In the 1800s, our ancestors would have drunk milk straight from the cow – and it appears some Brits are feeling nostalgic for the bygone era of untreated dairy.

According to a Guardian article, a growing number of us are drinking “raw milk”, aka milk from cows, sheep or other animals that has not been pasteurised or homogenised. 

Pasteurisation is the process of heating milk to specific temperatures to kill bacteria, while homogenisation is a mechanical process designed to prevent the cream in milk from rising to the top, keeping a thicker consistency throughout. The former process is about safety while the latter is about taste. 

The article cited figures from the Raw Milk Producers Association which suggest production of raw milk has gone up 600% in England, Wales and Northern Ireland since 2014 to cope with demand (it’s still illegal to sell raw milk in Scotland). 

A debate has since broken out on Twitter about the pros and cons of raw milk, when a microbiologist gained more than 38,000 likes after tweeting: “For the love of God, do not drink raw milk.” 

So, is drinking raw milk safe? It depends entirely on what you’re classing as raw milk. While the original article described raw milk as “unpasteurised, non-homogenised and unaltered from udder to bottle”, there seemed to be  confusion on Twitter, with some referring to homogenised milk as “raw milk”.

In reality, most milk that is advertised as homogenised is likely to have gone through the pasteurisation process first in order to make it safe.

But when “raw milk” refers to unpasteurised milk, it’s a different story. 

“In terms of food safety, from a microbiological point of view, drinking raw milk is not safe at all,” Dr Jorje Gutierrez, lecturer in food microbiology at the University of Surrey tells HuffPost UK.

“Raw milk may contain many different pathogenic microbes including some deadly bacteria such as Mycobacterium bovis, Listeria monocytogenes, Salmonella or enterohemorrhagic E. coli.” These pathogens could cause “fatal infections”, Dr Gutierrez adds. 

The UK’s Food Standards Agency warms vulnerable people in the following groups should not consume raw or unpasteurised milk for this reason:

• pregnant women

• infants and small children

• elderly people

• people with compromised immune system such as cancer patients.

The risk of food poisoning and associated illnesses is why pasteurisation and ultra-high-temperature processing (UHT) are commonly used in the food industry, Dr Gutierrez adds. 

“Either of these two heat treatments destroy any of the mentioned bacteria,” she says, adding that the only problem with heat treatment is that is may change the taste of milk and reduce some of the milk’s nutritional properties.

“The more severe the treatment is, the less tasty (and nutritious) the milk becomes, UHT is much more severe than pasteurisation, for instance,” she explains. “It is a question of safety rather than quality. Raw milk is more ‘natural’ but could have devastating consequences if contaminated with pathogenic bacteria.”

Raw or unpasteurised milk is sold at farms across England, Wales and Northern Ireland. The Food Standards Agency says it “regularly review[s] the controls on raw drinking milk and cream. We want to support consumer choice but have to balance this alongside protecting the health of the public.”

HuffPost UK has contacted the Raw Milk Producers Association in relation to safety concerns and will update this article if we receive a response.