if you seal up weed for a long time without fresh air, it'll turn brown over time. a few actually prefer this. I don't think it's too popular. O2 breaks down terps/thc, so it's a tough situation. You let fresh air in and avoid it, but then you hasten degredation of the buds exposing it to o2 to avoid anaerobic bacteria.
if it wasn't sealed for a long time and you opened up the container 1/week or more, then it might be some sort of rot.
smoke it.. if tastes bad and incredibly harsh, lol it's probably pathogen related. -- not the leaves, obviously rip those off. 1 puff won't kill you. ask a less-favored neighbor to smoke it, lol.