Ingredient profile: cream of tartar

You may know cream of tartar and you have probably seen it. Most likely you thought you were looking at sugar, as most people do. Tartar settles now and then at the bottom of wine bottles or grape juice and looks like small sugar crystals, similar to little rock candy or brown sugar.

What actually settles at the bottom of wine and grape juice is potassium bitartrate (E number E336) or calcium tartrate (E number E354).
Potassium bitartrate has the chemical formula KC₄H₅O₆
K for potassium
C for carbon
H for hydrogen
O for oxygen

and calcium tartrate: CaC₄H₄O₆
Ca for calcium

Tartar occurs not only in grapes but also in berries such as redcurrants and gooseberries, and in some other plants such as sugar beet.

The tartar that comes out of juice and wine production is usually ground even finer and dried, and can then be used further to make tartaric acid or baking powder.

As we just mentioned, tartar comes from grapes and forms there naturally out of tartaric acid and the minerals potassium and calcium. Tartar is not a flaw in the quality of the wine or the grape juice either. It is, however, a sign of the acidity of the wine or juice. The more tartaric acid the grapes contained, the more tartar can form.

The same goes for the minerals. The more minerals, that is potassium and calcium, the grape drew from the soil, so the longer it was allowed to hang on the vine, the more readily tartar forms. Temperature also has an important influence on solubility. The lower the temperature during fermentation, or later during storage, the more tartar crystallises out.

In the body itself, tartar as a baking ingredient has no specific effect and is largely used up during baking by the reactions that take place, much like bicarbonate of soda.

Tartar is used in baking powder mixtures and recipes as a source of acid for bicarbonate of soda. Perhaps you read our first ingredient profile on bicarbonate of soda and remember that it produces CO₂ both through heat and through the reaction with acid.

Tartar is also used to stabilise beaten egg white. If you bake with egg white more often, you know it can sometimes be tricky to keep it airy and voluminous. When you beat egg white, the long protein chains in it are untangled and new bridges form between certain amino acids. Air can then be trapped between those bridges and the foam gets its lovely volume. It may help to picture the proteins as a ball of wool that gets untangled by the beating and loosely crocheted at the same time, the way everyone does once in kindergarten.

Unfortunately you can also get a bit overenthusiastic while beating, which makes too many bridges form between the amino acids. The foam turns flaky and you can no longer use it. Tartar helps avoid too much bridging, so the foam is more stable and not so easily overbeaten. Tartar works similarly when stabilising whipped cream.

Tartar can also prevent sugar syrup from crystallising, and stop cooked vegetables from discolouring. Together with potassium chloride it is used as an acid carrier in low sodium salt substitutes. Pharmacy uses tartar too, as a laxative. Do not be alarmed, though. Using tartar as a laxative takes large amounts. In baking you only use knife tips of it.

And by the way: there is no alcohol in cream of tartar. It can be used in baked goods without any concern.

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