I am making cookies covered with a royal icing. I am going to use Antonia 74 cookie icing recipe which calls for 5 tablespoons of meringue powder and 1 teaspoon of cream of tartar. Why do I need to add more cream of tartar to the icing when meringue powder already has cream of tartar in it?
Sandy
Ah, we do not question the cookie great antonia74. 
Honestly, I'm not sure why since I'm no chemist but the recipe is fantastic and great to work with. I do replace some of the water with vanilla extract since the meringue powder antonia uses already has a vanilla flavor to it and the mp we would routinely find doesn't have any flavoring!
It must need a touch more acid...(that's what the tartar does), It also helps whiten. you could substitute a squeeze of fresh lemon or a few drops of vinegar for the tartar...but I TOTALLY agree with dodibug, don't mess with that recipe it's VERY tried and true...LOL
I use this recipe too and it works GREAT!!!! I'd just put it in. I never even thought about it already having the COT in it, but the icing is wonderful to work with and dries nicely too. I didn't realize what recipe you were using in the other post.. LOL.
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