Why it Works: Good Bacteria
Over 3,000 years ago, yogurt was probably invented as a way to preserve fresh milk. Today, even with refrigerators, we have learned to enjoy the creamy, acidic taste of yogurt, and the process of making it hasn't changed much. Ingredients used are milk (fat-free [skim], 2% or whole) and bacteria. In the beginning, the bacteria might have been added by simply letting warm milk sit uncovered in hopes that the correct bacteria would come along. Today, the process is more controlled (and safer): Pure bacteria are added directly to milk. As the bacteria “eat” the sugar in the milk it produces acid. And it's this acid that causes the milk to thicken into yogurt.