Citric Acid, powder, USP. It is found in small amounts in grapes and in larger amounts in many other fruits. It can be metabolized during fermentation, so usually very little remains at the end of fermentation. Best practice is to add it after the end of fermentation. As an acidulant it has the advantage of not upsetting tartrate stability, but at higher levels of addition it may impart a bright 'soda pop' character. Like tartaric acid, it buffers to a low pH. It takes about 3.4 grams per gallon to increase acidity by 0.1%