I often see the question, "Does this buttercream recipe crust well?" What does this mean? Why does it matter if the buttercream crusts? I always put fondant over my buttercream. I'm still learning to make it look good. Does crusting buttercream make a difference in the end result with fondant?
Crusting Buttercream refers to buttercream finished cakes. It will be used for a cake NOT covered with fondant (I think)
When you ice a buttercream cake, you will let it sit for about 20 minutes after you have iced it to get a slight crust to it. If you want a very smooth flawless finish, you run a fondant smoother and a Viva paper towel over the buttercream. (That is why you want it to crust, so the paper towel doesn't stick)
Some people go a step further after smoothing with a Viva towel. They will use either parchment paper or computer paper to get a perfect finish.
Using this method for a buttercream also allows for quick fixes when a finger is inadvertently stuck in the buttercream. You just pull out your handy dandy fondant smoother and paper towel and rub away on the cake, and the finger mark disappears like magic!
Hope this answers your question...
I use crusting buttercream under fondant. It allows you to wipe it down with a damp paper towel making it slightly tacky for the fondant to stick to it.
Crusting buttercream is usually a buttercream made from fat (crisco/butter) and powder sugar and is a non cooked buttercream.
The outside of the buttercream will form a crust so that when you touch it, after 10-20 mins it doesn't stick to your fingers. This is nice for smoothing with paper towels, wax paper or other like things.
Cooked buttercreams like IMBC or SMBC do not crust, so they remain sticky or tacky on the surface.
You can use either crusting or non crusting buttercreams under fondant. If it is a crusting one you just need to light wet the surface to get it to stick.