This is a naturally occurring acid found in all citrus fruits such as lemons, oranges, and grapefruits. Used in wine making to increase acidity and ensure a healthy environment for a vigorous fermentation. Wine lacking in the proper amount of acid can taste flat. The addition of citric acid can help bring out more fruit notes and add sharpness where needed. An acid testing kit is recommended but citric acid can also be added to taste before or after fermentation has taken place.