SC - non-member submission - daughter said with all the autho rity of Julia child that I should add a

[Decker, Terry D.]

It is usually one of the ingredients in baking powder, providing an acid to
help boost the action.

Bear

> Cream of Tartar is tartaric acid.  It would have the same tenderizing
> effect, in all liklihood, as the lemon
> juice or vinegar.  Cream of tartar is also added to egg whites to
> increase volumn by denaturing the proteins,
> making them easier to recombine in strands that will trap the air.
> 
> niccolo difrancesco
> (it's also one of the acids in acid blend sold for brewing 
> and vintning)