I gave a try to (mostly) the same grain bill this weekend and got a very bad mash efficiency (48%), my usual mash efficiency is between 65-70%. I was aiming at 1.062 pre-boil and got 1.046, so I ended up adding 500gr (1.1lb) of corn sugar at boil in order to bring the gravity up, not sure that was a wise decision, beer is still fermenting. My grain bill is:
Golden Promise (Thomas Fawcett) 43%
Chateau de-husked Oat Malt (Castle Malting) 41%
Unmalted wheat 8%
Munich I 14EBC/~7L (Weyermann) 3%
Milk sugar (boil) 5%
I do BIAB full volume, this time I did half a batch (2.5gal keg) because I wanted to adjust the recipe before doing a full batch (NEIPAs are expensive hop-wise). I warmed the strike water to 74C (165F) added grains and checked temperature after stirring it was 68C (155F). Did a 45min mash, stirred once in the middle. Temperature at the end of mash was 64C (147F), it was a warm day, didn't reheat the mash at all.
It's the first time I've used de-husked oat malt from Castle, and I'm unsure if that was the culprit. I've used Thomas Fawcett oat malt in the past, but not in this amounts (20-30% of the grain bill tops) and turned out fine. I don't mill my own grains and rely on LHBS to do that. Grains where ordered like 1 week ago, so should be fresh.
I'm attaching a photo of the milled oat malt, maybe it should be more finely crushed?
Should I increase my mash time for this kind of grain bill?
Do others get normal efficiency when brewing this style?
Thanks!