Calcium carbonate, also known as chalk, is a natural mineral that can be used to reduce acidity in wine. It is a safe and effective product that has been used for centuries by winemakers.
 
Calcium carbonate works by reacting with tartaric acid, the primary acid found in grapes, to form calcium tartrate. Calcium tartrate is a precipitate that settles to the bottom of the wine and can be removed by filtration.
 
Calcium carbonate is a good choice for acid reduction in white wines, as it does not significantly affect the flavor or aroma of the wine. It can also be used in red wines, but it is important to use it carefully, as too much calcium carbonate can strip the wine of its color.