This thread is a little old, but I see that there is still a huge lack of understanding about oat beers out there. I have been pursuing oat beer brewing now for about a year, and at this point I brew nothing except 100% oat beers in several styles.
I am not a beer judge, so I will not try to describe flavors and feelings in great detail. All I can say is they come out clear, and also tasty!
I use a Grainfather G30 for my mashtun, and a BrewBuilt X1 UNI+ for my fermenter.
Here is a grain bill. All of my recipes are variations of these 4 ingredients...
10 lb Oat Malt
5 lb Golden Naked Oats
1 lb Flaked Oats
.25 lbs Special ****
To make the special ****, line a cookie sheet with aluminum foil. Set the oven on 400 degrees F. Place .25 lb oat malt on the foil and bake for 55 minutes, or until the color is nice and dark. Let it cool. Everyone will tell you to put it in a paper bag for 2 weeks to let it "breath". I don't. I use it right after it has been roasted. Add more or less as you desire o adjust the color of your wart.
I mill all of the grains myself. I have found that the malted oats are more narrow than normal barley. The Golden naked oats (since they are de-husked) are even more narrow. You have to feel your way, but I have my mill set on it's smallest setting.
Don't expect a high efficiency. If you plug the grains into a recipe maker, you will get a high projected ABV. I get 61% efficiency, meaning for the above recipe I get a starting SG of 1.046 and a final gravity of 1.013 for a ABV of 4.33% in a 6 gallon batch. The low ABV is on purpose, I am trying to cut back on my alcohol intake
I'm not sure why the efficiency is so low, I am still working on that. I do know it is because of the oats - I get normal efficiency with barley.
The other thing to note is that I add .25oz Amylase enzyme in the mash. Honestly I don not know if it really requires it, or if there is enough enzyme in the oat malt to handle it. I have it scheduled as a future experiment to find out. For now I just add it in and everything seems to work.
The ratio of grains is important. I'm not exactly sure where the limits are, but the above grain bill works. As you increase the golden naked oats over 5lb or the flaked oats over 1 lb you run the risk of a stuck mash, so be careful with that. One time I tried 10lbs of Golden Naked oats. It did not go well. Oat malt itself will help with the sparge, and Golden naked will hinder it, as a general rule.
So, that is most everything that I have learned so far about 100% oat beer.
Hopefully you can get some useful information out of this. I haven't exactly been a saint my whole life, so if the world can benefit even just a smidge by this info maybe I will not be judged so harshly in the hereafter!