So I came across this thread and the thing that got me to read it was the "soft chest" in the title. I have an older buff orpington at home who has a really big chest. I was holding her in my lap the other day and when I push her feathers apart it seems like her chest is just there. lol. So reading this thread has me all terrified that she might actually have this sour crop as an issue. I tried looking up pictures online, but I havent found anything that looks like it, and she doesn't really have any of the symptoms as far as I can tell. But I am still new to the world of chickens and the thought of her having something wrong makes me sad. lol but overall interesting read thanks for the thread guys, always good to know about these things.
Impacted crop (sour crop, pendulous crop) is just a condition were something is stuck in the crop and food is not able to pass through to the gizzard. Your chicken's crop should fill throughout the day as they eat, especially if they are eating or grazing all day. What you should be worried about is if your chickens crop never empties and just keeps getting bigger and bigger. The best way to tell this is to check first thing in the morning. After they have been asleep all night and have not eaten anything yet the crop will be empty.
If you are concerned that your chicken may have an impacted crop then isolate the bird and stop feeding her completely. If she has not had any food for a day and her crop is still full then it is likely impacted.