Fermentation in food processing

Fermentation in food processing is the process where microorganisms like yeasts or bacteria convert carbohydrates into alcohol or organic acids, without an oxidizing agent being involved. The study of this process is called zymology or zymurgy. While the term can specifically refer to turning sugars into ethanol for alcoholic drinks such as wine, beer, and cider, similar reactions occur in bread leavening (where yeast produces carbon dioxide) and in preserving sour foods like sauerkraut and yogurt through lactic acid production. Other common fermented foods include vinegar, olives, and cheese, while more localized examples may be based on beans, grains, vegetables, fruit, honey, dairy, or fish.

Natural fermentation existed long before humans, and people likely discovered it by accident. Early humans probably stored excess food in containers, forgot about them, and later found that yeast and bacteria had grown. The oldest archaeological evidence of fermentation is a 13,000-year-old beer residue, with a gruel-like consistency, found in a cave near Haifa, Israel. Another early alcoholic drink, made from fruit, rice, and honey, dates from 7000 to 6600 BC in the Neolithic Chinese village of Jiahu. Winemaking goes back to around 6000 BC in Georgia, in the Caucasus region. Seven-thousand-year-old jars with wine remains, now at the University of Pennsylvania, were excavated in the Zagros Mountains in Iran. Strong evidence also shows fermented alcoholic drinks in Babylon (around 3000 BC), ancient Egypt (around 3150 BC), pre-Hispanic Mexico (around 2000 BC), and Sudan (around 1500 BC).

The science of fermentation was founded in 1856 by French chemist Louis Pasteur, who linked yeast to the process. Studying how yeast converts sugar to alcohol, Pasteur concluded that fermentation was driven by a vital force called "ferments" inside the yeast cells, which he believed worked only within living organisms. He wrote that alcoholic fermentation is tied to the life and organization of yeast cells, not to their death or decay.

However, it was already known that living yeast cells weren't strictly necessary. In 1897, German chemist Eduard Buchner at Humboldt University of Berlin discovered that sugar could ferment even without living yeast, thanks to an enzyme complex secreted by yeast, which he named zymase. He received the 1907 Nobel Prize in Chemistry for this work on cell-free fermentation. A year earlier, in 1906, studies on ethanol fermentation led to the early discovery of oxidized nicotinamide adenine dinucleotide (NAD+).

The byproducts of food fermentation—alcohol, preservative organic acids, and carbon dioxide—all have human uses. Alcohol turns fruit juices into wine, grains into beer, and starchy foods like potatoes into spirits such as gin and vodka. Carbon dioxide leavens bread. Organic acids preserve and flavor vegetables and dairy products. Fermentation serves five main purposes: enriching the diet with diverse flavors, aromas, and textures; preserving large amounts of food through lactic acid, alcohol, acetic acid, and alkaline fermentations; adding protein, essential amino acids, and vitamins to food substrates; removing antinutrients; and reducing cooking time and fuel use. Fermented beverages have likely always been linked to ceremonies and festivals, as shown by the design of drinkware and residues found inside.

Fermented foods vary by region. Worldwide examples include alcohol (beer, wine), vinegar, olives, yogurt, bread, and cheese. In East and Southeast Asia: amazake, atchara, belacan, burong mangga, com ruou, doenjang, douchi, fish sauce, lah pet, lambanog, kimchi, kombucha, leppet-so, narezushi, miso, nata de coco, nattō, ngapi, oncom, padaek, pla ra, prahok, ruou nep, sake, shrimp paste, soju, soy sauce, stinky tofu, tape, tempeh, tempoyak, and zha cai. Central Asia: kumis, kefir, shubat, and qatiq (yogurt). South Asia: achar, appam, dosa, dhokla, dahi (yogurt), idli, mixed pickle, ngari, sinki, tongba, and paneer. Africa: garri, injera, laxoox, mageu, ogi, ogiri, and iru. Americas: chicha, chocolate, vanilla, hot sauce, tepache, tibicos, pulque, muktuk, kiviak, and parakari. Middle East: torshi and boza. Europe: sourdough bread, elderberry wine, kombucha, pickling, rakfisk, sauerkraut, pickled cucumber, surströmming, mead, kvass, salami, sucuk, prosciutto, cultured milk products (quark, kefir, filmjölk, crème fraîche, smetana, skyr), rakı, tupí, and żur. Oceania: poi and kānga pirau.

Fermented foods can also be grouped by base ingredient. Beans: cheonggukjang, doenjang, douchi, fermented bean curd, miso, natto, soy sauce, stinky tofu, tempeh, oncom, soybean paste, Beijing mung bean milk, kinama, iru, and thua nao. Grains: amazake, beer, bread, choujiu, gamju, injera, kvass, makgeolli, murri, ogi, rejuvelac, sake, sikhye, sourdough, sowans, rice wine, malt whisky, grain whisky, idli, dosa, Bangla (drink), vodka, boza, and chicha. Vegetables: kimchi, mixed pickle, sauerkraut, Indian pickle, gundruk, and tursu. Fruit: wine, vinegar, cider, perry, brandy, atchara, nata de coco, burong mangga, asinan, pickling, vişinată, chocolate, rakı, and aragh s.