Tannin

File:Bottle of tannic acid.jpg

A bottle of tannic acid solution in water.

Tannins are any of various complex phenolic substances of plant origin; used in tanning and in medicine.

What are tannins?

Tannins are any of various complex phenolic substances of plant origin; used in tanning and in medicine.

Phenols

They are classified as phenolic compounds or simply phenols, which are found in many species of plants, from all climates and all parts of the globe.

Chemical properties

• They are large molecules that bind readily with proteins, cellulose, starches, and minerals.
• These resulting substances are insoluble and resistant to decomposition.

Cranberry plant, high in tannins

Cranberry plant, high in tannins

Sources

• Tannins occur in many species of coniferous trees as well as a number of flowering plant families.
• These tannins can leach out of the plants.
• The water in the soil becomes rich with tannins and seeps into the ground water or drains into lakes and streams.
• These waters become brown in color and look like tea.

Etiology

The word tannin comes from the old German word tanna meaning oak. It refers to the use of wood tannins derived from oak trees that were used to convert animal hides into leather.

Apple, unripe is rich in tannins

Apple, unripe is rich in tannins

Plants rich in tannins

In addition to oak trees, other sources of tannins are willows (Salix spp.), quebracho (Scinopsis balansae), sumac (Rhus spp.), maples (Acer spp.), wattle (Acacia spp.), eucalyptus (Eucalyptus spp.), and red mangrove (Rhizophora spp.).

Tanning

• Tanning is an ancient technique that is estimated to have occurred as long ago as 5000 B.C. in Egypt. Ancient Greeks and Romans are known to have used oak to tan animal skins into leather.
• In China tanning occurred many thousand years ago.
• Different colors, textures, and durability of leathers were achieved by using different formulations of plant tannins referred to as “tanning liqueurs”.

Bark of oak tree

Bark of oak tree

Function

• Tannins are found commonly in the bark of trees, wood, leaves, buds, stems, fruits, seeds, roots, and plant galls.
• In all of these plant structures, tannins help to protect the individual plant species.
• Tannins that become stored in the bark of trees protect the tree from being infected by bacteria or fungi.
• In this case, the tannins precipitate out the enzymes and other protein exudates from bacteria and fungi thus not allowing these organisms to infect the tree. Many bud scales on woody plants contain tannins to protect the inner leaf tissue from being consumed and in many seed plants the initial set of leaves from a germinating seed are also high in tannins.

Red wine is high in tannins

Red wine is high in tannins

Tannins and fruits

• Unripened fruits are high in tannin content.
• The high tannin content discourages fruit eating animals from consuming the fruit until the seeds are mature and ready for dispersal.
• As the fruit ripens the tannin content lessens.

Coffee and tee

Beside fruits, tannins are also contained in coffee, tea

Red wine and beer

• Tannins are also found in beer and red wine.
• The initial astringent taste when you sip a red wine actually comes from tannins in the wood of the oak barrels in which the wine was aged.

Cranberry juice and urinary infection

Medical research has shown that tannin found in cranberries is highly effective in preventing urinary tract infections by preventing E. coli bacteria from adhering to walls of the urinary tract.

Flower and leaves

Tannins are also responsible for many of the enchanting colors seen in flowers and the final beauty of autumn leaves.

Tannin on Wikipedia

• Wikipedia's article on Tannin

See also

• Polyphenol

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