I decided to run a little experiment today to determine how grain crush might affect mash efficiency for a BIAB set up. I think this was more to prove what is considered common knowledge: for BIAB, a finer crush will lead to better extraction. The basic setup: I crushed a Pils malt on 6 different settings on my Kitchen Aid grain mill. I added 2oz of each crush into hop bags and placed them in 6 coffee cups. (Color coordinated so I wouldn't forget which was which!) I heated a strike water to 155. "Mashed in" and placed the coffee cups in the oven at 155. Mashed for 90 minutes. Removed the bags, squeezed whatever wort I could get, and discarded the grains. Cooled to 68 and took gravity readings. Crushed grains from coarsest grind (top left) to finest (bottom right). Mash In Post Mash Gravity readings from coarsest grind to finest: Blue cup:1.040 Red: 1.044 Green: 1.046 Yellow: 1.046 Gray: 1.049 White: 1.050 Yellow reading: White reading: Blurry, but it was 1.050. I suspect there is a trade-off here at some point. The finer the crush, the more extraction and the more solids that will pass through the bag. Maybe that means more trub left behind in the kettle or in the fermenter?? Maybe water volumes would need to be adjusted to hit batch volumes?? Are there tannin issues to consider?? It's a process. But for me, the crush/extraction question is settled. Now to make some sense of it.