A sour food that results when bacteria consume the sugars in milk. The bacteria in yogurt must include Streptococcus thermophilus and Lactobacillus bulgaricus, with other species being optional.

Yoghurt is food produced by bacterial fermentation of milk. This process produces lactic acid, which acts on milk protein to give yoghurt its texture and characteristic tart flavor. Traditionally made yoghurt can be a very healthy and nutritious addition to our diets, but many commercial varieties have been… well, soured. Modern yoghurts are often pasteurized, killing the live microorganisms, and then doused in sugar, stripping it of its nutritional benefits.