Which of the following is NOT a type of milk used to make yogurt?

Heavy cream is not typically used to make yogurt because yogurt production relies on the fermentation of milk sugars through the activity of specific bacteria, primarily Lactobacillus species. These bacteria thrive in the presence of lactose, which is found in significant quantities in skim, whole, and low-fat milk, but not in heavy cream, which consists mainly of fat and lacks substantial lactose content.

Skim milk, whole milk, and low-fat milk all contain varying amounts of milk fat and lactose, making them suitable substrates for fermentation into yogurt. The fermentation process transforms the lactose into lactic acid, which gives yogurt its characteristic tangy flavor and helps in thickening the product. Heavy cream, while it can be fermented, does not provide the ideal environment for the desired yogurt texture and flavor profile. Additionally, it is more commonly used in making rich, creamy products rather than traditional yogurt.

So while skim milk, whole milk, and low-fat milk are integral to yogurt production, heavy cream does not typically serve as a base for yogurt.