Lactic acid
Gentle acidity for fine-tuning, especially after malolactic.
Typical dose
Bench-trial to taste; a soft acid, weaker per gram than tartaric.
When to add it
Finished wine, for a small final lift.
In practice
The soft acid malolactic itself produces, so adding a little back is the least jarring way to lift a wine that was deacidified a shade too far. It will not give the crunch of tartaric, which is exactly the point.
Others in acids and deacidifiers
Tartaric acid
Raises acidity and lowers pH using the acid grapes already contain.
Malic acid
Raises acidity with a sharper, greener sourness than tartaric.
Citric acid
Small acid corrections and iron-haze prevention, but microbially unstable.
Potassium bicarbonate
Deacidifier: lowers titratable acidity and raises pH.
Calcium carbonate
Deacidifier for large acid reductions, via the double-salt method.
Potassium carbonate
Deacidifier, stronger per gram than the bicarbonate.