I reserved some DME from my brew to use for priming. It wasn't much so I kept it in a clean and dry cup with some cling film (saran wrap) wrapped over the top and right around the entire cup, and then stored it in the cupboard along with the flour, sugar and teabags (all fine as normal).
I periodically had a look, and all looked fine, even a week ago, but now (3 weeks on from storing) it looks like this!:
ewww. It still smells nice, and looks somewhat spreadable :P
Has this happened to any of you reading? I wonder if it is still usable after a 10 minute boil, but If not and I go to my LHBS to by more DME, I'll have to worry about safely storing the rest of the bag for a month or two before any new batches.
I don't think it's particularly humid here (Scotland)!, but next time I'll be sealing it in a mason jar with a silica gel pack :P