Skimmed milk may carry risk of bacteria

Drinking low-fat rather than full-fat milk may seem like the healthy option - but it could lay you low with food-borne bacteria such as E.coli, the Public Health Laboratory Service (PHLS) has warned.

Drinking low-fat rather than full-fat milk may seem like the healthy option - but it could lay you low with food-borne bacteria such as E.coli, the Public Health Laboratory Service (PHLS) has warned.

The risk comes from smaller dairies which use machines built before skimmed milk became popular. Anita Rampling of the PHLS told its annual meeting that while larger dairies which supply supermarkets do use modern equipment which eliminates potentially harmful bacteria, the older systems at smaller companies skim off the cream in a way that means the milk is not pasteurised properly.

In the pasteurisation process, milk is heated to 72.5C and then chilled rapidly to 4C. The heating destroys most of the bacteria, and the rapid cooling prevents those that remain from multiplying.

But New Scientist magazine reports today that Ms Rampling and her colleague Melody Greenwood investigated two farms where the machinery had been modified to produce low-fat milk. These subsequently failed a test which detects inadequately treated milk. Ms Rampling said: "The flow-rate is speeded up, so the milk is not held at high temperature for long enough. These machines weren't designed to separate the milk during the pasteurisation process."

She said the problem was compounded by the way milk was checked to ensure pasteurisation had worked. The test looked for phosphatase, an enzyme which should be destroyed during pasteurisation. However, phosphatase tends to bind to the fat in milk, most of which is lost when the cream is skimmed off - so low-fat milk could test negative for the enzyme even if it is not safe.

A Food Standards Agency spokeswoman said: "There have been problems with on-farm pasteurisation in the past. But we are not aware of this particular problem." Any dairies which did not pasteurise their milk properly could, ultimately, be shut down, she added.