Acidification

The process of adding acid to grape must before fermentation to boost a naturally low level of acidity, and, thereby, balance a wine’s soft components (sugar, alcohol and fruit).

It is legal in some areas, including Bordeaux, Burgundy, Australia and California, to correct deficient acidity in this manner. However, it is illegal in Bordeaux and Burgundy to both chaptalize (add sugar to) and acidify a wine.

(The Wine Bible, Karen MacNeil; winespectator.com )