Unsugared Frosting Substitution question

[Phhase]

...baking counts as a science, right? Anyhow, I'm making a cake for a friend's birthday, and in order to be a bit nicer to their guts, I'm trying out some sugar-that-isn't to make it sugar free. I located some allulose (least disagreeable sugar substitute I've found to date, pretty good), and a test run of the cake base shows it works just fine for the sponge. Does anyone know if alluose can just be swapped out for sugar when making (buttercream type) frosting, though?

[Lord Torath]

You could probably use it for making icing.

Frosting, however, usually requires powdered sugar for texture. If you can get a powdered version of your sugar substitute, I forsee no difficulties. If not...

You might see if America's Test Kitchen or Milk Street Radio have any suggestions.

[tyckspoon]

If you have access to something like a spice grinder, mortar and pestle, coffee grinder, or even a good blender or food processor you can probably grind just about anything down to the level of fineness of powdered sugar/confectioner's sugar given sufficient time.

..note you can probably make a frosting or icing without doing so - the difference will be primarily in the texture of the resulting product. Larger crystals of sugar or sugar substitute will be more likely to not integrate completely and potentially leave your frosting feeling crunchy or gritty, which can be unpleasant to eat and may cause it to not spread or cover your cake as easily.

One of the other things to monitor will be your ingredient balance - looking it up it appears allulose is less sweet than standard sugar (which is interesting, most alternative sweeteners are notably more sweet than reference sucrose.) This suggests if you want to reach the same level of sweetness as a standard recipe you will need to use more allulose, so your resultant frosting will probably come out denser and heavier feeling, and it may be harder to whip or beat it into fluffiness if that is your desired texture.