I have not brewed in about 5 or 6 months and I have some DME left over. I am getting ready to brew a couple of batches. I want to use this left over DME if I can. It looks good, I don't see any mold or anything and it smells good too. Is there a way to tell if it is no longer usable? It was stored in a zip lock in a cool, dry place. Thanks....