Jody Dawber, age 9, of Hattesburg, Miss., for her question:
HOW IS CHEESE MADE?
Cheese is a food made from milk. It has been one of the most important foods of people throughout the world for thousands of years.
Almost all cheese from the United States and Canada is made in large factories. The process used involves four basic steps: processing the milk, separating the curd, ripening and packaging.
Milk is first inspected for quality and then any solid substances are removed by a process called clarification. The milk flows into a pasteurizer that kills any harmful bacteria. Pumps then force the pasteurized milk into large metal tanks or vats that hold from 8,000 to 35,000 pounds. It takes about 11,000 pounds of milk to make 1,000 pounds of cheese.
In the tanks, the milk forms a soft, custardlike substance called curd. The curd contains a liquid called whey, which must be expelled before cheese can be made. The curd is formed by first heating the milk to 86 to 96 degrees Fahrenheit.
Next, a liquid called a starter culture is added to the milk. Acids form and turn the milk sour. Then workers add rennet, a substance that contains enzymes. The rennet thickens the milk. This action, called curdling, may also be promoted by adding other enzymes.
Special knives cut the curd into thousands of small cubes and the whey oozes from them. Then paddles stir the curd and the temperature is raised to between 102 and 130 degrees. The whey is then drained off.
To make cottage cheese, workers rinse the curd with water and mix it with cream and salt. For most other cheeses, the curd rests undisturbed and the particles stick together and form a solid mass.
The curd is then packed by machine into metal hoops or molds. They are put into presses that keep the cheese under great pressure. Then the cheese is left to dry for several days.
A crust, called the rind, forms on cheese as it dries. Rindless cheeses are not dried. These cheeses are sealed into plastic film immediately after they are taken from the hoops.
Ripening, which is also called aging or curing, helps give some cheese its flavor and texture. Cheese is aged in storage rooms or warehouses that have a controlled temperature and humidity.
Aging times vary for different cheeses. Brick cheese and some other types need only two months to age, but Parmesan requires about a year. The longer the curing time, the sharper the flavor of the cheese.
After being aged, cheese is packaged in a wide variety of shapes and sizes. Some cheeses are sliced at the factory and sealed in foil or plastic. Others are sold whole in large blocks, wedges, balls ("rounds") and short cylinders ("wheels").
Much of the cheese is made into process cheese, a blend of natural cheeses. Process cheese and products called process cheese foods and process cheese spreads account for about 40 percent of the cheese eated by Americans.
Process cheese keeps better than natural cheese and it melts more evenly when used in cooking.