Yogurt is a thick, creamy food made by adding special bacteria to milk and letting it ferment. The bacteria eat the sugar in the milk and produce lactic acid, which gives yogurt its tangy taste and transforms the liquid milk into something thick enough to eat with a spoon.

People have been making yogurt for thousands of years, long before refrigerators existed. The fermentation process actually helps preserve the milk and can make it easier to digest. Today, yogurt comes in countless varieties: plain, flavored, Greek-style (which is extra thick), or mixed with fruit, honey, or granola.

Yogurt appears in cuisines around the world. In India, it's called dahi and often served alongside spicy dishes to cool your mouth. In the Middle East, people use yogurt in savory sauces and marinades. In America, it's popular for breakfast or as a healthy snack.

The bacteria in yogurt are sometimes called “good bacteria” or probiotics because they can help your digestive system work better. These same helpful bacteria are what transform ordinary milk into something completely different: tangier, thicker, and more interesting.