Fermenting: Put feed in bucket (about 1/2 full should allow for expansion), fill bucket with water. After everything settles and the feed has absorbed water, add more water so that the feed is at the bottom and there is a few inches of water over the feed. Add buttermilk, I usually put in a quart in a 5 gal bucket, but you can adjust up or down to "taste" (yeck). Cover and let sit for a few days, usually 3-5 days. Scoop out feed to give to your chickens, add more feed and water to the bucket. Once it has started fermenting you can just add more feed and water everyday to keep your supply up. Make sure you smell the feed....if it smells yeasty or bad in anyway, dump it and start again. Chickens will eat 1/2 to 1/3 less feed if you are feeding fermented feed. I know some skip the buttermilk, I think it just takes a little longer if you don't add it. Buttermilk should have live culture, most of the time it is labeled in the supermarket that way.
I'm sure everyone has their own formula, this is just the one that I have used in the past with success.