I know its been done before but I thought I would share my experience about brewing with 100% oat malt (some Golden Naked oats for color/flavor). Recipe is at the bottom.
I got the oat malt from a local craft maltster. He didnt even have a CoA yet. I have no idea what the diastatic power or extraction of the malt was. He told me that it was the easiest grain he'd ever malted. Grows the oats himself.
The oat malt that I got was much narrower than your standard two row barley. But the grains were a little longer too.
I milled the oat malt at a slightly narrower than normal gap and noticed that the malt was not really crushed at all - maybe 10% of the grains were broken open. Narrowed it quite a bit (didnt measure the mill gap but it was tight) and re-milled. The malt looked like it had a good-ish crush and I left it as is.
My goal was a easy drinking blonde ale. OG of about 1.045 and ~20 IBU.
I had anticipated poor efficiency (oats have a lot of husk compared to barley), but it surprised me just how bad it was. I also anticipated poor yeast attenuation (oats reportedly have higher lipids and proteins compared to barley), but again, I was surprised how poor it was.
Mashed for ~ 2 hours. Started at 140 and slowly worked my way up to 155, hoping to eek out every bit of fermentable sugar as possible. I mashed and boiled using the Digiboil 35L. I added 1 tsp of amylase enzyme at ~150 to try to account for a potential lack of enzymes in the oat malt. No problems with sparge/lauter - all of that husk in the oat malt really makes it easy.
Sparged just over 5 gallons to boil down to 4 gallons. I added the hops per the schedule below. A tsp of yeast nutrient was added at the end of the boil. OG was 1.035 with an estimated mash efficiency of 62% - this is a guess based upon what Thomas Fawcett states is the extraction of their oat malt (28ppg).
I suspect that I still didn't mill the malt fine enough - a post inspection of the mash showed a fair amount of malt that was not cracked. I think the malt needs to be milled twice, with the second mill gap needs to be tight enough that all the malt has been crushed.
Chilled to ~90f and pitched Omega Lutra yeast. A liter of oxygen was added prior to yeast pitch. Temperature was held at 93f for 4 days, the gravity had reached terminal of 1.017. I was hoping closer to 1.010. Alcohol came in at a whopping 2.5% abv.
Impressions out of the fermenter....More bitter than I expected. Aroma is strongly 'oaty'. Tastes like slightly hoppy oat milk. Doesnt taste like beer at all. I'll see how it is after its cold and carbonated.
I really want to get that CoA of the malt from the maltster...maybe it would explain some of the issues with mash efficiency and attenuation. If I do this again with the malt I have left I will ensure a better crush and add more enzymes (glucoamylase) to the mash to help with fermentability.
...on a positive note it is gluten free.
Batch Size 4.00 Gallons
Boil Size 5.00 Gallons @ 60 min
Color 5.0° SRM
Bitterness 23.1 IBU (tinseth)
Alcohol 2.5% ABV
Calories 116 per 12oz
89% 8lb Oat Malt
11% 1lb Golden Naked Oats
0.25oz Centennial Pellet Boil 60 minutes
0.25oz Cascade Pellet Boil 30 minutes
0.25oz Centennial Pellet Boil 15 minutes
0.25oz Cascade Pellet Boil 5 minutes