The term "Swiss cheese" encompasses a wide variety of cheeses produced in the country of Switzerland, including Gruyere cheese itself. But in the U.S., Swiss cheese refers to the traditional hole-filled Emmental style of cheese. And while Gruyere and Emmental both hail from the same country, they are very different products in many ways.
According to the Swiss Broadcasting Association, approximately 32,000 tons of Emmental cheese is produced in Switzerland ever year, with around 85 percent exported to other countries. The U.S. imported 3,200 tons of Emmental cheese in 2003, where it is then sold as simply "Swiss." Named for the canton of Berne's Emme Valley, this style of cheese dates all the way back to the 12th century. Its rubbery texture and mild flavor have given Emmental the distinction of being one of the most copied cheeses for its popularity all over the world.
The Swiss style of cheese known as Gruyere comes from a valley of the same name in the Swiss canton of Fribourg. Unlike the more bland-tasting Emmental variety, Gruyere's flavor is rich, nutty and slightly sweet. Where it shares similarities with the generic "Swiss" is its firm texture, yellow interior and, of course, holes. The style of Gruyere enjoyed today dates back to Medieval marketplaces in the 1600s, although earlier cheese traders in Gruyere can be traced back all the way to the 11th century.
Both Emmental and Gruyere cheese begin early in the morning with two copper vats filled with thousands of liters of milk, obtained from milking just the previous evening. The cheese maker then adds whey-based lacto-fermentation cultures to mature the milk, followed by the natural ingredient rennet, which contains enzymes to curdle the milk. After about 40 minutes, the milk takes on a more gelatinous texture and the cheese maker uses curd rakes to separate the curds into grains. This mixture is then heated and molded into cheese wheels.
For Emmental cheese, the storage process after molding is perhaps the most important step. To fully mature, the cheese takes at least 120 days or, in the case of Gruyere, between five and 12 months (the longer the maturation, the saltier the flavor). It is during this process that holes begin to form in the cheese, due to the heat within the storage cellar. The higher temperatures cause propanoic acid fermentation, which creates carbon dioxide. Since this gas cannot escape through the rind, it builds up and produces the holes for which Swiss cheese is known.