![Ethanol fermentation-1](https://upload.wikimedia.org/wikipedia/commons/0/08/Ethanol_fermentation-1.svg)
Ethanol fermentation, also called alcoholic fermentation, is a
biological process
Biological processes are those processes that are vital for an organism to live, and that shape its capacities for interacting with its environment. Biological processes are made of many chemical reactions or other events that are involved in the ...
which converts
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
s such as
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
,
fructose
Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...
, and
sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
into
cellular energy, producing
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
as by-products. Because
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
s perform this conversion in the absence of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, alcoholic
fermentation
Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
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:
* Anaerobic adhesive, a bonding a ...
process. It also takes place in some species of fish (including
goldfish
The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the wild have ...
and
carp
Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...
) where (along with lactic acid fermentation) it provides energy when oxygen is scarce.
Ethanol fermentation is the basis for
alcoholic beverage
An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of alcohol that acts as a drug and is produced by fermentation of grains, fruits, or other sources of sugar. The c ...
s,
ethanol fuel
Ethanol fuel is ethyl alcohol, the same type of alcohol found in alcoholic beverages, used as fuel. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. The first production car running entirely on ethanol was the ...
and
bread
Bread is a staple food prepared from a dough of flour (usually wheat) and water, usually by baking. Throughout recorded history and around the world, it has been an important part of many cultures' diet. It is one of the oldest human-made f ...
dough rising.
Biochemical process of fermentation of sucrose
![Yeast fermentation](https://upload.wikimedia.org/wikipedia/commons/d/d7/Yeast_fermentation.jpg)
The
chemical equation
A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities on the right-hand side with a plus sign between ...
s below summarize the fermentation of sucrose (C
12H
22O
11) into ethanol (C
2H
5OH). 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 Talpida ...
of
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
into two moles of ethanol and two moles of carbon dioxide, producing two moles of
ATP in the process.
:C
6H
12O
6 → 2 C
2H
5OH + 2 CO
2
Sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
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 that catalyzes the hydrolysis (breakdown) of sucrose (table sugar) into fructose and glucose. Alternative names for invertase include , saccharase, glucosucrase, beta-h-fructosidase, beta-fructosidase, invertin, sucrase, ma ...
cleaves the
glycosidic linkage
A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
A glycosidic bond is formed between the hemiacetal or hemiketal group ...
between the glucose and fructose molecules.
:C
12H
22O
11 + H
2O + invertase → 2 C
6H
12O
6
Next, each glucose molecule is broken down into two
pyruvate molecules in a process known as
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...
.
Glycolysis is summarized by the equation:
:C
6H
12O
6 + 2 ADP + 2 P
i + 2 NAD
+ → 2 CH
3COCOO
− + 2 ATP + 2 NADH + 2 H
2O + 2 H
+
CH
3COCOO
− is pyruvate, and P
i is inorganic
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
. Finally, pyruvate is converted to ethanol and CO
2 in two steps, regenerating oxidized NAD+ needed for glycolysis:
:1. CH
3COCOO
− + H
+ → CH
3CHO + CO
2
catalyzed by
pyruvate decarboxylase
:2. CH
3CHO + NADH + H
+ → C
2H
5OH + NAD
+
This reaction is catalyzed by
alcohol dehydrogenase
Alcohol dehydrogenases (ADH) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to N ...
(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 coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...
. 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 atta ...
.
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
The Entner–Doudoroff pathway (ED Pathway) is a metabolic pathway that is most notable in Gram-negative bacteria, certain Gram-positive bacteria and archaea. Glucose is the substrate in the ED pathway and through a series of enzyme assisted chem ...
.
Other
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s can produce ethanol from sugars by fermentation but often only as a side product. Examples are
*
Heterolactic acid fermentation in which
Leuconostoc
''Leuconostoc'' is a genus of gram-positive bacteria, placed within the family of Lactobacillaceae. They are generally ovoid cocci often forming chains. ''Leuconostoc'' spp. are intrinsically resistant to vancomycin and are catalase-negative (w ...
bacteria produce lactate + ethanol +
*
Mixed acid fermentation
In biochemistry, mixed acid fermentation is the metabolic process by which a six-carbon sugar (e.g. glucose, ) is converted into a complex and variable mixture of acids. It is an anaerobic (non-oxygen-requiring) fermentation reaction that is ...
where
Escherichia
''Escherichia'' () is a genus of Gram-negative, non- spore-forming, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastrointestinal tracts of warm-blooded animals, ...
produce ethanol mixed with lactate, acetate, succinate, formate, , and H
2
*
2,3-butanediol fermentation by
Enterobacter
''Enterobacter'' is a genus of common Gram-negative, facultatively anaerobic, rod-shaped, non-spore-forming bacteria of the family Enterobacteriaceae. It is the type genus of the order Enterobacterales. Several strains of these bacteria are ...
producing ethanol, butanediol, lactate, formate, , and H
2
Gallery
Image:Mthomebrew must.JPG, Grapes fermenting during wine production.
Image:Alpha-D-Glucopyranose.svg, Glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
depicted in Haworth projection
In chemistry, a Haworth projection is a common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective. Haworth projection approximate the shapes of the actual mole ...
Image:Pyruvate.png, Pyruvate
Image:Acetaldehyde-2D-flat.svg, Acetaldehyde
Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
Image:Ethanol-structure.svg, Ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
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 genetic studies and industrial applications. Its name comes from the ability to assimilate lactose and convert it into lactic acid.
''Kluyveromyces lactis'' (formerly ''S ...
'' or ''
Kluyveromyces lipolytica
''Kluyveromyces'' is a genus of ascomycetous yeasts in the family Saccharomycetaceae. Some of the species, such as '' K. marxianus'', are the teleomorphs of '' Candida species''.
The genus name of ''Kluyveromyces'' is in honour of Albert Jan K ...
'') will oxidize
pyruvate completely to carbon dioxide and water in a process called
cellular respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
, 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 describes how available oxygen inhibits ethanol fermentation, driving yeast to switch toward aerobic respiration for increased generation of the energy carrier adenosine triphosphate (ATP).
Discovery
The effect was described b ...
.
However, many yeasts such as the commonly used baker's yeast ''
Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) 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 o ...
'' or fission yeast ''
Schizosaccharomyces pombe
''Schizosaccharomyces pombe'', also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically meas ...
'' 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 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
* Aerobic respiration, the aerobic process of cel ...
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
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
![Primary fermentation cellar, Budweiser Brewery](https://upload.wikimedia.org/wikipedia/commons/d/d4/Primary_fermentation_cellar%2C_Budweiser_Brewery.jpg)
Ethanol contained in
alcoholic beverage
An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of alcohol that acts as a drug and is produced by fermentation of grains, fruits, or other sources of sugar. The c ...
s is produced by means of fermentation induced by yeast.
*
Wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
is produced by fermentation of the natural sugars present in grapes;
cider
Cider ( ) is an alcoholic beverage made from the fermented juice of apples. Cider is widely available in the United Kingdom (particularly in the West Country) and the Republic of Ireland. The UK has the world's highest per capita consumption, ...
and
perry
Perry, also known as pear cider, is an alcoholic beverage made from fermented pears, traditionally the perry pear. It has been common for centuries in England, particularly in Gloucestershire, Herefordshire, and Worcestershire. It is also made ...
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, wh ...
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 of genus ''Pyrus'' , in the family Rosaceae, bearing the p ...
s, respectively; and other
fruit wine
Fruit wines are fermented alcoholic beverages made from a variety of base ingredients (other than grapes); they may also have additional flavors taken from fruits, flowers, and herbs. This definition is sometimes broadened to include any alcohol ...
s are produced from the fermentation of the sugars in any other kinds of fruit.
Brandy
Brandy is a liquor produced by distilling wine. Brandy generally contains 35–60% alcohol by volume (70–120 US proof) and is typically consumed as an after-dinner digestif. Some brandies are aged in wooden casks. Others are coloured with ...
and
eaux de vie
An ''eau de vie'' ( French for spirit, §16, §17 literally " water of life") is a clear, colourless fruit brandy that is produced by means of fermentation and double distillation. The fruit flavor is typically very light.
In English-speakin ...
(e.g.
slivovitz
Slivovitz is a fruit spirit (or fruit brandy) made from damson plums, often referred to as plum spirit (or plum brandy). If anyone else has a dictionary of some Slavic language that translates your word for slivovitz as "plum brandy", please a ...
) are produced by
distillation
Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
of these fruit-
fermented beverages.
*
Mead
Mead () is an alcoholic beverage made by fermenting honey mixed with water, and sometimes with added ingredients such as fruits, spices, grains, or hops. The alcoholic content ranges from about 3.5% ABV to more than 20%. The defining character ...
is produced by fermentation of the natural sugars present in
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
.
*
Beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
,
whiskey
Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Various grains (which may be malted) are used for different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden cask ...
, and sometimes
vodka
Vodka ( pl, wódka , russian: водка , sv, vodka ) is a clear distilled alcoholic beverage. Different varieties originated in Poland, Russia, and Sweden. Vodka is composed mainly of water and ethanol but sometimes with traces of impuritie ...
are produced by fermentation of grain starches that have been converted to sugar by the enzyme
amylase
An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ') into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of ...
, which is present in grain kernels that have been
malted
Malting is the process of steeping, 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 malting, mo ...
(i.e.
germinated
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
). Other sources of starch (e.g.
potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
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 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 fermented and distilled from rice, traditionally consumed in East Asia, Southeast Asia and South Asia. Rice wine is made by the fermentation of rice starch that has been converted to sugars. Microbes are the so ...
s (including
sake
Sake, also spelled saké ( ; also referred to as Japanese rice wine), is an alcoholic beverage of Japanese origin made by fermenting rice that has been polished to remove the bran. Despite the name ''Japanese rice wine'', sake, and indee ...
) 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 mold) used in East Asia to saccharify rice, sweet potato, and barley in the making of alcoholic beverages such as ''sake'' and '' shōchū'', and also to ferment soybeans for m ...
''. ''
Baijiu
''Baijiu'' (), also known as ''shaojiu'' (/), is a colorless Chinese liquor typically coming in between 35% and 60% alcohol by volume (ABV). Each type of baijiu uses its own type of ''qū'' for fermentation to create a distinct and charact ...
'', ''
soju
(; Hangul: ; Hanja: ) is a clear and colorless Korean distilled alcoholic beverage. It is usually consumed neat. Its alcohol content varies from about 12.9% to 53% alcohol by volume (ABV), although since 2007 low alcohol soju below 20% h ...
'', and ''
shōchū'' are distilled from the product of such fermentation.
*
Rum
Rum is a liquor made by fermenting and then distilling sugarcane molasses or sugarcane juice. The distillate, a clear liquid, is usually aged in oak barrels. Rum is produced in nearly every sugar-producing region of the world, such as the Ph ...
and some other beverages are produced by fermentation and distillation of
sugarcane
Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...
. Rum is usually produced from the sugarcane product
molasses
Molasses () is a viscous substance resulting from refining sugarcane or sugar beets into sugar. Molasses varies in the amount of sugar, method of extraction and age of the plant. Sugarcane molasses is primarily used to sweeten and flavour foods ...
.
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 ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
.
The dominant ethanol feedstock in warmer regions is
sugarcane
Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...
.
In temperate regions,
corn
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
or
sugar beet
A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet (''Beta vulgaris''). Together wi ...
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 source ...
(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 is grown for grain, while many othe ...
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''; also known as 'Bajra' in Hindi, 'Sajje' in Kannada, 'Kambu' in Tamil, 'Bajeer' in Kumaoni and 'Maiwa' in Hausa, 'Mexoeira' in Mozambique) is the most w ...
is showing promise as an ethanol feedstock for the southeastern U.S. and the potential of
duckweed
Lemnoideae is a subfamily of flowering aquatic plants, known as duckweeds, water lentils, or water lenses. They float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Also known as bayroot, they arose ...
is being studied.
In some parts of Europe, particularly France and Italy,
grapes
A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters.
The cultivation of grapes began perhaps 8,000 years ago ...
have become a ''de facto'' feedstock for fuel ethanol by the
distillation
Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
of surplus
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
. Surplus sugary drinks may also be used. In Japan, it has been proposed to use rice normally made into
sake
Sake, also spelled saké ( ; also referred to as Japanese rice wine), is an alcoholic beverage of Japanese origin made by fermenting rice that has been polished to remove the bran. Despite the name ''Japanese rice wine'', sake, and indee ...
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, ...
or from sugars or starches. Starches are cheapest. The starchy crop with highest energy content per acre is
cassava
''Manihot esculenta'', common name, commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively ...
, 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 a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
, 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 source ...
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. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
**
Saccharomyces cerevisiae
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) 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 o ...
**
Schizosaccharomyces
''Schizosaccharomyces'' is a genus of fission yeasts. The most well-studied species is ''S. pombe''. At present five Schizosaccharomyces species have been described (''S. pombe'', ''S. japonicus'', ''S. octosporus'', ''S. cryophilus'' and ''S. ...
*
Zymomonas mobilis (a bacterium)
See also
*
Anaerobic respiration
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
In aerobic organisms undergoing re ...
*
Cellular respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
*
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
*
Fermentation (wine)
The process of fermentation in winemaking turns grape juice into an alcoholic beverage. During fermentation, yeasts transform sugars present in the juice into ethanol and carbon dioxide (as a by-product). In winemaking, the temperature and speed ...
*
Yeast in winemaking
The role of yeast in winemaking is the most important element that distinguishes wine from fruit juice. In the absence of oxygen, yeast converts the sugars of the fruit into alcohol and carbon dioxide through the process of fermentation.Jeff Co ...
*
Auto-brewery syndrome
*
Tryptophol
Tryptophol is an aromatic alcohol that induces sleep in humans. It is found in wine as a secondary product of ethanol fermentation. It was first described by Felix Ehrlich in 1912. It is also produced by the trypanosomal parasite in sleeping si ...
, 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)
References
{{DEFAULTSORT:Ethanol Fermentation
Fermentation
Ethanol