Yoghurt is a fermented dairy product made by adding bacterial cultures to milk, which causes the transformation of the milk's sugar, lactose, into lactic acid. This process gives yoghurt its refreshingly tart flavor and unique pudding-like texture, a quality that is reflected in its original Turkish name, Yoghurmak, which means "to thicken".

Ingredients:

Although milk of various animals has been used for yogurt production in various parts of the world, most of the industrialized yogurt production uses cow's milk. Whole milk, partially skimmed milk, skim milk or cream may be used. In order to ensure the development of the yogurt culture the following criteria for the raw milk must be met:

• low bacteria count
• free from antibiotics, sanitizing chemicals, mastitis milk, colostrum, and rancid milk
• no contamination by bacteriophages

Other yogurt ingredients may include some or all of the following:

• Other Dairy Products: concentrated skim milk, nonfat dry milk, whey, lactose. These products are often used to increase the nonfat solids content
• Sweeteners: glucose or sucrose, high-intensity sweeteners (e.g. aspartame)
• Stabilizers: gelatin, carboxymethyl cellulose, locust bean gum,  alginates, carrageenans, whey protein concentrate
• Fruit Preparations: including natural and artificial flavoring, color

Types of yoghurt:

Stirred yoghurt:
This type of yoghurt is incubated in a tank and the final coagulum is "broken" by stirring prior to cooling and packing. The texture of stirred yoghurt will be less firm than a set yoghurt somewhat like a very thick cream. There is some slight reformation of the coagulum after the yoghurt has been packed, however this is slight and can not be relied upon.

Drinking Yoghurt:
This type of yoghurt is very similar to stirred yoghurt, having the coagulum broken prior to cooling. In drinking yoghurt the agitation used to "break" the coagulum is severe. Little if any reformation of the coagulum will reoccur after packing.

Frozen Yoghurt:
Frozen yoghurt is inoculated and incubated in the same manner as a stirred yogurt. However cooling is achieved by pumping through a Whipper / chiller / freezer in a fashion similar to ice cream. The texture of the finished product is mainly influenced by the whipper/ freezer and the size and distribution of the ice crystals produced.

Concentrated yoghurt:
This type of yoghurt is inoculated and fermented in the same manner as a stirred yoghurt. Following the "breaking" of the coagulum the yoghurt is concentrated by boiling off some of the water, this is often done under vacuum to reduce the temperature required.

Heating of low pH yoghurt can often lead to protein being totally denatured and producing rough and gritty textures. This is often called strained yoghurt due to the fat that the liquid that is released from the coagulum upon heating used to be "strained" off in a manner similar to making soft cheese.

Flavored yoghurt:
Yoghurt with various flavors and aromas have become very popular. The flavors are usually added at or just prior to filling into pots. Common additives are fruit or berries, usually as a puree or as whole fruit in a syrup.

These additives often have as much as 50% sugar in them, however with the trend towards healthy eating gaining momentum, many manufacturers offer a low sugar and low fat version of their products.

Low or no sugar yoghurt are often sweetened with saccharin or more commonly aspartame. The use of "fruit sugars" in the form of concentrated apple juice is sometimes found as a way of avoiding "added sugar" on the ingredients declaration; this tends to be a marketing ploy and has no real added benefit.

Set Yoghurt:
This type of yoghurt is incubated and cooled in the final package and is characterized by a firm jelly" like texture.

Substitute: 1 cup buttermilk or sour milk , 1 cup sour cream , 1 cup cottage cheese.