Tannins are naturally found in the skins of grapes and is what gives grapes their bitter and astringent flavor which fades as the fruit ripens. Wine tannin powder is often added to non-grape wines to add astringency, dryness, and structure to the body of a wine. Tannin powder can also be added in smaller amounts to grape wines to boost these characteristics. Use 1/4 teaspoon per gallon for white or rosé wine must: 1/3 teaspoon per gallon for red wine must; 1/2 teaspoon per gallon for fruit wine must. 1 oz of tannin powder.