I had read enough about it under the fermented feed thread that I just jumped tight into it. I've had no problems but do suggest you smell it occasionally to make sure it's not going bad. Also if you see abnormal mold on it, there's a difference between what you should see growing on it and bad...
You can tell by looking at it, the difference between the yeast growing on it and mold. You can tell by the smell also, it should smell like fermenting sour dough, or fermenting veggies. If it smells bad, it is bad. Not to say that it smells great, but not like it is rotting. However, I refuse...
There's a couple of threads on the forum here about it. Essentially what you are doing is taking the chicken feed that you normally feed your birds, and adding water. Take 3-4 days worth of feed and cover it in water. Stir it up and let it sit for 3-4 days. The natural yeast that's on the grains...
Or, you can use that as a reason to start feeding fermented feed. Takes a little time but it's healthier, and easier for the chickens to derive the nutrition from. Also, you go through about 1/3 less feed with the fermented feed. Just sayin'.