"Tartaric Acid" is a reddish acid found in grapes and several other fruit. It increases acidity in low acid wines.
50 grams (1.8 oz.)

Tartaric Acid is the principal grape acid in the ripe fruit. Because of this authorities are in agreement that its use is invaluable in quality wine production. It is particularly valuable during maturation, where it freely enters ester forming reactions. If present in excess, it will tend to form potassium bitartrate or even argils.
DIRECTIONS: Acid according to specific recipe up to 2 tsp (10g) per gallon (4L) of must at the start of fermentation.