What do pickles, bread, yogurt, wine, beer, and cheese have in common?

All of these foods are made by fermentation. When you ferment a food, you encourage growth of "good" microorganisms in it, while preventing growth of spoilage-causing microorganisms. Doing this successfully may require special ingredients and carefully controlled conditions, such as temperature and pH. By eating spoilage-sensitive parts of the food, and releasing chemicals as a by-product, the microorganisms help preserve the food, and change its flavor and texture in interesting ways.

Here’s a brief look at how fermentation is used to make different foods:

Pickled Vegetables. The vegetable is soaked in a salt brine, allowing the growth of bacteria that eat the vegetable’s sugars and produce tart-tasting lactic acid.

Wines. Yeasts, added to crushed grapes, eat the grapes’ sugars and produce alcohol.

Breads . Yeasts, added to dough, digest sugars (derived from starches in dough) and produce carbon dioxide, causing the dough to rise.

Cheeses. Milk bacteria digest the milk sugar lactose and produce lactic acid, which acts with the added enzyme rennet to curdle the milk. The cheesemaker drains off the whey and compacts the curds, which various microbes then ripen into a mature cheese.