Potassium hydrogen tartrate is the systematic chemical name for cream of tartar, the white crystalline powder familiar to bakers. It forms naturally as a byproduct of winemaking, crystallising from grape juice during fermentation as potassium salts of tartaric acid precipitate. In the kitchen it serves three classic functions: the acid in baking powder that activates bicarbonate, a stabiliser for whipped egg whites that produces greater volume and finer texture, and an anti-crystallisation agent in sugar syrups and confectionery. Its natural origin, a purified fruit acid rather than a synthetic chemical, appeals to clean-label sensibilities. The compound must not be confused with tartaric acid itself, though the two are related, and its consistent performance has made it a staple of serious baking for over a century.