Calcium Carbonate (Precipitated Chalk), is a wine additive that is used to reduce the amount of acid in a juice or must. Wines too high in acid will typically have a unpleasant tart to sour taste. These wines may also create a burning sensation when being swallowed. Calcium Carbonate will help to reduce this sharp taste and unpleasant burning by lowering the amount of acid in the wine to a normal level. It does so by neutralizing the acid and causing it to drop out of the wine in the form of tiny crystals. The wine is then simply racked off the sediment deposits.