Production of Yogurt
Yogurt is a fermented milk product that is growing in popularity. It is made from whole, reduced fat, or skim milk that is pasteurized at high temperatures, cooled, and inoculated with a fresh culture of yogurt that has a 1:1 ratio of Lactobacillus bulgaricus and Streptococcus thermophilus. These organisms, which grow in a symbiotic relationship, are incubated at 110°F (43.3°C) to 114°F (45.6°C) for 5 to 6 hours. A mixture of Lactobacillus bulgaricus, Streptococcus thermophilus, and Lactobacillus acidophilus may also be used but the incubation temperatures must be lowered to 96.8°F (36°C) and held for 12 hours. A number of combinations will be used in this laboratory exercise, making whole milk yogurt and acidophilus yogurt and also skim milk yogurt and skim milk acidophilus yogurt using added nonfat dry milk solids and gelatin as a stabilizer.