Fermentation in food processing

Fermentation in food processing is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation usually implies that the action of microorganisms is desirable. The science of fermentation is also known as zymology or zymurgy.

The term "fermentation" is sometimes used to specifically refer to the chemical conversion of sugars into ethanol, a process which is used to produce alcoholic beverages such as wine, beer, and cider. Fermentation is also employed in the leavening of bread (CO2 produced by yeast activity); in preservation techniques to produce lactic acid in sour foods such as sauerkraut, dry sausages, kimchi, and yogurt; and in pickling of foods with vinegar (acetic acid).

Natural fermentation precedes human history. Since ancient times, however, humans have been controlling the fermentation process. The earliest evidence of an alcoholic beverage, made from fruit, rice, and honey, dates from 7000–6600 BCE, in the Neolithic Chinese village of Jiahu, and winemaking dates from 6000 BCE, in Georgia, in the Caucasus area. Seven-thousand-year-old jars containing the remains of wine have been excavated in the Zagros Mountains in Iran, which are now on display at the University of Pennsylvania. There is strong evidence that people were fermenting beverages in Babylon circa 3000 BC, ancient Egypt circa 3150 BC, pre-Hispanic Mexico circa 2000 BC, and Sudan circa 1500 BC.

French chemist Louis Pasteur was the first known zymologist, when in 1856 he connected yeast to fermentation. Pasteur originally defined fermentation as "respiration without air". Pasteur performed careful research and concluded: "I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development, and multiplication of cells, ... . If asked, in what consists the chemical act whereby the sugar is decomposed, ..., I am completely ignorant of it."

Contributions to biochemistry
When studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that the fermentation was catalyzed by a vital force, called "ferments," within the yeast cells. The "ferments" were thought to function only within living organisms. "Alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells," he wrote.

Nevertheless, it was known that yeast extracts can ferment sugar even in the absence of living yeast cells. While studying this process in 1897, Eduard Buchner of Humboldt University of Berlin, Germany, found that sugar was fermented even when there were no living yeast cells in the mixture, by a yeast secretion that he termed zymase. In 1907 he received the Nobel Prize in Chemistry for his research and discovery of "cell-free fermentation."

One year prior, in 1906, ethanol fermentation studies led to the early discovery of NAD+.

Uses
The primary benefit of fermentation is the conversion of sugars and other carbohydrates into preservative organic acids, e.g. converting juice into wine, grains into beer, carbohydrates into carbon dioxide to leaven bread, and sugars in vegetables.

Food fermentation has been said to serve five main purposes:
 * Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates
 * Preservation of substantial amounts of food through lactic acid, alcohol, acetic acid, and alkaline fermentations
 * Biological enrichment of food substrates with protein, essential amino acids, and vitamins
 * Elimination of antinutrients
 * A decrease in cooking time and fuel requirement

Fermented foods by region

 * Worldwide: alcohol, wine, vinegar, olives, yogurt, bread, cheese
 * Asia
 * East and Southeast Asia: amazake, atchara, bai-ming, belacan, burong mangga, com ruou, dalok, doenjang, douchi, jeruk, lambanog, kimchi, kombucha, leppet-so, narezushi, miang, miso, nata de coco, nata de pina, natto, naw-mai-dong, oncom, pak-siam-dong, paw-tsaynob, prahok, ruou nep, sake, seokbakji, soju, soy sauce, stinky tofu, szechwan cabbage, tai-tan tsoi, chiraki, tape, tempeh, totkal kimchi, yen tsai, zha cai
 * Central Asia: kumis (mare milk), kefir, shubat (camel milk)
 * South Asia: achar, appam, dosa, dhokla, dahi (yogurt), idli, kaanji, mixed pickle, ngari, hawaichaar, jaand (rice beer), sinki, tongba, paneer
 * Africa: fermented millet porridge, garri, hibiscus seed, hot pepper sauce, injera, lamoun makbouss, laxoox, mauoloh, msir, mslalla, oilseed, ogi, ogili, ogiri, iru
 * Americas: sourdough bread, cultured milk, chicha, elderberry wine, kombucha, pickling (pickled vegetables), sauerkraut, lupin seed, oilseed, chocolate, vanilla, tabasco, tibicos, pulque, mikyuk (fermented bowhead whale)
 * Middle East: kushuk, lamoun makbouss, mekhalel, torshi, boza
 * Europe: rakfisk, sauerkraut, pickled cucumber, surströmming, mead, elderberry wine, salami, prosciutto, cultured milk products such as quark, kefir, filmjölk, crème fraîche, smetana, skyr.
 * Oceania: poi, kaanga pirau (rotten corn), sago

Bean-based
Cheonggukjang, doenjang, miso, natto, soy sauce, stinky tofu, tempeh, soybean paste, Beijing mung bean milk, kinama, iru

Grain-based
Amazake, beer, bread, choujiu, gamju, injera, kvass, makgeolli, murri, ogi, sake, sikhye, sourdough, sowans, rice wine, malt whisky, grain whisky, idli, dosa, vodka

Vegetable based
Kimchi, mixed pickle, sauerkraut, Indian pickle, gundruk

Fruit based
Wine, vinegar, cider, perry, brandy, atchara, nata de coco, burong mangga, asinan, pickling, vişinată

Honey based
Mead, metheglin

Dairy based
Cheese, kefir, kumis (mare milk), shubat (camel milk), cultured milk products such as quark, filmjölk, crème fraîche, smetana, skyr, yogurt

Fish based
Bagoong, faseekh, fish sauce, Garum, Hákarl, jeotgal, rakfisk, shrimp paste, surströmming, shidal

Meat based
Jamón ibérico, Chorizo, Salami, pepperoni

Tea based
Pu-erh tea, Kombucha

Risks of consuming fermented foods
Alaska has witnessed a steady increase of cases of botulism since 1985. It has more cases of botulism than any other state in the United States of America. This is caused by the traditional Eskimo practice of allowing animal products such as whole fish, fish heads, walrus, sea lion, and whale flippers, beaver tails, seal oil, birds, etc., to ferment for an extended period of time before being consumed. The risk is exacerbated when a plastic container is used for this purpose instead of the old-fashioned, traditional method, a grass-lined hole, as the botulinum bacteria thrive in the anaerobic conditions created by the air-tight enclosure in plastic.

The World Health Organization has classified pickled foods as a possible carcinogen, based on epidemiological studies. Other research found that fermented food contains a carcinogenic by-product, ethyl carbamate (urethane). "A 2009 review of the existing studies conducted across Asia concluded that regularly eating pickled vegetables roughly doubles a person's risk for esophageal squamous cell carcinoma."