Eyes are the round holes that are a characteristic feature of Swiss-type cheese[1] (e.g. Emmentaler cheese) and some Dutch-type cheeses. The eyes are bubbles of carbon dioxide gas. The gas is produced by various species of bacteria in the cheese.[2]

Swiss cheese [ edit ]

In Swiss-type cheeses, the eyes form as a result of the activity of propionic acid bacteria (propionibacteria), notably Propionibacterium freudenreichii subsp. shermanii.[3][4] These bacteria transform lactic acid into propionic acid and carbon dioxide, according to the formula:

The CO 2 so produced accumulates at weak points in the curd, where it forms the bubbles that become the cheese's eyes.[3] Not all CO 2 is so trapped: in an 80 kg (180 lb) cheese, about 20 L CO 2 remain in the eyes, while 60 L remain dissolved in the cheese mass and 40 L are lost from the cheese.[1]

Dutch cheese [ edit ]

In Dutch-type cheeses, the CO 2 that forms the eyes results from the metabolisation of citrate by citrate-positive ("Cit+") strains of lactococci.[1]

Bibliography [ edit ]

Polychroniadou, A. (2001). Eyes in cheese: a concise review. Milchwissenschaft 56, 74-77.

References [ edit ]