The production of yogurt primarily involves lactic acid bacteria, specifically from the Lactococcus and Lactobacillus genera, rather than enzymes. These bacteria initiate fermentation by converting lactose, the sugar in milk, into lactic acid, which lowers the pH and causes milk proteins to coagulate into yogurt. The key enzyme produced by these bacteria is β-galactosidase, also known as lactase, which facilitates the breakdown of lactose into glucose and galactose. No enzymes present in milk contribute to yogurt fermentation; all biochemical processes occur internally within the bacteria. For further research on enzymes involved in yogurt production, introductory biochemistry textbooks such as "Lehninger Principles of Biochemistry" and "Biochemistry" are recommended.