Tannins

You’ve heard of tannins, but what are they?

The word tannin comes to us from Medieval Latin and it refers to oak bark. Oak, chestnut, and other tanbarks were used in tanning leather. Now, I do not mean some cow slathered itself with cocoa butter and lounged on the beach. Hardly. The process of tanning a raw animal skin and converting it into durable leather requires a lot of hard work and some powerful chemicals.

​Tannins.

Chestnut tree (Public Domain)

Tannin molecules

Tannins are large acidic molecules that bind to and alter proteins, which is why they were used in tanning leather. Tannins also bind to starches, minerals, and cellulose. This binding action slows decomposition. You may have seen ponds in forest environments with brownish water. That brown color is likely caused by tannins leaching out of nearby plants and into the water. In the plant world, tannins are used as pesticides, to protect against predators, and to regulate growth. 

Protective tannins

Plants produce tannins to make themselves less palatable and harder to digest. This discourages feeding by some herbivores. To counteract the presence of those tannins, some plant eaters have evolved to include a tannin-binding protein in their saliva. [Isn’t the world amazing?] The latex produced by dandelions contains tannins.

Chickpea seedlings contain tannins

Tannins as growth regulators

Tannins also have antimicrobial and allelopathic actions. Allelopathy is a type of plant chemical warfare in which one plants releases chemicals that inhibit the growth of neighboring plants. This growth regulation can occur by reducing the available nitrogen or oxygen in the soil, killing nearby beneficial soil microorganisms that support plant life.

Edible tannins

If you bite into an unripe fruit, it is the tannins that cause your mouth to pucker. As fruits approach maturity, the level of tannins decreases. Many popular garden plants contain tannins, to one degree or another, including:

• almonds
• blueberries
• chestnuts
• chickpeas
• cranberries
• cumin
• hazelnuts
• legumes
• pecans
• persimmons
• pomegranates
• sorrel
• strawberries
• tarragon
• thyme
• walnuts
• witch hazel

Tarragon contains tannins

Red wine, beer, cloves, chocolate, coffee, cinnamon, vanilla, and tea also contain tannins

Persimmon tree in autumn (Gphoto)

In autumn, when leaves turn color, the golds and yellows you see are the result of tannins.

Now you know.