Cream of tartar is the potassium salt of tartaric acid, KHC₄H₄O₆. It is a byproduct of wine making. Tartar or argol crystallizes in wine casks during the fermentation of grape juice. This crude form is collected and purified to produce the white, odorless, acidic powder used for many culinary and other household purposes (e.g. stabilizes egg whites, increasing their heat tolerance and volume, prevents sugar syrups from crystallizing, reduces discoloration in boiled vegetables, and as a laxative, is combined with baking soda in some formulations of baking powder). When placed in a Bunsen burner's flame, it turns purple.