would a poor crush lead to a major decrease in mash efficiency?

yes, it is the first thing that people here ask about when someone complains about a low efficiency. Are you talking about 1055 vs 1065? Then that is very much a crush issue. I think you had switched to RO water, did you use that for this batch?

 

Also, did you happen to make a beer with a larger than usual grain bill?

 

Yes, my efficiency varied a lot when I had a homebrew shop crush grains. Presumably mill settings vary among shops, and probably from time to time within shops. The variability in my own efficiency seems to have been reigned in some since I got my own mill. It puts the crush in your control, so you can learn through experience what a quality crush looks like.

FWIW I also have experienced reduced efficiency when I have wheat in the recipe, which I think is because the grain is smaller and huskless - more kernels get through the gap without being crushed. Since 2 row varies in size, perhaps you get some variation due to grain variety too, but I have not consciously linked such an observation to my efficiency.

 

All of the above. Bigger beer = lower efficiency. Poor crush = potentially terrible efficiency.

I used about 10% rye malt in my recipe yesterday and neglected to account for the small kernel size, and knowing my gap is wider than it was previously (I opened the gap slightly about 18 months ago to avoid the potentially adverse effect of high 90% efficiency on perception of malt flavor and body in the final beer), so my efficiency turned out 2% lower than normal, resulting in missing my OG target by one point. Oh well.

I figure gravity points plus brewhouse efficiency to be almost constant. So if your average batch starts at 1.060 and your average efficiency is 75%, then your constant is 60 + 75 = 135. So then if you want to make a 1.074 beer, you would be wise to guess that your efficiency might fall from 75% to 135 - 74 = 61%. In reality it's not quite that bad but it's in the right ballpark -- maybe you should have assumed 65%. The reverse is also true for smaller beers, where efficiency can easily approach 85-90% with a really fine crush. For very small beers you can consider doing no-sparge to hit closer to ~70% efficiency like normal.

Hope this helps.

 

A good habit to get into is tasting the spent grain…still some crunch to it? poor crush…still sweet? poor sparge. A good brew should have basically tasteless husks you want to spit out.

 

That seems like good advice. For similar reasons, I'll never use spent grains in bread anymore... because it's only husks! When I make beer bread, I do however add crushed malted wheat to the bread. This gives it a lovely sweetish malty crunch... and with no husks!

 

I agree with this for fly sparging and to a lesser extent for batch. But I do a lot of "no sparge" and am used to some significant sweetness left over in the spent grains. For most styles, I just like the resulting beer better. Or at least I think I do.

 

My mash efficiency was all over the place and the only thing I could really point to was that people were likely "adjusting" the grain mill at my LHBS. I bought a grain mill about four months ago and my efficiency has been very consistent. Another plus to owning your own grain mill is that you can do malt conditioning and mill at a tighter gap. I won't mill grain any other way now.

 

Plus, buying base grains by the sack leads to major savings!