I'm fairly new to making royal icing (I'm just a home baker, I don't sell my baked goods), and I wanted to make some iced sugar cookies.

I followed a recipe that called for Meringue powder... It turned out really good, tasted great, I was really happy with it. Until it dried. It took a LONG time, it stayed tacky on top for pretty much an entire day. Finally it dried, but it was flaky and had a crystal-y texture. It also went from shiny & pretty to really dull & flat finish...

I read on here that RI can be stored at room temp for a couple weeks in a sealed container, and since I made such a HUGE batch, I put the leftovers in a container. I checked it after a couple days, and it had seperated & the top layer was crystal-y, & had a "fluffy" consistency...

I have NO idea what the heck was up with my icing, but the texture was gross enough that I ended up tossing the cookies out. Any ideas??

Not sure why it went crystally. Haven't had that happen. But when you store leftover RI it gets a marshmallow spongy type texture, that is normal. Just stir it up gently with a spoon or whatever, you don't want to incorporate air into the mix.

Hopefully someone else knows about the crystallization of the RI. I haven't had that and I use the Wilton Brand Meringue Powder and their recipe. I also use pasteurized egg whites with out issue.