Potassium bitartrate

Potassium bitartrate also potassium hydrogen tartrate has formula KC4H5O6. It is a byproduct of winemaking. It is also known as cream of tartar. It is the potassium acid salt of tartaric acid.

Occurrence
Potassium bitartrate crystallises in wine casks during the fermentation of grape juice. In wines bottled before they are fully ripe, argol can precipitate on the side of the bottle in a sort of crust, thus forming what is called "crusted wine".

This crude form (known as beeswing) is collected and purified to produce the white, odorless, acidic powder used for many culinary and other household purposes.

In food
In food, potassium bitartrate is used for:
 * Stabilizing egg whites, increasing their heat tolerance and volume;
 * Preventing sugar syrups from crystallising;
 * Reducing discolouration of boiled vegetables;
 * Frequent combination with baking soda (which needs an acid ingredient to activate it) in formulations of baking powder.
 * Commonly used in combination with potassium chloride in sodium-free salt substitutes

A similar acid salt sodium acid pyrophosphate is confused with cream of tartar due to their similar function in baking powder.

Chemistry
Potassium acid tartrate, also known as potassium hydrogen tartrate, is also used as a primary reference standard for a pH buffer, according to NIST. Using an excess of salt in water, a saturated solution is created with a pH of 3.557 at 25°C. Upon dissolution in water, potassium bitartrate will dissociate into acid tartrate, potassium cation, and the tartarate dianion. Thus, a saturated solution creates a buffer with standard pH. Before use as a standard, it is recommended that the solution be filtered or decanted between 22° and 28°C.

Folk Remedy
Cream of Tartar mixed with orange juice is a folk remedy for smoking cessation, the purpose being to replace the potassium that smoking depletes.