Heating the Milk
Yogurt, like cheese begins with curdling the milk. Most often, cow 's milk is used, but some yogurts are made with sheep's or even buffalo's milk. Some countries where the animal is indigenous use camel's milk. Yogurt manufacturing companies select premium milk and separate the types of milk---non-fat skim milk for fat-free yogurt, whole milk for regular yogurt---in large stainless steel vats. The milk is then heated in the vats to 200 degrees Fahrenheit for 10 to 30 minutes, depending on the desired thickness of the yogurt. The longer the milk is heated, the thicker the viscosity the finished yogurt product will have. Next, the vats are cooled down quickly to around 112 degrees and then the yogurt starter mix is added.
The Yogurt Starter Mix
The yogurt starter mix begins with friendly bacteria. Streptococcus thermophilus and Lactobacillus bulgaricus or Lactobacillus acidophilus and Lactobacillus casei---are added to the warm milk. The bacteria eat milk sugars and then excrete lactic acids which begins to ferment or curdle the milk. Most yogurts are not pasteurized because the process would destroy the live bacteria. Pasteurized yogurts are appropriately labeled, need no refrigeration, but lack the healthy qualities of unpasteurized live-cultured yogurt. Some companies add milk solids, whey proteins and other thickening agents. Once the correct acidity, thickness and texture is achieved, the yogurt is pumped from the vats into sterile storage containers for an incubation period of four hours or more at 100 degrees. The longer the yogurt is stored, the tarter the yogurt will be. Once the desired viscosity and tartness of the yogurt is achieved, it is then refrigerated at 38 degrees to control further fermentation.
Other Ingredients in Yogurt
Yogurt comes in many different flavors and uses different products. Non-fat yogurt would start the recipe with skim milk instead of whole milk. Flavored yogurt would add specific ingredients like fruit along with sugar or alternative sweetening agents. The sweetening agent not only sweetens the yogurt, but also aids in preserving the fruit. Sugar free yogurt uses an artificial sweetener in place of sugar. Most companies add the desired flavoring ingredients to the finished, plain and unsweetened yogurt before packaging.