Which product is a fermented milk product?

Yogurt is considered a fermented milk product because it is made through the fermentation of milk by specific bacteria, primarily Lactobacillus bulgaricus and Streptococcus thermophilus. During this process, these bacteria convert lactose, the sugar found in milk, into lactic acid. This fermentation not only thickens the milk but also gives yogurt its characteristic tangy flavor and health benefits, such as improving digestion and providing probiotics.

While cheese does involve fermentation, it is primarily categorized as a solid dairy product that undergoes additional processes beyond just fermentation, including curdling and aging. Milk itself is not fermented; it is the base ingredient from which fermented products like yogurt and cheese are made. Butter, on the other hand, is produced by churning cream, separating the fat from the buttermilk, and does not involve fermentation. Thus, yogurt stands out as the correct answer in this context.