Why Does Yogurt Taste Sour?

Our food scientist Jared Levan has soloved the mysteries of brain freeze, the emotions caused by chopping raw onions and the source behind Jell-O's Jiggles. Today he takes on yogurt's sour taste.

While most informed consumers, like you, know that yogurt is loaded with protein, calcium and a slew of other nutrients, few know the science behind its characteristic taste and texture. Have you ever wondered why every spoonful of your favorite fruit-on-the-bottom snack has such a tang to it?

Why does yogurt taste sour?

Plain and simple, yogurt is the result of bacterial fermentation of milk. All you need is pasteurized milk and bacteria. During this process, bacterial strains such as Lactobacillus and Bifidus — just two of the many types of lactic acid microorganisms — convert lactose sugars in milk into lactic acid. Standard starter cultures often number in the millions, and these little guys are active as hell; now you know why yogurt always contains "active culture" in the list of ingredients.

With such a high volume of active bacteria chugging away, the end result becomes supremely tangy. For some, that sour taste is anything but tasty, so many varieties of yogurt come adorned with additives ranging from honey to fruit preserves to balance out the flavor.

What is yogurt so thick?

Again, this is a direct result of the acidic environment created by fermentation. When casein proteins found in the milk are exposed to the highly acidic environment created by bacterial metabolism, they begin to curdle and form the thick yogurt texture you know and love. If you like your yogurt extra thick, stick with Greek-style strained yogurts — the straining process thickens by removing a massive amount of excess water without the need for increasing the fat content.