Calcium Carbonate is a white, odorless, and tasteless powder that is used in winemaking to reduce acidity. It is also known as chalk or precipitated chalk. Calcium Carbonate is added to winemaking must in powder form. It is typically used in red wines, but it can also be used in white wines.
 
Used to lower acidity levels. 2.5 grams per gallon will roughly lower acidity by .1%. It does not require cold stabilization to precipitate-out acid like Potassium Carbonate does, but it takes longer, affects flavor, and it reduces tartaric before dropping out malic or citric acids.