The majority of holes in Swiss cheese, by USDA regulation, must measure between 11/16 and 13/16 of an inch in diameter.
Armies of microbes consume lactic acid excreted by other bacteria. They belch and otherwise exude carbon dioxide gas. This produces the familiar Swiss cheese holes. These big holes are tough on current cheese slicing machines, so the industry is asking that the regulations for Grade A Swiss be revised to make the average hole 6/16 of an inch in diameter. Many are upset that the government even bothers to regulate Swiss cheese hole size.