Milk ‘crushed’ under pressure lasts more than 7 weeks in fridge


Written on Friday, November 24, 2006 by Gemini

Crushing milk at high pressures could help it last for weeks in the refrigerator without the unfavourable flavours associated with other long-lasting milks, researchers now report. Conventionally, milk is pasteurised, or heated at high temperatures to kill harmful germs, at roughly 71° C for 15 seconds.

While pasteurisation kills most germs, it does not wipe out bacterial spores, the dormant versions of the germs, which are resistant to any form of destruction. Bacterial spores and remaining germs eventually spoil conventionally pasteurised milk, which is why it typically has a shelf life of only about 20 days when refrigerated.

Heating milk to between 135 and 150 ° for three to five seconds can kill both bacteria and their spores, leading to milk that is stable at room temperature for up to six months. Instead, researcher J. Antonio Torres, chemical engineer at Oregon State University are now investigating squeezing milk at high pressures while using a moderate amount of heat to kill germs. “Pressure inhibited the formation of key undesirable flavour compounds in milk,” Torres said.

The researchers found pressurising milk at 85,000 pounds per square inch for five minutes at about 130° C kills germs while retaining the taste of fresh milk. The result is milk that stays fresh at least 45 days in the refrigerator. If the researchers can make this process commercially viable, Torres anticipated such milk could appear on the market in three to five years.

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