Raw milk cheeses, bacteria at work

published on Wednesday, June 15, 2022 at 10:14 a.m.

Prized in France for their unique flavor, banned in other countries, raw milk cheeses are regularly talked about again during food poisoning. Between health concerns and gastronomic interest, it is the action of thousands of bacteria, “good” or “bad”, which illustrates its complexity.

“The richness of taste and the typicality that we associate with raw milk cheeses results both from the richness in bacteria and from the native character of the milk”, no constituent being denatured, explains to AFP Yves Le Loir , director of the milk and egg science and technology unit at Inrae.

A “raw” milk has not undergone any major heat treatment, such as sterilization or pasteurization. These processes kill micro-organisms present after milking.

The objective is to avoid, among other things, dangers related to pathogens that can be transmitted by animals, from their digestive tract, or by equipment (milking, storage, transport).

But “the + good + bacteria (lactic, sometimes propionic) are absolutely necessary for fermentation at the heart of cheese processing”, a source of acidification and curd formation, according to the expert from the National Research Institute for the agriculture, food and the environment (Inrae).

This makes it necessary to reintroduce external yeasts into the pasteurized milk to allow its transformation. And certain elements of milk (vitamins, proteins, etc.) are found to be denatured anyway.

Because, if a few hours are enough to transform the milk into cheese, it is sometimes several weeks of work of the bacteria and yeasts which bring out the taste, the texture or the rind of the raw milk cheese.

– No increase in contamination –

But alongside them, “bad” bacteria, including salmonella, E. coli, listeria, can contaminate raw milk cheeses.

Often the cause: a manufacturing failure (too slow fermentation, break in the cold chain, etc.) or subsequent contamination (handlers carrying pathogens, poorly maintained equipment, etc.).

In France, in the last decade, 34%, 37% and 60% of outbreaks of salmonellosis, listeriosis and enterohaemorrhagic E. coli infections were linked to the consumption of raw milk cheeses, according to the National Agency for health security (ANSES).

“We cannot say that there is an increase, but there are regular foodborne epidemics originating from raw milk cheeses,” Laurent Guillier, coordinator of an expertise on these cheeses at Anses.

The symptoms can sometimes resemble those of gastroenteritis, but others can be much more serious, such as kidney failure, or even fatal.

For young children (under 5 years old), pregnant women, immunocompromised people, those over 65 years old, the French health authorities always recommend avoiding raw milk cheeses.

– “Let’s not kill germs” –

In order to refine the perception of the dangers and the levers to reduce them, ANSES recently defined the categories of cheese most at risk: soft cheeses with a bloomy rind (camembert, brie, crottin, etc.), and uncooked pressed cheeses with short ripening (Morbier, Reblochon, Saint-Nectaire…). Next come soft, washed-rind cheeses (Munster, Maroilles).

The danger remains very limited: “The levels of hygiene and risk control are now very high within farms” and “a large number of problematic batches” are detected from processing, judges the National Food Safety Agency ( Handles). But a “residual risk” remains and, on the consumer side, vigilance is still required.

Should we go so far as to give up raw milk cheeses, as is the case in many countries that prohibit them? No, for researchers who believe that the interest of “good” bacteria exceeds the danger of “bad”.

“Let’s not kill microbes, let’s use them”, thus pleaded in mid-April, in the JDD, Marc-André Selosse, professor of the National Museum of Natural History, and Joël Doré, a microbiota specialist.

On a similar line, Yves Le Loir, of Inrae, judges that certain “good” bacteria can influence the balance of the intestinal microbiota of humans, this set of microorganisms to which we attribute a growing role in health.

.

Leave a Comment