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Ethanol fermentation, also called alcoholic fermentation, is a
biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, propert ...
which converts
sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose and fructose. Simple sugars, ...

sugar
s such as
glucose Glucose is a simple sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose and ...

glucose
,
fructose Fructose, or fruit sugar, is a simple ketonic simple sugar found in many plants, where it is often bonded to glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the most abundant monosac ...

fructose
, and
sucrose Sucrose is a type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose a ...

sucrose
into cellular energy, producing
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), o ...

ethanol
and
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

carbon dioxide
as by-products. Because
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are esti ...

yeast
s perform this conversion in the absence of
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
, alcoholic
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The mo ...

fermentation
is considered an
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic adh ...

anaerobic
process. It also takes place in some species of fish (including
goldfish The goldfish (''Carassius auratus'') is a freshwater fish in the Family (biology), family Cyprinidae of Order (biology), order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular List of freshwater aqu ...

goldfish
and
carp Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. They f ...
) where (along with lactic acid fermentation) it provides energy when oxygen is scarce. Ethanol fermentation has many uses including
alcoholic beverage An alcoholic drink is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, o ...
and
ethanol fuel Ethanol fuel is ethyl alcohol, the same type of alcohol File:Alcohol general.svg, upright=0.8, The bond angle between a hydroxyl group (-OH) and a chain of carbon atoms (R) In chemistry, alcohol is an organic compound that carries at least ...
production, and
bread Bread is a staple food prepared from a dough of flour and water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, wh ...
dough rising.


Biochemical process of fermentation of sucrose

The
chemical equation A chemical equation is the symbolic representation of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is ...
s below summarize the fermentation of sucrose (C12H22O11) into ethanol (C2H5OH). Alcoholic fermentation converts one
mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpidae ...
of
glucose Glucose is a simple sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose and ...

glucose
into two moles of ethanol and two moles of carbon dioxide, producing two moles of
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...
in the process. :C6H12O6 → 2 C2H5OH + 2 CO2
Sucrose Sucrose is a type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose a ...

Sucrose
is a sugar composed of a glucose linked to a fructose. In the first step of alcoholic fermentation, the enzyme
invertase Invertase is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme con ...
cleaves the
glycosidic linkage A glycosidic bond or glycosidic linkage is a type of covalent bond A covalent bond is a chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may ...
between the glucose and fructose molecules. :C12H22O11 + H2O + invertase → 2 C6H12O6 Next, each glucose molecule is broken down into two
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
molecules in a process known as
glycolysis Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO−, and a hydrogen ion, H+. The Thermodynamic free energy, free energy released in this process is used to form the high-energy molecules ATP (adenosine tri ...

glycolysis
. Glycolysis is summarized by the equation: :C6H12O6 + 2 ADP + 2 Pi + 2 NAD+ → 2 CH3COCOO + 2 ATP + 2 NADH + 2 H2O + 2 H+ CH3COCOO is pyruvate, and Pi is inorganic
phosphate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they un ...

phosphate
. Finally, pyruvate is converted to ethanol and CO2 in two steps, regenerating oxidized NAD+ needed for glycolysis: :1. CH3COCOO + H+ → CH3CHO + CO2 catalyzed by
pyruvate decarboxylase Pyruvate decarboxylase is a homotetrameric enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), s ...
:2. CH3CHO + NADH + H+ → C2H5OH + NAD+ This reaction is catalyzed by
alcohol dehydrogenase Alcohol dehydrogenases (ADH) () are a group of dehydrogenase A dehydrogenase is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may ...

alcohol dehydrogenase
(ADH1 in baker's yeast). As shown by the reaction equation, glycolysis causes the reduction of two molecules of NAD+ to
NADH Nicotinamide adenine dinucleotide (NAD) is a Cofactor (biochemistry), coenzyme central to metabolism. Found in all living cell (biology), cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate ...
. Two ADP molecules are also converted to two ATP and two water molecules via
substrate-level phosphorylation Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP or GTP by the transfer of a phosphate group from a substrate directly to ADP or GDP. Transferring from a higher energy (whether phosphate group attached ...
.


Related processes

Fermentation of sugar to ethanol and can also be done by '' Zymomonas mobilis'', however the path is slightly different since formation of pyruvate does not happen by glycolysis but instead by the
Entner–Doudoroff pathway 200px, Diagram of the Entner-Doudoroff pathway (KDPG: 2-keto-3-deoxy-6-phosphogluconate) The Entner-Doudoroff Pathway (ED Pathway) is a metabolic pathway that is most notably in Gram-negative bacteria, certain Gram-positive bacteria and archaea. G ...

Entner–Doudoroff pathway
. Other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties ...
s can produce ethanol from sugars by fermentation but often only as a side product. Examples are *
Heterolactic acid fermentation
Heterolactic acid fermentation
in which
Leuconostoc ''Leuconostoc'' is a genus of gram-positive bacterium, bacteria, placed within the family of Leuconostocaceae. They are generally ovoid cocci often forming chains. ''Leuconostoc'' spp. are intrinsically resistant to vancomycin and are catalase-ne ...
bacteria produce lactate + ethanol + *
Mixed acid fermentation Mixed acid fermentation is the biological process by which a six-carbon sugar e.g. glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the most abundant monosaccharide, a subcategory of car ...
where
Escherichia ''Escherichia'' is a genus of Gram-negative, non-Endospore, spore-forming, Facultative anaerobic organism, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastrointest ...
produce ethanol mixed with lactate, acetate, succinate, formate, , and H2 * 2,3-butanediol fermentation by
Enterobacter ''Enterobacter'' is a genus of common Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized by their cell e ...
producing ethanol, butanediol, lactate, formate, , and H2


Gallery

Image:Mthomebrew must.JPG, Grapes fermenting during wine production. Image:Alpha-D-Glucopyranose.svg,
Glucose Glucose is a simple sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to sucrose, a disaccharide composed of glucose and ...

Glucose
depicted in
Haworth projection 275px, Haworth projection of the structures for α-D-glucopyranose and L-Glucose, α-L-glucopyranose. A Haworth projection is a common way of writing a structural formula to represent the cyclic molecular geometry, structure of monosaccharides with ...
Image:Pyruvate.png,
Pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

Pyruvate
Image:Acetaldehyde-2D-flat.svg,
Acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
Image:Ethanol-structure.svg,
Ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), o ...

Ethanol


Effect of oxygen

Fermentation does not require oxygen. If oxygen is present, some species of yeast (e.g., ''
Kluyveromyces lactis ''Kluyveromyces lactis'' is a '' Kluyveromyces'' yeast commonly used for genetics, genetic studies and industrial applications. Its name comes from the ability to assimilate lactose and convert it into lactic acid. ''Kluyveromyces lactis'' (forme ...
'' or '' Kluyveromyces lipolytica'') will oxidize
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
completely to carbon dioxide and water in a process called
cellular respiration upright=2.5, Typical eukaryotic cell Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities ...

cellular respiration
, hence these species of yeast will produce ethanol only in an anaerobic environment (not cellular respiration). This phenomenon is known as the
Pasteur effect The Pasteur effect is an inhibiting effect of oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly C ...
. However, many yeasts such as the commonly used baker's yeast ''
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been originally isolated from the skin of ...

Saccharomyces cerevisiae
'' or fission yeast ''
Schizosaccharomyces pombe ''Schizosaccharomyces pombe'', also called "fission yeast", is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species i ...
'' under certain conditions, ferment rather than respire even in the presence of oxygen. In wine making this is known as the counter-Pasteur effect. These yeasts will produce ethanol even under
aerobic Aerobic means "requiring Earth's atmosphere, air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Cellular respiration#Aerobic r ...
conditions, if they are provided with the right kind of nutrition. During batch fermentation, the rate of ethanol production per milligram of cell protein is maximal for a brief period early in this process and declines progressively as ethanol accumulates in the surrounding broth. Studies demonstrate that the removal of this accumulated ethanol does not immediately restore fermentative activity, and they provide evidence that the decline in metabolic rate is due to physiological changes (including possible ethanol damage) rather than to the presence of ethanol. Several potential causes for the decline in fermentative activity have been investigated. Viability remained at or above 90%, internal pH remained near neutrality, and the specific activities of the glycolytic and alcohologenic enzymes (measured in vitro) remained high throughout batch fermentation. None of these factors appears to be causally related to the fall in fermentative activity during batch fermentation.


Bread baking

The formation of carbon dioxide – a byproduct of ethanol fermentation – causes bread to rise. Ethanol fermentation causes bread dough to rise. Yeast organisms consume sugars in the dough and produce ethanol and carbon dioxide as waste products. The carbon dioxide forms bubbles in the dough, expanding it to a foam. Less than 2% ethanol remains after baking.


Alcoholic beverages

All ethanol contained in
alcoholic beverage An alcoholic drink is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, o ...
s (including ethanol produced by
carbonic maceration Carbonic maceration is a winemaking technique, often associated with the French wine region of Beaujolais, in which whole grapes A grape is a fruit, botanically a berry (botany), berry, of the deciduous woody vines of the flowering plant gen ...
) is produced by means of fermentation induced by yeast. *
Wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different v ...

Wine
is produced by fermentation of the natural sugars present in grapes;
cider Cider ( ) is an alcoholic beverage An alcoholic drink is a drink that contains ethanol, a type of alcohol produced by Ethanol fermentation, fermentation of grains, fruits, or other sources of sugar. The consumption of alcohol plays an import ...
and
perry upA traditional perry (''poiré'' in French) bottled under cork and cage from Normandy Perry is an alcoholic beverage An alcoholic drink is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid ...

perry
are produced by similar fermentation of natural sugar in
apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wher ...
s and
pear Pears are fruits produced and consumed around the world, growing on a tree and harvested in the Northern Hemisphere in late summer into October. The pear tree and shrub are a species In biology Biology is the natural science that stu ...

pear
s, respectively; and other
fruit wine Fruit wines are fermented alcoholic beverage An alcoholic drink is a drink that contains ethanol, a type of alcohol produced by Ethanol fermentation, fermentation of grains, fruits, or other sources of sugar. The consumption of alcohol plays an ...
s are produced from the fermentation of the sugars in any other kinds of fruit.
Brandy Brandy is a liquor produced by Distillation, distilling wine. Brandy generally contains 35–60% alcohol by volume (70–120 alcohol proof, US proof) and is typically consumed as an Apéritif and digestif, after-dinner digestif. Some brandies ar ...
and eaux de vie (e.g.
slivovitz Slivovitz, slivovitza, slivovitsa, sliboviță, šljivovica, śliwowica, Schlivowitz, slivovice, slivovica or slivovka is a fruit spirit (or fruit brandy) made from damson plums, often referred to as plum spirit (or plum brandy). If anyone else h ...

slivovitz
) are produced by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous prod ...
of these fruit-fermented beverages. *
Mead Mead () is an Alcoholic drink, alcoholic beverage created by Ethanol fermentation, fermenting honey with water, sometimes with various fruits, spices, grains, or hops. The alcoholic content ranges from about 3.5% Alcohol by volume, ABV to more t ...

Mead
is produced by fermentation of the natural sugars present in
honey Honey is a sweet, viscous food substance made by honey bees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science o ...
. *
Beer Beer is one of the oldest and most widely consumed alcoholic drink An alcoholic drink is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually ...
,
whiskey Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain A grain is a small, hard, dry seed, with or without an attached husk, hull or fruit layer, harvested for human or animal consumption. A grain crop is a gr ...
, and sometimes
vodka Vodka ( pl, wódka , russian: водка , sv, vodka ) is a clear distilled beverage, distilled alcoholic beverage. Different varieties originated in Poland, Russia, and Sweden. Vodka is composed mainly of water and ethanol but sometimes with t ...

vodka
are produced by fermentation of grain starches that have been converted to sugar by the enzyme
amylase An amylase () is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enz ...
, which is present in grain kernels that have been
malted Malting is a process of steeping, Germination, germinating and drying grain to convert it into malt. The malt is mainly used for brewing or whisky making, but can also be used to make malt vinegar or malt extract. Various grains are used for mal ...
(i.e.
germinated
germinated
). Other sources of starch (e.g.
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found throu ...

potato
es and unmalted grain) may be added to the mixture, as the amylase will act on those starches as well. It may also be amylase-induce fermented with saliva in a few countries. Whiskey and vodka are also distilled;
gin , United States, 2010) Gin is a Liquor, distilled alcoholic drink that derives its predominant flavour from juniper berries (''Juniperus communis''). Gin originated as a medicinal liquor made by monks and alchemists across Europe, particularly ...
and related beverages are produced by the addition of flavoring agents to a vodka-like feedstock during distillation. *
Rice wine Rice wine is an alcoholic beverage An alcoholic drink is a drink that contains ethanol, a type of alcohol produced by Ethanol fermentation, fermentation of grains, fruits, or other sources of sugar. The consumption of alcohol plays an impor ...
s (including
sake ''Sake'' barrel offerings at the Shinto shrine Tsurugaoka Hachiman-gū in Kamakura ">Kamakura.html" ;"title="Tsurugaoka Hachiman-gū in Kamakura">Tsurugaoka Hachiman-gū in Kamakura ''Sake'', also spelled ''saké'' ( , also referred to as ...

sake
) are produced by the fermentation of grain starches converted to sugar by the mold ''
Aspergillus oryzae ''Aspergillus oryzae'', also known as , is a filamentous fungus A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well ...

Aspergillus oryzae
''. ''
Baijiu ''Baijiu'' (), also known as ''shaojiu'' (/), is a colourless liquor Liquor or spirit (also distilled alcohol) is an alcoholic drink produced by distillation of grains, fruits, or vegetables that have already gone through alcoholic ferme ...
'', ''
soju (; from Korean: ) is a clear, colorless distilled alcoholic beverage An alcoholic drink is a drink that contains ethanol, a type of alcohol produced by Ethanol fermentation, fermentation of grains, fruits, or other sources of sugar. The con ...

soju
'', and ''
shōchū is a Japanese distilled beverage Liquor or spirit (also distilled alcohol) is an alcoholic drink produced by distillation of grains, fruits, or vegetables that have already gone through alcoholic fermentation. The distillation proce ...
'' are distilled from the product of such fermentation. *
Rum Rum is a liquor Liquor or spirit (also hard liquor, or distilled alcohol) is an alcoholic drink produced by distillation of grains, fruits, or vegetables that have already gone through alcoholic fermentation. The distillation process conce ...
and some other beverages are produced by fermentation and distillation of
sugarcane Sugarcane or sugar cane refers to several species and hybrids of tall Perennial plant, perennial grass in the genus ''Saccharum'', tribe Andropogoneae, that are used for sugar Sugar industry, production. The plants are 2-6 m (6-20 ft) tall wi ...

sugarcane
. Rum is usually produced from the sugarcane product
molasses Molasses () or black treacle Treacle () is any uncrystallised syrup In cooking, a syrup or sirup (from ar, شراب; ''sharāb'', beverage, wine and la, sirupus) is a condiment that is a thick, viscous The viscosity of a fluid ...

molasses
. In all cases, fermentation must take place in a vessel that allows carbon dioxide to escape but prevents outside air from coming in. This is to reduce risk of contamination of the brew by unwanted bacteria or mold and because a buildup of carbon dioxide creates a risk the vessel will rupture or fail, possibly causing injury or property damage.


Feedstocks for fuel production

Yeast fermentation of various carbohydrate products is also used to produce the ethanol that is added to
gasoline Gasoline () or petrol () (see the #Etymology, etymology for naming differences and the use of the term ''gas'') is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignition engine, spark-ignited ...

gasoline
. The dominant ethanol feedstock in warmer regions is
sugarcane Sugarcane or sugar cane refers to several species and hybrids of tall Perennial plant, perennial grass in the genus ''Saccharum'', tribe Andropogoneae, that are used for sugar Sugar industry, production. The plants are 2-6 m (6-20 ft) tall wi ...

sugarcane
. In temperate regions,
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can ...
or
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose Sucrose is common sugar. It is a disaccharide, a molecule composed of two monosaccharides: glucose and fructose. Sucrose is produced naturally in plants, from which ta ...
s are used. In the United States, the main feedstock for the production of ethanol is currently corn. Approximately 2.8 gallons of ethanol are produced from one bushel of corn (0.42 liter per kilogram). While much of the corn turns into ethanol, some of the corn also yields by-products such as
DDGS Distillers grains are a cereal byproduct of the distillation process. Brewer's spent grain usually refers to barley produced as a byproduct of brewing, while distillers grains are a mix of corn, rice and other grains. There are two main sources ...
(distillers dried grains with solubles) that can be used as feed for livestock. A bushel of corn produces about 18 pounds of DDGS (320 kilograms of DDGS per metric ton of maize). Although most of the fermentation plants have been built in corn-producing regions,
sorghum ''Sorghum'' is a genus of about 25 species of flowering plants in the grass family ( Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species, '' Sorghum bicolor'', was originally ...

sorghum
is also an important feedstock for ethanol production in the Plains states.
Pearl millet Pearl millet (''Cenchrus americanus'', commonly known as the synonym ''Pennisetum glaucum'') is the most widely grown type of millet. It has been grown in Africa and the Indian subcontinent since prehistoric times. The center of diversity, and sug ...

Pearl millet
is showing promise as an ethanol feedstock for the southeastern U.S. and the potential of
duckweed Lemnoideae is a subfamily of flowering aquatic plant Aquatic plants are plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things tha ...

duckweed
is being studied. In some parts of Europe, particularly France and Italy,
grapes A grape is a fruit, botanically a berry (botany), berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes can be eaten fresh as table grapes or they can be used for making wine, jam, grape juice, Jelly (fruit preserv ...

grapes
have become a ''de facto'' feedstock for fuel ethanol by the
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous prod ...
of surplus
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different v ...

wine
. Surplus sugary drinks may also be used. In Japan, it has been proposed to use rice normally made into
sake ''Sake'' barrel offerings at the Shinto shrine Tsurugaoka Hachiman-gū in Kamakura ">Kamakura.html" ;"title="Tsurugaoka Hachiman-gū in Kamakura">Tsurugaoka Hachiman-gū in Kamakura ''Sake'', also spelled ''saké'' ( , also referred to as ...

sake
as an ethanol source.


Cassava as ethanol feedstock

Ethanol can be made from
mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, h ...
or from sugars or starches. Starches are cheapest. The starchy crop with highest energy content per acre is
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody plant. Unlike herb ...

cassava
, which grows in tropical countries. Thailand already had a large cassava industry in the 1990s, for use as cattle feed and as a cheap admixture to wheat flour. Nigeria and Ghana are already establishing cassava-to-ethanol plants. Production of ethanol from cassava is currently economically feasible when crude oil prices are above US$120 per barrel. New varieties of cassava are being developed, so the future situation remains uncertain. Currently, cassava can yield between 25 and 40 tonnes per hectare (with irrigation and fertilizer), and from a tonne of cassava roots, circa 200 liters of ethanol can be produced (assuming cassava with 22% starch content). A liter of ethanol contains circa 21.46 MJ of energy. The overall energy efficiency of cassava-root to ethanol conversion is circa 32%. The yeast used for processing cassava is ''Endomycopsis fibuligera'', sometimes used together with bacterium ''Zymomonas mobilis''.


Byproducts of fermentation

Ethanol fermentation produces unharvested byproducts such as heat, carbon dioxide, food for livestock, water, methanol, fuels, fertilizer and alcohols. The cereal unfermented solid residues from the fermentation process, which can be used as livestock feed or in the production of
biogas Biogas is the mixture of gases produced by the breakdown of organic matter in the absence of oxygen (anaerobically), primarily consisting of methane and carbon dioxide. Biogas can be produced from raw materials such as agricultural waste, manure ...

biogas
, are referred to as
Distillers grains Distillers grains are a cereal byproduct of the distillation process. Brewer's spent grain usually refers to barley produced as a byproduct of brewing, while distillers grains are a mix of corn, rice and other grains. There are two main sources ...
and sold as WDG, ''Wet Distiller's grains'', and DDGS, ''Dried Distiller's Grains with Solubles'', respectively.


Microbes used in ethanol fermentation

*
Yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are esti ...

Yeast
**
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been originally isolated from the skin of ...

Saccharomyces cerevisiae
**
Schizosaccharomyces ''Schizosaccharomyces'' is a genus (biology), genus of binary fission, fission yeasts. The most well-studied species is ''Schizosaccharomyces pombe, S. pombe''. At present four Schizosaccharomyces species have been described (''Schizosaccharomyce ...
* Zymomonas mobilis (a bacterium)


See also

*
Anaerobic respiration Anaerobic respiration is respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenan ...
*
Cellular respiration upright=2.5, Typical eukaryotic cell Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities ...

Cellular respiration
*
Cellulose Cellulose is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ...

Cellulose
*
Fermentation (wine) The process of fermentation in winemaking turns grape juice into an alcoholic beverage. During fermentation, yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originate ...
*
Yeast in winemaking The role of yeast in winemaking is the most important element that distinguishes wine from grape juice. In the :wikt:anaerobic, absence of oxygen, yeast converts the sugar in wine, sugars of wine grapes into ethanol, alcohol and carbon dioxide throu ...
* , a chemical compound found in wine or in beer as a secondary product of alcoholic fermentation (Article in French) (a product also known as
congener Congener may refer to: * A thing or person of the same kind as another, or of the same group. * Congener (biology) Biological specificity is the tendency of a characteristic such as a behavior or a biochemical Biochemistry or biological chemist ...
)


References

{{DEFAULTSORT:Ethanol Fermentation Fermentation Ethanol