Does cream of tartar:
1. Alter the taste of buttercream?
2. Making the buttercream stiffen on the outside after it's been sitting out?
3. Help the buttercream be less greasy? I use 2 parts shortening and 1 part butter (very slightly soft). It comes out greasy looking but tastes great.

Thanks!
Tina

I've never heard of adding cream of tartar. I know you can add meringue powder to make it crust though. Sorry, I'm not much help!

I've also never heard of using cream of tartar in icing, but here's some info I found via www.ask.com:

http://www.ask.com/bar?q=what+does+cream+of+tartar+do&page=1&qsrc=178&ab=0&u=http%3A%2F%2Fwww.kitchenproject.com%2FAskWebChef%2Fquestions%2Fcream_of_tartar.htm

Web Chefs:From Stephen Block

Cream of Tartar is used in cookies mainly as a substitute for baking powder. Baking powder is mainly a combination of cream of Tartar and Baking soda. You can use as a substitute for Baking powder 1/4 teaspoon of baking soda plus 1/2 teaspoon of cream of tartar.

Interesting facts about cream of Tartar
From this website: http://www.foodreference.com/html/fcreamoftartar.html

Cream of tartar is an acid powder. Combined with baking SODA it makes baking POWDER.

Cream of tartar is also used to give a creamier texture to sugary things like candy and frosting and to stabilize and increase the volume of beaten egg whites.

It is supposed to make the Buttercream crusts, That is what we use in Culinary School In place of Meringue Powder, But personally I like Meringue Powder.

actually cream of tartar is a type of stabilizer. I bet the recipe say to put the cream of tartar with the egg whites. if so the tartar stabilizes the eggs whites kinda of like putting agar agar or salt to make it a little stiff. It doesn't alter the taste. And most traditional buttercreams do look greasie well because it uses grease or butter. and you can either freeze it or if its well wrapped you can leave it out for up to like three weeks depending on the humidity level.

Informative excerpt from:

http://www.ochef.com/933.htm

Cream of tartar is best known in our kitchens for helping stabilize and give more volume to beaten egg whites. It is the acidic ingredient in some brands of baking powder. It is also used to produce a creamier texture in sugary desserts such as candy and frosting, because it inhibits the formation of crystals. It is used commercially in some soft drinks, candies, bakery products, gelatin desserts, and photography products. Cream of tartar can also be used to clean brass and copper cookware.

i have seen recipes with the imbc or smbc.. some use cream of tartar with the beating of the eggwhites.. not all recipes call for it though. i don,t think most people use it in reg. american buttercream.. but don,t know that though.. i don,t anyway... i don,t even use meringue powder in my american style buttercream.. either hi-ratio shortening or hi-ratio shortening and butter ..