From The Food Encyclopedia by Jacques Rolland and Carol Sherman
A pale yellow cheese with slightly nutty flavor and large holes in its flesh, called "eyes." Swiss cheese is a North American and Australian version of a variety of cheeses originating in Switzerland, such as Emmental and Gruyère. Bacteria used in the production of Swiss cheese release carbon dioxide, which slowly form bubbles creating the eyes; in general, the larger the eyes the more intense the flavor. As well, longer aging or higher temperatures give the acting bacteria more time to produce flavor. No one can say for certain, but it is believed the first cheeses with holes began to appear during the Middle Ages.
