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Next time you buy a piece of cheese with a mottled natural rind, such as a clothbound Cheddar or Tomme de Savoie, take a close look at the rind with a magnifying glass. If you look long enough, you will see tiny pieces of the rind are moving! These specks are microscopic arachnids known as cheese mites. Gophers of the cheese world, these tiny mites can both impart flavors as well as cause headaches for cheese producers.
Cheese mites are only found in long-aged cheeses that develop a natural rind. They prefer cheeses that are dry and have a rind densely colonized by molds, their main source of food. As they wander across the cheese rind landscape, they munch on the fungi on and in the rind and burrow into the paste. When you enter a cheese cave that has a high cheese mite population, you will see lots of dust around the wheels of cheese. This dust contains the mites as well as their feces.
Two major groups of mites are found on cheeses: Tyrophagus and Acarus. These are normally soil-dwelling mites that feed on fungi in forest soils. When they encounter a cheese production facility, they multiply rapidly because of the high density of their favorite food: mold. These mites are also commonly found in grains and other types of stored foods where mold can grow. Outside of cheese, these mites are called storage mites.
When I started doing research on cheese rinds, I made a video of cheese mites munching on the mold Penicillium. You can’t see the fuzzy mold because the mites have completely mowed down the lawn of fungus. But you can see plenty of mites! Be sure to look out for baby mites and mites piggy-backing on other mites.
Here is another shot that takes a closer look at a single cheese mite munching on hyphae of the fungus Scopulariopsis. The hyphae are the individual threads or hairs that make up the fuzzy mold network. Watch as this mite munches on the hyphae as if they were spaghetti!
A few mites living on the surface of a cheese will not cause problems for cheese producers. But if a cheese is being aged for a long time, mites can wreak havoc. As they munch on the fungi in the rind, they can make their way into the paste of the cheese, taking mold spores along with them. These molds can then burrow deep into the cheese paste, causing aesthetic and flavor defects.
To manage mite populations, cheese makers have come up with a variety of approaches. Many cheese producers use vacuums to suck off cheese mites from the surface of cheeses. Others use high-pressure air guns to blow the mites off of the cheese. Reduced aging temperatures can also limit mite damage. None of these approaches completely eliminates the mites, but each can help reduce the overall population sizes and minimize damage to cheese.
Are cheese mites a safety threat to cheese consumers? There is no published evidence that consumer exposure to cheese mites can cause any harm. However, there are several reports of short-term rashes and respiratory allergies caused by exposure of cheese workers or cheese distributors to high concentrations of mites. But these cases are rare and were situations where individuals were exposed to millions of these creatures. Most pieces of cheese that a consumer would take home from a store will have just a few cheese mites on them, if any.
Cheese mites created a stir in 2013 as the United States Food and Drug Administration banned imports of Mimolette, a cheese that is intentionally aged with high densities of cheese mites. The mites purportedly give Mimolette unique flavors and its characteristic pitted rind, and are considered an essential part of the production process. The FDA concluded that some shipments of Mimolette had densities of cheese mites above acceptable levels. Mimolette is now available again in the United States.
Despite their potential positive and negative impacts on cheese production, there are quite a few questions that remain unanswered about the biology of cheese mites. Do they prefer specific types of molds over others? Can cheese makers manage molds as a means to control mites? Have the cheese mites that live in cheese caves adapted to the cheese environment relative to their wild soil ancestors? Hopefully some future acarologists (scientists who study mites) will provide us with some answers.
Post written by Benjamin Wolfe.
For more information on cheese mites, check out the following resources:
Melnyk, J. P., et al. “Identification of cheese mite species inoculated on Mimolette and Milbenkase cheese through cryogenic scanning electron microscopy.” Journal of Dairy Science 93.8 (2010): 3461-3468.
Anderson, Nelson Paul, and Harold C. Fishman. “Cheese mite dermatitis occurring in the United States.” Archives of Dermatology and Syphilology 57.2 (1948): 227-234.
Eales, Nellie B. “The life history and economy of the cheese mites.” Annals of Applied Biology 4.1‐2 (1917): 28-35.