The crop is the storage pouch at the base of a hen's neck where food sits before moving on to be ground and digested. Overnight, a healthy crop empties completely. Sour crop develops when that emptying slows and yeast multiplies in the warm, stagnant contents, fermenting what should have passed through. The condition rewards a simple habit: feeling the crop first thing in the morning, before the flock is let out to feed.
The morning crop that never emptied
The single most useful sign is timing. Catch the hen before breakfast and feel the crop low on the front of her neck. A sour crop feels full, soft, and doughy or fluid-filled, sometimes with a gentle squelch when pressed lightly, on a bird that has had nothing to eat for hours. Compare her with a flock mate handled the same way; the healthy crop is flat and hard to find. A crop that is hard and packed suggests impacted crop instead, a different problem, so the squishy, fluid feel is the detail to report.
The smell and what you can see
Fermentation gives sour crop its name. Bring the hen close and you will often catch a sour, yeasty odour from the beak, particularly if she is handled or tips forward. Some hens develop white or cream-coloured patches inside the mouth and throat, visible if you open the beak gently in good light. Regurgitation of sour fluid when the bird is picked up happens in more advanced cases and is a sign to handle her carefully and upright, since inhaling that fluid is a real risk.
How the hen herself behaves
A hen with sour crop gradually loses interest in the feeder, picks at food without eating much, and may drink a great deal. She will look fluffed up, spend time standing apart from the flock, and lose weight over days because little of what she swallows is getting through. Laying usually drops off. Because the crop problem can follow other illnesses, antibiotics, or a spell of eating long grass and other slow-to-clear material, note what the flock has been eating and any recent treatments.
Keeping track across the flock
Record which hen is affected, when you first felt the full crop, what the flock's feed and ranging have been, and whether more than one bird shows signs. One hen with a slow crop after gorging on long grass is a different story from several hens affected at once, which points back to feed storage, mouldy feed, or something shared in the environment. Dates and details written down at the time beat a reconstruction a week later.
When a vet should see her
Book a vet visit if the crop stays full for more than a day, if the hen stops eating, loses noticeable weight, or keeps regurgitating, or if sour crop returns repeatedly in the same bird. A vet can check for an underlying blockage or illness driving the yeast problem rather than treating the fermentation alone. Keeping each hen's episodes, laying changes, and feed notes together in KinsLe's Pet Passport makes those repeat patterns easy to show at the appointment.