Why raw milk is dangerous
Raw milk is untreated milk that typically comes from cows, goats, or sheep. This means it has not been heat treated to kill the harmful bacteria (pathogens), and nothing has been added or removed.
Pasteurisation is the process that eliminates almost all harmful bacteria through a specific heat treatment. Pasteurisation is achieved by heating milk to 72°C for 15 seconds. Consumers at home can achieve the same result by heating milk to 70°C and holding it at that temperature for 1 minute.
Is unpasteurised milk safe to drink?
No matter how carefully animals are milked, there is always a risk of harmful bacteria being present. Consuming raw milk can cause severe illness due to the possible presence of harmful bacteria. Pregnant women, young children (particularly babies), the elderly, and people with weakened immune systems are at greatest risk of getting sick and the consequences for them can be more severe.
How does milk get contaminated?
Harmful bacteria can pass directly into milk from various sources, but faecal contamination is the main cause of pathogens in raw milk. Faecal contamination can come from: • poor hygienic practices, such as teats that haven’t been cleaned and sanitised, or milk harvesters with dirty hands; • milking equipment that is poorly designed or not properly cleaned and sanitised; • the farm dairy environment during milking; • Udder infections can also result in pathogens in raw milk - animals can look healthy even when infected, so farmers may not realise there is a risk; • Poor cooling, storage, and handling will allow the pathogens present to grow.
Even if care is taken in producing raw milk, there is still the risk that it contains harmful bacteria (pathogens). This is because there is no process used to destroy the harmful bacteria.
How can I tell if raw milk is contaminated?
There is no way of telling by taste, sight, or smell that raw milk contains harmful bacteria. However, any milk that appears to have gone off or looks abnormal should be avoided as this indicates that it has not been cooled, stored or handled correctly and the pathogens present in the milk, whether good or bad, have had an opportunity to grow. An outbreak is recorded when two or more people have become sick and the illness is linked to a common source.
Globally, outbreaks of illness caused by raw milk consumption occur regularly. Recorded outbreaks include cases of severe illnesses, which can be lifethreatening. According to the US Center for Disease Control and Prevention, raw milk is responsible for nearly three times more hospitalisations than any other foodborne source.
The number of outbreaks of foodborne illness in NZ where raw milk consumption is a recorded risk factor have been consistently higher since 2009. In 2013, raw milk was recorded as a risk factor in eight outbreaks affecting 33 people.
All outbreaks that recorded people’s age included children younger than five years old. In addition, raw milk was a risk factor for two children younger than five years old who were hospitalised with serious renal problems.
An on-going MPI survey has sporadically identified the presence of harmful bacteria such as Shiga toxin–producing E. coli, campylobacter and salmonella in raw milk. No matter how carefully the animals are milked, there is always a possibility of harmful bacteria being present in raw milk. This is because pathogens regularly occur in animal guts and are ever-present on farms. Pasteurisation is one of the few proven methods to kill harmful bacteria in milk. There is little evidence that ‘good’ bacteria or other components in raw milk kill the ‘bad’ bacteria to prevent illness.
The current scientific evidence shows that the nutritional value of raw milk is not substantially different to that of pasteurised milk.
There is no reason to believe that raw milk would benefit lactose-intolerant people. All milk contains lactose. Heat treatment can convert lactose into a more soluble and easily absorbed form, but this happens at temperatures much higher than those required for pasteurisation.
There is no conclusive evidence to show that raw milk helps protect against serious disease. There are a few studies that suggest that drinking raw milk at an early age, along with other factors, may help reduce the risk of developing asthma, hay fever, or eczema, but the science is not conclusive because of a lack of data, and the absence of any biological reason for why raw milk could help protect against these conditions.
What is known is that raw milk may contain harmful bacteria that can lead to serious consequences, such as renal failure and paralysis. This is why it’s recommended that young children and other people with lowered immunity should not drink it. Keeping raw milk under refrigeration (4°C or less) reduces the risk of any harmful bacteria in the milk growing to levels which make people sick when they drink it. People should discard raw milk if it has been left out of the fridge and has reached room temperature.
Scientific evidence shows that the best way to minimise the risk of getting ill from drinking raw milk is to heat it, for example to 70°C for one minute. This will kill off the bad bugs but still leave behind healthy milk.
To view MPI’S literature review: