I made my regular recipe and used the same brands as usual. This was a new batch of sugar as I had just bought a case (with a 10% discount, yay!!)of iciing sugar. 2 of the 5 bags used so far produced a gritty frosting. Other than sifting the sugar what can I do to prevent this?
Will it make a difference if I use shortening or margarine?

TIA

I made a batch of wilton buttercream last week that turned out a little gritty - I lost count of the sugar as I was measuring I think I added too much sugar - anyway, I added just a little more shortening and it was fine. Hope it helps.

I see that grocery stores are now caring "baker's sugar" in large boxes, instead of the tiny boxes they use to sell. This is the same stuff as the old English recipes refer to as "super fine" sugar. It is a fine textured sugar that breaks down into frostings and does not leave a gritty taste. I would suggest trying this if nothing else works.