Brewhouse Efficiency Primer

Having about 15 all-grain batches under my belt, I have a pretty solid grasp of my equipment and I’ve done well at hitting my brew-day numbers with one nagging exception: original gravity.

In all-grain brewing, OG is a product of brewhouse efficiency, a simple calculation using the amount and type of grains and volume of wort produced. It essentially describes how well brewers are able to extract sugars from a grain bill, measured against the theoretical maximum gravity that might be obtained from said grains.  A oft-used rule used by homebrewers is to aim for 75% if you’re unsure what to expect. As an example, if we apply that to a grain bill like the following…

  • 8# Marris Otter
  • 1# Crystal 40L
  • 8oz Carapils
…we can expect our OG to be 1.053 for 5 gallons of wort. If your pre-boil gravity is 6.5 gallons, you should expect that wort to be 1.041 before it’s boiled down. So having glossed over the math entirely, the point I’m really getting at is this:

Brewer’s Axiom #17: In order to craft recipes and make an informed expectation about the kind of beer a given grain bill will produce, a brewer must know his expected brewhouse efficiency

I made that up just now, but that doesn’t make it any less true.

At the homebrew scale, grain crush is a primary driving factor in one’s brewhouse efficiency, and it’s the first thing to look at if you’re getting consistently low or sporadic numbers (people mess with the mill gap at homebrew shops constantly).  I started to realize just how big of a problem this has been for me while cleaning up from my New Years Day brew, which was Northern Brewer’s Extra Pale Ale kit. They list an expected OG of 1.045, which is about 70% efficiency based on a final volume of 5 gallons and the grain bill they list. I hit that volume dead on, but my gravity was a paltry 1.038, or 61% efficiency. The beer is drinkable, but only just. It tastes overly sweet  given the low alcohol level in the final beer (3.68% vs 4.59% expected). I dubbed it the Extra Mild Ale.

Just before mash-in, I looked at the crushed grains and thought, “That is waaay too course”, but there was little I could do at that point but brew, so brew I did. I thought this was an isolated incident, but after the brew was in the fermenter, I pulled out my brew sheets and found my efficiency has ranged anywhere from 59% to 78%, which is too wide a gap to base any recipes on. It’d be better to be be consistently at 60% than all over the board, so I set about to solving the issue the best way that I could: buying a mill.

I wanted something that would last me, made by a company that would stand behind their product if it didn’t. I settled on the mill that Rebel Brewer is having manufactured under their name. It arrived a couple weeks ago, and I was able to use it for the latest round of my India Rye Ale.

I’ll have a full writeup coming this week covering the unboxing and crush in-depth, along with some numbers to go along with it, but my initial impressions are nothing but good. This thing is built to last, and I’m excited to put it through it’s paces this spring with some more batches.

Stay tuned!

Rebel Mill