Swiss cheese is often jokingly referred to as "rat cheese," because it's the type of cheese always depicted in cartoons featuring mice and rats. Not all cheese with holes is Swiss cheese and not all Swiss cheese has holes.
The two most famous original Swiss cheeses are Emmental and Gruyére, both of which are highly prized in fondues. There are some excellent American cheesemakers who closely follow Swiss traditions and make very tasty facsimiles of Emmentaler and Gruyére cheeses.
American Swiss Cheese
The large corporations use bulk operations to make Swiss-type cheese available at a reasonable price. These cheeses are generally labeled simply by the generic "Swiss cheese" term and are made from pasteurized cow's milk. This cheese is available sliced and shredded, in regular and low-fat varieties. Due to mass production for quick distribution, it is aged only about 4 months and generally has a much milder flavor than the real thing. It melts easily and is widely used in sandwiches.
Also known as Emmentaler and Emmenthaler, this cheese takes its name from the Emmental Valley where it originated circa 1293. Emmental is considered Switzerland's oldest and most prestigious cheese. This pale yellow cheese is made from part-skim, unpasteurized cow's milk and has a mild, slightly nutty, buttery, almost fruity flavor. The holes range from small to large olive-size. USA versions use pasteurized milk or follow US law and age the unpasteurized cheese at least 60 days. It is made in giant (up to 220 pounds) wheels and can be easily identified by its hometown stamped on the rind. This firm cheese melts easily, making it good for sauces, and it goes equally well with fruits and nuts.
This cheese's namesake is the valley of the same name in Fribourg, Switzerland. It differs from Emmental in that it uses a cow's milk with more fat, which naturally sweetens the nutty, buttery flavor. Gruyére is also aged anywhere from 10 to 12 months, giving it a brownish-gold rind. The center is pale yellow and the holes are much smaller and more evenly spaced than those of Emmental. Indeed, during the aging process, the holes may shrink down to a nearly indiscernible size.
Gruyére is made in huge 100-pound wheels and sold by the wedge. Unlike Emmental, the Gruyére name is not protected; thus there are many imitations on the market, including processed versions. Read the label to be sure you are getting aged Gruyére and not an imitation. Gruyére also melts easily, making it great for gratins, and goes well with meats and vegetables. It also shines as an appetizer or dessert cheese.