I made a batch yesterday, and it was my first time making smb by the way. Was super smooth and beautiful. So I stored it in an airtight container and put in the refrigerator overnight. I took it out today morning to frost my cakes and it was slightly hard to work with (naturally). So I started whipping it (as I read in a blog where I got the recipe from) and it started clumping! It looks horrible and I've tried everything but I can't save it :(((( it's got that grainy texture and I've attached a picture for reference. Is it wasted or can I save it somehow?
While we are on the topic, how do I use it after taking it out from the refrigerator? It can't be stored for later? 
You needed to let it come back to room temperature...
Whipping it while it was still cold probably caused it to separate...
You may be able to salvage it by letting it warm up and trying to re-whip it... Possibly warming up a small portion just slightly in the microwave... Not really sure though...
Others will have more and better information than I though...
I agree. too cold when mixed. When this happens I put it in the microwave on defrost for just a few seconds at a time, until it starts to soften around the edges then try mixing again until it comes together. OR, I keep slowly mixing in the mixer and gently warm the bowl with a blow dryer until it comes together which is easier, and fewer bowls since my mixer bowls are metal. I have had it separate to the point of clear syrup and buttery looking chunks when I wasn't paying attention, and I still "saved" it with the blow dryer trick. I routinely refrigerate, and even more commonly, freeze large batches of SMBC. Just have to allow lots of time for a complete thaw. Cutting the cold or frozen buttercream into smaller chunks and/or very carefully defrosting in the microwave can speed up the defrosting process, but I usually just set it out the night before. HTH.
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