Small-ScaleDairy Farming Manual |
Volume 1 |
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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)
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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). |
How can you treat milk on a small scale?
Separation
5 You can filter
milk
to remove large dirt particles
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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. |
Standardization
What is standardization?
10 After separation, you can
mix:
- whole milk with - skim milk to get - milk with a fat content between 0-4 %. |
11
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).
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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.
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13 You test the mixed sample
for milk acidity.
You:
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15 You also test the mixed sample
for fat content.
You: - 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. |
19 You record the results in a milk analysis note book:
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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. |
25 Never drink milk which has not been heated.
It can make you sick.
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What are the effects of heat treatment on milk?
Fat
26 Only high
temperatures
change fat, but pasteurization melts fat so that rough treatment
easily breaks the membrane.
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Proteins and enzymes
27 If milk is
good quality,
normal
pasteurization:
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Lactose
28 Very high temperatures
cause:
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Minerals and vitamins
Normal pasteurization does
not change
minerals.
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page 166
What is important in heat treatment?
29 Make sure you:
- measure temperature accurately - stir the milk throughout the heat treatment |
30
- 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?
Pasteurization
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. |
You can pasteurize at different times
and temperatures.
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34 Use:
- lower temperatures for market milk - higher temperatures for yoghurt and fermented
products.
Sanitize the stirrer before use. Stir continuously. |
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
reinfected. If your milk is not cool, keep it for only 1 day. |
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. |
How does the dairy plant treat milk on a large scale?
Pre-treatment
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. |
46 Next, the plant homogenizes
the milk.
This changes the milk to have: - smaller fat globules
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47 At different degrees of homogenization,
the fat globules are different sizes:
- not homogenized - partially homogenized (viscolized) - totally homogenized (micronized). |
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Homogenization may also have some disadvantages:
- cannot separate easily - flavour becomes
- lipase attacks easily - low protein stability.
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Important
Heat treat immediately after homogenization. |
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.
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Continuous flow system
50 This plate heat exchanger
can
heat treat milk and then cool it.
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Advantages
- strict control over large volumes - little effect on taste - low processing cost - automatic cleaning - uses little space to another - fixed heat treatment time |
Disadvantages
- minimum economic use: 3 hours/day - high investment cost - cannot add flavour or other ingredients - cannot change easily from one product |
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: |
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Continual sterilization
53 Equipment used for continual sterilization. |
Packaging
56 A modern packaging machine. |
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