If mine have a sour crop I will separate them from the others and I withhold food and only give water with Apple Cider Vinegar in it for the first day. I also massage the crop and to try and get things broken up and moving through in there. You might need to massage every hour or two to work things through. The next morning, if the crop is down pretty well, I will then give olive oil soaked in bread. I still use the ACV in the water. If things look good after that, I will start them off on some yogurt and then progress to feed if everything else seems to be moving through OK. The sour crop is from grasses or seeds that get stuck in there and start to ferment and grow yeast in there. For the impacted crop that isn't sour, I concentrate more on the olive oil and massage to get that ball broken up in there. However, I just learned from my sweet Favorelle hen Shirley that I lost yesterday, not all sour crops feel like a water balloon. I found hers to late. It felt more like sludge was in there and it was not real large. I started to massage her crop and feel around and an awful odor came from her mouth. I figured it out too late. So, I will also say if the crop feel sludgey in there, I would treat for sour crop. You can also treat sour crop with Nystatin but you do need a prescription for that.