Eyes (cheese)
{{short description|Round holes in cheese}}
File:Emmentaler aoc block.jpg with eyes]]
Eyes are the round holes that are a characteristic feature of Swiss-type cheese{{Cite book |title=Cheese: Chemistry, Physics and Microbiology |volume=2 |chapter=Metabolism of Residual Lactose and of Lactate and Citrate |last1=McSweeney |first1=Paul L.H. |last2=Fox |first2 = Patrick F. |publisher=Elsevier |doi=10.1016/S1874-558X(04)80074-5 |year=2004|pages=366–367 |isbn=9780122636523 }} (e.g. Emmentaler cheese) and some Dutch-type cheeses. The eyes are formed by bubbles of carbon dioxide gas during the cheesemaking process. The gas is produced by various species of bacteria in the cheese.{{cite journal |doi=10.3168/jds.S0022-0302(17)94362-0 |title=On the Formation of "Eyes" in Emmental Cheese |journal=Journal of Dairy Science |volume=1 |issue=2 |pages=91–113 |year=1917 |last1=Clark |first1=William|url=https://zenodo.org/record/1520810 |doi-access=free }}
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.P.L.H. McSweeney, Biochemistry of Cheese Ripening: Introduction and Overview, in: Fox, p. 349{{cite journal|title=Propionibacterium freudenreichii ssp shermanii ATCC9614: A bacterium used in the production of Emmental|journal=Genoscope|date=16 January 2008|url=http://www.genoscope.cns.fr/spip/propionibacterium-freudenreichii,467.html|access-date=23 October 2010|archive-url=https://web.archive.org/web/20160826155845/http://www.genoscope.cns.fr/spip/Propionibacterium-freudenreichii,467.html|archive-date=26 August 2016|url-status=dead}} These bacteria transform lactic acid into propionic acid and carbon dioxide, according to the formula:
:3 lactate → 2 propionate + acetate + CO2 + H2OT. Beresford, A. Williams; The Microbiology of Cheese Ripening, in: Fox, p. 303
The CO2 so produced accumulates at weak points in the curd, where it forms the bubbles that become the cheese's eyes. Not all CO2 is so trapped: in an {{convert|80|kg|abbr=on}} cheese, about 20 L of CO2 remain in the eyes, while 60 L remain dissolved in the cheese mass and 40 L are lost from the cheese.
In Swiss cheese production, the number and size of eyes declined in the 2000s. This was the result of increasing standards of hygiene, which reduced the number of dust particles in the milk around which gas bubbles form. In 2025, the Swiss Federal Administrative Court approved the addition of {{interlanguage link|hay flower|de|Heublumen}} powder (Flores graminis) to the milk during cheesemaking, to allow for eyes of the typical number and size to form.{{Cite web |title=Emmentaler Käse: zurück zur Tradition oder Industrialisierung? |url=https://www.srf.ch/news/schweiz/schweizer-kaese-loecher-im-emmentaler-werden-zukuenftig-kuenstlich-herbeigefuehrt |access-date=2025-04-16 |website=Schweizer Radio und Fernsehen (SRF) |language=de}}Decision [https://bvger.weblaw.ch/pdf/B-6947-2023_2025-04-02_7b7e6047-4678-4f05-958f-53145f87e545.pdf B-6947/2023] of 2 April 2025
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.
Bibliography
- Polychroniadou, A. (2001). Eyes in cheese: a concise review. Milchwissenschaft 56, 74–77.
References
- {{cite book|title=Cheese: Chemistry, Physics, and Microbiology, Volume 1: General Aspects|date=13 October 2004|publisher=Academic Press|isbn=978-0-12-263652-3|editor=Fox, P.F.}}