Demystifying science | Mold in the freezer

Every week, our journalist answers scientific questions from readers

Bacteria cannot grow in the freezer, but mold can grow if the freezer temperature is not below -18 degrees Celsius.

“This is a very, very, very rare case,” says Alexandre Thibodeau, microbiologist at the faculty of veterinary medicine at the University of Montreal. “The consumer is very unlucky. When I saw the photo I thought I should put this in a review. »

A freezer normally has a temperature of -18 to -20°C. But if snow has formed there, which often happens, the temperature can rise to around -12 to -15°C.

Swelling is linked to CO emission₂ during the slow growth of mold at such a low temperature. “It was probably a bag where there was too much humidity, it encouraged the growth of mold,” says Mr. Thibodeau.

Is it dangerous?

Normally, an airtight bag of almonds can be stored in the freezer for two years, according to Mr. Thibodeau. It’s the same thing for meat, although, over time, there can be aging of the meat, with a breakdown of fat.

“Critical point control”

Pathogenic bacteria such as Listeria or salmonella do not grow below freezing temperature. Other non-dangerous bacteria, which alter the appearance and texture of food, can survive down to -15°C.

Are almonds tested during packaging? “There is control at critical points in the packaging line,” says Mr. Thibodeau. We check if the product is washed correctly and afterwards, if it is dry enough. There is also a sampling of some almonds. Normally, there will be a mold test on dry products, and perhaps also a salmonella test, depending on the food. »

Almonds are sporadically responsible for cases of salmonellosis. In 2022, a Californian producer, Blue Diamond, recalled nearly 200 tons of contaminated almonds in the United States, but no human cases had been reported. There are also recalls related to peanut butter and almond butter. In 2001, 160 cases of salmonellosis were linked to a case of contaminated almonds in Canada.

A search of the Government of Canada’s recall notice site shows 60 almond recalls since 2013, mostly due to almonds of undeclared origin.