Reduction or transformation of the acids contained in the wine through various cellar measures. This is particularly necessary in bad wine years when the grapes have not reached a sufficient degree of ripeness. According to EU law, this is generally permitted for fresh grapes, grape must, partially fermented grape must, young wine and wine. However, this depends on the wine-growing zone.
For wine-growing zone A (Germany, except cultivation area Baden) and wine-growing zone B (German cultivation area Baden and Austria) partial deacidification is permitted (but not acidification). A high acid content in the grape must with a low pH value causes a purer fermentation, but is very much appropriate from 12 g/l onwards. Grape musts are usually deacidified to about 9 to 10 g/l.