On a recent visit to Paris, I bought some milk that had not been pasteurised, but micro-filtered. The label claimed that filtering out the bacteria kept the milk fresh for longer than by pasteurisation. Does it? How does the process work and what stops the filter from getting clogged with milk fat? And would it get around European Union and other regulations that prevent, for example, unpasteurised milk being sold in Scotland?
鈥� Micro-filtration is a pressure-activated separation process using a membrane that is permeable to substances with a low molecular weight but rejects material with a high molecular weight.
In the mid-1990s, France鈥檚 Union of Milk Cooperatives took this technological leap when it began producing the Marguerite brand of fresh, micro-filtered milk. During micro-filtration, bacteria are removed from skimmed milk using ceramic filters with 1.4-micrometre holes. The cream that had been removed in the skimming process is then pasteurised at 90 掳C and reincorporated into the micro-filtered milk. Because the procedure does not involve heating the milk, it is claimed the milk retains its original proteins, vitamins and flavour.
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Pasteurised, micro-filtered milk is now also on sale and this does, of course, undergo heat treatment. The micro-filtration adds an extra level of cleanness, which can extend shelf life to 45 days when stored at temperatures of up to 7 掳C. This is how micro-filtered milk meets the law in many countries that requires pasteurisation.
Ionel Rosenthal, Rehovot, Israel
鈥淏ecause the procedure of micro-filtration does not involve heating the milk, it is claimed that the milk retains its proteins, vitamins and flavour鈥�
鈥� Micro-filtration has been used for decades as an alternative to pasteurisation for some high-quality wines. It prevents harm to flavour and it removes heat-resistant bacteria that pasteurisation would, in any case, leave untouched.
Jon Richfield, Somerset West, South Africa