Calcium carbonate is used to reduce the acidity of wine. It does not require cold-stabilization to force complete precipitation, as does potassium carbonate, however it is more likely to affect the flavor. Calcium Carbonate may take a few months to fully precipitate. You will notice ‘wine diamonds’ in the bottom of your fermenter.
Calcium carbonate is a chemical compound with the formula CaCO₃. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of eggshells, snail shells, seashells and pearls. Historically used as the main ingredient in white wash, a la Tom Sawyer.
Usage: One-quarter ounce (about 4 teaspoons) of calcium carbonate reduces acidity in one gallon by about 0.25%. Foaming may occur because of the production of CO2. Do not use more than one ounce per gallon. Wait 24 hours and rack wine. 16 gm/hl (0.66 oz/bbl) will increase calcium content of mash by 50 mg/liter.