Cream of Tartar will make the batter taste bad but after baking the taste is gone. Cream of Tartar prevents crystallization of the sugar. I left it out of a batch of snickerdoodles and I could tell a big difference. If you aren't use to the cookies with it you probably won't know the difference. It will last almost forever sealed and stored in a low humidity place so no need to buy new every year. It doesn't get new or old, you are just buying more of it.
Last edited by Onebyone; 12-18-2014 at 12:21 PM.