Milling questions: specialty grains crush well, base malts do not

[ManSkirtBrew]

Been trying to diagnose low efficiency issues. The culprit seems to be a low conversion efficiency. I've been in the low to mid 80%s based on my first wort gravities. My understanding is conversion efficiency should be close to 100%.

When I used pre-crushed base malt, my efficiency jumped, so that helps confirm my theory.

I'm using a 3-roller mill with a 0.047 gap. Specialty grains look perfect, but base malts seem to have a lot of uncrushed grain. Seems to be worst with Maris Otter, which I use a lot of. Is this normal? Do I need a set of sieves to evaluate further? Should I just run base malts through twice? Should I go to a finer setting on the mill?

Specialty:



Base (Belgian Pils in this shot):

[stephenstraub]

Based on your pictures, I agree with your own assessment regarding the crush. That belgian pils doesn't look like it is being milled finely enough. In my experience, marris otter is more friable than the 2-row american base malt that I use, so I guess that I would expect a better crush from the MO than implied in your message. IMO, try closing the gap...keep in mind that (generally) your C malts are much less than your base, so even if they're getting too fine a crush, it's not likely that it will effect your lauter performance. Small steps --> don't make too large of an adjustment at once. What data are you using to calculate your efficiency (hopefully the lot data for your base malts etc)?

[ManSkirtBrew]

Thanks for the input. I'll tighten up the crush on my next batch and let you know how it goes.

I've been calculating conversion efficiency based on the chart here.

[CharlosCarlies]

Yeah, looks like your gap is set too wide based off the base malt. As mentioned above, we pretty much expect our specialty malts to be completely obliterated, but since it's such a small % of the grist it doesn't have a significant effect on lautering performance.

When testing our crush, we always use our most popular base malt and make minor adjustments if/when switching things up for a one-off/specialty beer. We haven't had much luck w/ sieves simply because we didn't plan a good way to get a meaningful sample; however, our SOP now is to slowly widen the gap until we can see uncrushed kernels w/o having to try very hard, then tighten back a step or two. Not perfect, but for a lot of small breweries it's just going to be (hopefully educated) trial and error.