric acid and sodium citrate, sodium salts of ortho-
phosphoric acid and poly phosphoric acid not exceeding
0.3 per cent by weight of the finished product. Such
addition need not be declared on the label.
 Sweetened condensed milk should contain not less than
9.0 per cent milk fat, and not less than 31 per cent milk
solids and40.0 per cent cane sugar.

 Unsweetened condensed skim milk (evaporated
skimmed milk) : the product obtained from cow or
buffalo milk or a combination thereof, by partial removal of
water.
 It may contain added calcium chloride, citric acid and
sodium citrate, sodium salts of ortho-phosphoric acid and
poly phosphoric acid not exceeding 0.3 per cent by weight
of the finished product. Such addition need not be
declared on the label.
 Unsweetened condensed skim milk should contain not less
than 20.0 per cent total milk solids.
 The fat content should not exceed 0.5 per cent by weight.

 Sweetened condensed skim milk : the product obtained
from cow or buffalo skimmed milk or a combination
thereof by the partial removal of water and after addition of
cane sugar.
 It may contain added refined lactose, calcium chloride,
citric acid and sodium citrate, sodium salts of
orthophosphoric acid and polyphosphoric acid not
exceeding 0.3 per cent by weight of the finished product.
Such addition need not be declared on the label.
 Unsweetened condensed skim milk should contain not
less than 26.0 per cent total milk solids and not less than
40 per cent cane sugar.
 The fat content should not exceed 0.5 percent by weight.

Composition of condensed milk
Condensed milk Skim sweetened
water 26 29
Total solids 74 71
Fat 9 0.5
Milk solids not fat 22 25.5
Protein 8.3 9.3
Lactose 12.2 14
Ash 1.5 2.2
Total milk solid 31 26
Sucrose 43 45

Indian Standard Specifications for
condensed milk
Characteristics Requirement for
Condensed milk Skim sweetened
Total milk solids (%wt.)
Min
31 26
Fat (% wt) Not less than 9 Not more than 0.5
Sucrose (% wt.) min 40 40
Acidity (% lactic) max 0.35 0.35
Bacterial count (per g) 500 500
Coliform count (per g) Negative Negative
Yeast and mould count
(per g.) Max
10 10

Manufacture of condensed milk
Receiving milk
↓
Filtration /Clarification (38-40ºC)
↓
Standardization
↓
Fore warming/preheating (115-118 ºC / No Hold)
↓
Condensing (2.5:1)
↓
Addition of sugar

Cont..
Homogenization
↓
Quickly cooled to 30ºC
↓
Seeded with 0.1 - 0.3% lactose
↓
Vigorous stirring and slow cooling for 1 hour.
↓
Temperature of 15 ºc reached
↓
Stirring continued until packed.
↓
Storage at 10 ºc.

 The basic principle in the production of condensed milk
and evaporated milk is that high quality milk is filtered
/clarified, standardized, fore-warmed and condensed
/evaporated to the desired level.
 The concentrated product is preserved by the addition of
sugar for condensed milk and by heat sterilization for
evaporated milk.
 When the milk is received at the plant, its temperature
should be at 10ºC or below.
 The milk should be clean, sweet, and free from off-flavours
and odours and reasonably free form extraneous material.

 Filtration/clarification: This is done in order to remove
the visible foreign matter at a temperature of 35-40ºC, and
then cooled.
 First standardization: the ratio of milk fat to non fat
solids is adjusted so that compositional quality
requirements for the final product are met.
 Yield and quantity of the final product depends on this
step.
 It establishes desired ratio of fat:SNF in milk.
 It is carried out by the addition of milk with different fat
contents, such as skim milk or cream, based on the
requirement of the final product.

 Preheating: heat treating the milk before it is
concentrated.
 it is required to destroy all pathogenic and potential
spoilage organisms, to inactivate all enzymes and regulate
viscosity and age thickening.
 Additional consequences of the thermal processing are:
 The decrease of milk fat separation.
 The retardation of oxidative changes.
 Economic and technological effects.
 The time temperature combination varies over82-93ºC for
5-15 minutes.
 Tubular heat exchangers are commonly used.

 Homogenisation:
 Not always applied.
 Depends on the product type, market (shelf life) and
preference of the manufacturer.
 If the product need to be shelf-stable it should be
homogenized at a pressure of 5-10 MPa.
 Also it helps to regulate viscosity.
 Recombined sweet condensed milk is always
homogenised.

 Condensation: usually done by evaporation, but
reverse osmosis can also be used.
 Same as that for evaporated milk.
 Usually condensed in a multistage falling film
evaporator.
 Because of the high viscosity of the product,
evaporators are usually equipped with a finisher, in
which the concentrate is reheated before
concentrating into final solids content.
 Otherwise flow of the product over evaporator will not
be uniform resulting in fouling and low heat transfer.

 Addition of sugar: sugar can be dissolved in cold
milk before pre heating.
 Microorganisms present in the milk will be killed in
pre heating.
 But adding sugar will make the process of evaporation
more difficult.
 Alternative method is addition of sugar after pre
heating or at the end of the condensing.
 If sugar as added as a syrup it should be properly heat
treated to kill osmophilic yeasts.

 Refined cane sugar or beet sugar is used in the
manufacture of sweet condensed milk.
 Sucrose must be microbiologically approved, with no
acids or invert sugar.
 Advantages of sucrose – good solubility, low
susceptibility to fermentation, and user preference.
 One method of addition of sugar is – running a part of
fore warmed milk into a sugar mixing pan where sugar
is mixed in a fine stream with proper agitation.
 The sweetened milk is then drawn into the vacuum
pan.

 Another method is to dissolve sugar by boiling in
water in a separate tank called sugar well.
 This is then added to milk in the vacuum pan towards
the end of evaporation process.
 Disadvantage – additional water need to be removed
from added sugar solution.

 Striking the batch: refers to the end of concentration
operation in the vacuum pan.
 Determined by specific gravity or density test.
 The dry matter content which is acquired by the
evaporation step is determined by determining the
density of the concentrate.
 Should be 1.30 for SWM and 1.35 for SSM when the
correct dry matter has been reached.
 Baume’ hydrometer or a viscometer is used to
determine the progress of concentration.

 Hydrometer scale record the density.
 For condensing milk Baume’ reading ranges from 30-
37° Be’ at 49°C.
 When desired concentration as indicated by Baume’
reading is reached milk is removed from the pan –
striking the batch.
 Second sterilization: final standardization.
 Carried out after evaporation and sugar addition.
 During this stage total solids, sugar and milk fat
content are controlled.

 Cooling: essential to control the texture of SCM.
 Most critical and most important stage.
 The quantity of sugar that milk can carry in solution varies
according to the temperature of milk.
 The water in the condensed milk can hold only half of the
lactose in solution.
 Remaining will be allowed to precipitate in the form of crystals.
 If surplus lactose is allowed to precipitate freely – gritty and
unsuitable product.
 Largest crystal permitted in first grade milk - 10µm.
 They remain dispersed under normal temperature (15-25 °C) and
are not felt on the tongue.

 Forced crystallization: to produce mass crystallization of
lactose.
 Before seed lactose is added condensed milk must be
cooled to a temperature where lactose will be
supersaturated – seed lactose will not dissolve.
 After seeding the cooling should be continued to crystallize
the lactose.
 A vacuum cooler is used in which a thin layer of milk passes
the wall of the vat that is under vacuum.
 Alternatively it can be cooled in a scrap surface heat
exchanger.

 Seeding : crystallization of lactose is usually assisted by
the addition of fine powder of lactose or small quantity of
condensed milk from previous batch in which lactose
crystals are in minute form.
 other alternative is to use spray dried skim milk powder as
seed material.
 Seeding refers to the addition of fine spray of lactose
during cooling so as to provide nuclei for crystallization.
 The purpose is to give lactose an added incentive to
crystallize.
 Recommended amount of finely pulverized lactose for
seeding is 375-500 per 1000 kg of initial milk taken or 0.1-
0.3% of condensed milk.

 Required amount of seed lactose is blended with small
quantity of condensed milk and then added to the batch
with vigorous agitation at 30°C
 After forced crystallization and seeding, cooling is
continued slowly to 24-25°C for about an hour or longer.
 Robust agitator is needed as viscosity of condensed milk
is very high.
 Packaging:
 For large quantity / bulk transport – barrels of size
varying from 50-300 kg.
 Retail sale – cans of various sizes ranging from 200 g to 5
kg

 Dried milk or milk powder is the product obtained by
removal of water from milk by heat or any other
suitable means to produce a solid containing 0.5% or
less moisture.
 Whole milk, partly skimmed milk or skim milk can be
used for drying.

CLASSIFICATION
 Based on the type of drier:
 Spray dried
 Roller dried
 Freeze dried.
 Based on fat content of milk:
 Skim milk powder
 Partly skim milk powder
 Whole milk powder

 Heat applied for drying of milk:
 Low heat
 Medium heat
 High heat
 Based on method of manufacture:
 Instantized
 Foam dried

COMPOSITION
WHOLE MILK
POWDER
SKIM MILK POWDER
Moisture 3 4
Fat 27 1
Protein 26 35
Lactose 38 51.5
Ash 6 8

Legal standards - PFA
 Milk powder : the product obtained from cow or buffalo milk or
a combination thereof , or from standardized milk, by the
removal of water.
 It may contain added calcium chloride and sodium citrate,
sodium salts of ortho-phosphoric acid, and poly-phosphoric
acid, not exceeding 0.3% of the weight of the finished product
and 0.01% of BHA by weight of finished product.
 It may contain lecithin to a maximum limit of 0.5%.
 It shall contain not more than 5% moisture and not less than
26% fat.
 The maximum acidity expressed as lactic acid shall not be more
than 1.2%.
 Plate count shall not exceed 50,000/g and coliform shall be
absent in 0.1g of the powder.

 Skimmed milk powder: the product obtained from cow
or buffalo milk or a combination thereof , or from
standardized milk, by the removal of water.
sodium salts of ortho-phosphoric acid, and poly-
phosphoric acid, not exceeding 0.3% of the weight of the
finished product
 It shall contain not more than 5% moisture and fat not
more than 1.5%.
 The maximum acidity expressed as lactic acid shall not be
more than 1.5%.
 Plate count shall not exceed 50,000/g and coliform shall be
absent in 0.1g of the powder.

 Partly skimmed milk powder: the product obtained
from cow or buffalo milk or a combination thereof , or from
standardized milk, by the removal of water.
sodium salts of ortho-phosphoric acid, and poly-
phosphoric acid, not exceeding 0.3% of the weight of the
finished product
 It shall contain not more than 5% moisture and fat content
should be more than 1.5% and less than 26%.
 0.01% of BHA by weight of finished product could be
added.
 The exact fat content shall be indicated on the label.

BIS STANDARDS
 MILK POWDER (IS:1165-2002)
Characteristics Requirements
Moisture % by mass, max 4
Total milk solids % by mass,
min
96
Fat, % by mass, min 26
Insolubility index, max 2 ml
Total ash, % by mass , max 7.3
Titratable acidity, % by mass,
max
1.2
Bacterial count/g, max 40,000
Coliform count Absent in 0.1 g
Staphylococcus aureus Absent in 0.1g
Salmonella & shigella Absent in 25g

 SKIMMED MILK POWDER (IS:13334 (part I)-1998)
Moisture % by mass, max 4
min
96
Fat, % by mass, min 1.5
Insolubility index, max 15 (roller dried), 1.5( spray
dried)
max
1.5
Coliform count Absent per 0.1 g

EXTRA GRADE SKIMMED MILK POWDER
(IS:13334(part II)-1992)
Moisture % by mass, max 3.5
min
96.5
Fat, % by mass, min 1.25
Insolubility index, max 0.5 ml
max
1.5
Coliform count Absent in 0.1 g
Staphylococcus aureus Absent in 0.1g
Salmonella & shigella Absent in 25g

 PARTLY SKIMMED MILK POWDER (IS: 14542-1998)
Type I Type II
Moisture % by mass, max 4 4
min
96 96
Fat, % by mass, min 1.526 1.526
Insolubility index, max 15(RD),1.5 (SD) ---
Total ash, % by mass , max 8.2 8.2
max
1.5 1.5
Bacterial count/g, max 50,000 50,000
Coliform count Absent in 0.1 g Absent in 0.1
g

Manufacturing of milk powder
 Standardization:
 The objective is to adjust the ratio of milk fat and total
solids to the level required for the final product.
 Pre heat treatment: is done for the production of safe
and better stable milk powders and also for inducing
in it other desirable attributes.
 Usually carried out at a temperature higher than that
for pasteurization.

 Main objectives of pre heat treatment :
To destroy all pathogenic bacteria and most of the
saprophytic organisms.
To inactivate enzymes, especially lipase.
To activate –SH groups of α- lactalbumin , thus increasing
resistance to the oxidative changes during storage.
It also contributes to the shelf lie of the product primarily
through the development of antioxidant or reducing
substances.
 Most commonly followed heating regime is 88-95°C for 15-30
seconds.

 Evaporation: compulsory step in powder processing.
 Milk powder produced from evaporated milk has
longer shelf life and large powder particles.
 Also help in reducing the duration of drying process.
 For this purpose , a continuous multiple effect
evaporator, usually of tubular type is used.
 For spray drying, milk is concentrated to 40-45% total
solids, while for roller drying it is up to 18-20%.

 Homogenization:
 Is not an obligatory process but is usually applied to
decrease free fat content.
 It also helps to prevent clumping of fat during
reconstitution and improves keeping quality of
powder.
 It is conducted after evaporation or in partly
concentrated milk.
 The customary homogenisation is at 2500-3000 psi at
63-75°C.

 Drying:
 A number drying process are followed
Spray drying.
Fluid bed drying.
Drum drying.
Batch drying in rays.
Freeze drying.
Microwave drying.
Super heated steam drying

SPRAY DRYING
 The predominant method of drying milk and milk
products.
 Basic principle is the exposure of a fine dispersion of
droplets, created by means of atomization of pre-
concentrated milk to a hot air stream.
 The small droplets created – more surface area- faster
evaporation of water and minimized heat damage.
 Spray dryer utilizes a product which is first pre
concentrated in a vacuum pan or an evaporator, the
product is then atomized inside a drying chamber of
the dryer.

 The most common method of atomization – force the
product by high pressure pump through the nozzle to assist
the break up of the liquid.
 As the atomized product is introduced into the drying
chamber, heated air is forced through the chamber.
 This air provides heat for evaporation and it also act as a
carrier for moisture to be removed from the dryer.
 The air may be forced through the dryer either by air or by
suction.
 Air and product is separated following drying.
 The product is then cooled and packed.

 In nutshell, spray drying comprises of 5 essential sub
processes
Atomization of the feed
Mixing of the spray drying air.
Evaporation.
Separation of the product from drying air.
Cooling of the powder.

 Ice cream is a frozen dairy product made by freezing a
mix with agitation to incorporate air and ensure
uniformity and consistency.
 According to the PFA rules (1976) ice cream is the
frozen product obtained from the cow or buffalo milk
or a combination thereof or from cream and or on the
milk products, with or without the addition of cane
sugar, eggs, fruits, fruit juices , preserved fruits, nuts,
chocolate, edible flavours and permitted colours. It
may contain permitted stabilizers and emulsifiers not
exceeding 0.5 per cent by weight.

 The mixture must be suitably heated before freezing.
 The product should contain not less than 10%milk fat,
3.5% protein, and 36% total solids.
 However, when any of the aforesaid preparations
contains fruits or nuts or both, the content of milk fat
may be proportionately reduced but not less than 8 %
by weight, starch may be added to a maximum extent
of 5 %, with a declaration to that effect on the label.

Composition
 ISI specifications for ice cream are:
Weight (g/litre, min) 525
Total solids (% wt, min) 36
Milk fat (% wt, min) 10 (tentative)
Acidity (% lactic acid, max) 0.25
Sucrose (% Wt., max) 15
Stabilizers and emulsifiers (% Wt.,
max)
0.5
Standard plate count (per g) Not more than
2,50,000
Coliform count (per g) Not more than
90

Manufacturing of ice cream
 Ingredients:
 I. dairy products
 Source of fat
 Sweet cream: this is the most desirable concentrated source of
fat for use in a mix
 Frozen cream
 Plastic cream
 Unsalted butter
 Butter oil.
 Source of milk-solids- not fat
 Skim milk.

 Skim milk powder-this is most frequently used in the
spray dried or flaked form.
 Condensed skim milk
 Sweet cream buttermilk.
 Sources of both fat and solids not fat
 Whole milk.
 Whole milk powder
 Condensed whole milk
 Evaporated milk

 II.Non-dairy products
 Sweetening agents
 Cane sugar or beet sugar.
 Corn sugar (dextrose)
 Corn syrup solids (dextrose + maltose)
 Corn syrup
 Invert sugar (glucose +fructose)
 Saccharin.
 Stabilizers
 Gelatin-of animal origin .

 Commonly gelatin is used at the rate of 0.25 to 0.5 %
for a 250 bloom gelatin.
 The ice-cream mix stabilized with gelatin usually
requires about 4 hours of ageing to develop complete
stabilizing properties, while other stabilizing materials
do not require an ageing period.
 The amount of gelatin used depends on several factors
such as the source of gelatin whether from calf, pork
skin or bonematerials.

 Sodiumalginate – of vegetable origin . The basic stabilizing principle
‘algin’ is extracted from ocean kelp (seaweed) growing on the shores of
California and in Japan.
 This product improves whipping ability and leaves a slightly cleaner
flavour in the mouth. It dissolves properly only when added to the mix
at about 68-71 °C.
 Guargum –of Indian origin.
 Carageenan
 Agar agar:
 Carboxy methyl cellulose
 Pectin

 Emulsifiers: They are substances which help to form
emulsions.
 Glycerol Mono Stearate (GMS).
 Flavours
 Colour
 Egg solids - Egg yolk solids improve the whipping
ability.
 Fruits and nuts

Figuring the mix
 Knowledge of calculation of ice cream mix is helpful in
properly balancing the mix, in establishing and
maintaining a uniform quality and in producing ice cream
that conforms to legal standards.
 Ice cream mix - simple and complex.
 Simple mixes - require the least calculation and are made
of ingredients, each of which supplies one constituent.
 Complex mixes - difficult to calculate as they include mixes
where at least, one constituent is obtained from two or
more products.
 Complex mixes require the use of the Pearson’s square,
algebraic methods.

Making the mix
 The order in which ingredients are added is as follows:
 All liquid ingredients are placed in a jacketed vat provided with a
power stirrer, and the agitation and heating started at once, the
dry ingredients, including skim milk powder, sugar, and
stabilizers are added while the liquid material is agitated before
the temperature reaches 49ºC.
 Proper suspension to avoid lumpiness of the dry ingredients may
be obtained by either mixing the dry materials thoroughly with
part of the sugar before slowly adding it to the liquid, or by
sifting / slowly adding these substances to the liquid.
 If gelatin is the stabilizer used, it is best added after it is
thoroughly mixed with equal volume of sugar, and before the
liquid material reaches 49ºC.

 Alternatively, it can be sprinkled on the surface of the cold liquid
and allowed to soak before the mixture is heated or soaked in
water and the mixture heated to completely dissolve the gelatin,
which is usually added to warm(38-49ºC) mix.
 If sodium alginate is used, it should not be added until the
temperature of the liquid material has reached at least 66ºC.
 If butter, plastic cream, frozen cream, or other products are used,
they should be cut into small pieces and added after time has
been given to allow for complete melting before the pasteurizing
temperature is reached.
 With a few exceptions, colouring and flavouring materials are
added when the mix is frozen.

 The ISI specification for pasteurization
temperature – time combination for ice cream mix
are as follows:
Batch system- 68.5 °C for not less than 30min.
HTST method - 80 °C for not less than 25 sec.
 In batch system the heating and holding may be
accomplished in the vat used for mixing the
ingredients
Pasteurization of mix

Homogenization of mix
 The main purpose of homogenization -make a
permanent and uniform suspension of the fat by
reducing the size of the fat globules to a very small
diameter, preferably not more than 2 microns.
 The mix is usually homogenized at temperature from
63 to 77º C at pressure of 2500to 3000 psi with one
valve, or 2,500 to 3000 psi at the first stage and 500 psi
at the second stage will usually give good results for an
average mix (with 3 - 12% fat).

Cooling and ageing of mix
 Cooling the mix immediately after homogenization to
0-5ºC is essential, after which it should be held in
ageing tanks until used.
 Ageing refers to holding the mix at a low temperature
for a definite time before freezing.
 The ageing temperature should not exceed 5ºC.
 The ageing time under commercial conditions may
range from 3 to 4 hours, except for sodium alginate
which requires no ageing.

Advantages of aging
 Improves the body and texture of ice cream
 Improves the whipping capacity
 Increases maximum overrun
 Increases melting resistance.

Freezing the mix
 Freezing is one of the most important operations in the making
of ice cream for upon it depends the quality, palatability and
yield of the finished product.
 The freezing process may be divided into two parts.
 The mix with the proper amount of colour and flavouring
materials generally added at the freezer, is quickly frozen while
being agitated to incorporate air in such away as to produce and
control the formation of small ice crystals which is necessary to
give smoothness in body and texture, palatability and
satisfactory overrun in the finished product.
 When ice cream is partially frozen to a certain consistency it is
drawn from the freezer into packages and quickly transferred to
cold storage rooms where the freezing and hardening is
completed without agitation.

Overrun in ice cream
 Overrun is usually defined as the volume of ice
cream obtained in excess of the volume of the mix. It is
usually expressed as a percentage.
 This increased volume is composed mainly of the air
incorporated during the freezing process.
 The amount of air incorporated depends on the
composition of the mix and the way it is processed; and is
regulated so as to give that percentage overrun or yield
which will give the proper body, texture and palatability
necessary to a good quality product.
 Too much air will produce a snowy, fluffy, unpalatable ice
cream while too little, a soggy, heavy product.

 The desirable over run percentage in different ice
creams is
Product % OR
Ice cream packaged 70-80
Ice cream bulk 90-100
Softy ice cream 30-50

 May be defined as a coagulum obtained by lactic acid
fermentation of prescribed milk or milk products by
the action of Lactobacillus delbrueckii subsp.
bulgaricus and Streptococcus thermophilus.
 The addition of additives is optional.
 The two yoghurt bacteria are added as the starter
culture at 2-5% inoculum, preferably at 1:1 ratio and
incubated at 42-45°C for 3-6 hours until pH 4.4 and
titratable acidity 0.9-1.2% is achieved.
 Final product should contain large quantities of the
above micro organisms.

CLASSIFICATION:
 Set type: incubated and chilled in the packet.
 Stirred type: incubated in tanks and chilled before
packaging.
 Drinking type: similar to stirred type, but coagulum is
broken down to a liquid before being packed.
 Frozen type: incubated in tanks and frozen like ice
cream.
 Concentrated: incubated in tanks, concentrated and
chilled before being packed. Also called as strained
yoghurt/ labneh or labaneh.

Composition
Fat (%) SNF(%)
Yoghurt ≥3 8.2
Partly skimmed yoghurt 0.5-3 ≥8.2
Skimmed yoghurt <0.5 ≥8.2

 Standardization: the standardization of yoghurt is
done by means of
o Evaporation, 10-20% of the water in the milk is
normally evaporated. This corresponds to an increase
in 1-2.3% TS content.
o Addition of milk concentrate.
o Addition of skim milk powder, usually 0.5-3%.
o Addition of ultra filtered retentate from skim milk

 Deaeration: air content of the milk used for cultured
milk production should be as low as possible.
 Advantages of deaeration-
Improved working condition for the homogenizer.
Less risk of fouling.
Improved stability and viscosity of yoghurt.
Removal of off-flavours.

 Homogenization: main objective is to prevent
creaming during the incubation period and to assure
uniform distribution of the milk fat.
 It also improves the stability and consistency of the
cultured milk, even those with low fat content.
 Milk is generally homogenized at 65-70°C and 20-
25MPa to obtain optimum physical properties in the
product.

 Heat treatment: the milk is heat treated before being
inoculated with the starter.
 The main advantages are-
Improve the properties of milk as a substrate for the
growth of micro organism.
Ensure that the coagulum of the finished yoghurt will
be firm.
Reduce whey separation in the finished product.
 Optimum results are obtained by heat treatment at
90-95°C for 5 min

 Culture preparation: the bacteria used are strains of the
Lactobacillus delbrueckii subsp. bulgaricus and
Streptococcus thermophilus.
 It is added at a ratio of 1:1 or 2:1.
 The cultures must be replaced at regular intervals.
 In batch method of yoghurt manufacturing clarified milk is
adjusted to specific solid content , then heated in a
jacketed vat to 90-95°C , inoculated with 1-3% yoghurt
culture and thoroughly mixed with milk and then filled in
retail containers, incubated at 42-43°C for 2-3 hours
followed by cooling.

 The sweet acidophilus milk is low in fat, tangier and
lactose-free due to the presence of Lactobacillus
acidophilus, a healthy bacterium (Probiotic) that aids
in digestion.
 The low fat acidophilus milk has many health benefits
and is especially known for prevention of allergies.
 Acidophilus milk is highly acidic product made by
fermentation of milk with L.acidophilus, a probiotic
bacterium.

 Acidophilus milk is prepared by heating the milk at
a relatively higher temperature (115°C/ 15 min)
followed by cooling (38-40°C) and inoculation with
active culture at 2-5%.
 The curd forms in about 18-24 hours.
 Final product contains 1.5-2 lactic acid but no
alcohol.
 It is then cooled to 10°C before agitation and
pumped to a filler where it is filled into bottles or
cartons.

 One of the most ancient product prepared from mares
milk and is popular in Eastern Europe.
 Consumed as a food as well as alcoholic drink.
 Mares milk does not curdle at isoelectric point of
casein and it is not considered as a curdled product.
 It is of liquid consistency and casein will be present in
the form of fine flakes (not felt in the tongue)
 Its counterpart can be prepared from cows milk.

 It is an effervescent acidic, alcoholic fermented, milky
white/greyish liquid.
 The starter culture consists of L.delbrueckii
subsp.bulgaricus and lactose fermenting yeasts, like
Saccharomyces lactis.
 L.acidophilus may also be present.
 The major end products in kumis are lactic acid (0.7-
1.8%), ethanol (1.3%) and carbon-di-oxide (0.50-
0.88%).

 Kumis from mare’s milk consists of lactose 2.3%
lactose, 1.5% fat and 2% protein.
 Based on different concentration of lactic acid and
alcohol – 3 types of kumis
Low acid & low alcoholic – lactic acid 0.6% and alcohol
0.7%.
Medium acidic and medium alcoholic - lactic acid
0.8% and alcohol 1.1 - 1.7%.
High acidic and high alcoholic - lactic acid 1% and
alcohol 1.7-2.5%.

 Mare’s milk or cow milk or skim milk with added
sucrose may be used.
 Milk is heated to 90-95°C for 5 minutes followed by
cooling to 26-28°C.
 The inoculum is then added at the rate of 10-30% to
give an acidity of 0.7-0.8% lactic acid followed by
agitation and cooling to 20°C.
 The product is then packaged and stored at 4-5°C.

 Mildly alcoholic, distinctly effervescent product with
sour cream like consistency and distinct flavour.
 It contains around 0.9-1.1% lactic acid and 0.3-1%
alcohol along with sufficient carbon-di-oxide which
causes effervescence as well as traces of acetaldehyde,
diacetyl and acetoin.
 Highly popular in Eastern Europe but limited in other
areas. (may be due to problems in packaging and
distribution).
 pH of the product is usually 4.3-4.4.

 It is usually made from goat milk or sheep milk or cow
milk.
 Process stages includes homogenization, heat
treatment and cooling to the inoculum temperature,
starter addition, coagulation and cooling of the
coagulum.
 Milk is preheated to 70°C i.e., homogenization
temperature.
 the homogenization pressure should be 17.5-20MPa in
order to obtain a kefir of good consistency

 Heat treatment of the homogenized milk is important as
all coagulable proteins should be denatured.
 Attained by a time temperature combination of 90-
95°C/% min.
 After heat treatment, milk is cooled to the inoculation
temperature, usually about 23°C.
 The starter is then added at the rate of 2-3%.
 A mixture of bacteria and yeasts, called as kefir grains,
forms the inoculum.
 Acid is produced by bacteria while alcohol is produced
by lactose fermenting yeasts.

 Incubation takes place at 23°C for 18-24 hours when
the product will contain up to 0.8% ethanol and 1%
carbon-di-oxide.
 Thereafter it is rapidly cooled to 4-6°C in a plate heat
exchanger when the pH has dropped to 4.5-4.6.
 This step will stop fermentation.

Manufacture of dairy products

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