Keeping Royal Icing Stiff

Lauren - once in the bag, mine stays pretty stiff.  I have actually used stiff icing I froze without having to remix after thawing.  I work from a very thick "concrete" base and add a few spritzes of water to make stiff icing.  I do tend to make smaller quantities though because it hurts my hand to have to squeeze a bigger bag filled with very stiff icing.  If I'm worried about the color and making more, I make a bigger batch and store it covered with plastic in a small storage container. 

I have more trouble keeping my flood icing at proper consistency - the more water I spritz in the mix, the more the chance of separation happening and having to remix the next day. 

I use Ali's Sweet Tooth's royal icing recipe.

Not sure what to advise. I only have separation of my icing, thick or relatively thin, after a few days in the fridge, and I rarely ever hold it that long. As it's used well before then.

I've been making a large batch of very stiff RI every two weeks.  I keep it in my mixing bowl, cover with a damp cloth, put a plate over it and put in refrigerator.  I think this was Callye's (Sugarbelle)  idea but I read so much, if I have misquoted, sorry.  If I have piping left in bag, I put a tip on the end, put it in a zip lock and throw that in the refrigerator until the next day.  I have not had to remix as yet but if I do, I will just put the bowl back on the mixer and mix until stiff again.  Flood icing usually has to be re-stirred the next day and sometimes I need to add a bit more icing.  I wrap my icing in Saran wrap per Karen at Karen's Kitchen, and it isn't any problem to dump it back ino a bowl, and then rewrap and put it back in the piping bag.  I haven't had much luck with icing holding up in the bottles.  It always seems to separate, but I will dump it out and remix it.  Hope this helps.  

Lauren, you might also try adding some cream of tartar into your icing if you don't already as well.