MILK is a highly nutritious food, and an important source of amino acids and minerals such as phosphorus and calcium, which contributes to bone health.
Historically, milk was prone to contamination by bacteria from cows that could cause severe illness in humans. This remains the case with raw (unpasteurised) milk. The tragic death of a Victorian toddler is a stark reminder of these risks.
Pasteurisation involves heating the product to 72 degrees Celsius for 15 seconds. It was introduced in Australia in the late 1950s and remains a legal requirement.
Nowadays, some of the important bacteria that pasteurisation targeted, such as those that cause tuberculosis, are no longer as problematic.
The animals we use for milking can sometimes carry other pathogenic organisms that are capable of causing disease.
Even healthy animals may be a source of organisms that are harmful to people.
These can enter the milk during milking, and if such milk is consumed, it can cause disease.
The most common pathogens found in association with dairy farms include bacteria such as Escherichia coli (E. coli), campylobacter and salmonella. Parasites such as cryptosporidium may also be present.
Campylobacter and salmonella can cause severe diarrhoea and types of E. coli can cause severe disease which impairs kidney function and can lead to death.
Milk is highly nutritious to bacteria. E. coli can go from 10 cells to 100million cells in six hours at 30 degrees. Only 10 cells may be required to make someone ill. These bacteria have caused outbreaks and disease associated with the consumption of raw milk in many countries. In the US over a 13-year period to 2011, there were 2384 illnesses, 284 hospitalisations and two deaths associated with consumption of raw milk.
In Australia, raw milk contaminated by campylobacter and salmonella caused at least nine outbreaks of disease between 1997 and 2008, and 117 cases of illness.
Advocates of raw milk often claim improved health benefit and nutritional value, or desire a product that has not undergone further processing, retaining bacteria naturally present in milk.
But there is no evidence that the health benefits of milk are compromised by pasteurisation.
The difference is only in the presence of harmful bacteria.
Raw milk continues to have a far higher risk of causing illness, so pasteurisation remains an important step in ensuring we can continue to enjoy milk safely.
Edward Fox is food safety and microbiology research scientist at CSIRO. Narelle Fegan is a food microbiologist at CSIRO. This first ran on The Conversation