Dairy Farming Manual
What should you know about milk treatment?
You should know about the four main methods:
- 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).
How can you treat milk on a small scale?
|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
It treats 60-200 l of milk per hour.
What is standardization?
|9 Standardization is a method
of controlling the
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
- 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
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.
|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.
|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
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
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:
Small scale heat treatment
Why heat milk?
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.
What are the effects of heat treatment on milk?
|Proteins and enzymes|
|Minerals and vitamins
Normal pasteurization does
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.
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
- lower temperatures for market milk
- higher temperatures for yoghurt and fermented
Sanitize the stirrer before use.
|35 You can also heat treat in
bottles or packets of milkunder water.
This reduces the chances of reinfection
Bottles : 80 C for 10 minutes
|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.
Important in all milk treatment:
|39 - keep everything
- store milk in a cool place away from sunlight.
|40 - use a thermometer and
- 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?
|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
This changes the milk to have:
- smaller fat globules
|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
- lipase attacks easily
- low protein stability.
Heat treat immediately after homogenization.
Large-scale heat treatment systems
What large-scale heat treatment systems are there?
There are two types of holder system.
|49 and then puts the milk in:
|Continuous flow system|
- 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:
- high investment cost
- cannot add flavour or other
- 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:|
Sterilization is a heat treatment which kills almost all cells. There are various methods:
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.
53 Equipment used for continual sterilization.
There are two main methods of UHT treatment:
| Indirect heating
55 Steam heats water which passes through a plate heat exchanger. The water indirectly heats the steam to 137 C
56 A modern packaging machine.