Potassium bitartrate also potassium hydrogen tartrate has formula KC4H5O6. It is a byproduct of wine making. It is also known as Cream Of Tartar. It is a potassium acid salt of tartaric acid.

Tartar crystallises in wine casks during the fermentation of grape juice. 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, such as:

• Stabilising 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.

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".

When placed in a Bunsen burner's flame, it turns purple, indicating the presence of potassium.

When cream of tartar is added to water, a suspension results which serves to clean coins very well. The solution loosens surface dirt and grime on the coins. Then, the dirt can be wiped off quite easily.

Cream of tartar and vinegar combine to make a powerful cleaning agent used to clean encrusted pots, pans and stove tops.

A similar acid salt Sodium Acid Pyrophosphate is confused with Cream of Tartar due to their similar function in Baking powder.