I will be piping with SMBC using the grass tip. I've done a trial run, and the icing doesn't want to hold it's shape very well. I'd like to know if anyone has tips on how to stiffen the buttercream for piping.

Should I add powdered sugar to it?

TIA

I agree on the PS, but the it won't be SMBC. A better way to do it and to give it stability is to make a shortening/PS based frosting and combine the two.

But take a little bit and experiment with the PS before you add it to the whole batch. Sift the PS and stir it in by hand a bit at a time til you have a consistency you like. At least that is how I would experiment on it first.

Does anyone use ABC with butter/shortening to pipe only and use European buttercreams as usual?