Eyes (cheese)
Eyes are the round holes that are a characteristic feature of Swiss-type cheese[1] (e.g. Emmentaler cheese) and some Dutch-type cheeses. They are bubbles of carbon dioxide gas that is produced by bacteria in the cheese.
Historically (Middle Ages),[2] the holes were considered a sign of imperfection and cheese makers would try to avoid them.[3]
Swiss cheese
In Swiss-type cheeses, the eyes form as a result of the activity of propionic acid bacteria (propionibacteria), notably Propionibacterium freudenreichii subsp. shermanii.[4][5] These bacteria transform lactic acid into propionic acid and carbon dioxide, according to the formula:
- 3 Lactate → 2 Propionate + Acetate + CO2 + H2O[6]
The CO2 so produced accumulates at weak points in the curd, where it forms the bubbles that become the cheese's eyes.[4] Not all CO2 is so trapped: in a 80 kg cheese, about 20 l CO2 remain in the eyes, while 60 l remain dissolved in the cheese mass and 40 l are lost from the cheese.[1]
Dutch cheese
In Dutch-type cheeses, the CO2 that forms the eyes results from the metabolisation of citrate by citrate-positive ("Cit+") strains of lactococci.[7]
Bibliography
- Polychroniadou, A. (2001). Eyes in cheese: a concise review. Milchwissenschaft 56, 74-77.
References
- Fox, P.F., ed. Cheese: Chemistry, Physics, and Microbiology, Volume 1: General Aspects. Academic Press. ISBN 9780122636523.
- ^ a b P.L.H. McSweeney and P.R Fox; Metabolism of Residual Lactose and of Lactate and Citrate, in: Fox, p. 366
- ^ Serowe peregrynacje [in:] Początki [in:] Świat Nauki (Scientific American Polska) No 9/2010 (229), Prószyński Media, Warsaw, 2010.
- ^ Scientific American, Cheese Story August 2010, p. 33
- ^ a b P.L.H. McSweeney, Biochemistry of Cheese Ripening: Introduction and Overview, in: Fox, p. 349
- ^ "Propionibacterium freudenreichii ssp shermanii ATCC9614: A bacterium used in the production of Emmental". Genoscope. 16 January 2008. http://www.genoscope.cns.fr/spip/propionibacterium-freudenreichii,467.html. Retrieved 23 October 2010.
- ^ T. Beresford, A. Williams; The Microbiology of Cheese Ripening, in: Fox, p. 303
- ^ P.L.H. McSweeney and P.R Fox; Metabolism of Residual Lactose and of Lactate and Citrate, in: Fox, p. 367