Tannic acid or tannin occurs naturally in plants. Apart from fruits, leaves and stems of some trees, some vegetables also contain tannic acid. When you consume vegetables with tannic acid, they have an acerbic sour taste that varies from plant to plant depending on the type of tannins in the plant.
Tarragon is a green perennial vegetable plant, commonly known as the dragon herb. Tannic and flavanoids can be extracted from its elongated glossy leaves. Like most vegetable tannins, it has a molecular weight that ranges between 500 to 3,000 gallic acid esters, and up to 20,000 proanthocyanidins. Tarragon leaves are used to spice up food, prepare alcoholic beverages, tartar sauce and mustard as well as tarragon vinegar. They are also effective for treatment of digestive disorders. In Siberia and parts of Europe, tarragon is grown commercially for its perfumed leaves that pass on a licorice-anise essence to salads, sauces and foods prepared with vinegar. When using the leaves to spice up your food, always add them a few minutes before serving as they release their flavor instantly.
American sumac, also known as shoemac or shumac, is a domesticated herb with green leaves that you can use to produce liquor. The leaves of the three most renowned American sumacs -- the white sumac, dwarf sumac and staghorn -- attain their highest quantity of tannins just before they turn yellow. You can dry the leaves and then grind them to coarse powder and later use to make vegetable tanning liquor. Sumac can be found east of Mississippi.
Gambir is a domesticated shrub that produces a watery extract called gambier, obtained from the leaves and the young shoots. Condensed tannic acid from gambir contains compounds derived from flavones such as quercetin, known to be a source of yellow coloration in nature. Apart from catechol tannins, gambier also contains waxes, sugar, oils and salts. Gambir is found in China, Malaysia and most parts of southeast Asia. The Chinese initially used it for medicinal purposes to control dizziness, hypertension and high blood pressure, given its ability to expand peripheral blood vessels.
Rhubarb is a herbaceous perennial plant with large triangular-shaped leaves. It contains vegetable tannins with molecular weights ranging from 500 to over 3,000 gallic acid esters. Various parts of rhubarb have culinary and medicinal value. Although leaves sometimes tend to have too much tannic acid, rendering them toxic and qualifying them as pseudo-tannins, rhubarb is considered a vegetable and normally the stalks are cooked and used in pies due to their tart flavor. The Royal Horticultural Society domesticated the rheum x hybridum variety for human consumption.