Eyes
The round holes in Emmental, Gouda and similar cheeses, made by gas from bacteria during ripening.
Also: holes, openings, trous
Eyes are the round, shiny-walled holes inside cheeses such as Emmental, Jarlsberg, Gruyère and Gouda. They form when bacteria produce carbon dioxide inside the closed, elastic paste of a ripening cheese. In Emmental the main gas makers are propionibacteria, working in a warm cellar for weeks, and the eyes can be as big as cherries. In Gouda and Edam smaller eyes come from lactic bacteria that ferment citrate in the milk. A cheese with no eyes where some are expected is called blind, and one with too many or split eyes is faulty. Very clean modern milk makes fewer eyes, because tiny hay particles that once seeded them are filtered out.