Difference between revisions of "Fermentation" - New World Encyclopedia

Latest revision as of 06:53, 2 April 2008

In biochemistry, fermentation is an enzyme-catalyzed, energy-generating process in which organic compounds act as both donors and acceptors of electrons. Fermentation can occur in the absence of oxygen, and the term is sometimes defined as the pathway in cells by which fuel molecules are broken down anaerobically.

Sugars are the common substrate of fermentation, and typical examples of fermentation products are ethanol, lactic acid, and hydrogen. However, more exotic compounds can be produced, such as butyric acid and acetone.

Glycolysis is an important type of fermentation that is common to muscle cells, yeast, some bacteria, and plants. In glycolysis, the six-carbon sugar glucose (Glc) is oxidized to two molecules of pyruvic acid (Pyr), yielding a small net gain of chemical energy (ATP) to power cellular function. In the absence of oxygen, there are two main pathways for the pyruvate end-product:

Ethanol fermentation (performed by yeast and some types of bacteria) breaks the pyruvate down into ethanol and carbon dioxide. Yeast famously carries out the fermentation that produces ethanol in beer, wine, and other alcoholic beverages.
Lactic acid fermentation breaks down the pyruvate into lactic acid. It occurs in some bacteria and fungi. For example, in the production of yogurt, bacteria convert lactose into lactic acid, giving yogurt its sour taste. In vertebrates, during periods of intense exercise, cellular respiration may deplete oxygen in the muscles faster than it can be replenished. The shift to glycolysis produces lactic acid.

In an industrial context, the term fermentation is used more broadly to refer to the bulk growth of microorganisms on a growth medium. There are many microbiological processes that occur in the presence of air (aerobically) while yielding incomplete oxidation products. Examples include the formation of acetic acid (vinegar) from alcohol by vinegar bacteria, and of citric acid from sugar by certain molds (such as Aspergillus niger). These microbial processes have gained industrial importance, and are often referred to as fermentations, although they do not conform to Louis Pasteur's concept of fermentation as a decomposition in the absence of air.

People have devised innumerable ways to utilize fermentation to produce food and drinks, creating such products as beer, wine, cheese, yogurt, sauerkraut, miso, soy sauce, kimchi, and so forth.

Fermentation is thought to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere; thus, it would represent a more ancient form of energy production in cells than aerobic respiration.

Fermentation in biochemistry

Reactions

The reactions of fermentation vary according to the fuel molecule and end-product involved. In the chemical equation below, the sugar is glucose (C₆H₁₂O₆), and the end-product is ethanol (2C₂H₅OH):

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP (Energy Released:118 kJ mol⁻¹)

The equation can be written verbally as follows:

Sugar (glucose, fructose, or sucrose) → Alcohol (ethanol) + Carbon Dioxide + Energy (ATP)

Energy yield

In its strictest sense, fermentation is the anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation does not release all the available energy in a molecule; it merely allows glycolysis (a process that yields two ATP per glucose) to continue by replenishing reduced coenzymes.

Fermentation products contain chemical energy (i.e., they are not fully oxidized), but they are considered waste products since they cannot be metabolized further without the use of oxygen (or other more highly-oxidized electron acceptors). A consequence is that the production of ATP by fermentation is less efficient than oxidative phosphorylation, where pyruvate is fully oxidized to carbon dioxide. Fermentation produces two ATP molecules per molecule of glucose compared to approximately 36 ATP yielded by aerobic respiration.

Although human metabolism is primarily aerobic, in the partial or complete absence of oxygen (for example, in overworked muscles that are starved of oxygen or in infarcted heart muscle cells), pyruvate can be converted to the waste product lactate, donating its hydrogen to pyruvate. This reaction, which is an example of a fermentation, is a solution to maintaining the metabolic flux through glycolysis in the absence of oxygen or when oxygen levels are low. While fermentation is helpful during short, intense periods of exertion, it is not sustained over extended periods in complex aerobic organisms. In humans, for example, lactic acid fermentation provides energy for a period ranging from 30 seconds to 2 minutes.

The final step of fermentation, the conversion of pyruvate to an end-product, does not produce energy. However, it is critical for an anaerobic cell since it regenerates nicotinamide adenine dinucleotide (NAD⁺), which is required to sustain the flow through the glycolytic pathway in anaerobic conditions.

Products

There are several types of fermentations in which pyruvate and NADH are anaerobically metabolized to yield any of a variety of products, with an organic molecule acting as the final hydrogen acceptor. For example, the bacteria involved in making yogurt simply reduce pyruvate to lactic acid. In organisms such as brewers' yeast, a carboxyl group is first removed from pyruvate to form acetaldehyde and carbon dioxide; the acetaldehyde is then reduced to yield ethanol and NAD⁺. Anaerobic bacteria are capable of using a wide variety of compounds other than oxygen as terminal electron acceptors.

Vinegar (acetic acid) is the direct result of bacterial metabolism. (Bacteria need oxygen to convert the ethanol to acetic acid.) In milk, the acid coagulates the casein, producing curds. In pickling, the acid preserves the food from pathogenic and putrefactive bacteria.

Fermentation in food production

Grapes covered in yeast growth observable as a white film, also known as the blush.

Fermentation in food production typically refers to the conversion of sugar to alcohol using yeast under anaerobic conditions. A more general definition of fermentation is the chemical conversion of carbohydrates into alcohols or acids. Fermentation is used to produce wine, beer, and vinegar. It is also employed in food preservation to create lactic acid in sour foods, such as pickled cucumbers, kimchi, and yogurt. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt.

According to Steinkraus (1995), food fermentation serves 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, essential fatty acids, and vitamins.
Detoxification during food-fermentation processing.
A decrease in cooking times and fuel requirements.

Food can be preserved by fermentation, since fermentation can make conditions unsuitable for undesirable microorganisms. For example, in pickling, the acid produced by the dominant bacteria inhibit the growth of other microorganisms.

Relation to advances in biochemistry

Although the biochemistry of fermentation was fully elaborated only in the twentieth century, alcoholic fermentation has been practiced since antiquity. By 1500 B.C.E., the production of beer from germinating cereals (malt) and the preparation of wines from crushed grapes were established practices in a large part of the Middle East. The scientific discipline of biochemistry, particularly the study of enzymes, has emerged in part from an earlier interest in food and beverage production. One of the earliest laboratories established for the study of biochemistry was the Carlsberg Laboratory founded in Copenhagen in 1875 and financed by the brewing family of Jacob Christian Jacobsen. The species of yeast used to make pale lager (Saccharomyces carlsbergensis) was isolated at the Laboratory and named after it. The concept of pH was also developed there, and its members made significant contributions to the study of protein chemistry.

History

Louis Pasteur in his laboratory. Painting by Albert Edelfelt (1885).

French chemist Louis Pasteur was the first zymologist (an early term for a scientist who studies fermentation) when in 1857 he connected yeast to the process of fermentation. Pasteur demonstrated that fermentation is caused by the growth of microorganisms, and that the growth of microorganisms in nutrient broths is not due to spontaneous generation (a theory which held that complex, living organisms can be generated from decaying organic substances).

In the nineteenth century, Pasteur used the term fermentation in a narrow sense to describe the changes brought about by yeasts and other microorganisms growing in the absence of air (anaerobically); he also recognized that ethyl alcohol and carbon dioxide are not the only products of fermentation. Pasteur originally defined fermentation as respiration without air. After performing careful research, he 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."

The German Eduard Buchner, winner of the 1907 Nobel Prize in chemistry, later determined that fermentation was actually caused by a yeast secretion that he termed zymase. The experiment for which Buchner won the Nobel Prize consisted of producing a cell-free extract of yeast cells and showing that this "press juice" could ferment sugar. This finding dealt yet another blow to vitalism by demonstrating for the first time that fermentation could occur outside living cells.

In the 1920s, scientists discovered that, in the absence of air, extracts of muscle catalyze the formation of lactate from glucose; in addition, they learned that the same intermediate compounds formed in the fermentation of grain are produced by muscle. This discovery revealed an underlying unity in biochemistry: fermentation reactions are not peculiar to the action of yeast but also occur in many other instances of glucose utilization. The elucidation of the glycolytic pathway in the early decades of the twentieth century involved the pioneering efforts of Gustav Embden, Otto Meyerhof, Carl Neuberg, Jacob Parnas, Otto Warburg, and Gerty and Carl Cori.

References
ISBN links support NWE through referral fees

Bamforth, C. W. 2005. Food, Fermentation, and Microorganisms. Oxford: Blackwell Science. ISBN 0632059877.
Steinkraus, K. H. (ed.). 1995. Handbook of Indigenous Fermented Foods. New York, NY: Marcel Dekker, Inc. ISBN 0824793528.
Stryer, L. 1995. Biochemistry, 4th edition. New York, NY: W.H. Freeman. ISBN 0716720094.

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History of "Fermentation"

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@@ Line 1: / Line 1: @@
-{{Claimed}}{{Contracted}}
+{{Ebapproved}}{{Paid}}{{Approved}}{{Images OK}}{{Submitted}}{{Copyedited}}
-[[Image:Fermenting.jpg|thumb|right|Fermentation in progress]]
+In [[biochemistry]], '''fermentation''' is an [[enzyme]]-catalyzed, energy-generating process in which organic compounds act as both donors and acceptors of [[electron]]s. Fermentation can occur in the absence of [[oxygen]], and the term is sometimes defined as the pathway in [[cell (biology)|cells]] by which fuel molecules are broken down ''anaerobically''.
-'''Fermentation''' is a process of energy production in a [[Cell (biology)|cell]] in an [[anaerobic]] environment (with no oxygen present). In common usage fermentation is a type of [[anaerobic respiration]], however a more strict definition exists which defines fermentation as [[Cellular_respiration|respiration]] in an anaerobic environment with no external [[electron acceptor]].
-Sugars are the common substrate of fermentation, and typical examples of fermentation products are [[ethanol]], [[lactic acid]], and [[hydrogen]]. However, more exotic compounds can be produced by fermentation, such as [[butyric acid]] and [[acetone]]. [[Yeast]] famously carries out [[fermentation (food)|fermentation]] in the production of [[ethanol]] in [[beer]]s, [[wine]]s and other alcoholic drinks, along with the production of large quantities of [[carbon dioxide]]. Anaerobic respiration in [[mammal|mammalian]] [[muscle]] under periods of intense exercise (which has no external electron acceptor) is, under the strict definition, a type of fermentation.<!---innappropriate content, converges this article with [[Fermentation (food)]]:"== Common Example ==
+[[Sugar]]s are the common substrate of fermentation, and typical examples of fermentation products are [[ethanol]], [[lactic acid]], and [[hydrogen]]. However, more exotic compounds can be produced, such as [[butyric acid]] and [[acetone]].
-Fermentation can be simply defined, in this context, as the conversion of [[sugar]] molecules, into [[ethanol]] and [[carbon dioxide]] by [[yeast]].
+[[Glycolysis]] is an important type of fermentation that is common to [[muscle]] cells, [[yeast]], some [[bacteria]], and [[plant]]s. In glycolysis, the six-carbon sugar [[Glucose|glucose (Glc)]] is oxidized to two molecules of pyruvic acid (Pyr), yielding a small net gain of chemical energy ([[ATP]]) to power cellular function. In the absence of oxygen, there are two main pathways for the pyruvate end-product:
+* Ethanol fermentation (performed by yeast and some types of bacteria) breaks the pyruvate down into ethanol and carbon dioxide. Yeast famously carries out the fermentation that produces ethanol in [[beer]], [[wine]], and other alcoholic beverages.
+* Lactic acid fermentation breaks down the pyruvate into lactic acid. It occurs in some bacteria and [[fungi]]. For example, in the production of [[yogurt]], bacteria convert [[lactose]] into lactic acid, giving yogurt its sour taste. In [[vertebrate]]s, during periods of intense exercise, cellular respiration may deplete oxygen in the [[muscle]]s faster than it can be replenished. The shift to glycolysis produces lactic acid.
-:::C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> → 2C<sub>2</sub>H<sub>5</sub>OH + 2CO<sub>2</sub>" --->
+In an industrial context, the term ''fermentation'' is used more broadly to refer to the bulk growth of [[microorganism]]s on a growth medium. There are many microbiological processes that occur in the presence of air ''(aerobically)'' while yielding incomplete oxidation products. Examples include the formation of acetic acid ([[vinegar]]) from alcohol by vinegar bacteria, and of citric acid from sugar by certain [[mold]]s (such as ''Aspergillus niger''). These microbial processes have gained industrial importance, and are often referred to as fermentations, although they do not conform to [[Louis Pasteur]]'s concept of fermentation as a decomposition in the absence of air.
-==History==
-[[France|French]] chemist [[Louis Pasteur]] was the first [[zymologist]], when in [[1857]] 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."''.
+People have devised innumerable ways to utilize fermentation to produce food and drinks, creating such products as beer, wine, [[cheese]], yogurt, [[sauerkraut]], [[miso]], [[soy sauce]], [[kimchi]], and so forth.
-The [[Germany|German]] [[Eduard Buchner]], winner of the [[1907]] [[Nobel Prize]] in chemistry, later determined that fermentation was actually caused by a yeast secretion that he termed ''[[zymase]]''.
+Fermentation is thought to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere; thus, it would represent a more ancient form of energy production in cells than [[aerobic respiration]].
-The research efforts undertaken by the [[Denmark|Danish]] [[Carlsberg]] scientists greatly accelerated the gain of knowledge about yeast and brewing. The Carlsberg scientists are generally acknowledged with jump-starting the entire field of [[molecular biology]].
+==Fermentation in biochemistry==
+===Reactions===
+The reactions of fermentation vary according to the fuel molecule and end-product involved. In the chemical equation below, the sugar is [[glucose]] (C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>), and the end-product is [[ethanol]] (2C<sub>2</sub>H<sub>5</sub>OH):
-== Reaction ==
-{{seealso|glycolysis}}
-The reaction of fermentation differs according to the sugar being used and the product produced. Below the sugar will be [[glucose]] (C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>) the simplest sugar, and the product will be [[ethanol]] (2C<sub>2</sub>H<sub>5</sub>OH). This is one of the fermentation reactions carried out by yeast, and is used in food production.
-'''Chemical Equation'''
 :::C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> → 2C<sub>2</sub>H<sub>5</sub>OH + 2CO<sub>2</sub> + 2 ATP (Energy Released:118&nbsp;kJ mol<sup>&minus;1</sup>)
-'''Word Equation'''
+The equation can be written verbally as follows:
 :::Sugar (glucose, fructose, or sucrose) → Alcohol (ethanol) + Carbon Dioxide + Energy (ATP)
-The actual [[biochemical pathway]] the reaction takes varies depending on the sugars involved, but commonly involves part of the [[glycolysis]] pathway, which is shared with the early stages of [[aerobic respiration]] in most organisms. The later stages of the pathway vary considerably depending on the final product.
+===Energy yield===
+In its strictest sense, ''fermentation'' is the anaerobic [[metabolism|metabolic]] breakdown of a nutrient molecule, such as [[glucose]], without net oxidation. Fermentation does not release all the available energy in a molecule; it merely allows [[glycolysis]] (a process that yields two [[ATP]] per glucose) to continue by replenishing reduced [[coenzyme]]s.
-==Energy source in anaerobic conditions==
-Fermentation is thought to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere and thus would represent a more ancient form of energy production in cells.
-Fermentation products contain chemical energy (they are not fully oxidized) but are considered waste products since they cannot be metabolised further without the use of oxygen (or other more highly-oxidized electron acceptors). A consequence is that the production of ATP by fermentation is less efficient than oxidative phosphorylation, where pyruvate is fully oxidized to carbon dioxide. Fermentation produces two ATP molecules per molecule of glucose compared to approximately 36 by [[aerobic respiration]].
-[[Aerobic glycolysis]] is a method employed by muscle cells for the production of lower-intensity energy over a longer period of time when oxygen is plentiful.  Under low-oxygen conditions, however, vertebrates use the less-efficient but faster ''anaerobic glycolysis'' to produce ATP.  The speed at which ATP is produced is about 100 times that of [[oxidative phosphorylation]].{{fact}}  While fermentation is helpful during short, intense periods of exertion, it is not sustained over extended periods in complex aerobic organisms. In humans, for example, lactic acid fermentation provides energy for a period ranging from 30 seconds to 2 minutes.
-The final step of fermentation, the conversion of pyruvate to fermentation end-products, does not produce energy. However, it is critical for an anaerobic cell since it regenerates nicotinamide adenine dinucleotide ([[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]]), which is required for glycolysis. This is important for normal cellular function, as glycolysis is the only source of ATP in anaerobic conditions.
-== Products ==
-Products produced by fermentation are actually waste products produced during the reduction of pyruvate to regenerate NAD+ in the absence of oxygen. Bacteria generally produce acids. Vinegar ([[acetic acid]]) is the direct result of bacterial metabolism (Bacteria need oxygen to convert the alcohol to acetic acid). In milk, the acid coagulates the [[casein]], producing curds. In pickling, the acid preserves the food from pathogenic and putrefactive bacteria.
-When yeast ferments, it breaks down the [[glucose]] (C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>) into exactly two molecules of [[ethanol]] (C<sub>2</sub>H<sub>6</sub>O) and two molecules of [[carbon dioxide]] (CO<sub>2</sub>).
-* [[Ethanol fermentation]] (performed by [[yeast]] and some types of [[bacterium|bacteria]]) breaks the pyruvate down into ethanol and carbon dioxide. It is important in [[bread]]-making, [[brewing]], and [[wine]]-making. When the ferment has a high concentration of [[pectin]], minute quantities of [[methanol]] can be produced. Usually only one of the products is desired; in bread the alcohol is baked out, and in alcohol production the carbon dioxide is released into the atmosphere.
-* [[Lactic acid fermentation]] breaks down the pyruvate into [[lactic acid]]. It occurs in the muscles of animals when they need energy faster than the [[blood]] can supply oxygen. It also occurs in some [[bacterium|bacteria]] and some [[fungi]]. It is this type of bacteria that convert [[lactose]] into lactic acid in [[yogurt]], giving it its sour taste.
-In vertebrates, during intense exercise, [[cellular respiration]] will deplete oxygen in the muscles faster than it can be replenished. An associated burning sensation in muscles has been attributed [[lactic acid]] causing a decrease in the pH during a shift to '''anaerobic glycolysis'''. While this does partially explain [[acute muscle soreness]], lactic acid may also help delay muscle fatigue{{fact}}, although, eventually the lower pH will inhibit enzymes involved in glycolysis.{{fact}} Contrary to currently popular belief, the lactic acid is not the primary causes for the drop in pH, but rather ATP-derived hydrogen ions.{{fact}}
-[[Delayed onset muscle soreness]] cannot be attributed to the lactic acid and other waste products as they are quickly removed after exercise. It is actually due to [[microtrauma]] of the [[muscle fibres]]. Eventually the [[liver]] metabolises the lactic acid back to pyruvate. So do a bunch of stuff on decomposition reactions, organic chemistry, chemical nomenclature, and acidity and basicity
-==Fermentation (Food)==
-[[Image:MM ferment.jpg|thumb|right|250px|Yeast fermenting the wort at [[Maker's Mark]] distillery, a step in the production of a [[distilled beverage]].]]
+Fermentation products contain chemical energy (i.e., they are not fully oxidized), but they are considered waste products since they cannot be metabolized further without the use of oxygen (or other more highly-oxidized electron acceptors). A consequence is that the production of ATP by fermentation is less efficient than [[oxidative phosphorylation]], where [[pyruvate]] is fully oxidized to carbon dioxide. Fermentation produces two ATP molecules per molecule of glucose compared to approximately 36 ATP yielded by [[aerobic respiration]].
-'''Fermentation''' typically refers to the conversion of [[sugar]] to [[alcohol]] using [[yeast]] under anaerobic conditions. A more general definition of fermentation is the chemical conversion of carbohydrates into alcohols or acids. The science of fermentation is known as '''zymology'''.
-The process is used to produce [[wine]], [[beer]], and [[vinegar]], but fermentation is also employed in preservation to create [[lactic acid]] in sour [[food]]s such as [[pickled cucumber]]s, [[kimchi]] and [[yoghurt|yogurt]].
+Although [[human]] metabolism is primarily aerobic, in the partial or complete absence of oxygen (for example, in overworked muscles that are starved of oxygen or in infarcted heart muscle cells), pyruvate can be converted to the waste product [[lactic acid|lactate]], donating its hydrogen to pyruvate. This reaction, which is an example of a fermentation, is a solution to maintaining the metabolic flux through glycolysis in the absence of oxygen or when oxygen levels are low. While fermentation is helpful during short, intense periods of exertion, it is not sustained over extended periods in complex aerobic organisms. In humans, for example, lactic acid fermentation provides energy for a period ranging from 30 seconds to 2 minutes.
-== History ==
+The final step of fermentation, the conversion of pyruvate to an end-product, does not produce energy. However, it is critical for an anaerobic cell since it regenerates nicotinamide adenine dinucleotide ([[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]]), which is required to sustain the flow through the glycolytic pathway in anaerobic conditions.
-{{Seealso|History of beer|Brewing}}
-{{unreferenced|section|date=January 2007}}
-Since fruits ferment naturally, fermentation precedes human history. Since prehistoric times, however, humans have been taking control of the fermentation process. The earliest evidence of winemaking dates from 6000 B.C.E., in [[Georgia (country)|Georgia]], the former Soviet Republic.<ref name=Ref1>http://www.stonepages.com/news/archives/000498.html</ref> 7000 year old jars of [[wine]] have been excavated in the [[Zagros Mountains]], which are now on display at the [[University of Pennsylvania]].<ref name=Ref2> http://www.museum.upenn.edu/new/research/Exp_Rese_Disc/NearEast/wine.shtml</ref> There is strong evidence that people were fermenting beverages in [[Babylon]] circa [[5000 B.C.E.]],{{cn}} [[ancient Egypt]] circa [[3000 B.C.E.]],{{cn}} pre-Hispanic Mexico circa [[2000 B.C.E.]],{{cn}} and [[Sudan]] circa [[1500 B.C.E.]].{{cn}} There is also evidence of leavened bread in [[ancient Egypt]] circa [[1500 B.C.E.]]{{cn}} and of milk fermentation in Babylon circa [[3000 B.C.E.]].{{cn}} The Chinese were probably the first to develop vegetable fermentation.{{cn}}
-[[France|French]] chemist [[Louis Pasteur]] was the first ''zymologist'', when in [[1857]] he connected yeast to fermentation. Pasteur originally defined fermentation as ''respiration without air''.
+=== Products ===
+There are several types of fermentations in which [[pyruvate]] and NADH are anaerobically metabolized to yield any of a variety of products, with an organic molecule acting as the final hydrogen acceptor. For example, the [[bacterium|bacteria]] involved in making yogurt simply reduce pyruvate to [[lactic acid]]. In organisms such as brewers' [[yeast]], a carboxyl group is first removed from pyruvate to form acetaldehyde and [[carbon dioxide]]; the acetaldehyde is then reduced to yield [[ethanol]] and NAD<sup>+</sup>. Anaerobic bacteria are capable of using a wide variety of compounds other than oxygen as terminal electron acceptors.
-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."''.
+[[Vinegar]] ([[acetic acid]]) is the direct result of bacterial metabolism. (Bacteria need oxygen to convert the ethanol to acetic acid.) In milk, the acid coagulates the [[casein]], producing curds. In pickling, the acid preserves the food from pathogenic and putrefactive bacteria.
-The [[Germany|German]] [[Eduard Buchner]], winner of the [[1907]] [[Nobel Prize]] in chemistry, later determined that fermentation was actually caused by a yeast secretion that he termed ''[[zymase]]''.
+==Fermentation in food production==
+[[Image:Yeast on grapes.jpg|thumb|left|250px|Grapes covered in yeast growth observable as a white film, also known as the ''blush''.]]
-The research efforts undertaken by the [[Denmark|Danish]] [[Carlsberg]] scientists greatly accelerated the gain of knowledge about yeast and brewing. The Carlsberg scientists are generally acknowledged with jump-starting the entire field of [[molecular biology]].{{cn}}
+Fermentation in food production typically refers to the conversion of [[sugar]] to [[alcohol]] using [[yeast]] under anaerobic conditions. A more general definition of fermentation is the chemical conversion of [[carbohydrate]]s into alcohols or acids. Fermentation is used to produce [[wine]], [[beer]], and [[vinegar]]. It is also employed in food preservation to create lactic acid in sour foods, such as pickled [[cucumber]]s, [[kimchi]], and [[yoghurt|yogurt]]. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as [[cheese]], pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt.
-== Uses ==
-The primary benefit of fermentation is the conversion of sugars and other [[carbohydrates]], e.g., converting [[juice]] into [[wine]], grains into [[beer]], carbohydrates into [[carbon dioxide]] to leaven [[bread]], and sugars in vegetables into preservative organic acids.
 According to Steinkraus (1995), food fermentation serves 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 fermentation]]s.
+#Preservation of substantial amounts of food through lactic acid, alcohol, [[acetic acid]], and alkaline fermentations.
-#Biological enrichment of food substrates with protein, essential [[amino acid]]s, essential [[fatty acid]]s, and vitamins.
+#Biological enrichment of food substrates with protein, essential [[amino acid]]s, essential [[fatty acid]]s, and [[vitamin]]s.
 #Detoxification during food-fermentation processing.
 #A decrease in cooking times and fuel requirements.
-Fermentation has some uses exclusive to foods. Fermentation can produce important [[nutrients]] or eliminate [[antinutrients]]. Food can be preserved by fermentation, since fermentation uses up food energy and can make conditions unsuitable for undesirable microorganisms. For example, in [[pickling]] the acid produced by the dominant bacteria inhibit the growth of all other microorganisms. Depending on the type of [[freeze distillation|fermentation]], some products (e.g., [[fusel alcohol]]) can be harmful to people's health.
+Food can be preserved by fermentation, since fermentation  can make conditions unsuitable for undesirable microorganisms. For example, in [[pickling]], the acid produced by the dominant bacteria inhibit the growth of other microorganisms.
-In [[alchemy]], fermentation is often the same as [[putrefaction]], meaning to allow the substance to naturally [[rot]] or [[decomposition|decompose]].
+===Relation to advances in biochemistry===
+Although the biochemistry of fermentation was fully elaborated only in the twentieth century, [[alcohol]]ic fermentation has been practiced since antiquity. By 1500 B.C.E., the production of beer from germinating cereals (malt) and the preparation of wines from crushed [[grape]]s were established practices in a large part of the [[Middle East]]. The scientific discipline of biochemistry, particularly the study of [[enzyme]]s, has emerged in part from an earlier interest in food and beverage production. One of the earliest laboratories established for the study of biochemistry was the Carlsberg Laboratory founded in Copenhagen in 1875 and financed by the brewing family of Jacob Christian Jacobsen. The [[species]] of yeast used to make [[pale lager]] ''(Saccharomyces carlsbergensis)'' was isolated at the Laboratory and named after it. The concept of [[pH]] was also developed there, and its members made significant contributions to the study of [[protein]] chemistry.
-== Fermented foods by region ==
+==History==
-* '''Worldwide:''' [[alcohol]], [[wine]], [[vinegar]], [[olives]], [[yogurt]], [[bread]]
+[[Image:Tableau Louis Pasteur.jpg|thumb|250px|Louis Pasteur in his laboratory. Painting by Albert Edelfelt (1885).]]
-* '''[[Asia]]'''
-** '''[[East Asia|East]] and [[Southeast Asia|Southeast]] Asia:''' [[amazake]], [[asinan]], [[bai-ming]], [[belacan]], [[burong mangga]], [[dalok]], [[doenjang]] (된장), [[douchi]], [[jeruk]], [[lambanog]], [[kimchi]] (김치), [[kombucha]], [[leppet-so]], [[Sushi#Narezushi_.28old_style_fermented_sushi.29|narezushi]], [[miang (food)|miang]], [[miso]], [[nata de coco]], [[nata de pina]], [[natto]], [[naw-mai-dong]], [[pak-siam-dong]], [[paw-tsaynob in snow]] (雪裡蕻), [[prahok]], [[sake]], [[seokbakji]], [[soy sauce]], [[stinky tofu]], [[szechwan cabbage]] (四川泡菜), [[tai-tan tsoi]], [[takuan]], [[Tape (fermented food)|tape]], [[tempeh]], [[totkal kimchi]], [[yen tsai]] (醃菜), [[zha cai]] (榨菜)
-** '''[[Central Asia]]:''' [[kumis]] (mare milk), [[kefir]], [[shubat]] (camel milk)
-** '''[[India]]:''' [[achar]], [[appam]], [[dosa]], [[dhokla]], [[dahi]], [[gundruk]], [[idli]], [[mixed pickle]]
-* '''[[Africa]]:''' [[garri]], [[hibiscus]] seed, hot pepper sauce, [[injera]], [[lamoun makbouss]], [[laxoox]], [[mauoloh]], [[msir]], [[mslalla]], [[oilseed]], [[Ogi (cereal ferment)|ogi]], [[ogili]], [[ogiri]]
-* '''[[Americas]]:''' [[cheese]], [[chicha]], [[elderberry wine]], [[kombucha]], [[pickling]] (pickled vegetables), [[sauerkraut]], [[lupin]] seed, [[oilseed]], [[chocolate]], [[vanilla]], [[Tabasco sauce|tabasco]], [[tibicos]]
-* '''[[Middle East]]:''' [[kushuk]], [[lamoun makbouss]], [[mekhalel]], [[torshi]],  [[boza]]
-* '''[[Europe]]:''' [[cheese]], [[rakfisk]], [[sauerkraut]], [[surströmming]], [[soured milk]] products such as [[Quark (food)|quark]], [[kefir]], [[filmjölk]], [[crème fraîche]], [[Smetana (cream)|smetana]], [[skyr]], [[mead]] [[elderberry wine]].
-* '''[[Oceania]]:''' [[Poi (food)|poi]], [[kaanga pirau (rotten corn)]]
-==Fermentation vs. putrefaction and rancidification==
+[[France|French]] chemist [[Louis Pasteur]] was the first zymologist (an early term for a scientist who studies fermentation) when in 1857 he connected [[yeast]] to the process of fermentation. Pasteur demonstrated that fermentation is caused by the growth of [[microorganism]]s, and that the growth of microorganisms in nutrient broths is not due to [[spontaneous generation]] (a theory which held that complex, living organisms can be generated from decaying organic substances).
-There are a number of animal-based foods from different parts of the world that are described as being "fermented." However, the term is erroneous when applied to such foods because fermentation properly means the decomposition of carbohydrates, and since animal tissues are composed of [[protein]]s and [[lipids]], and contain at most only traces of carbohydrates, the operative processes in the transformation undergone by these foods are actually [[putrefaction]] and [[rancidification]].
-The difference is more than technical since the end products of these processes are quite different from those of fermentation, and also because putrefied/rancidified foods are often dangerous for human consumption. For instance, [[Alaska]], despite its small population, witnesses more cases of [[botulism]] than any other U.S. state [http://www.phppo.cdc.gov/phtn/botulism/alaska/alaska.asp]. 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 decompose for an extended period of time before being consumed raw. The risk is exacerbated when a plastic container is used for this purpose instead of the old-fashioned method, a grass-lined hole, as the [[Clostridium botulinum|botulinum]] bacteria thrive in the anaerobic conditions created by the former method.
+In the nineteenth century, Pasteur used the term ''fermentation'' in a narrow sense to describe the changes brought about by yeasts and other microorganisms growing in the absence of air (anaerobically); he also recognized that ethyl alcohol and carbon dioxide are not the only products of fermentation. Pasteur originally defined fermentation as ''respiration without air''. After performing careful research, he 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."
-Other putrefied/rancidified foods include [[fish sauce]] from [[Southeast Asia]], [[Iceland|Icelandic]] [[hákarl]], [[Surströmming|fermented Baltic herring]] and certain speciality sausages from [[Sweden]], and [[Limburger]] cheese. Most putrefied/rancified foods are considered to have an exceptionally foul odor, but if the process of decomposition is allowed to reach completion, the smell is greatly diminished, as with some varieties of fish sauce.
+The [[Germany|German]] [[Eduard Buchner]], winner of the 1907 [[Nobel Prize]] in chemistry, later determined that fermentation was actually caused by a yeast secretion that he termed [[zymase]]. The experiment for which Buchner won the Nobel Prize consisted of producing a cell-free extract of [[yeast]] cells and showing that this "press juice" could ferment sugar. This finding dealt yet another blow to [[vitalism]] by demonstrating for the first time that fermentation could occur outside living cells.
-In its strictest sense, '''fermentation''' (formerly called '''zymosis''') is the anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation does not release all the available energy in a molecule; it merely allows [[glycolysis]] (a process that yields two ATP per glucose) to continue by replenishing reduced [[coenzyme]]s. Depending on which organism it is taking place in, fermentation may yield [[lactic acid|lactate]], [[acetic acid]], [[ethanol]], or other [[redox|reduced]] [[metabolite]]s. Yeast produces ethanol and CO<sub>2</sub>; human muscle (under anaerobic conditions) produces lactic acid.
+In the 1920s, scientists discovered that, in the absence of air, extracts of [[muscle]] catalyze the formation of lactate from [[glucose]]; in addition, they learned that the same intermediate compounds formed in the fermentation of grain are produced by muscle. This discovery revealed an underlying unity in biochemistry: fermentation reactions are not peculiar to the action of yeast but also occur in many other instances of glucose utilization. The elucidation of the glycolytic pathway in the early decades of the twentieth century involved the pioneering efforts of Gustav Embden, Otto Meyerhof, Carl Neuberg, Jacob Parnas, Otto Warburg, and Gerty and Carl Cori.
-'''Fermentation''' is also used much more broadly to refer to the bulk growth of [[microorganism]]s on a [[growth medium]]. No distinction is made between [[Cellular respiration|aerobic]] and [[Glycolysis|anaerobic]] metabolism when the word is used in this sense.
-Fermentation usually implies that the action of the microorganisms is desirable. Occasionally wines are enhanced through the process of [[cofermentation]]. When fermentation stops prior to complete conversion of sugar to alcohol, a [[stuck fermentation]] is said to have occurred.
+==Related Topics==
+=== Fermented foods by region ===
+* '''Worldwide:''' [[alcohol]], [[wine]], [[vinegar]], [[olive]]s, [[yogurt]], [[bread]]
+* '''[[Asia]]'''
+** '''East and Southeast Asia:''' amazake, asinan, bai-ming, belacan, burong mangga, dalok, doenjang (된장), douchi, jeruk, lambanog, [[kimchi]] (김치), kombucha, leppet-so, narezushi, miang, [[miso]], nata de coco, nata de pina, natto, naw-mai-dong, pak-siam-dong, paw-tsaynob in snow (雪裡蕻), prahok, [[sake]], [[seokbakji]], [[soy sauce]], stinky tofu, szechwan cabbage (四川泡菜), tai-tan tsoi, takuan, tape, [[tempeh]], totkal kimchi, yen tsai (醃菜), zha cai (榨菜)** '''Central Asia:''' kumis (mare milk), [[kefir]], [[shubat]] (camel milk)
+** '''[[India]]:''' achar, appam, dosa, dhokla, dahi, gundruk, idli, mixed pickle
+* '''[[Africa]]:''' garri, [[hibiscus]] seed, hot pepper sauce, injera, lamoun makbouss, laxoox, mauoloh, msir, mslalla, oilseed, ogi, ogili, ogiri
+* '''[[Americas]]:''' [[cheese]], chicha, [[elderberry wine]], kombucha, [[pickling]] (pickled vegetables), [[sauerkraut]], [[lupin]] seed, [[oilseed]], [[chocolate]], [[vanilla]], [[Tabasco sauce|tabasco]], tibicos
+* '''[[Middle East]]:''' kushuk, lamoun makbouss, mekhalel, torshi, boza
+* '''[[Europe]]:''' [[cheese]], rakfisk, [[sauerkraut]], surströmming, soured milk products such as quark, [[kefir]], filmjölk, crème fraîche, smetana, skyr, mead [[elderberry wine]].
+* '''[[Oceania]]:''' [[Poi (food)|poi]], [[kaanga pirau (rotten corn)]]
 == References ==
-* Steinkraus, K. H., Ed. (1995). Handbook of Indigenous Fermented Foods. New York, Marcel Dekker, Inc.
-* The 1811 ''Household Cyclopedia''
+* Bamforth, C. W. 2005. ''Food, Fermentation, and Microorganisms''. Oxford: Blackwell Science. ISBN 0632059877.
+* Steinkraus, K. H. (ed.). 1995. ''Handbook of Indigenous Fermented Foods''. New York, NY: Marcel Dekker, Inc. ISBN 0824793528.
+* Stryer, L. 1995. ''Biochemistry,'' 4th edition. New York, NY: W.H. Freeman. ISBN 0716720094.
-{{credit2|Fermentation_(biochemistry)101030396|Fermentation_(food)|101230254}}
+{{credit2|Fermentation_(biochemistry)|101030396|Fermentation_(food)|101230254|Yeast|135916410|Louis_Pasteur|136056452|Germ_theory_of_disease|132942193|Abiogenesis|135908114}}
+[[Category:Life sciences]]
+[[Category:Biochemistry]]