Definition: potassium bitartrate

Tasteless crystals that precipitate in vats or bottles when wine is cooled. They are a combination of tartaric acid and potassium, originating from an acidic salt contained in grapes. They are found in the form of tartar on the walls of vats and barrels. To prevent it from forming spontaneously in the bottle, the winemaker cools the wine in vats to around 4°C. This cooling process causes the tartar to precipitate to the bottom of the vat before bottling. However, if the bottled wine is subsequently stored at an even lower temperature, a bitartrate deposit may reappear in the bottle. This does not alter the taste of the wine in any way. It is simply unpleasant at the bottom of a glass. See synonym: gravelle.