Paula Puchala, age 10, of Trumbull, Conn., for her question:

WHY DOES SWISS CHEESE HAVE HOLES

There are more than 400 different kinds of cheese and they are available under more than 2,000 different names. The tasty, nourishing food is made from milk and for thousands of years it has been a favorite of man. Two million tons of cheese are made in the United States each year, with Russiaand India making almost as much.

Experts group cheeses into four types: soft, semisoft, hard and very hard. The amount of moisture in the cheese determines how it is classified, with those having more moisture being softer.

Swiss cheese, one of the hard group, was actually originated in Switzerland, although it is now enjoyed in every part of the world. It is also called Emmentaler.

Swiss cheese, and also a variety called Gruyere, has holes that are called eyes. Cheese makers form these eyes by adding a certain type of bacteria to the cheese that produces bubbles of carbon dioxide gas. When the cheese is sliced, the bubbles become holes. It's that easy.

Another of the hard cheeses like Swiss is cheddar which originated in England but has since often been called American cheese because of its wide use in the United States.

While most cheese is made from the milk of cows, it is also made from the milk of buffaloes, sheep and goats. In Lapland cheese is made from reindeer's milk and in Tibet yak milk is used. Cheese is also made from the milk of zebras, horses, donkeys and camels.

Almost every state in the United States makes cheese, with Wisconsin leading the way and Minnesota and New York following second and third. In Canada, Quebec and Ontario provide most of the cheese supply.

Forty percent of the cheese used by Americans is process cheese, a blend of natural cheeses. Cheese is ground up, heated and blended with chemicals called emulsifiers. It melts more evenly than ordinary cheese, when used in cooking, and it also keeps better than natural cheese. Swiss and cheddar are two leading types of process cheese.

Process cheese spreads are also very popular. Along with natural cheese, milk, cream or whey is added to make them more moist. Fruit, meat, vegetables or spices are also added occasionally to provide extra flavor. Wine is also added to some of the special blends of process cheese.