It’s nearly certain that each of us consumes some fermented food or beverage daily. Bread, cheese, yogurt, beer, cured salami, cocoa and pickled foods such as sauerkraut and kim chee are some examples of fermented products.

Fermentation is a metabolic process that occurs in yeast and bacteria to convert sugar to acids, gases or alcohol. It also takes place in oxygen-starved muscle cells. And fermentation refers to the controlled growth of microorganisms on a growth medium with the goal of producing a specific chemical product, usually some type of food.

In 1907 Eduard Buechner won the Nobel Prize in chemistry for demonstrating that the enzymes that these microorganisms produce cause fermentation.

Evidence suggests that fermented foods coexisted with Neolithic humans. Records go back only about 10,000 years, but there can be little doubt that fermentation, such as leavening of bread and creation of alcoholic brews, preceded written records.

Although most microorganisms render foods inedible, we have learned over tens of thousands of years to nurture and control the good strains of yeast and bacteria that produce fermented food and beverages.

Most of the bacteria are some variety of lactobacillus, of which there are at least 180 species, or of streptococcus.

Unbeknownst to our anonymous culinary ancestors who isolated and cultivated yeast and lactobacilli while brewing beer or baking bread, lactobacilli also power our muscles.

Fermentation occurs in mammalian muscle during periods of intense exertion with limited oxygen supply, resulting in the creation of lactic acid. In the presence of adequate oxygen, lactobacilli act on six-carbon sugars and their disaccharides to produce pyruvate by glycolysis, which oxidizes to produce energy in the form of adenosine triphosphate, a high-energy molecule found in every cell.

Some lactobacilli species produce only lactic acid from fermentation of sugars, while other species can produce either alcohol or lactic acid depending on the amount of oxygen. Many forms of yeast produce carbon dioxide and alcohol during fermentation.

Lactobacilli are not the only bacteria used in milk fermentation. Yogurt sold in the United States, for example, must contain both Lactobacillus bulgaricus and Streptococcus thermophiles. Certain fungi and bacteria consume lactose from milk and produce a range of products in the form of cheese. Cheese and other milk products such as sour cream and yogurt are fermented primarily by lactobacillus, which turns the sugars into lactic acid that give them their sour bite, while other flavors develop from other bacteria or molds in various controlled environments.

Since many different kinds of yeast, mold and fungi act on milk from a whole host of mammals — not to mention legumes and nuts — and cheese can be stored and cured in a plethora of environments, is it any wonder that the number of different cheeses might approach infinity?

Lactic acid is likewise the culprit for pickling foods as pickled cucumbers, sauerkraut and kim chee, as well as alcoholic beverages such as wine and beer.

Fermentation can even occur within the stomachs of animals. In cows it aids in digestion of the complex starches and silica in grasses and other vegetation that are indigestible to humans. However, in the human gastrointestinal tract, fermentation of complex starches in certain foods such as beans produces the gas that no one admits to passing in the elevator.