Cheese is a dairy product, derived from milk and produced in wide ranges of flavors, textures, and forms. There are hundreds of different types of cheese around the world, and they are made mostly from the milk of cows but also other mammals, including sheep, goats, buffalo, reindeer, camels, and yaks. Cheese also contains water. A soft cheese, like Brie, contains more water than a hard cheese, like Parmesan. Since it contains vitamins and protein, cheese is nutritious, which can be used both as a food itself and in many different types of cooking. Cheese is produced through a process called “fermentation.” The process of making cheese was probably discovered by chance. Ancient people used to make bags, using the skin from an animal’s stomach. When they used these skin bags to carry milk, bacteria from the animal’s skin reacted with the milk. Then the milk was fermented, and the result was cheese. Around 4,000 years ago, people started to breed animals and process their milk. Today, cheese making is a very scientific process. First, the milk that will be used is pasteurized, which means that it is heated to remove all bacteria. Then specially cultivated bacteria, called “cultures,” are added to the milk. The milk is kept fairly warm during this period to help the cultures grow. As they grow, the cultures sometimes release bubbles of carbon dioxide. These bubbles help make the holes in Swiss cheese. Next, as the milk ripens, it forms a solid substance. This substance is called “curd.” The curd is removed, and the water is drained from it. The curd forms the basis of the cheese and may be treated in different ways. Finally, once it is matured and dried, the cheese is ready.