Deacidification

deacidification, winemaking process of decreasing the excessive acidity of grape juice or wine made in cold wine regions or, in particularly cool years, in temperate wine regions. A number of techniques for making excessively acid wines more palatable have been developed and are usually strictly governed by local regulations.

malolactic conversion is a way of lowering acidity biologically, but it is difficult to persuade lactic acid bacteria to work in very acid conditions.

Winemakers generally prefer to rely on biological methods for reducing acidity but there are other forms of deacidification which rely on chemical processes, notably adding compounds to must or wine that will precipitate significant amounts of acidity as insoluble solids that can be filtered or settle out. Calcium carbonate, or chalk, is the most satisfactory of these, since its addition results in insoluble calcium tartrates and the liberation of harmless carbon dioxide. In some very cool regions, where grapes have higher malic acid levels, the addition of calcium carbonate can lead to an imbalance in the proportion of malic to tartaric acid. Double salt deacidification resolves this by reducing the acidity in the juice and yet maintaining similar proportions of tartaric to malic acid. Other methods include reverse osmosis and electrodialysis.