Why cream of tartar for egg whites and not another acid?

[Shalmanese]

Virtually every single egg white recipe will say add some cream of tartar to egg whites to help them whip better because the cream of tartar will lower the pH and make it more stable. But if all it's doing is making it more acidic, why exclusively cream of tartar over the dozens of far more common acids found in the kitchen?

One difference is cream of tartar is the only solid acid so it wouldn't add more water to the egg whites except many books *also* say that adding a tbsp of water to egg whites increases stability as well. Is there something else in cream of tartar that isn't in other acids?

[HungryC]

I can't answer your cream of tartar question, but a little lemon juice will also work. I have seen many recipe references to lemon juice used for this purpose.

[ruthcooks]

If your cream of tartar goes bad, you will have a baking failure. I switched to lemon juice decades ago.

[ChrisZ]

Vinegar is commonly used in pavlova recipes (which are just giant meringues). According to McGee, the effectiveness of an acid on egg whites depends on the age of the eggs. I can't recall whether it's very new or very old eggs, but one of them will whip better without the acid.

[pastrygirl]

My guess is because it has a more neutral flavor than lemon or vinegar.

[lesliec]

... and the water increases the volume of the whipped whites (a Hervé This revelation, I think).

[DianaM]

I don't think there's anything particular to cream of tartar that makes it better for meringues. I too have been using lemon juice, with great results.

[auzzi]

Paraphrasing:

Egg whites naturally have a pH of about 8.7 to 9.0.

Acid substances reduces the pH 8 thus decreasing the tendency of the egg proteins to coagulate with the application of heat.

weak acids, such as cream of tartar, citric acid [lemon juice] and acetic acid [vinegar] stabilize egg-white foams by lowering pH which increases the stability of the foam.

Lowering egg white pH to an optimal 6.5 is acheived with cream of tartar. This keeps the foam loose and elastic, and stable enough to hold air: this in turn allows the cells to expand well when heated.

From an interesting book: Experimental Cookery From The Chemical And Physical Standpoint by Belle Lowe [1937]