John Melnyk1, Diana Binder1, Massimo Marcone1, Cynthia Scott-Dupree2 and Art Hill1. Departments of Food Science1 and Environmental Biology2, University of Guelph
biology · mites &cheese · controls · good mites · survey · bibliography
In earlier times, the presence of mites on old cheese was considered normal. As the cheese aged, mites would eventually pierce its protective cloth wrap or wax coating and establish colonies on the cheese surface. For example, in Canada as late as the 1940s many families would purchase 90 lb wheels of Cheddar during the summer months for consumption during the following winter. When the first portions of cheese were removed from the blocks in December or January, mite colonies would be well established and would quickly colonize the newly cut surfaces. By the time all the cheese was consumed, the accumulated mite dust could be as much as 25% of the weight of the original cheese.
Modern cheese making practices with better hygiene, better waxes or film wraps, and more controlled cheese ripening conditions, have largely eliminated cheese mite infestations. However, there is evidence that development of the “artisan cheese” industry is associated with increased incidence of cheese mite infestations. The purpose of this article is to initiate a discussion about the incidence and control of cheese mites that will, hopefully, help us develop an integrated pest management (IPM) program for mites based only on environmentally friendly and bio-control strategies. At the moment we’re gathering information and conducting preliminary studies on mite culturing and species identification. To help us with information gathering, we would greatly appreciate your responses to the five questions posted (link is at the end of this article).
Mites are invertebrates (no skeletons) with eight hairy legs and a large non-segmented abdomen that appears somewhat translucent under a microscope. The mouth parts are attached to a protrusion on the head. Length varies from 0.35 - 0.70 mm (about the size of a pin head), which is technically big enough to see with the naked eye. In practice you need a low power light microscope to see them. Where populations are high, dead mites and their waste accumulates as gray/brown dust. If the dust is gathered together in a pile, mite activity will redistribute it into a uniform layer within a few hours. Most species of mites grow well at relative humidity (RH) greater than 70% and temperatures between 15 and 30°C. Few if any can tolerate RH less than 55% or temperature greater than 40°C or less than 3°C. As illustrated in Figure 1, the typical life cycle of the mite is: nit or egg ->six legged nymph or larvae ->eight legged nymph ->adult.
There are 45,000 known species of mites, about 100 of which are known to infest stored foods such as ham, herring meal and grains. Other than eating your food and lowering its nutritional value and aesthetic appeal, mite infestations also pose low level health risks: allergic reactions to mites may occur and they may carry pathogenic bacteria and toxin producing moulds. Basically, mites result from and contribute to poor hygienic conditions.
Figure 1 – Life cycle of Acarus siro including egg, 6-legged larva, 8-legged protonymph, deutonymph (hypopus), 8-legged tritonymph, adult male, and adult female (larger than male).
Note: Not all nymphal stages occur in all species. Two or three nymphal stages are most common, while only one nymphal stage is rare.
Diagrams obtained from: Solomon ME. 1962. Ecology of the flour mite, Acarus siro L. (= Tyroglyphus farinea DeG.). Annals of Applied Biology 50: 178-184.
Mite infestations on cheese can be recognized as a layer of gray dust and cavities on the surface of the cheese. Colonies usually include two or three species growing together. The species most often identified on cheese is Acarus siro. Mites are able to grow on any cheese of any age. Protein break down during ripening makes old cheese a better source of nutrients, but old cheese also contains more fatty acids such as butyric acid which inhibits egg-laying by mites. Young cheese has no inhibitors but the intact casein in young cheese is less digestible for the mites. Another factor is mould growth, including mould ripening cultures for blue and white mould cheese varieties. The moulds produce pheromones that attract mites and breakdown the casein, again making it more digestible for the mites. Mites return the benefit by distributing mould spores deeper into the cheese. Sometimes they also eat the fungi. Cheese surface properties also affect growth; for example, mites are too small to ‘navigate’ wet or oily surfaces.
Canadian regulations include cheese mites in a list of extraneous matter and The Compendium of Analytical Methods, Health Protection Branch – division of Health Canada, which includes a protocol to enumerate mites in cheese, states, “Cheese…shall contain no more than 5 dead mites per 2.5 cm2 and to a depth of 0.6 cm. Live mites [are] not tolerated”. But, if you want to see live mites, you can check out this link to a video of ‘mite city’ on a blue cheese [cheese_mites.mpg; 7.3 MB].
Cheese mites are sometimes intentionally introduced as cheese ripening agents. Two examples are Mimolette and Milbenkase.
Mimolette, said to be the favorite cheese of Charles de Gaulle, originated in Flanders, Northern France in the 17th century. It is sometimes called Vieux Hollande because it’s make procedure is similar to that of Edam except that it is colored orange and rind ripened rather than waxed. Mite dust is applied to the surface of the cheese after the rind is formed. The growing mite colonies form small cavities on the cheese creating an orangey-gray rind with lots of pockmarks. The cheese is turned and brushed regularly to ensure a uniform distribution of mites and pockmarks. As it ages for 6 to 24 months, the rind thickens and the interior color turns more orange-brown. Flavor notes are nutty, piquant and fruity.
Milbenkäse is a German cheese produced only by a few small family firms in the city of Wuerchwitz in the eastern state of Saxony Anhalt. Quark (a soft German cheese made from goat, sheep or cow milk) is seasoned with salt and caraway, shaped into bars or balls, which are placed in a wooden box and covered in the dust of cheese mites for at least 3 months. The excrement of the mites, which are fed with rye flour, diffuse into the cheese and cause fermentation. The cheese is ripe when the color is reddish-brown and the texture is firm to hard due to dehydration. Some producers allow the cheese to ripen until it turns black after about 1 year of aging. Mites are consumed with the cheese. You can see a video of Milbenkase production at www.milbenkaese.de
If you are a cheese maker or distributor/retailer we would greatly appreciate hearing from you. Please take a moment to complete the online survey posted here.
Anonymous. Accessed June 2008. Mimolette. The World Wide Gourmet. http://www.theworldwidegourmet.com/?action=ingredient_show&id=691&lg=en
Anonymous. Accessed June 2008. Damp polders for Dutch cows – Mimolette. Cheese of the Month Club. Retrieved http://www.cheesemonthclub.com/pastnewsletters/vol4no9.htm
Anonymous. Accessed June 2008. Milbenkase. Wikepedia. http://en.wikipedia.org/wiki/Milbenk%C3%A4se
Anonymous. Accessed June 2008. Treatment with ozone in the nourishing industry. Ozone in cheese manufacture and industry. http://www.hidritec.com/English/Library/nourishing.htm
Anonymous, 1964. Effects of temperature and humidity on cheese mites. U.S. Department of Agriculture in cooperation with University of Wisconsin. Marketing Research Report No. 599, Sep 1964.
Armentia. A., Fernandez, A., Perez-Santos, C., de la Fuente, R., Sanchez, P., Sanchis, F., Mendez, J., Stolle, R. 1994. Occupational allergy to mites in salty ham, chorizo and cheese. Allergol Immunopathol (Madr) 22(4):152-4.
Food Directorate, Health Protection Branch, Health Canada, 1983. Reproductive success of the mite Acarus siro L. on stored Cheddar cheese of different ages. Journal of Stored Products Research 19(3): 97-104.
Food Directorate, Health Protection Branch, Health Canada. Determination of extraneous material in cheese. Compendium of Analytical Methods, Volume 4, Accessed June 2008. http://www.hc-sc.gc.ca/fn-an/res-rech/analy-meth/microbio/volume4/exflp05-01_e.html
Hill, S.B. 1986. Diatomaceous earth: a non toxic pesticide. Ecological Agriculture Projects, Publication 4. Accessed June 2008. http://eap.mcgill.ca/Publications/eap4.htm
Mercer, C. 2006. EU ban threatens UK specialist cheese. Food Quality News.com. 08 Dec 2006. Accessed June 2008. http://www.foodqualitynews.com/news/ng.asp?id=72647-eu-specialist-cheese-methyl-bromide
Robertson, P.L. 1952. Cheese mite infestation. An important storage problem. International Journal of Dairy Technology 5(2): 86–95 .
Sánchez-Ramosa, I., Álvarez-Alfagemea, F. and Castañera, P. 2007. Development and survival of the cheese mites, Acarus farris and Tyrophagus neiswanderi (Acari: Acaridae), at constant temperatures and 90% relative humidity. Journal of Stored Products Research. 43(1):64-72.
Van Asselt, L. 1999. Interactions between domestic mites and fungi. Indoor and Built Environment, 8(4):216-220. http://ibe.sagepub.com/cgi/content/abstract/8/4/216
Van Asselt, L. 1999. Interactions between domestic mites and fungi. Indoor and Built Environment. 8(4):216-220. Accessed June 2008. http://content.karger.com/ProdukteDB/produkte.asp?Doi=24644
Dr. Art Hill
Department of Food Science
University of Guelph,
Guelph, ON, N1G 2W1
arhill@uoguelph.ca