[kpfoleyjr]

My last two batches have missed the OG reading (by as much as 10 points low) and FG reading (by as much as 6 high).  The only thing that has changed is the use of a new Barley Crusher Malt Mill - everything else is as before (in which the grain crushed instead at the LHBS), where I usually got the readings spot on.  The mill is set to .036; I didn't readjust it any higher or lower from the factory setting because it seemed about right.  Could the new grain mill and its setting be causing the missed gravities? 

And after 7 days in the primary fermenting at 68 degrees, all bubbling in the airlock has apparently stopped, and my Christmas Porter reading is 1.025, where it should have been the estimated (by BeerSmith3) 1.019 - is there anything I can do to get it lower (add more Wyeast 1056?  Raise the temp of the beer?).  Everything was going fine until now!

[a10t2]

That's pretty much a smoking gun as far as the OGs go. Tighten the gap a bit (I have my BC set at 0.030") and presumably things should go back to normal.

FG is harder to troubleshoot; even if your software was making good predictions before there's a ton of variables that could explain a couple batches being off. I definitely wouldn't take any action until you determine if crush alone solves the problem - assuming there is one.

[BrewBama]

If the only thing that changed is the mill then I think that’s your smoking gun.  You might give the LHBS store a call and see what their mill gap is. Maybe adjusting yours to the same gap will solve the mystery.


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[Robert]

^^^^
+1, set it up like the shop if they were milling your grain before.

And might this explain fermentability to some degree?  I'm thinking, longer mashing at a given temperature generally results in a more fermentable wort.  If the crush is causing it to take longer to get all the starch hydrated accessible to the enzymes,  that effectively means a shorter mash time for some of the starch, ergo, less fermentable.  Just a thought.

[kpfoleyjr]

Just left the LHBS after measuring the gap on its Barley Crusher.  Wouldn’t have believed it unless I measured it myself, but it was .053!  Stopped at Three Floyd’s to think about it; going back home afterwards to do some experimenting and comparing crushes at my .036, the LHBS .053, something in between, and something tighter than .036.  I’ll see what looks best, and brew again to see if there’s a difference.


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[Robert]

Now you've got a real head-scratcher there haven't you?!

[BrewBama]

This reminds me of an MBAA podcast (?) I heard a cpl months ago that describes a brewpub chain increasing efficiency by doing nothing more than increasing mill gap. The speaker was discussing fluid flowing thru a medium. He said by crushing finer, the liquor could not get to all the starches as easily due to compaction of the grain bed. The same liquor could flow thru a more course grist which allowed greater starch conversion. He said by opening the gap — he gave the measurement but I don’t recall what it was/is — he increased efficiency and lauter time. Of course, this is a much larger brew pub batch scale so YMMV.

Edit —

Here it is if interested: http://masterbrewerspodcast.com/079-brewhouse-efficiency-for-the-small-brewer

...and the presentation he discusses: http://www.craftbrewersconference.com/wp-content/uploads/ImprovingBrewhouseEfficiency-Havig.pdf

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[Robert]

BrewBama, I expect this is very equipment-specific.  For instance, you and I have recently had very different experiences tightening up our mill gaps, as I recall.   I also recall your confusing me with that Darcy's Law business,  so I probably can't tease out the details as I'd like.  But I can imagine that conversion and lautering might both be affected more in a single vessel, especially if you recirculate,  due to the issues you raise.  If you use a separate mash mixer that is stirred and a lauter tun, finer should (as in my experience) be just fine.  Conversion is ensured by stirring,  which won't compact the bed, and then it's just a matter of letting the flow rate in the lauter tun set itself.  Maybe.  It seems every topic lately on grain milling has come down to the caveat that you have to empirically determine what works best in your brewery.  I vaguely remember that podcast but not the brewhouse design involved.

(Looking back on my logs I don't seem to have seen any change in efficiency since going from 0.030" to 0.025".  It just lets me run wheat together with the rest of the grist.)

[BrewBama]

Which is why I included the disclaimer “YMMV”. I think it is VERY system and process specific.


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