Add 1/8 teaspoon max per gallon of wine to start. Be careful - powdered tannin can produce bitterness in wine.
Tannin also known as tannic acid is a compound found in wines, most notably red wines that give them a pleasing dryness. Wine tannin is also an additive for increasing the tannin present particularly in country wines that use fruit, vegetables or flowers.
Tannins are naturally occurring compounds that exist inside grape skins, seeds and stems. The scientific word for these compounds is polyphenols. Polyphenols release from the skins, seeds and stems when they soak in the grape juice just after the grapes have been pressed and are what give certain wines, such as big bold red wines, their characteristic dryness or astringency. You experience the effect of tannins any time you drink a wine that creates a drying sensation in your mouth. Depending on how dry your mouth feels, you can determine whether a wine is high or low in tannins. We say a wine that is high in tannins is tannic.