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1. Raw milk at 4°C is heated by the outgoing milk up to about
71°C.
2. This milk is finally heated by hot water up to the pasteurizing
temperature of 75°C (or hotter for UHT milk) and held for a
few seconds.
3. The milk is cooled by the incoming milk, down to about 10°C.
4. The final stage of cooling from 10°C to 4°C is by chilled water
at 2°C.
Milk for other products is treated:
1. In a centrifuge to obtain cream and skim milk
2. In churning devices to make butter and buttermilk
3. With rennet to make cheese (leaving whey)
4. With cultured bacteria to make yoghurt
5. By drying, to milk powder
Butter is made from cream in continuous churning machines. At
stages during this process, the butter is washed in clean, cold water
to keep it cold and remove surplus buttermilk. At the end of the
churning stage, butter is still in a plastic state and, after packaging,
must be stored at 5°C to crystallize the fat. Long-term storage of
butter is at – 25°C.
Cheeses may be pressed into a homogeneous block, or left to
settle, depending on the type and methods of manufacture. They
then undergo a period of ripening, to give the characteristic flavour
and texture. The cold storage of cheese during the ripening period
must be under strict conditions of humidity and hygiene, or the
cheese will be damaged. Some cheeses can be frozen for long-term
storage, but must then be allowed to thaw out gradually and complete
their ripening before release to the market.
Other processes (except milk drying) require the finished product
to be cooled to a suitable storage temperature, usually 4°C or
thereabouts, and kept cool until the point of sale. Conventionaltype
cold stores can be used for mixed dairy products, since all of
them will be packaged and sealed after manufacture. |
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