|Tartaric acid is naturally occurring in grapes and other fruits and plants. In the wine and grappa industries, it can be found in the solid residues that remain after the grape juice has been produced.
Crude tartaric acid can be recovered from the following sources:
- The press cakes from grape juice [i.e., unfermented (marcs) or partly fermented (pomace)] are boiled with water, and any alcohol that is present is distilled off. The hot mash is settled, decanted and the clear liquor is cooled to crystallize. The recovered high-test crude cream of tartar (vinaccia) has an 85-90% tartaric acid content.
- Lees, which are the dried sediments in the wine fermentation vats, consist of yeast cells, pectinous substances, and tartars. Their content of tartaric acid equivalents ranges from 16% to 40%.
- The crystalline crust (argols) formed in the vats in the secondary fermentation period contains more than 40% tartaric acid.
Calcium tartrate is a sparingly soluble salt that can be precipitated by adding calcium chloride to these residues.