A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. The formula of the tartrate dianion is O-OC-CH(OH)-CH(OH)-COO− or C4H4O62−.[1]
The main forms of tartrates used commercially are pure crystalline tartaric acid used as an acidulant in non-alcoholic drinks and foods, cream of tartar used in baking, and Rochelle salt, commonly used in electroplating solutions.
As food additives, tartrates are used as antioxidants, acidity regulators, and emulsifiers. Examples include
In wine, tartrates are the harmless crystalline deposits that separate from wines during fermentation and aging. The principal component of this deposit is potassium bitartrate, a potassium salt of tartaric acid. Small amounts of pulp debris, dead yeast, and precipitated phenolic materials such as tannins make up the impurities contaminating the potassium acid tartrate.
The wine industry is the only source of commercial tartrates, and the crystalline encrustations left inside fermentation vessels are regularly scraped off and purified for commercial use.
Tartrates separate from new wines because they are less soluble in alcohol than in non-alcoholic grape juice. The exact figures vary according to variety and region, but approximately half of the tartrate soluble in grape juice is insoluble in wine. The problem is that the tartrate may remain in a supersaturated state after bottling, only to crystallize at some unpredictable later time.
Tartrates precipitated in red wine usually take on some red pigment and are commonly dismissed as mere sediment; in white wines they can look alarmingly like shards of glass. The modern wine industry has decided that tartrate stabilization is preferable to consumer education.[2]
Tartrate is also used as a retarder to delay the setting time of concrete when temperature is too high.