Calcium carbonate
chalk, CaCO3
Deacidifier for large acid reductions, via the double-salt method.
Typical dose
About 0.67 g/L lowers titratable acidity by roughly 1 g/L; more effective per gram than bicarbonate but slower to stabilise.
When to add it
Best on a portion of juice before fermentation as a double salt, not the whole finished wine.
In practice
Removes both tartaric and malic acid when done as a double salt, which potassium bicarbonate cannot. The catch is the calcium: it precipitates as calcium tartrate slowly and unpredictably over months, so a wine treated this way can still throw a haze long after bottling unless it is given time and cold first.
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.
Potassium bicarbonate
Deacidifier: lowers titratable acidity and raises pH.
Potassium carbonate
Deacidifier, stronger per gram than the bicarbonate.