ESL - innovation or misleading packaging?

Monday, 14 September, 2009

Extended shelf life (ESL) milk has already pushed the fresh milk we know so well off many refrigerator shelves. Some people say that this is a clear signal that consumers are accepting the milk. Others disagree, saying that the retail trade and industry are just using ESL to optimise their margins. But what’s the real story?

The shelf life of ESL milk in the refrigerator is around three weeks while conventionally pasteurised fresh milk usually goes off after a week. Bacterial spores are responsible for this, as they are not destroyed in traditional pasteurisation conditions and tend to germinate sooner rather than later. ESL reduces these bacterial spores and so extends the shelf life.

The most common process is VTIS, in which the milk is heated to 127° in fractions of seconds using steam injection and stays at this temperature for around two seconds. For comparison, in pasteurisation the milk is heated to 72 to 75° for 30 seconds. And in the case of long-life milk, with its distinctive boiled taste, it is three seconds at 150°.

The two other processes focus on mechanically separating the bacteria and spores using membrane filtration or centrifugation. Here, too, individual fractions of the milk are heated longer for safety reasons but as these amounts are so small, no boiled taste is transmitted to the end product.

It has been proved that none of these three ESL processes substantially alter the nutritional value of the milk. The same is true of the taste, because the thermal load to which ESL milk is subjected is not much greater than in conventional pasteurisation. When it comes to quality the longer shelf life is much more important: for example many vitamins are very light sensitive, so the amount of light to which milk is subjected during the initial milking process on the farm, then during processing in the dairy and later when being stored in the kitchen, has more effect on the product quality than the ESL process itself.

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