Food microbiology studies microorganisms that affect foods, including those involved in fermentation and spoilage. Many fermented foods use bacteria like Lactobacillus and Streptococcus. Milk products provide nutrition but raw milk can harbor pathogens. Pasteurization kills harmful bacteria in milk while allowing production of foods like yogurt, cheese and butter using cultures of Lactobacillus, Lactococcus, and Streptococcus.