Acidification and deacidification

Acidity falls as grapes ripen, so warm regions and warm seasons routinely arrive with fruit that is analytically ripe and short of acid.

The regulatory symmetry with chaptalisation is deliberate: cool zones may add sugar, warm zones may add acid, and doing both to the same wine is generally prohibited.

Tartaric acid is the usual addition, because it is the grape’s own principal acid and is microbiologically stable. Malic and lactic acid are permitted in some jurisdictions.

The objective is often pH rather than taste. Lowering pH improves colour stability in red wine, increases the effectiveness of sulfur dioxide, and reduces microbial risk — the sensory change can be a side effect rather than the point.

Deacidification uses carbonates, typically calcium carbonate or potassium bicarbonate, which precipitate tartaric acid out as a salt. Malolactic fermentation is the other route, and is a biological rather than chemical one.

Timing matters. Acid added before fermentation integrates differently from acid added afterwards, and post-fermentation additions are more likely to be noticed.

Rules vary substantially by jurisdiction and by vintage — some authorities grant exceptional permission in unusual years.