|Milk is an important part of many people’s diet. It is a complete food containing water, fats, proteins, vitamins and minerals. However, this mix of nutrients and a pH of around 7 also make it an ideal growth material for many microbes. |
In its raw state ‘straight from the cow’ milk contains bacteria from several sources:
- the inside and the outside of the cows teats
- the udder
- the hide of the animal.
More microbes can be picked up from the milking equipment and the people handling it. If these microbes grow, the milk soon "goes off".
There is also a strong likelihood of faecal contamination and so raw milk may contain harmful bacteria, like Salmonella and E. coli O157, which cause serious diseases. It can also carry certain pathogens directly from the animal, such as Mycobacterium bovis which caused outbreaks of TB in the past.
Most milk is drunk fresh. Therefore, to make it safe from pathogens and to extend its storage life, it has to be heat-treated. Various methods are used.
In the UK over 90% of milk is pasteurised; nearly all the rest is UHT or sterilized. Hardly any milk is drunk untreated; because of the health hazards the sale of raw milk is prohibited in many countries. Most milk products such as yoghurt and cheese are also made from milk that has been pasteurised.