There are many different fermented milk products available around the world. These products were first made in Asia, Africa, and Europe, where milk producing animals such as sheep, camels, horses, cows, and goats were domesticated. Cheese, yogurt, kefir, and soured milk are the main varieties of fermented milk products, though there are many types of regional cultured milk foods.
Sour, or fermented, milk is the most basic fermented milk product. It is made by adding live bacteria cultures to fresh milk and letting the milk sit until it sours. Though this process is similar to the process that would make milk spoil, the bacteria added to milk have been specially selected as healthful bacterias. These bacteria eat lactose and excrete lactic acid which makes the milk sour, preserving it so that it will last longer than fresh milk would.
One of the most common fermented milk products is cheese. Though not all cheeses are fermented, many are because the fermentation process allows cheese to last at room temperature for a long time without going bad. Cheese has been produced for thousands of years and is now made throughout the world. Cow, sheep, goat, and buffalo milk are most frequently used in its production, though it is possible to make cheese out of the milk of any mammal.
Also made all over the world, yogurt is another of the more popular fermented milk products. The process of making yogurt is similar to that of making cheese. Live bacteria are added to fresh milk and allowed to ferment for a short time. Yogurt has a flavor similar to fresh milk, though more sour. Another of the commonly seen fermented milk products, sour cream is made in essentially the same manner, though cream or light cream is used in lieu of milk.
Kefir is another fermented milk product that is found throughout the world. This product is similar to yogurt but is thin enough to be drunk from a glass. Though similar in flavor to yogurt, kefir is made through a different process. This product is fermented through the use of grains of kefir, which are colonies of many different types of bacteria that have clumped together. These bacteria clumps are placed in fresh dairy products and then removed once the dairy product has been cultured and is properly fermented.