Is Black Tea High in Tannic Acid?

Like fine wines, teas -- especially black teas -- are often described by tasters as "tannic." This means they contain high levels of certain phenolic flavor compounds, collectively called tannins, that give the tea its refreshingly astringent, slightly bitter taste. This strikes some health-conscious consumers as alarming since they associate tannins with the tannic acid that's used in leather making. Although there are persistent myths about the hazards of tannic acid, the truth is that no tea contains any tannic acid at all.

What Tannins Are

Tannins are among the phenolic compounds, a group of complex organic molecules that serve several purposes in plants. They perform a range of metabolic functions; act as chemical defenses; provide food plants with a variety of flavors, aromas and colors; and are often potent antioxidants as well. In the case of tea, the tannins are mostly a type called catechins, which aren't used to make tannic acid. In the green, freshly harvested tea leaf, their flavor is mouth-puckeringly bitter and astringent and acts as a deterrent to herbivores. However, tea harvesters can manipulate those catechin tannins to create a range of potent flavors.

Tea Production

The freshly picked tea leaves begin to wither, as all leaves do when severed from the plant. They're usually rubbed or rolled at this stage to break down their internal cell walls, enabling their natural enzymes to begin breaking down the catechins into complex and flavorful compounds, especially theanine. Green tea is heated at this point to stop the enzymes, then dried. For black tea the leaves are rubbed and rolled for a period of hours as the enzymes are given free rein, generating more flavor compounds and a deep, brown color. The color comes from an oxydizing reaction, similar to the one that causes browning in apples. Finally, the leaves are toasted and dried to stop the reaction.

The Beverage

When you steep your black tea, you're creating a rich brew of complicated flavors. The main flavor compound, theanine, has both savory and sweet notes. Part of the theanine breaks down into glutamic acid, which enhances savory flavors and explains why tea is such a good companion to foods. The tea's caffeine, a bitter alkaloid, binds with the bitter tannins and -- oddly -- the two bitter compounds make each other less bitter, leaving the tea brisk and refreshing.

The Tannins

Although black tea doesn't contain tannic acid, the tannins that are present have been rumored to have adverse health effects. For example, some studies in the 1980s and 1990s suggested a possible correlation between tea consumption and cancer. However, more recent research has concluded that the tannins -- polyphenols with potent antioxidant properties -- might in fact suppress various cancers. They've also demonstrated strong antimicrobial properties. Tannins are known to bind to dietary iron and prevent its absorption, but this applies only to the "nonheme" iron found in plant foods. Omnivores get most of their iron from animal foods, while vegetarians can simply avoid tea around mealtimes or increase their consumption of iron-rich green vegetables to compensate for this effect.

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