Eyes (cheese)


Eyes are the round holes that are a characteristic feature of Swiss-type 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.

Swiss cheese

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

Dutch cheese

In Dutch-type cheeses, the CO2 that forms the eyes results from the metabolisation of citrate by citrate-positive strains of lactococci.

Footnotes