Swiss cheese is characterized by the holes or eyes that develop during early stages of ripening. This cheese is one of the more difficult types of cheese to manufacture, involving several complicated procedures. Both rind and rindless Swiss cheeses are made; although today, most of the Swiss cheese made in the U.S. is rindless. The principles involved in making both types of Swiss cheese are essentially the same.

For either style of cheese, good quality milk is generally clarified to improve eye formation. The milk is ripened at 88° to 94°F by a starter culture consisting primarily of Streptococcus thermophilus, with small amounts of Lactobacillus bulgaricus and Lactobacillus helveticus. These heat-tolerant species of bacteria grow well at the relatively high temperature of 125° to 129°F used in cooking the curd. The addition of a culture of Propionibacterium shermanii is largely responsible for the characteristic eye formation and sweet flavor of Swiss cheese. When the desired acidity has been reached, a coagulating enzyme is added.

The curd is cut and recut until the particles are about 0.625 inch in diameter. The mixture of curd and whey is then cooked with constant stirring for about an hour at 125° to 129°F until the curd becomes firm. This is a stirred type of cheese with no matting. In the traditional method, after the curds are cooked, they are dipped out in one bag and transferred to a single round form.

Rindless Swiss cheese in blocks is an American innovation. The milk is set, and the curd cut and cooked as described above for traditional Swiss cheese. In rindless Swiss cheese, the curd and whey are pumped into a forming tank, where the curd settles and pressure is applied with press plates before the whey is removed. After the whey is drained off, the curd is pressed overnight, then cut into blocks of the desired size (usually 80 to 100 pounds). The blocks of cheese are salted in brine similar to traditional wheels of Swiss cheese, usually from 1 to 3 days. The surface of the cheese is dried at 50° to 55°F for 5 to 10 days.

The cheese is then wrapped in plastic film and placed in a box under pressure in a cold room (50° to 55°F) for 6 to 10 days to prepare the cheese for eye formation. Thereafter, it is transferred to a warm room maintained at 70° to 76°F, the optimum growth temperature for Propionibacterium shermanii. During this principal ripening period, propionic acid fermentation occurs. Proprionibacterium shermanii and related organisms convert lactic acid and lactates to propionic and acetic acids and carbon dioxide. The propionic acid contributes to the characteristic sweet flavor and the carbon dioxide collects to form holes of eyes. The development of eyes is completed in 3 to 4 weeks. The cheese is then returned to a cold (35° to 40°F) curing room for 3 to 9 months or longer for slower ripening and more flavor development. Most of the Swiss cheese manufactured in the United States is marketed after ripening for 3 to 4 months.