Tuesday 17th May 12:33 pm
Raw milk: separating facts from fads
Tuesday 17th May 2016 12:33 pm
Not all raw foods are good for you. Dr Karl explains why raw milk is one of the world’s most risky food products.
If you hang around health food shops, you might hear the words, “raw milk” whispered reverentially. This is milk that has not been pasteurised, and it’s supposed to be much better for you than regular pasteurised milk. Well, that’s not right.
But before we get into raw milk, what is pasteurisation? And furthermore, if pasteurisation is supposed to kill all the germs in raw milk, why does pasteurised milk go off after a week or so?
Basically, pasteurisation is a heat process that kills most of the bacteria in liquid foods — let me emphasise “most”, not “all”.
Pasteurisation aims to kill 99.999 per cent of the microbes (yeasts, moulds, bacteria and the like). The remaining microbes are so few in number that you’ve got about a week to a fortnight after pasteurisation, before they multiply enough to cause a problem.
Pasteurisation was invented by the French chemist, Louis Pasteur, to treat wine, not milk. On a summer holiday in the community of Arbois in 1864, he found that the local winemakers had a problem with their wines turning acid. Pasteur discovered he could kill microbes in wine by heating it to about 55 degrees C for a few minutes. Bingo, the wines no longer turned acid.
But it took many decades to be applied to milk. In the USA, routine pasteurisation of raw milk began in the 1920s, and was widespread by 1950.
The reason for pasteurising milk is to make it safer. Milk, by an unfortunate coincidence, is one of the best culture mediums for growing bacteria. Raw milk has not been pasteurised, and is crawling with nasties.
In the USA between 1998 and 2011, thanks to raw milk or raw cheese products, there were 284 hospitalisations and two deaths. In Australia, raw milk killed a three-year-old Melbourne child in December, 2014.
Regular pasteurisation can be done by heating the milk either at around 60 degrees C for about 20 minutes, or about 72 degrees C for about 15 seconds.
Does pasteurisation destroy nutrients?
The nutritional losses are insignificant — calcium and phosphorus drop by 5 per cent, vitamins B1 and B12 10 per cent, and vitamin C down by 20 per cent.
UHT, or ultra-heat-treating, heats the milk to about 140 degrees C for four seconds. This should kill all bacteria.
If the UHT milk is then packed, under sterile conditions, into a pre-sterilised airtight container, it should last for nine months.
The high-temperature sets off the Maillard reaction, which alters the taste and flavour. The structure of the milk proteins is also changed, so is not really suitable for making cheese. Most other nutrients are at similar levels to regularly pasteurised milk, except for folate — it’s dropped by about 90 per cent.
This is what makes raw milk so attractive — the fact that the potential goodness in the milk is still there, untouched.
For example, it’s claimed that raw milk has special enzymes so that your body can better digest the fats, proteins and carbohydrates, and get more nutrition from them. That’s simply incorrect.
Can raw milk cure or prevent diseases?
Another claim is that raw milk can cure or prevent diseases such as cancer, heart disease, allergies and asthma. These claims are also incorrect.
However, immune system conditions such as allergies and asthma can sometimes be very sensitive to certain chemical triggers in the environment. It can be worthwhile trying different pasteurised milks.
Another claim is that raw milk has special enzymes that kill bad bacteria. Unfortunately, it doesn’t and bacteria love to grow in milk.
According to the US Centers for Disease Control, raw milk is one of the world’s most risky food products. Here is a typical example. Before widespread pasteurisation, in England and Wales, between 1912 and 1937, about 65,000 people died from tuberculosis they got from milk.
Is raw milk safer it if comes from a healthy cow?
Another claim is that if the milk-producing animal (cow, goat, etc) is clean and healthy, and raised in sanitary conditions, then the milk will end up free of bacteria. Again, no.
An animal can be perfectly healthy, and still carry bacteria that don’t affect that animal. But these bacteria can affect us. Of course, once the bacteria get into the milk, their numbers increase very rapidly.
Are products processed from raw milk safe?
It’s also claimed that because cheeses and yoghurts made from raw milk have been processed more, that means they are safe to eat.
No. In fact, the two US deaths (between 1998 and 2011) caused by raw milk and its products were caused by a fresh Mexican-style cheese made from raw milk.
Raw onions only make you cry, but raw milk might make you die.
This blog first appeared on Dr Karl's Great Moments in Science
© 2017 Karl S. Kruszelnicki Pty Ltd