Fermentation - wikipedia Fermentation For other uses, see Fermentation ( disambiguation ). Fermentation in progress : Bubbles of CO form a froth on top of the fermentation mixture. Fermentation is a metabolic process that consumes sugar in the absence of oxygen. The products are organic acids, gases, or alcohol. It occurs in yeast and bacteria, and also in oxygen - starved muscle cells, as in the case of lactic acid fermentation. The science of fermentation is known as zymology. In microorganisms, fermentation is the primary means of producing ATP by the degradation of organic nutrients anaerobically. Humans have used fermentation to produce foodstuffs and beverages since the Neolithic age. For example, fermentation is used for preservation in a process that produces lactic acid as found in such sour foods as pickled cucumbers, kimchi and yogurt ( see fermentation in food processing ), as well as for producing alcoholic beverages such as wine ( see fermentation in winemaking ) and beer. Fermentation occurs within the gastrointestinal tracts of all animals, including humans. Contents 1 Definitions 2 Biological role 3 Biochemical overview 4 Products 4.1 Ethanol 4.2 Lactic acid 4.3 Hydrogen gas 5 Modes of operation 5.1 Batch 5.2 Fed - batch 5.3 Open 5.4 Continuous 6 History of human use 7 Etymology 8 See also 9 References 10 External links Definitions Below are some definitions of fermentation. They range from informal, general usages to more scientific definitions. Preservation methods for food via microorganisms ( general use ). Any process that produces alcoholic beverages or acidic dairy products ( general use ). Any large - scale microbial process occurring with or without air ( common definition used in industry ). Any energy - releasing metabolic process that takes place only under anaerobic conditions ( becoming more scientific ). Any metabolic process that releases energy from a sugar or other organic molecule, does not require oxygen or an electron transport system, and uses an organic molecule as the final electron acceptor ( most scientific ). Biological role Along with photosynthesis and aerobic respiration, fermentation is a way of extracting energy from molecules, but it is the only one common to all bacteria and eukaryotes. It is therefore considered the oldest metabolic pathway, suitable for an environment that did not yet have oxygen. Yeast, a form of fungus, occurs in almost any environment capable of supporting microbes, from the skins of fruits to the guts of insects and mammals and the deep ocean, and they harvest sugar - rich materials to produce ethanol and carbon dioxide. The basic mechanism for fermentation remains present in all cells of higher organisms. Mammalian muscle carries out the fermentation that occurs during periods of intense exercise where oxygen supply becomes limited, resulting in the creation of lactic acid. In invertebrates, fermentation also produces succinate and alanine. Fermentative bacteria play an essential role in the production of methane in habitats ranging from the rumens of cattle to sewage digesters and freshwater sediments. They produce hydrogen, carbon dioxide, formate and acetate and carboxylic acids ; and then consortia of microbes convert the carbon dioxide and acetate to methane. Acetogenic bacteria oxidize the acids, obtaining more acetate and either hydrogen or formate. Finally, methanogens ( which are in the domain Archea ) convert acetate to methane. Biochemical overview Comparison of aerobic respiration and most known fermentation types in eucaryotic cell. Numbers in circles indicate counts of carbon atoms in molecules, C6 is glucose C H O, C1 carbon dioxide CO. Mitochondrial outer membrane is omitted. Fermentation reacts NADH with an endogenous, organic electron acceptor. Usually this is pyruvate formed from sugar through glycolysis. The reaction produces NAD+ and an organic product, typical examples being ethanol, lactic acid, carbon dioxide, and hydrogen gas ( H ). However, more exotic compounds can be produced by fermentation, such as butyric acid and acetone. Fermentation products contain chemical energy ( they are not fully oxidized ), but are considered waste products, since they can not be metabolized further without the use of oxygen. Fermentation normally occurs in an anaerobic environment. In the presence of O, NADH and pyruvate are used to generate ATP in respiration. This is called oxidative phosphorylation, and it generates much more ATP than glycolysis alone. For that reason, fermentation is rarely utilized when oxygen is available. However, even in the presence of abundant oxygen, some strains of yeast such as Saccharomyces cerevisiae prefer fermentation to aerobic respiration as long as there is an adequate supply of sugars ( a phenomenon known as the Crabtree effect ). Some fermentation processes involve obligate anaerobes, which can not tolerate oxygen. Although yeast carries out the fermentation in the production of ethanol in beers, wines, and other alcoholic drinks, this is not the only possible agent : bacteria carry out the fermentation in the production of xanthan gum. Products Ethanol Main article : Ethanol fermentation Overview of ethanol fermentation. In ethanol fermentation, one glucose molecule is converted into two ethanol molecules and two carbon dioxide molecules. It is used to make bread dough rise : the carbon dioxide forms bubbles, expanding the dough into a foam. The ethanol is the intoxicating agent in alcoholic beverages such as wine, beer and liquor. Fermentation of feedstocks including sugarcane, corn and sugar beets produces ethanol that is added to gasoline. In some species of fish, including goldfish and carp, it provides energy when oxygen is scarce ( along with lactic acid fermentation ). The figure illustrates the process. Before fermentation, a glucose molecule breaks down into two pyruvate molecules. The energy from this exothermic reaction is used to bind inorganic phosphates to ATP and convert NAD+ to NADH. The pyruvates break down into two acetaldehyde molecules and give off two carbon dioxide molecules as a waste product. The acetaldehyde is reduced into ethanol using the energy and hydrogen from NADH and the NADH is oxidized into NAD+ so that the cycle may repeat. The reaction is catalysed by the enzymes pyruvate decarboxylase and alcohol dehydrogenase. Lactic acid Main article : Lactic acid fermentation Homolactic fermentation ( producing only lactic acid ) is the simplest type of fermentation. The pyruvate from glycolysis undergoes a simple redox reaction, forming lactic acid. It is unique because it is one of the only respiration processes to not produce a gas as a byproduct. Overall, one molecule of glucose ( or any six - carbon sugar ) is converted to two molecules of lactic acid : C H O → 2 CH CHOHCOOH It occurs in the muscles of animals when they need energy faster than the blood can supply oxygen. It also occurs in some kinds of bacteria ( such as lactobacilli ) and some fungi. It is the type of bacteria that converts lactose into lactic acid in yogurt, giving it its sour taste. These lactic acid bacteria can carry out either homolactic fermentation, where the end - product is mostly lactic acid, or Heterolactic fermentation, where some lactate is further metabolized and results in ethanol and carbon dioxide ( via the phosphoketolase pathway ), acetate, or other metabolic products, e.g. : C H O → CH CHOHCOOH + C H OH + CO If lactose is fermented ( as in yogurts and cheeses ), it is first converted into glucose and galactose ( both six - carbon sugars with the same atomic formula ) : C H O + H O → 2 C H O Heterolactic fermentation is in a sense intermediate between lactic acid fermentation, and other types, e.g. alcoholic fermentation ( see below ). The reasons to go further and convert lactic acid into anything else are : The acidity of lactic acid impedes biological processes ; this can be beneficial to the fermenting organism as it drives out competitors that are unadapted to the acidity ; as a result, the food will have a longer shelf life ( part of the reason foods are purposely fermented in the first place ) ; however, beyond a certain point, the acidity starts affecting the organism that produces it. The high concentration of lactic acid ( the final product of fermentation ) drives the equilibrium backwards ( Le Chatelier 's principle ), decreasing the rate at which fermentation can occur, and slowing down growth. Ethanol, into which lactic acid can be easily converted, is volatile and will readily escape, allowing the reaction to proceed easily. CO is also produced, but it is only weakly acidic, and even more volatile than ethanol. Acetic acid ( another conversion product ) is acidic, and not as volatile as ethanol ; however, in the presence of limited oxygen, its creation from lactic acid releases additional energy. It is a lighter molecule than lactic acid, that forms fewer hydrogen bonds with its surroundings ( due to having fewer groups that can form such bonds ), thus is more volatile and will also allow the reaction to move forward more quickly. If propionic acid, butyric acid, and longer monocarboxylic acids are produced ( see mixed acid fermentation ), the amount of acidity produced per glucose consumed will decrease, as with ethanol, allowing faster growth. Hydrogen gas Main article : Fermentative hydrogen production Hydrogen gas is produced in many types of fermentation ( mixed acid fermentation, butyric acid fermentation, caproate fermentation, butanol fermentation, glyoxylate fermentation ), as a way to regenerate NAD from NADH. Electrons are transferred to ferredoxin, which in turn is oxidized by hydrogenase, producing H. Hydrogen gas is a substrate for methanogens and sulfate reducers, which keep the concentration of hydrogen low and favor the production of such an energy - rich compound, but hydrogen gas at a fairly high concentration can nevertheless be formed, as in flatus. As an example of mixed acid fermentation, bacteria such as Clostridium pasteurianum ferment glucose producing butyrate, acetate, carbon dioxide and hydrogen gas : The reaction leading to acetate is : C H O + 4 H O → 2 CH COO + 2 HCO + 4 H + 4 H Glucose could theoretically be converted into just CO and H, but the global reaction releases little energy. Modes of operation Most industrial fermentation uses batch or fed - batch procedures, although continuous fermentation can be more economical if various challenges, particularly the difficulty of maintaining sterility, can be met. Batch In a batch process, all the ingredients are combined and the reactions proceed without any further input. Batch fermentation has been used for millennia to make bread and alcoholic beverages, and it is still a common method, especially when the process is not well understood. However, it can be expensive because the fermentor must be sterilized using high pressure steam between batches. Strictly speaking, there is often addition of small quantities of chemicals to control the pH or suppress foaming. Batch fermentation goes through a series of phases. There is a lag phase in which cells adjust to their environment ; then a phase in which exponential growth occurs. Once many of the nutrients have been consumed, the growth slows and becomes non-exponential, but production of secondary metabolites ( including commercially important antibiotics and enzymes ) accelerates. This continues through a stationary phase after most of the nutrients have been consumed, and then the cells die. Fed - batch See also : Fed - batch culture Fed - batch fermentation is a variation of batch fermentation where some of the ingredients are added during the fermentation. This allows greater control over the stages of the process. In particular, production of secondary metabolites can be increased by adding a limited quantity of nutrients during the non-exponential growth phase. Fed - batch operations are often sandwiched between batch operations. Open The high cost of sterilizing the fermentor between batches can be avoided using various open fermentation approaches that are able to resist contamination. One is to use a naturally evolved mixed culture. This is particularly favored in wastewater treatment, since mixed populations can adapt to a wide variety of wastes. Thermophilic bacteria can produce lactic acid at temperatures of around 50 degrees Celsius, sufficient to discourage microbial contamination ; and ethanol has been produced at a temperature of 70 ° C. This is just below its boiling point ( 78 ° C ), making it easy to extract. Halophilic bacteria can produce bioplastics in hypersaline conditions. Solid - state fermentation adds a small amount of water to a solid substrate ; it is widely used in the food industry to produce flavors, enzymes and organic acids. Continuous In continuous fermentation, substrates are added and final products removed continuously. There are three varieties : chemostats, which hold nutrient levels constant ; turbidostats, which keep cell mass constant ; and plug flow reactors in which the culture medium flows steadily through a tube while the cells are recycled from the outlet to the inlet. If the process works well, there is a steady flow of feed and effluent and the costs of repeatedly setting up a batch are avoided. Also, it can prolong the exponential growth phase and avoid byproducts that inhibit the reactions by continuously removing them. However, it is difficult to maintain a steady state and avoid contamination, and the design tends to be complex. Typically the fermentor must run for over 500 hours to be more economical than batch processors. History of human use The use of fermentation, particularly for beverages, has existed since the Neolithic and has been documented dating from 7000 -- 6600 BCE in Jiahu, China, 5000 BCE in India, Ayurveda mentions many Medicated Wines, 6000 BCE in Georgia, 3150 BCE in ancient Egypt, 3000 BCE in Babylon, 2000 BCE in pre-Hispanic Mexico, and 1500 BC in Sudan. Fermented foods have a religious significance in Judaism and Christianity. The Baltic god Rugutis was worshiped as the agent of fermentation. Louis Pasteur in his laboratory In 1837, Charles Cagniard de la Tour, Theodor Schwann and Friedrich Traugott Kützing independently published papers concluding, as a result of microscopic investigations, that yeast is a living organism that reproduces by budding. Schwann boiled grape juice to kill the yeast and found that no fermentation would occur until new yeast was added. However, a lot of chemists, including Antoine Lavoisier, continued to view fermentation as a simple chemical reaction and rejected the notion that living organisms could be involved. This was seen as a reversion to vitalism, and was lampooned in an anonymous publication by Justus von Liebig and Friedrich Wöhler. The turning point came when Louis Pasteur ( 1822 -- 1895 ), during the 1850s and 1860s, repeated Schwann 's experiments and showed that fermentation is initiated by living organisms in a series of investigations. In 1857, Pasteur showed that lactic acid fermentation is caused by living organisms. In 1860, he demonstrated that bacteria cause souring in milk, a process formerly thought to be merely a chemical change, and his work in identifying the role of microorganisms in food spoilage led to the process of pasteurization. In 1877, working to improve the French brewing industry, Pasteur published his famous paper on fermentation, `` Etudes sur la Bière '', which was translated into English in 1879 as `` Studies on fermentation ''. He defined fermentation ( incorrectly ) as `` Life without air '', but correctly showed that specific types of microorganisms cause specific types of fermentations and specific end - products. Although showing fermentation to be the result of the action of living microorganisms was a breakthrough, it did not explain the basic nature of the fermentation process, or prove that it is caused by the microorganisms that appear to be always present. Many scientists, including Pasteur, had unsuccessfully attempted to extract the fermentation enzyme from yeast. Success came in 1897 when the German chemist Eduard Buechner ground up yeast, extracted a juice from them, then found to his amazement that this `` dead '' liquid would ferment a sugar solution, forming carbon dioxide and alcohol much like living yeasts. Buechner 's results are considered to mark the birth of biochemistry. The `` unorganized ferments '' behaved just like the organized ones. From that time on, the term enzyme came to be applied to all ferments. It was then understood that fermentation is caused by enzymes that are produced by microorganisms. In 1907, Buechner won the Nobel Prize in chemistry for his work. Advances in microbiology and fermentation technology have continued steadily up until the present. For example, in the 1930s, it was discovered that microorganisms could be mutated with physical and chemical treatments to be higher - yielding, faster - growing, tolerant of less oxygen, and able to use a more concentrated medium. Strain selection and hybridization developed as well, affecting most modern food fermentations. Etymology The word `` ferment '' is derived from the Latin verb fervere, which means to boil. It is thought to have been first used in the late 14th century in alchemy, but only in a broad sense. It was not used in the modern scientific sense until around 1600. See also Biotechnology portal Acetone - butanol - ethanol fermentation Dark fermentation Fermentation lock Gut fermentation syndrome Industrial fermentation Non-fermenter Photofermentation Aerobic fermentation References ^ Jump up to : Klein, Donald W. ; Lansing M. ; Harley, John ( 2006 ). Microbiology ( 6th ed. ). New York : McGraw - Hill. ISBN 978 - 0 - 07 - 255678 - 0. Jump up ^ Bowen, Richard. `` Microbial Fermentation ''. Hypertexts for biological sciences. Colorado State University. Retrieved 29 April 2018. Jump up ^ Tortora, Gerard J. ; Funke, Berdell R. ; Case, Christine L. ( 2010 ). `` 5 ''. 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( 2006 ). `` Genetic characterization and relationships of traditional grape cultivars from Transcaucasia and Anatolia ''. Plant Genetic Resources : characterization and utilization. 4 ( 2 ) : 144. doi : 10.1079 / PGR2006114. Jump up ^ Cavalieri, D ; McGovern P.E. ; Hartl D.L. ; Mortimer R. ; Polsinelli M. ( 2003 ). `` Evidence for S. cerevisiae fermentation in ancient wine '' ( PDF ). Journal of Molecular Evolution. 57 Suppl 1 : S226 -- 32. doi : 10.1007 / s00239 - 003 - 0031 - 2. PMID 15008419. 15008419. Archived from the original ( PDF ) on December 9, 2006. Retrieved 2007 - 01 - 28. ^ Jump up to : `` Fermented fruits and vegetables. A global perspective ''. FAO Agricultural Services Bulletins - 134. Archived from the original on January 19, 2007. Retrieved 2007 - 01 - 28. Jump up ^ Dirar, H., ( 1993 ), The Indigenous Fermented Foods of the Sudan : A Study in African Food and Nutrition, CAB International, UK Jump up ^ `` Gintaras Beresneviius. M. Strijkovskio Kronikos '' lietuvi diev sraas ``. spauda.lt. Jump up ^ Rūgutis. Mitologijos enciklopedija, 2 tomas. Vilnius. Vaga. 1999. 293 p. Jump up ^ Shurtleff, William ; Aoyagi, Akiko. `` A Brief History of Fermentation, East and West ''. Soyinfo Center. Soyfoods Center, Lafayette, California. Retrieved 30 April 2018. ^ Jump up to : Lengeler, Joseph W. ; Drews, Gerhart ; Schlegel, Hans Günter, eds. ( 1999 ). Biology of the prokaryotes. Stuttgart : Thieme ( u.a. ) ISBN 9783131084118. Jump up ^ Accomplishments of Louis Pasteur Archived 2010 - 11 - 30 at the Wayback Machine... Fjcollazo.com ( 2005 - 12 - 30 ). Retrieved on 2011 - 01 - 04. Jump up ^ HowStuffWorks `` Louis Pasteur ''. Science.howstuffworks.com ( 2009 - 07 - 01 ). Retrieved on 2011 - 01 - 04. Jump up ^ Louis Pasteur ( 1879 ) Studies on fermentation : The diseases of beer, their causes, and the means of preventing them. 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Works of Louis Pasteur Pasteur Brewing. The chemical logic behind fermentation and respiration Metabolism, catabolism, anabolism General Metabolic pathway Metabolic network Primary nutritional groups Energy metabolism Aerobic respiration Glycolysis → Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation ( electron transport chain + ATP synthase ) Anaerobic respiration Electron acceptors are other than oxygen Fermentation Glycolysis → Substrate - level phosphorylation ABE Ethanol Lactic acid Specific paths Protein metabolism Protein synthesis Catabolism Carbohydrate metabolism ( carbohydrate catabolism and anabolism ) Human Glycolysis ⇄ Gluconeogenesis Glycogenolysis ⇄ Glycogenesis Pentose phosphate pathway Fructolysis Galactolysis Glycosylation N - linked O - linked Nonhuman Photosynthesis Anoxygenic photosynthesis Chemosynthesis Carbon fixation Xylose metabolism Radiotrophism Lipid metabolism ( lipolysis, lipogenesis ) Fatty acid metabolism Fatty acid degradation ( Beta oxidation ) Fatty acid synthesis Other Steroid metabolism Sphingolipid metabolism Eicosanoid metabolism Ketosis Reverse cholesterol transport Amino acid Amino acid synthesis Urea cycle Nucleotide metabolism Purine metabolism Nucleotide salvage Pyrimidine metabolism Other Metal metabolism Iron metabolism Ethanol metabolism Metabolism map Carbon Fixation Photo - respiration Pentose Phosphate Pathway Citric Acid Cycle Glyoxylate Cycle Urea Cycle Fatty Acid Synthesis Fatty Acid Elongation Beta Oxidation Peroxisomal Beta Oxidation Glyco - genolysis Glyco - genesis Glyco - lysis Gluconeo - genesis Decarb - oxylation Fermentation Keto - lysis Keto - genesis feeders to Gluconeo - genesis Direct / C4 / CAM Carbon Intake Light Reaction Oxidative Phosphorylation Amino Acid Deamination Citrate Shuttle Lipogenesis Lipolysis Steroidogenesis MVA Pathway MEP Pathway Shikimate Pathway Transcription & Replication Translation Proteolysis Glycosy - lation Sugar Acids Double / Multiple Sugars & Glycans Simple Sugars Inositol - P Amino Sugars & Sialic Acids Nucleotide Sugars Hexose - P Triose - P Glycerol P - glycerates Pentose - P Tetrose - P Propionyl - CoA Succinate Acetyl - CoA Pentose - P P - glycerates Glyoxylate Photosystems Pyruvate Lactate Acetyl - CoA Citrate Oxalo - acetate Malate Succinyl - CoA α - Keto - glutarate Ketone Bodies Respiratory Chain Serine Group Alanine Branched - chain Amino Acids Aspartate Group Homoserine Group & Lysine Glutamate Group & Proline Arginine Creatine & Polyamines Ketogenic & Glucogenic Amino Acids Amino Acids Shikimate Aromatic Amino Acids & Histidine Ascorbate ( Vitamin C ) δ - ALA Bile Pigments Hemes Cobalamins ( Vitamin B ) Various Vitamin B 's Calciferols ( Vitamin D ) Retinoids ( Vitamin A ) Quinones ( Vitamin K ) & Carotenoids ( Vitamin E ) Cofactors Vitamins & Minerals Antioxidants PRPP Nucleotides Nucleic Acids Proteins Glycoproteins & Proteoglycans Chlorophylls MEP MVA Acetyl - CoA Polyketides Terpenoid Backbones Terpenoids & Carotenoids ( Vitamin A ) Cholesterol Bile Acids Glycero - phospholipids Glycerolipids Acyl - CoA Fatty Acids Glyco - sphingolipids Sphingolipids Waxes Polyunsaturated Fatty Acids Neurotransmitters & Thyroid Hormones Steroids Endo - cannabinoids Eicosanoids Major metabolic pathways in metro - style map. Click any text ( name of pathway or metabolites ) to link to the corresponding article. Single lines : pathways common to most lifeforms. Double lines : pathways not in humans ( occurs in e.g. plants, fungi, prokaryotes ). Orange nodes : carbohydrate metabolism. Violet nodes : photosynthesis. Red nodes : cellular respiration. Pink nodes : cell signaling. Blue nodes : amino acid metabolism. Grey nodes : vitamin and cofactor metabolism. Brown nodes : nucleotide and protein metabolism. Green nodes : lipid metabolism. GND : 4129537 - 7 NDL : 00562847 Metabolism portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Fermentation&oldid=842802457 '' Categories : Fermentation Anaerobic digestion Oenology Fermented drinks Brewing Food science Metabolism Food preservation Alchemical processes Mycology Catalysis Hidden categories : Webarchive template wayback links Pages using div col without cols and colwidth parameters Wikipedia articles with GND identifiers Talk Contents About Wikipedia Wikibooks Alemannisch Asturianu বাংলা Bân - lâm - gú Беларуская Български Bosanski Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Gàidhlig Galego 한국어 Հայերեն हिन्दी Hrvatski Ido Bahasa Indonesia Íslenska Italiano עברית Basa Jawa Қазақша Latviešu Lietuvių Magyar Македонски Bahasa Melayu Mìng - dĕ̤ng - ngṳ̄ မြန်မာဘာသာ Nederlands 日本 語 Norsk Norsk nynorsk Oʻzbekcha / ўзбекча Piemontèis Polski Português Runa Simi Русский Саха тыла Shqip Sicilianu Simple English Slovenščina Ślůnski Soomaaliga Српски / srpski Srpskohrvatski / српскохрватски Basa Sunda Suomi Svenska Tagalog தமிழ் ไทย Türkçe Українська Vèneto Tiếng Việt 粵語 中文 62 more Edit links This page was last edited on 24 May 2018, at 19 : 15. 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Question: what type of gas is produced during fermentation
Answer: hydrogen gas (H2)