De-acidification may be necessary in poor years in cool climates, particularly as the major acid in these cases is often malic acid. De-acidification is legal in zone A of the European Union, with no limit on musts but a maximum of 1 g/l (as tartaric acid) for wine itself.
The first de-acidification operation of the vintage must be notified to the Wines Standard Board at least 48 hours before the event.

The permitted methods for de-acidification are:

• The addition of calcium carbonate to musts post-clarification but before the alcoholic fermentation.0.67 g/l of calcium carbonate will reduce the acidity of a must by 1 g/l.
  Unfortunately, as tartaric acid is more reactive than malic acid, this reduction will be almost entirely due to the neutralisation of tartaric acid.
• An alternative, if a high level of de-acidification is required, it is recommended to use the ‘double salts’ method by adding Acidex™.
• The malo-lactic fermentation
• The addition of calcium or potassium bicarbonate after fermentation

There is also some natural de-acidification through tartrate deposition after the alcoholic fermentation.

It is important to note that de-acidification also increases pH.