I made a batch of royal icing Sept. 4, ten days ago. I usually never save anything leftover, unless I'm going to use within a day or two. But as a test, I saved 3 containers of it in different colors. I stored them in air tight plastic bowls with covers, kept them on a shelf in dining room where there was light, but also kept out of sun.
Today they look sick. The ingredients have seperated, there is a liquid on the bottom of each bowl and everything above the liquid is "very foamy".
There is no sign of mold, bad smell or discoloration.
Because I was just testing this, I'm wondering if this is bad batch, or is it the norm? I know it would have to be remix to reuse. Does this happen to your icing or should I have kept it in mason jars?
That is normal I believe - as long as they were cool and in a sealed container - you should be able to just whip them back together.
I make mine with powdered egg white and they seperate like that. I keep mine in those little gladware containers.
I have read many posts where people just say to whip it back up. I would say as long as it doesn't have a foul odor and it re-incorprates itself you should be ok.
HTH 
Mine also does that. I notice it more with the darker colors I use. I have always just mixed it back together and used it and things turn out well. Good luck.
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