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Food safety issues with raw milk consumption

What is the issue?

In studies carried out both in New Zealand and overseas raw milk has been shown to occasionally contain pathogenic micro-organisms (bacteria that make you sick). People may become sick if they drink milk containing these organisms especially if the milk is not properly refrigerated, allowing growth of the pathogens. Outbreaks of foodborne diseases such as salmonellosis, campylobacteriosis and Escherichia coli O157:H7 infection have been attributed to drinking raw milk.

What can go wrong?

Pathogenic bacteria can be shed into milk while it is still in the udder (via unrecognised mastitis) or milk can be contaminated from the dairy farm environment during milking. Once contaminated, raw milk is not subjected to any step between harvest and consumption that will rid milk of the pathogens (in contrast with pasteurised milk, which receives a heat treatment that kills pathogens). In addition, pathogens may grow if the raw milk is stored improperly, and even if stored at refrigeration temperatures, some, like Listeria monocytogenes, are still able to grow. The more pathogens consumed, the greater the chance of getting sick.

How can I tell if raw milk is contaminated?

Bacteria that cause food poisoning do not, in general, produce changes in foods that would warn the consumer that the food is not fit to eat. There is, therefore, no way of telling by taste, sight or smell that raw milk contains pathogens.

What can I do to minimise the risk of food poisoning from raw milk?

The only completely safe way is to avoid drinking raw (unpasteurised) milk. To minimise risks, keep raw milk under refrigeration (4°C or less) and discard if it has spent more than two hours at room temperature. The young, elderly, pregnant and immuno-compromised should especially avoid this food as they are at greatest risk from infection.

This fact sheet was prepared on behalf of New Zealand Food Safety Authority by Environmental Science and Research.