Tartic Acid / Cream of Tartar

Tartaric acid (KHC₄H₄O₆ in scientific terms, dihydroxy-succinic acid, or potassium bitartrate) is a salt found in plants. It’s actually a byproduct of wine making, because during fermentation a white crust called argol crystallizes along the inside of wine casks, and this can be precipitated to make tartaric acid. After tartaric acid forms, it is mixed with potassium hydroxide to neutralize the acid. This mixture results in cream of tartar. Cream of tartar is a potassium-based salt derived from tartaric acid. It is an acid salt, meaning that when it is dissolved into a liquid it will lower the pH of the liquid.

Cream of tartar is most often used in baking as either a stabilizer or a leavening agent. For example: egg whites have a pH of about 9, which makes them a base. Cream of tartar is about a 3 so just a little bit edges the egg whites towards the acid side of things. The acidity helps the coiled strands of protein (egg whites) relax and unwind. The long strands stay whipped up. Cream of tartar is added to activate alkaline baking soda to create baking powder. One more way cream of tartar gets used in the kitchen is when working with sugar. Where cream of tartar is a stabilizing agent for egg whites, a pinch added to boiling sugar is actually an interfering agent. The cream of tartar gets in the way of sugar's natural tendency to bind together and prevents those dreaded sugar crystals from forming.
Generally, cream of tartar is used to clean and remove stains because of its acidic properties, but other times it is also used for its mildly abrasive qualities. Cream of tartar is one of nature’s best bleaching agents.  Cream of tartar can be mixed with an acidic liquid such as lemon juice or white vinegar to make a paste-like cleaning agent for metals such as brass, aluminum or copper, or with water for other cleaning applications such as removing light stains from porcelain. This mixture is sometimes mistakenly made with vinegar and sodium bicarbonate (baking soda), which actually react to neutralize each other.  Cream of tartar, when mixed into a paste with hydrogen peroxide, can be used to clean rust from some hand tools. The paste is applied and allowed to set for a few hours and then washed off with a baking soda/water solution. Another rinse with water, a thorough drying and a thin application of oil will protect tools from further rusting.