The primary ingredient used to make yogurt is milk. The process of yogurt production involves fermenting milk with specific bacterial cultures, typically Lactobacillus bulgaricus and Streptococcus thermophilus. These bacteria convert lactose, the sugar in milk, into lactic acid, which gives yogurt its tangy flavor and thick texture. The fermentation process also aids in preserving the milk and enhancing its nutritional profile by increasing beneficial probiotics. Yogurt can be made from various types of milk, including cow, goat, and plant-based alternatives, catering to diverse dietary preferences and restrictions. It is a popular and versatile food consumed in many cultures around the world.