Definition - What does Citric Acid mean?
Citric Acid is one of three primary acids found in grapes and converted by the winemaking process. Grapes naturally have 0.1 to 0.7 grams per liter of citric acid, which is about 10% of all acids. Though it is a minor naturally occurring acid, it plays a significant role in winemaking.
Most of the naturally occurring citric acid is consumed during the fermentation process; without citric acid, the fermentation process would grind to a halt. Citric acid is used to increase acidity, complement a specific flavor, prevent ferric hazes and give a fresh sensation to whites and rosés, but rarely in reds. Winemakers sometimes add additional citric acid to balance the wine.
WineFrog explains Citric Acid
Acidity in wine counteracts the sweet and bitter characteristics in a wine. The naturally occurring citric acid in grapes is consumed by bacteria and transformed usually into lactic acid or, rarely, into acetic acid. Citric acid specifically makes a wine taste fresh and is best used in balancing a malic dominant fruit base. It also imparts a citric character to the wine.
Citric acid is naturally occurring in:
Winemakers add additional citric acid to wines after fermentation has completed to acidify wines that are too basic or as a flavor additive. However, citric acid can cause microbial instability in a wine if the still has active bacteria (this promotes the growth of unwanted microbes). While adding citric acid to wine is permitted in some locations, there are laws against adding citric acid in the European Union; the only time a winemaker can add it is if they need to remove excess iron and copper.