In the past week I noticed that the sweet, pleasant odor that I normally smell while standing near the front of my hive had taken on a sour tinge. Today while inspecting my hive I noticed it even stronger. I have read that European foulbrood may cause a sour odor, but I didn't notice anything visibly out of the ordinary in the hive. Does a large amount of unripe honey in the hive cause this? I have been feeding the bees sugar syrup heavily because they were queenless for a long time and the stores weren't good. There is now a large amount of uncapped honey in the hive. I just finished treating them with terramycin. Any info on this would ease my mind and educate me, as this is my first year keeping bees.