Apple #33: Swiss Cheese

So I was eating some Swiss cheese yesterday, and I wondered, what makes the holes in this cheese? The answer, it turns out, is "gassy bacteria."

• Making cheese requires bacteria. Different kinds of cheese use different kinds of bacteria as well as different kinds of milk.

• Swiss cheese uses three types of bacteria, but the one that makes the holes is called Propionibacter shermani. When a cheesemaker adds this bacteria to the mix, it makes bubbles of carbon dioxide. The cheesemaker can control the size of the bubbles by changing the acidity, temperature, and curing time of the mix.

• The holes in Swiss cheese are technically called "eyes."

• Swiss cheese made in the US is aged only four months. Swiss cheese made in Switzerland is aged four to fourteen months.

• The Swiss make two types of Swiss cheese, Emmentaler and Gruyere, named for the places where they were first made. It is believed that the first Emmentaler was made as long ago as 50 B.C. The holes in Gruyere cheese may be considerably smaller than Emmentaler.

Emmentaler

Gruyere

About cheese in general:

• Cheese was the result of an accidental discovery. It is presumed that people put milk in a bag made from the stomach of a cow and discovered that the next day, it had cured into chunks (curds) and liquid (whey). They took out the curds and ate it and thought it was pretty tasty. Then they added salt to it and found that the curds would last even longer.

• The recipe for cheese basically goes like this: milk + starting culture (bacteria + rennet for coagulation) = soft curd. The curd is then manipulated in various ways: the whey is removed, it gets salted, then it gets molded and pressed, sometimes salted some more, it gets "bandaged," and then it's allowed to mature.

• Interestingly, when a calf drinks milk, its four stomachs supply various kinds of bacteria at the various stages of digestion, turning the milk into a soft curd. The curd passes into the intestine, and now that the milk is in curd form, its passage to the exit is slowed long enough that the nutrients can be absorbed into the calf's body. So the production of cheese kind of mimics what happens to milk in a cow's stomach.

Sources
Why Does Swiss Cheese Have Holes in It? Ask Yahoo, June 10, 2002
Swiss Cheese Recipes and Cooking Tips, by Peggy Trowbridge
The Basics of Making Cheese, Early Cheesemaking in Scotland, part of a course taught through the Edinburgh Business School
Rennet for Making Cheese, David B. Fankhauser PhD, Professor of Biology and Chemistry, University of Cincinnati Clermont
Photos from a cheese website in German and The Cook's Thesaurus