Citric acid is a natural acid that is used to adjust the acidity of wine. It is a white, odorless, and tasteless powder that is soluble in water. Citric acid is typically added to wine during the fermentation process, but it can also be added later.
 
To use citric acid in winemaking, dissolve the desired amount in water and add it to the wine. The amount of citric acid that you need to add will depend on the acidity of the wine and the desired outcome. A good rule of thumb is to start with 1 tsp of citric acid per gallon of wine and adjust as needed, 1 tsp of citric acid will increase the acidity of wine by about 0.15%.