Tannins (or tannoids) are a class of

astringent An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, witch hazel, and yerba mansa, a Californian plant ...

polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...

biomolecule A biomolecule or biological molecule is a loosely used term for molecules present in organisms that are essential to one or more typically biological processes, such as cell division, morphogenesis, or development. Biomolecules include large ...

s that bind to and

precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s and various other organic compounds including

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s and

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...

s. The term ''tannin'' (from

Anglo-Norman Anglo-Norman may refer to: *Anglo-Normans, the medieval ruling class in England following the Norman conquest of 1066 * Anglo-Norman language **Anglo-Norman literature * Anglo-Norman England, or Norman England, the period in English history from 10 ...

''tanner'', from

Medieval Latin Medieval Latin was the form of Literary Latin used in Roman Catholic Western Europe during the Middle Ages. In this region it served as the primary written language, though local languages were also written to varying degrees. Latin functioned ...

''tannāre'', from ''tannum'',

oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

bark) refers to the use of oak and other bark in

tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

animal hides into

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, ...

. By extension, the term ''tannin'' is widely applied to any large

ic compound containing sufficient

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

s and other suitable groups (such as

carboxyl In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

s) to form strong complexes with various

macromolecule A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...

s. The tannin compounds are widely distributed in many species of plants, where they play a role in protection from

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

(acting as

pesticides Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampric ...

) and might help in regulating plant growth. The

astringency An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, witch hazel, and yerba mansa, a Californian plant ...

from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit, red wine or tea. Likewise, the destruction or modification of tannins with time plays an important role when determining harvesting times. Tannins have

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

s ranging from 500 to over 3,000 (

gallic acid Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. It i ...

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

s) and up to 20,000 Daltons (

proanthocyanidin Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex ...

s).

Structure and classes of tannins

There are three major classes of tannins: Shown below are the base unit or monomer of the tannin. Particularly in the flavone-derived tannins, the base shown must be (additionally) heavily hydroxylated and polymerized in order to give the high molecular weight

motif that characterizes tannins. Typically, tannin molecules require at least 12 hydroxyl groups and at least five phenyl groups to function as protein binders.

Oligostilbenoid Oligostilbenoids (oligo- or polystilbenes) are oligomeric forms of stilbenoids. Some molecules are large enough to be considered polyphenols and constitute a class of tannins. Examples Dimers * Ampelopsin A * Epsilon-viniferin * Pallidol * ...

s (oligo- or polystilbenes) are oligomeric forms of

stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are prod ...

s and constitute a minor class of tannins.

Pseudo-tannins

Pseudo-tannins are low molecular weight compounds associated with other compounds. They do not change color during the

Goldbeater's skin Goldbeater's skin is the processed outer membrane of the intestine of an animal, typically cattle, which is valued for its strength against tearing. The term derives from its traditional use as durable layers interleaved between sheets of gold s ...

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...

, unlike hydrolysable and condensed tannins, and cannot be used as tanning compounds. Some examples of pseudo tannins and their sources are:

History

Ellagic acid Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid. Name The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ob ...

, and

pyrogallic acid Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols. Production and reac ...

were first discovered by chemist

Henri Braconnot Henri Braconnot (29 May 1780 – 13 January 1855) was a French chemist and pharmacist. He was born in Commercy, his father being a counsel at the local parliament. At the death of his father, in 1787, Henri began his instruction in an elementa ...

in 1831.

Julius Löwe Julius Gustav Neubronner (8 February 1852 – 17 April 1932) was a German apothecary, inventor, company founder, and a pioneer of amateur photography and film. He was part of a dynasty of apothecaries in Kronberg im Taunus. Neubronner was court ap ...

was the first person to synthesize ellagic acid by heating

with

arsenic acid Arsenic acid or trihydrogen arsenate is the chemical compound with the formula . More descriptively written as , this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as ...

or silver oxide.

Maximilian Nierenstein Maximilian Nierenstein (also known as Moses Max Nierenstein or Max Nierenstein; 1877–1946) was a professor of biochemistry at the University of Bristol. He is known for the Nierenstein reaction, an organic reaction describing the conversion of ...

studied natural phenols and tannins found in different plant species. Working with

Arthur George Perkin Arthur George Perkin DSc FRS FRSE (1861–1937) was an English chemist and Professor of Colour Chemistry and Dyeing at the University of Leeds. Life Perkin was the second son of Sir William Henry Perkin FRS, who founded the aniline dye indus ...

, he prepared

ellagic acid Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid. Name The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ob ...

from

algarobilla Algarrobilla, small carob (algarrobo (disambiguation), algarrobo) in Spanish, also written ''algarovilla'', may refer to : * ''Balsamocarpon brevifolium'', a plant species found in Chile * ''Prosopis humilis'', a flowering plant and a tree species f ...

and certain other

fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...

s in 1905. He suggested its formation from

galloyl Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula carbon, C6hydrogen, H2(hydroxide, OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, Witch-hazel, witch hazel, tea l ...

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogeni ...

by ''

Penicillium ''Penicillium'' () is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production. Some members of the genus produce pe ...

'' in 1915.

Tannase The enzyme tannase (EC 3.1.1.20) catalyzes the following reaction: :digallate + H2O = 2 gallate It is a key enzyme in the degradation of gallotannins and ellagicitannins, two types of hydrolysable tannins. Specifically, tannase catalyzes the hy ...

is an enzyme that Nierenstein used to produce m-

digallic acid Digallic acid is a polyphenolic compound found in '' Pistacia lentiscus''. Digallic acid is also present in the molecule of tannic acid. Digalloyl esters involve either ''-meta'' or ''-para'' depside bonds. Tannase is an enzyme that uses digallat ...

from

gallotannin A gallotannin is any of a class of molecules belonging to the hydrolysable tannins. Gallotannins are polymers formed when gallic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose. Meta ...

s. He proved the presence of

catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...

cocoa bean The cocoa bean (technically cocoa seed) or simply cocoa (), also called the cacao bean (technically cacao seed) or cacao (), is the dried and fully fermented seed of ''Theobroma cacao'', from which cocoa solids (a mixture of nonfat substances ...

s in 1931. He showed in 1945 that

luteic acid Luteic acid is a natural phenol found in numerous fruits. It is a monolactonized tergalloyl group. Maximilian Nierenstein showed in 1945 that luteic acid was a molecule present in the myrobalanitannin, a tannin found in the fruit of ''Terminalia ch ...

, a molecule present in the myrobalanitannin, a tannin found in the fruit of ''

Terminalia chebula ''Terminalia chebula'', commonly known as black- or chebulic myrobalan, is a species of ''Terminalia'', native to South Asia from India and Nepal east to southwest China (Yunnan), and south to Sri Lanka, Malaysia, and Vietnam.Flora of China''Term ...

'', is an intermediary compound in the synthesis of

. At these times, molecule formulas were determined through

combustion analysis Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions where the resul ...

. The discovery in 1943 by Martin and Synge of

paper chromatography Paper chromatography is an analytical method used to separate coloured chemicals or substances. It is now primarily used as a teaching tool, having been replaced in the laboratory by other chromatography methods such as thin-layer chromatography ...

provided for the first time the means of surveying the phenolic constituents of plants and for their separation and identification. There was an explosion of activity in this field after 1945, including prominent work by

Edgar Charles Bate-Smith Edgar Charles Bate-Smith (1900-1989Practical Polyphenolics, Edwin Haslam, 1998, ) was an English chemist and phytochemist specialising in food chemistry. He worked in the Low Temperature Research Station in Cambridge where his main fields of re ...

and Tony Swain at

Cambridge University , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Schola ...

. In 1966,

Edwin Haslam Edwin Haslam (1932 – 3 October 2013)Edwin HAS ...

proposed a first comprehensive definition of plant polyphenols based on the earlier proposals of Bate-Smith, Swain and Theodore White, which includes specific structural characteristics common to all phenolics having a tanning property. It is referred to as the White–Bate-Smith–Swain–Haslam (WBSSH) definition.

Occurrence

Tannins are distributed in species throughout the

plant kingdom Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

. They are commonly found in both

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό� ...

s and

angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s. Mole studied the distribution of tannin in 180 families of

dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, t ...

s and 44 families of

monocotyledon Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...

s (Cronquist). Most families of dicot contain tannin-free species (tested by their ability to precipitate proteins). The best known families of which all species tested contain tannin are:

Aceraceae Aceraceae were recognized as a family of flowering plants also called the maple family. They contain two to four genera, depending upon the circumscription, of some 120 species of trees and shrubs. A common characteristic is that the leaves are ...

Actinidiaceae The Actinidiaceae are a small family of flowering plants. The family has three genera and about 360 species and is a member of the order Ericales. Distribution They are temperate and subtropical woody vines, shrubs, and trees, native to Asia ( ...

Anacardiaceae The Anacardiaceae, commonly known as the cashew family or sumac family, are a family of flowering plants, including about 83 genera with about 860 known species. Members of the Anacardiaceae bear fruits that are drupes and in some cases produce ...

Bixaceae The Bixaceae are a family of dicotyledonous plants commonly called the achiote family. Under the Cronquist system, the family was traditionally placed in the order Violales. However, newer arrangements move it, with some other families previousl ...

Burseraceae The Burseraceae are a moderate-sized family of 17-19 genera and about 540 species of flowering plants. The actual numbers differ according to the time period in which a given source is written describing this family. The Burseraceae are also know ...

Combretaceae The Combretaceae, often called the white mangrove family, are a family of flowering plants in the order Myrtales. The family includes about 530 species of trees, shrubs, and lianas in ca 10 genera. The family includes the leadwood tree, ''Combre ...

Dipterocarpaceae Dipterocarpaceae is a family of 16 genera and about 695 known species of mainly tropical lowland rainforest trees. The family name, from the type genus ''Dipterocarpus'', is derived from Greek (''di'' = two, ''pteron'' = wing and ''karpos'' = fru ...

Ericaceae The Ericaceae are a family of flowering plants, commonly known as the heath or heather family, found most commonly in acidic and infertile growing conditions. The family is large, with c.4250 known species spread across 124 genera, making it th ...

Grossulariaceae ''Ribes'' is a genus of about 200 known species of flowering plants, most of them native to the temperate regions of the Northern Hemisphere. The various species are known as currants or gooseberries, and some are cultivated for their edible f ...

Myricaceae The Myricaceae are a small family of dicotyledonous shrubs and small trees in the order Fagales. There are three genera in the family, although some botanists separate many species from ''Myrica'' into a fourth genus ''Morella''. About 55 specie ...

for dicot and Najadaceae and

Typhaceae The Typhaceae () are a family of flowering plants, sometimes called the cattail family. The botanical name for the family has been recognized by most taxonomists. Description Members can be recognized as large marsh herbs with alternate two-rank ...

in Monocot. To the family of the oak,

Fagaceae The Fagaceae are a family of flowering plants that includes beeches, chestnuts and oaks, and comprises eight genera with about 927 species. Fagaceae in temperate regions are mostly deciduous, whereas in the tropics, many species occur as evergre ...

, 73% of the species tested contain tannin. For those of acacias,

Mimosaceae The Mimosoideae are a traditional subfamily of trees, herbs, lianas, and shrubs in the pea family (Fabaceae) that mostly grow in tropical and subtropical climates. They are typically characterized by having radially symmetric flowers, with petals ...

, only 39% of the species tested contain tannin, among

Solanaceae The Solanaceae , or nightshades, are a family of flowering plants that ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of agricultural crops, medicinal plants, spices, weeds, and orn ...

rate drops to 6% and 4% for the

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. Some families like the

Boraginaceae Boraginaceae, the borage or forget-me-not family, includes about 2,000 species of shrubs, trees and herbs in 146, to 156 genera with a worldwide distribution. The APG IV system from 2016 classifies the Boraginaceae as single family of the order ...

Cucurbitaceae The Cucurbitaceae, also called cucurbits or the gourd family, are a plant family consisting of about 965 species in around 95 genera, of which the most important to humans are: *''Cucurbita'' – squash, pumpkin, zucchini, some gourds *''Lagena ...

Papaveraceae The Papaveraceae are an economically important family of about 42 genera and approximately 775 known species of flowering plants in the order Ranunculales, informally known as the poppy family. The family is cosmopolitan, occurring in temperat ...

contain no tannin-rich species. The most abundant polyphenols are the

condensed tannin Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues. They ...

s, found in virtually all families of plants, and comprising up to 50% of the dry weight of leaves.

Cellular localization

In all vascular plants studied, tannins are manufactured by a

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

-derived

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...

, the

tannosome Tannosomes are organelles found in plant cells of vascular plants. Formation and functions Tannosomes are formed when the chloroplast membrane forms pockets filled with tannin. Slowly, the pockets break off as tiny vacuoles that carry tannins t ...

. Tannins are mainly physically located in the

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

s or surface wax of plants. These storage sites keep tannins active against plant predators, but also keep some tannins from affecting plant metabolism while the plant tissue is alive. Tannins are classified as

ergastic substance Ergastic substances are non-protoplasmic materials found in cells. The living protoplasm of a cell is sometimes called the bioplasm and distinct from the ergastic substances of the cell. The latter are usually organic or inorganic substances that ...

s, i.e., non-protoplasm materials found in cells. Tannins, by definition, precipitate proteins. In this condition, they must be stored in organelles able to withstand the protein precipitation process.

Idioblast An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. ...

s are isolated plant cells which differ from neighboring tissues and contain non-living substances. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin or pigments etc. They also can contain tannins. In Japanese persimmon (''

Diospyros kaki ''Diospyros kaki'', the Oriental persimmon, Chinese persimmon, Japanese persimmon or kaki persimmon, is the most widely cultivated species of the genus '' Diospyros''. Although its first botanical description was not published until 1780,Publis ...

'') fruits, tannin is accumulated in the vacuole of tannin cells, which are idioblasts of parenchyma cells in the flesh.

Presence in soils

The

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

of tannin-rich plant communities has occurred on nutrient-poor acidic soils throughout the world. Tannins were once believed to function as anti-herbivore defenses, but more and more ecologists now recognize them as important controllers of decomposition and nitrogen cycling processes. As concern grows about global warming, there is great interest to better understand the role of polyphenols as regulators of carbon cycling, in particular in northern boreal forests. Leaf litter and other decaying parts of kauri (''

Agathis australis ''Agathis australis'', commonly known by its Māori name kauri (), is a coniferous tree in the family ''Araucariaceae'', found north of 38°S in the northern regions of New Zealand's North Island. It is the largest (by volume) but not t ...

''), a tree species found in New Zealand, decompose much more slowly than those of most other species. Besides its acidity, the plant also bears substances such as waxes and phenols, most notably tannins, that are harmful to

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 ...

Presence in water and wood

The

leaching Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to: * Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...

of highly

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

tannins from decaying vegetation and leaves along a stream may produce what is known as a

blackwater river A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. As vegetation decays, tannins leach into the water, making a transparent, acidic water that is darkly stained, resembling black te ...

. Water flowing out of

bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...

s has a characteristic brown color from dissolved

peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficien ...

tannins. The presence of tannins (or

humic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th ...

) in

well water A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

can make it smell bad or taste bitter, but this does not make it unsafe to drink. Tannins leaching from an unprepared driftwood decoration in an aquarium can cause pH lowering and coloring of the water to a tea-like tinge. A way to avoid this is to boil the

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

in water several times, discarding the water each time. Using peat as an aquarium substrate can have the same effect. Many hours of boiling the driftwood may need to be followed by many weeks or months of constant soaking and many water changes before the water will stay clear. Raising the water's

pH level In chemistry, pH (), historically denoting "potential of hydrogen" (or "power of hydrogen"), is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of ions) are mea ...

, e.g. by adding

baking soda Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...

, will accelerate the process of leaching.

Softwood file:Pinus sylvestris wood ray section 1 beentree.jpg, Scots Pine, a typical and well-known softwood Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The main diff ...

s, while in general much lower in tannins than hardwoods, are usually not recommended for use in an aquarium so using a

hardwood Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood (which comes from ...

with a very light color, indicating a low tannin

content Content or contents may refer to: Media * Content (media), information or experience provided to audience or end-users by publishers or media producers ** Content industry, an umbrella term that encompasses companies owning and providing mas ...

, can be an easy way to avoid tannins. Tannic

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

is brown in color, so in general white woods have a low tannin content. Woods with a lot of yellow, red, or brown coloration to them (like cedar, redwood, red oak, etc.) tend to contain a lot of tannin.

Extraction

There is no single protocol for extracting tannins from all plant material. The procedures used for tannins are widely variable.''The Tannin Handbook'', Ann E. Hagerman, 1998
book
) It may be that

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscib ...

in the extraction solvent increases the total yield by inhibiting interactions between tannins and

s during extraction or even by breaking hydrogen bonds between tannin-protein complexes.

Tests for tannins

There are three groups of methods for the analysis of tannins: precipitation of proteins or alkaloids, reaction with phenolic rings, and depolymerization.

Alkaloid precipitation

Alkaloids such as

caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...

cinchonine Cinchonine is an alkaloid found in '' Cinchona officinalis''. It is used in asymmetric synthesis in organic chemistry. It is a stereoisomer and pseudo- enantiomer of cinchonidine. It is structurally similar to quinine, an antimalarial Antima ...

quinine Quinine is a medication used to treat malaria and babesiosis. This includes the treatment of malaria due to ''Plasmodium falciparum'' that is resistant to chloroquine when artesunate is not available. While sometimes used for nocturnal leg cr ...

strychnine Strychnine (, , US chiefly ) is a highly toxic, colorless, bitter, crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine, when inhaled, swallowed, or absorbed through the eye ...

, precipitates polyphenols and tannins. This property can be used in a quantitation method.

Goldbeater's skin test

When

goldbeater's skin Goldbeater's skin is the processed outer membrane of the intestine of an animal, typically cattle, which is valued for its strength against tearing. The term derives from its traditional use as durable layers interleaved between sheets of gold s ...

or ox skin is dipped in

HCl HCL may refer to: Science and medicine * Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia * Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development * Hollow-cathode lamp, a spe ...

, rinsed in water, soaked in the tannin solution for 5 minutes, washed in water, and then treated with 1% FeSO₄ solution, it gives a blue black color if tannin was present.

Ferric chloride test

Use of ferric chloride (FeCl₃) tests for phenolics in general. Powdered plant leaves of the test plant (1.0 g) are weighed into a beaker and 10 ml of distilled water are added. The mixture is boiled for five minutes. Two drops of 5% FeCl₃ are then added. Production of a greenish precipitate is an indication of the presence of tannins. Alternatively, a portion of the water extract is diluted with distilled water in a ratio of 1:4 and few drops of 10% ferric chloride solution is added. A blue or green color indicates the presence of tannins (Evans, 1989).

Other methods

The hide-powder method is used in tannin analysis for

tannin and the Stiasny method for wood adhesives. Statistical analysis reveals that there is no significant relationship between the results from the hide-powder and the Stiasny methods. ;Hide-powder method 400 mg of sample tannins are dissolved in 100 ml of distilled water. 3 g of slightly chromated hide-powder previously dried in vacuum for 24h over CaCl₂ are added and the mixture stirred for 1 h at ambient temperature. The suspension is filtered without vacuum through a sintered glass filter. The weight gain of the hide-powder expressed as a percentage of the weight of the starting material is equated to the percentage of tannin in the sample. ;Stiasny's method 100 mg of sample tannins are dissolved in 10 ml distilled water. 1 ml of 10M HCl and 2 ml of 37% formaldehyde are added and the mixture heated under reflux for 30 min. The reaction mixture is filtered while hot through a sintered glass filter. The precipitate is washed with hot water (5× 10 ml) and dried over CaCl₂. The yield of tannin is expressed as a percentage of the weight of the starting material.

Reaction with phenolic rings

The bark tannins of ''

Commiphora angolensis ''Commiphora angolensis'', also known as sand commiphora or sand corkwood, is a shrub species in the genus ''Commiphora'' growing mainly in Angola and Namibia. The adults and larvae of '' Diamphidia nigroornata'' feed on ''C. angolensis''. The ...

'' have been revealed by the usual color and precipitation reactions and by quantitative determination by the methods of Löwenthal-Procter and of DeijsChemical study of bark from Commiphora angolensis Engl. Cardoso Do Vale, J., Bol Escola Farm Univ Coimbra Edicao Cient, 1962, volume 3, page 128
abstract
) (

formalin Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section Fo ...

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

method). Colorimetric methods have existed such as the Neubauer-Löwenthal method which uses

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

as an oxidizing agent and

indigo Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', m ...

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...

as an indicator, originally proposed by Löwenthal in 1877. The difficulty is that the establishing of a titer for tannin is not always convenient since it is extremely difficult to obtain the pure tannin. Neubauer proposed to remove this difficulty by establishing the titer not with regard to the tannin but with regard to crystallised

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...

, whereby he found that 83 g oxalic acid correspond to 41.20 g tannin. Löwenthal's method has been criticized. For instance, the amount of indigo used is not sufficient to retard noticeably the oxidation of the non-tannins substances. The results obtained by this method are therefore only comparative. A modified method, proposed in 1903 for the quantification of tannins in wine, Feldmann's method, is making use of

calcium hypochlorite Calcium hypochlorite is an inorganic compound with formula Ca(OCl)2. It is the main active ingredient of commercial products called bleaching powder, chlorine powder, or chlorinated lime, used for water treatment and as a bleaching agent. Thi ...

, instead of potassium permanganate, and indigo sulfate.

Food items with tannins

Pomegranates

Accessory fruits

Strawberries The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...

contain both hydrolyzable and condensed tannins.

Berries

Most berries, such as

cranberries Cranberries are a group of evergreen dwarf shrubs or trailing vines in the subgenus ''Oxycoccus'' of the genus ''Vaccinium''. In Britain, cranberry may refer to the native species ''Vaccinium oxycoccos'', while in North America, cranberry m ...

, and

blueberries Blueberries are a widely distributed and widespread group of perennial flowering plants with blue or purple berries. They are classified in the section ''Cyanococcus'' within the genus ''Vaccinium''. ''Vaccinium'' also includes cranberries, bi ...

, contain both hydrolyzable and condensed tannins.

Nuts

Nuts vary in the amount of tannins they contain. Some species of acorns of

contain large amounts. For example, acorns of

Quercus robur ''Quercus robur'', commonly known as common oak, pedunculate oak, European oak or English oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native plant, native to most of Europe west of the Caucasus ...

and

Quercus petraea ''Quercus petraea'', commonly known as the sessile oak, Cornish oak, Irish Oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an unofficial emble ...

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...

were found to contain 2.4–5.2% and 2.6–4.8% tannins as a proportion of dry matter, but the tannins can be removed by leaching in water so that the acorns become edible. Other nuts – such as

hazelnuts The hazelnut is the fruit of the hazel tree and therefore includes any of the nuts deriving from species of the genus ''Corylus'', especially the nuts of the species ''Corylus avellana''. They are also known as cobnuts or filberts according t ...

walnuts A walnut is the edible seed of a drupe of any tree of the genus ''Juglans'' (family Juglandaceae), particularly the Persian or English walnut, ''Juglans regia''. Although culinarily considered a "nut" and used as such, it is not a true bot ...

pecans The pecan (''Carya illinoinensis'') is a species of hickory native to the southern United States and northern Mexico in the region of the Mississippi River. The tree is cultivated for its seed in the southern United States, primarily in Georgia, ...

, and

almonds The almond (''Prunus amygdalus'', Synonym (taxonomy)#Botany, syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of th ...

– contain lower amounts. Tannin concentration in the crude extract of these nuts did not directly translate to the same relationships for the condensed fraction.

Herbs and spices

Clove Cloves are the aromatic flower buds of a tree in the family Myrtaceae, ''Syzygium aromaticum'' (). They are native to the Maluku Islands (or Moluccas) in Indonesia, and are commonly used as a spice, flavoring or fragrance in consumer products, ...

tarragon Tarragon (''Artemisia dracunculus''), also known as estragon, is a species of perennial herb in the family Asteraceae. It is widespread in the wild across much of Eurasia and North America and is cultivated for culinary and medicinal purposes. ...

cumin Cumin ( or , or Article title
) (''Cuminum cyminum'') is a

thyme Thyme () is the herb (dried aerial parts) of some members of the genus ''Thymus'' of aromatic perennial evergreen herbs in the mint family Lamiaceae. Thymes are relatives of the oregano genus ''Origanum'', with both plants being mostly indigenou ...

vanilla Vanilla is a spice derived from orchids of the genus ''Vanilla (genus), Vanilla'', primarily obtained from pods of the Mexican species, flat-leaved vanilla (''Vanilla planifolia, V. planifolia''). Pollination is required to make the p ...

, and

cinnamon Cinnamon is a spice obtained from the inner bark of several tree species from the genus ''Cinnamomum''. Cinnamon is used mainly as an aromatic condiment and flavouring additive in a wide variety of cuisines, sweet and savoury dishes, breakfa ...

all contain tannins.

Legumes

Most

legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...

s contain tannins. Red-colored beans contain the most tannins, and white-colored beans have the least.

Peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...

s without shells have a very low tannin content.

Chickpea The chickpea or chick pea (''Cicer arietinum'') is an annual legume of the family Fabaceae, subfamily Faboideae. Its different types are variously known as gram" or Bengal gram, garbanzo or garbanzo bean, or Egyptian pea. Chickpea seeds are high ...

s (garbanzo beans) have a smaller amount of tannins.

Chocolate

Chocolate liquor Chocolate liquor (cocoa liquor) is pure cocoa mass (cocoa paste) in solid or semi-solid form. Like the cocoa beans (nibs) from which it is produced, it contains both cocoa solids and cocoa butter in roughly equal proportion. It is produced fr ...

contains about 6% tannins.

Drinks with tannins

Principal human dietary sources of tannins are tea and coffee. Most wines aged in

charred Charring is a chemical process of incomplete combustion of certain solids when subjected to high heat. Heat distillation removes water vapour and volatile organic compounds ( syngas) from the matrix. The residual black carbon material is char, as d ...

oak barrel Oak is used in winemaking to vary the color, flavor, tannin profile and texture of wine. It can be introduced in the form of a barrel during the fermentation or aging periods, or as free-floating chips or staves added to wine fermented in a v ...

s possess tannins absorbed from the wood. Soils high in clay also contribute to tannins in wine grapes.Oz Clarke ''Encyclopedia of Grapes'' pp. 155–162 Harcourt Books 2001 This concentration gives wine its signature

. Coffee pulp has been found to contain low to trace amounts of tannins.

Fruit juices

Although citrus fruits do not contain tannins, orange-colored juices often contain tannins from food colouring. Apple, grape and berry juices all contain high amounts of tannins. Sometimes tannins are even added to juices and ciders to create a more astringent feel to the taste.

Beer

In addition to the

alpha acid Alpha acids (α acids) are a class of chemical compounds primarily of importance to the production of beer. They are found in the resin glands of the flowers of the hop plant and are the source of hop bitterness. Alpha acids may be isomerized ...

s extracted from

hops Hops are the flowers (also called seed cones or strobiles) of the hop plant ''Humulus lupulus'', a member of the Cannabaceae family of flowering plants. They are used primarily as a bittering, flavouring, and stability agent in beer, to whi ...

to provide bitterness in

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 ...

, condensed tannins are also present. These originate both from malt and hops. Trained brewmasters, particularly those in Germany, consider the presence of tannins to be a flaw. However, in some styles, the presence of this astringency is acceptable or even desired, as, for example, in a

Flanders red ale Flanders red ale or Flemish red-brown, is a style of sour ale brewed in West Flanders, Belgium. Flanders red ale is fermented with organisms other than ''Saccharomyces cerevisiae'', especially ''Lactobacillus'', which produces a sour character ...

. In lager type beers, the tannins can form a precipitate with specific haze-forming proteins in the beer resulting in

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

at low temperature. This chill haze can be prevented by removing part of the tannins or part of the haze-forming proteins. Tannins are removed using PVPP, haze-forming proteins by using

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

or tannic acid.

Properties for animal nutrition

Tannins have traditionally been considered antinutritional, depending upon their chemical structure and dosage. Many studies suggest that chestnut tannins have positive effects on

silage Silage () is a type of fodder made from green foliage crops which have been preserved by fermentation to the point of acidification. It can be fed to cattle, sheep and other such ruminants (cud-chewing animals). The fermentation and storage p ...

quality in the round bale silages, in particular reducing NPNs (non-protein nitrogen) in the lowest wilting level. Improved fermentability of soya meal nitrogen in the

rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allow ...

may occur. Condensed tannins inhibit herbivore digestion by binding to consumed plant proteins and making them more difficult for animals to digest, and by interfering with protein absorption and digestive enzymes (for more on that topic, see

plant defense against herbivory Plant defense against herbivory or host-plant resistance (HPR) describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants can sense being touched, and they can ...

). Histatins, another type of salivary proteins, also precipitate tannins from solution, thus preventing alimentary adsorption.

Legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...

fodders containing condensed tannins are a possible option for integrated sustainable control of gastrointestinal

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

s in ruminants, which may help address the worldwide development of resistance to synthetic

anthelmintics Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may a ...

. These include nuts, temperate and tropical barks, carob, coffee and cocoa.

Tannin uses and market

Tannins have been used since antiquity in the processes of tanning hides for leather, and in helping preserve iron artefacts (as with Japanese iron teapots). Industrial tannin production began at the beginning of the 19th century with the industrial revolution, to produce tanning material for the need for more leather. Before that time, processes used plant material and were long (up to six months). There was a collapse in the vegetable tannin market in the 1950s–1960s, due to the appearance of synthetic tannins, which were invented in response to a scarcity of vegetable tannins during World War II. At that time, many small tannin industry sites closed. Vegetable tannins are estimated to be used for the production of 10–20% of the global leather production. The cost of the final product depends on the method used to extract the tannins, in particular the use of solvents, alkali and other chemicals used (for instance

glycerin Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

). For large quantities, the most cost-effective method is

hot water extraction Hot Water Extraction (HWE) is a method of carpet cleaning. It involves a combination of hot water and cleaning agents being injected into the fibers of a carpet at high pressure and the lifted soil being removed by a powerful vacuum. Process T ...

Tannic acid Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity ( pKa around 6) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as C76H52O46, which correspon ...

is used worldwide as clarifying agent in alcoholic drinks and as aroma ingredient in both alcoholic and soft drinks or juices. Tannins from different botanical origins also find extensive uses in the wine industry.

Uses

Tannins are an important ingredient in the process of tanning leather.

Tanbark Tanbark is the bark of certain species of trees, traditionally used for tanning hides into leather. The words "tannin", "tanning", "tan," and " tawny" are derived from the Medieval Latin ''tannare'', "to convert into leather." Bark mills are ...

from

mimosa ''Mimosa'' is a genus of about 590 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. The generic name is derived from the Greek word (''mimos''), an "actor" or "mime", and the feminine suffix -''osa'', "resembl ...

, chestnut and

quebracho tree Quebracho is a common name in Spanish to describe very hard (density 0.9–1.3) wood tree species. The etymology of the name derived from ''quiebrahacha'', or ''quebrar hacha'', meaning "axe-breaker". Species There are at least three similar c ...

has traditionally been the primary source of

tannery Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

tannin, though inorganic tanning agents are also in use today and account for 90% of the world's leather production. Tannins produce different colors with

ferric chloride Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The colo ...

(either blue, blue black, or green to greenish-black) according to the type of tannin.

Iron gall ink Iron gall ink (also known as common ink, standard ink, oak gall ink or iron gall nut ink) is a purple-black or brown-black ink made from iron salts and tannic acids from vegetable sources. It was the standard ink formulation used in Europe for t ...

is produced by treating a solution of tannins with

iron(II) sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the heptahydrate (''x'' = 7) but several values for x are know ...

. Tannins can also be used as a

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

, and is especially useful in

natural dye Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi. Archaeol ...

ing of

cellulose fiber Cellulose fibers () are fibers made with ethers or esters of cellulose, which can be obtained from the bark, wood or leaves of plants, or from other plant-based material. In addition to cellulose, the fibers may also contain hemicellulose and l ...

s such as cotton. The type of tannin used may or may not have an impact on the final color of the fiber. Tannin is a component in a type of industrial

particleboard Particle board, also known as chipboard or low-density fiberboard, is an engineered wood product manufactured from wood chips and a synthetic resin or other suitable binder, which is pressed and extruded. Particle board is often confused with ori ...

adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

developed jointly by the Tanzania Industrial Research and Development Organization and Forintek Labs Canada. ''

Pinus radiata ''Pinus radiata'' ( syn. ''Pinus insignis''), the Monterey pine, insignis pine or radiata pine, is a species of pine native to the Central Coast of California and Mexico (Guadalupe Island and Cedros island). It is an evergreen conifer in the fa ...

'' tannins has been investigated for the production of wood adhesives.

Condensed tannin Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues. They ...

s, e.g., quebracho tannin, and

Hydrolyzable tannin A hydrolyzable tannin or pyrogallol-type tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids. At the center of a hydrolyzable tannin molecule, there is a carbohydrate (usually D-glucose ...

s, e.g., chestnut tannin, appear to be able to substitute a high proportion of synthetic phenol in phenol-formaldehyde resins for wood

. Tannins can be used for production of anti-

corrosive A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction. Etymology The word ''corrosive'' is derived from the Latin verb ''corrodere'', which means ''to gnaw'', ...

primers for treating rusted steel surfaces prior to painting, converting rust to iron tannate and condolidating and sealing the surface. The use of

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...

s made of tannins has been investigated to remove

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

and

methylmercury Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a ...

from solution. Immobilized tannins have been tested to recover

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

from seawater.

References

External links

Tannins: fascinating but sometimes dangerous molecules
* * {{Authority control Nutrition Oenology Organic polymers Wine terminology Astringent flavors Phenol antioxidants Wood products Food stabilizers Phytochemicals

Structure and classes of tannins

Pseudo-tannins

History

Occurrence

Cellular localization

Presence in soils

Presence in water and wood

Extraction

Tests for tannins

Alkaloid precipitation

Goldbeater's skin test

Ferric chloride test

Other methods

Reaction with phenolic rings

Food items with tannins

Pomegranates

Accessory fruits

Berries

Nuts

Herbs and spices

Legumes

Chocolate

Drinks with tannins

Fruit juices

Beer

Properties for animal nutrition

Tannin uses and market

Uses

See also

References

External links