Squeeze harder for fresher milk

Researchers in the US have shown that a high-pressure food-processing technology may offer a way to extend the shelf-life of milk without affecting its flavour.  

Fresh milk contains disease-causing bacteria, eg those responsible for tuberculosis and typhoid. Left out at room temper-ature these and other bacteria will cause milk to spoil. To destroy such bacteria, milk is pasteurised.  

Commercial pasteurisation involves heating milk to 72°C for 15 s and then cooling rapidly to below 10°C. Stored in refrigerators pasteurised milk has a shelf-life of 20 days. Longer-life milk, known as UHT (ultrahigh temperature) milk, is pasteurised by heating to 135-150°C for 3-5 s. The resultant UHT milk has a shelf-life of ca  six months at room temperature. However, the UHT process causes the formation of chemicals in the milk, such as volatile sulfur compounds (eg  hydrogen sulfides), methyl ketones and aldehydes. According to food scientist Michael Qian and his team at Oregan State University, these chemicals impart a 'cooked' flavour to the milk, which has limited the popularity of UHT milk with consumers.