Potassium bicarbonate
KHCO3
Deacidifier: lowers titratable acidity and raises pH.
Typical dose
About 0.9 g/L lowers titratable acidity by roughly 1 g/L. Keep the total drop under about 2 g/L.
When to add it
Finished wine, then cold stabilise to drop the tartrate it forms.
In practice
Neutralises tartaric acid to potassium bitartrate, which then has to be cold-stabilised out or it precipitates later. Past a two-gram drop it leaves a soapy, salty note, so a wine that needs more than that wants the double-salt method with calcium carbonate instead, or blending.
Linked faults are the ones this addition either treats or, used wrongly, causes. The fault page says which, and whether it can be undone.
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.
Lactic acid
Gentle acidity for fine-tuning, especially after malolactic.
Calcium carbonate
Deacidifier for large acid reductions, via the double-salt method.
Potassium carbonate
Deacidifier, stronger per gram than the bicarbonate.