I call it mock buttercream, as it doesn't contain any actual butter. The recipe I use is this:
- 1kg Crisco
- 3kg Icing Sugar
- 1 1/2cups Water
- 2 Tbs butter flavouring

and then, depending on the flavour, I'll also add 1 cup of either dark chocolate or white chocolate ganache (I always have it in the freezer).

What would the shelf life be for the above mixture, prior to adding the ganache? I'd like to make it in bulk and store it either at room temp in a big air tight container (I'm assuming as it's basically just sugar and fat that it'd be stable?).

Please correct me if I'm wrong!

Personally I'd store it on the cabinet for a couple of weeks, fridge for up to a month and freezer for longer than that.

They use that as practice icing in culinary school because it never goes bad (until it develops mold) and you can just scoop it up and use it again. I wouldn't use it on a real cake if it had been sitting around for a long time, but that's just me. I think that people do it all the time, since it's probably what they use at supermarkets etc.