I have a lot in my pantry to use up since I was making American buttercream for a couple years now but want to start making SMBC ( Swiss Meringue Buttercream). No recipe I've found uses powdered sugar. What's the science behind not being able to use it?
you're making a meringue with hot eggs and sugar
I do not know the science behind it, but I really do not think it would work. I use a lot of powdered sugar making my own fondant and gum paste. Just a thought.
Many brands of powdered sugar contain small amounts of cornstarch. I've read that the cornstarch will dry out the meringue too much.
That being said, I have seen recipes for French meringues and pavlovas that use a mixture of granulated and powdered sugars. I've never tried it with an SMBC recipe, though.