I've made Antonia74's recipe quite a few times now. Placed it in the freezer everytime. But this time I've taken out my colored RI & some still white but was thinned before freezing & it's grainy after thawing. I have used the same containers everytime & can't think of what could've gone wrong. When I thawed a few days ago I thought popping it in a microwave at 50% for a few sec was what did it, but after taking some other jars out that wasn't it. Why?

did you use a different brand of sugar? Usually a grainy icing is from using beet sugar instead of cane so that is where i would look first.

i would think the sugar didnt dissolve properly when it was made

I try another batch. I don't remember it being grainy when I made it, but I may not have tried it either. I always use Domino PS