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Dairy Farming Manual

Volume 1

Technology Unit 9
Milk Treatment

page 157

>Extension Materials

What should you know about milk treatment?

You should know about the four main methods:

1 Cooling

- to store the milk longer before further treatment (see T.4) 


2 Separation (5-8)

- to remove dirt

- to separate cream from skim milk. 

3 Standardization (9-21)

- to obtain the correct percentage of fat

- to obtain the correct percentage of total solids.

4 Heat treatment (22-42)

- to kill bacteria which spoil the milk (see 43-58 for large scale heat treatment). 

 page 159

How can you treat milk on a small scale?

5 You can filter milk to remove large dirt particles


6 but more milk passes through the dirt and dissolves some of it
and carries bacteria to the milk already filtered.
7  By using a separator you can separate cream from skim milk.
Heavier particles (skim milk) move to the outside.
8 You can work this separator by hand.
It treats 60-200 l of milk per hour.
page 160


What is standardization?

9 Standardization is a method of controlling the fat content of milk.
Whole milk has a fat content of 3-5 % (buffalo milk may have 7-8 % fat).
Low-fat milk has a fat content of 1.5-1.8 %.
Skim milk has less than 0.1 % fat.
Cream has 35-70 % fat.
10 After separation, you can mix:

- whole milk with

- skim milk to get

- milk with a fat content between 0-4 %.


For example, to make a certain cheese, you may need milk with a fat content of 2.6 % (see T 12 Standardization and Production Costs).


page 161

How do you sample and test milk for standardization on a small scale?

12 In milk reception, you weigh, filter, test the density of your milk.

You may make other tests.

Then you take a sample of milk from each can and mix together.


13 You test the mixed sample for milk acidity.

- put 20 ml of the milk sample into a glass with a pipette
- add 8-10 drops of phenolphthalein with a dropper.


14 With the burette, you:
- add NaOH 0.1N solution drop by drop into the glass until the solution has a stable pink colour.
The number of 0.1N NaOH used is multiplied by 5 to give ml per 100 ml of milk.
Normal milk will have a value between 17 and 21 ml per 100 ml milk.  If higher the milk is sour.
page 162

15 You also test the mixed sample for fat content.
- put 10 ml of sulphuric acid in the butyrometer
- add 11 ml of milk from the average sample
- add 1 ml of amyl alcohol
16 - cork the butyrometer and shake well to dissolve the milk elements (use a cloth to hold - hot!) 
- put the butyrometer in the centrifuge
- centrifuge for 5 minutes
17 - put the butyrometer cork down into a water bath (60 - 70 C)

- leave for 5 minutes.

18 Make sure

- the butyrometer is vertical

- You read at eye level.

The sample here contains 3.6 % fat.

page 163

19 You record the results in a milk analysis note book:
page 164

Small scale heat treatment

Why heat milk?

22  Heating milk kills most bacteria and other micro-organisms.

Pasteurization is heating with controlled temperature and time.

There are different combinations of temperature and time.

 23  After you cool the milk you can keep it longer.
24  Use a thermometer to heat to the correct temperature.
For small scale processing, heat to 65 C and keep for 30 minutes.
Stir the milk regularly to keep even temperature throughout the milk.
25 Never drink milk which has not been heated.

It can make you sick.

page 165

What are the effects of heat treatment on milk?


26 Only high temperatures change fat, but pasteurization melts fat so that rough treatment easily breaks the membrane.
Then, enzymes can oxidize the fat.

Proteins and enzymes

27 If milk is good quality, normal pasteurization:
- does not change proteins
- does not usually change enzymes from bacteria.
Pasteurization coagulates sour milk.


28  Very high temperatures cause:
- browning of milk
- change in flavour.
Normal pasteurization does not cause browning.

Minerals and vitamins

Normal pasteurization does not change minerals.
Heat treatment can destroy water soluble vitamins. Normal pasteurization destroys about 5-20 % Vitamin C.

 page 166

What is important in heat treatment?

29 Make sure you:
- measure temperature accurately

- stir the milk throughout the heat treatment

- heat the milk up to a certain temperature 

- maintain the temperature for a fixed time 

- cool the milk (stirring until cool). 

How do you treat milk on a small scale?
31 Thermatization is a soft heat treatment, for example, 65 C for a short time.
This boiler/water bath uses peat or wood for energy.
Use thermatization only if you cannot pasteurize the milk within 24 hours of delivery to the plant.
  page 167

32 The temperature range for pasteurization is 63 C to 100 C.
This kills most harmful bacteria.
This is a wood-fueled metal boiler with a jacket.
33  This is a gas-fuelled metal boiler.
page 168

You can pasteurize at different times and temperatures.
Time Temperature
30 minutes 63oC
3 minutes  68oC
20 seconds  73oC
34 Use:
- lower temperatures for market milk

- higher temperatures for yoghurt and fermented products.

Sanitize the stirrer before use.

Stir continuously.

35 You can also heat treat in containers, bottles or packets of milkunder water.

This reduces the chances of reinfection after treatment.
Allow longer times than above to warm up the containers.

Bottles : 80 C for 10 minutes
Bags : 80 C for 5 minutes.

page 169

36 You can cool the milk with running water in a vat.

Use ice if available, in the water not in the milk!

37 You can also cool the milk by running water through a jacket.
38 You can keep pasteurized milk for up to a week if you keep it cool and not
If your milk is not cool, keep it for only 1 day.
page 170

Important in all milk treatment:

39 - keep everything clean

- store milk in a cool place away from sunlight.

40 - use a thermometer and stirrer

- do not use copper equipment, it may start unwanted chemical reactions in the milk

41 - treat milk gently

- do not whip air into it

42 - never drink milk or products which you do not heat treat.
page 171

How does the dairy plant treat milk on a large scale?


43 The plant pumps the milk through a filter and a plate cooler to a storage tank

44 A centrifuge separates the cream from the skim milk.

Some separators also remove dirt.

45 The plant automatically standardizes the milk by adding part of the cream to the skim milk flow.
  page 172
46 Next, the plant homogenizes the milk.
This changes the milk to have:

- smaller fat globules
- lower creaming ability
so the milk has:
- no cream line
- a whiter, more appetizing colour
- less oxidation.

47 At different degrees of homogenization, the fat globules are different sizes:
- not homogenized
- partially homogenized (viscolized)
- totally homogenized (micronized).



Homogenization may also have some disadvantages:

   - cannot separate easily

   - flavour becomes 
     metallic quickly in sunlight

   - lipase attacks easily

   - low protein stability.


Heat treat immediately after homogenization.
 page 173

Large-scale heat treatment systems
What large-scale heat treatment systems are there?
Holder system
There are two types of holder system.

48 This plant heat treats and cools milk in a vat (batch pasteurizer)

49 and then puts the milk in:

- bottles

- sachets

- cartons.
Some plants put the milk in bottles, sachets or cartons first and then heat treat the milk.

Continuous flow system

50 This plate heat exchanger can heat treat milk and then cool it.

- strict control over large volumes 
- little effect on taste 
- low processing cost 
- automatic cleaning 
- uses little space to another
- fixed heat treatment time
- minimum economic use: 
   3 hours/day
- high investment cost
- cannot add flavour or other
- cannot change easily from one product
  page 174

Continuous flow pasteurization

51  In the HTST (high-temperature short-time process) the plate heat exchanger heats the milk to 72 C for 15 seconds:
page 175


Sterilization is a heat treatment which kills almost all cells. There are various methods:

In-bottle sterilization
52 The plant pre-heats milk to 70-75 C and bottles it. The plant then heats the sealed bottles to 110 C for about 30 minutes.

Two-stage sterilization
The plant heats the milk to 75 C to stabilize it and then to 130-140 C for 20 seconds to sterilize it.
The plant then cools the milk to 80 C and bottles it.
Continual sterilization

53 Equipment used for continual sterilization.

page 176

UHT treatment
There are two main methods of UHT treatment:
Direct heating

54 The steam passes into the milk and directly heats it to 140 C. Remove excess water by evaporation. You can also use electricity for direct heating.

 Indirect heating
55 Steam heats water which passes through a plate heat exchanger. The water indirectly heats the steam to 137 C
page 177

56 A modern packaging machine.
 page 178

What do you know about milk treatment?
    Small scale milk treatment
    1.   Separation  
         - dirt from milk 
          - cream from skimmilk
    2.   Standardization
         - Adjusting fat contents of
         - milk 
         - cheese 
         - Sampling and testing for
         - milk acidity 
         - fat content 
         - Calculation quantities 
    3.   Heat treatment
         - Reasons for heat treatment 
         - Important points 
         - Effects of heat treatment on
         - fat 
         - proteins and enzymes 
          - lactose 
         - minerals and vitamins
    4.   Methods
          - thermatization
         - pasteurization 
    Large scale milk treatment
    1 Pre-treatment
    2 Heat treatment  
    - Holder systems 
    - Continuous flow systems 
    3 Sterilization 
    4 UHT treatment 
    5 Packaging 
page 179

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