Efficiency Confusion

First, I would like to say that I finished an AG brew session in less than 4 hours today. It was incredible. 5 Gallons of my haus pale ale. That included clean up.

I guess when you factor in the 45 minutes I spent grinding 12 lbs of grain, it was 4.75 hours, but I did that before breakfast so that doesn't count.

Anyways--this was my first time using a corona type mill and crushing grain myself. I have to say I think I got the grain crush perfect, and the brew session went well--but now that I look at my efficiency numbers I am a tad bit confused.

My pre boil o.g. with about 6.75 gallons of wort (roughly, give or take .25 gallons) was 1.050 (this was temp corrected). Running my numbers into an efficiency calculator, I found that I had 80% efficiency. EXCITING!!!

However. my post boil gravity (again temp corrected) was 1.056. This was with about 5.5 gallons of wort.

This would be about efficiency of 70%. So how did I go from 80% to 70%? I'm confused.

My grain bill was this:

8 lb 2 Row Pale Malt
2.5 Lb Crystal 10
1 Lb Munich
12 Oz Carapils

Is it that when you talk about efficiency, you're really meaning how much sugar you extract? So that's the 80%? And then total efficiency (which people dont often talk about?) is what you actually get into the brew pot (The 70%)?

Can someone explain?

In theory it shouldn't change because during the boil the volume goes down and the SG goes up. But in practice you lose wort to hops and trub. I only ever calculate the over all beer in the carboy efficiency, which I call brewhouse efficiency, but that might not be the technical term.

Ben_Persitz said:

Is it that when you talk about efficiency, you're really meaning how much sugar you extract? So that's the 80%? And then total efficiency (which people dont often talk about?) is what you actually get into the brew pot (The 70%)?

Can someone explain?

Click to expand...

I think what is throwing you off is that final volume of 5.5 gallons. If you were planning on a 5 gallon batch and using 5 gal to find your target gravity, your OG is going to come in low at 5.5 gallons.


Here is how I look at it to help myself be consistent. I always take the OG and volume from the kettle. So if my target OG is 1.052 at 5 gallons, that is what want post-boil.

Now my "Mash" efficiency is typically 75% (or more accurately Mash + Lauter/Sparge Efficiency) so I know I need about 6.25 gallons of pre-boil gravity 1.042. Pre-boil gravity and volume for me, are the most important number regarding efficiency. Knowing that for given amount of grain I will extract 75% of the potential gravity into the kettle helps me determine how grain I will need for a given recipe.

On brewhouse efficiency, I am not as consistent. I always lose between a quart and 3/4 of a gallon going to the fermenter due to the amount of hops / break material I leave in the kettle.

I have found this to be really helpful:

http://braukaiser.com/wiki/index.php/Understanding_Efficiency

And this:

http://braukaiser.com/wiki/index.php/Troubleshooting_Brewhouse_Efficiency

It seems something in your measurements was off.

Did you correct for temp when measuring volumes? If you measured 6.75 gal at mash temp multiply by .97 (which gives 6.55 gal) and if you measured it near boiling temp multiply by .96 (which yields 6.48). Often people measure preboil volume at (at least) mash temp and measure postboil volume at room temp.

Also, when you measured the post boil gravity, was that volume measured in the kettle or in the fermenter? When you measure the preboil volume there usually are no hops in the wort. If you measure post boil volume in the kettle there are hops in there taking up volume, but if you measure post boil volume in the fermenter there are usually no hops. It also matters whether you use whole hops or pellet, whole hops absorb more wort which means more sugars are stuck in the hops (a bigger loss).

The other issue is that your preboil sample may have been pulled from a higher gravity strata if you didn't stir it.