Author Topic: preboil vs postboil gravity  (Read 636 times)

Offline goschman

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preboil vs postboil gravity
« on: January 20, 2014, 02:54:36 PM »
Had a preboil volume of 6.5 gallons and 1.042 gravity. Postboil gravity was 1.047 which means I should have had a post boil volume of 5.8 gallons correct? My post boil volume looks closer to 5.4 gallons and I doubt I lost 0.4 gallons when transferring from the kettle to the fermenter.

I made one small change to my process and my preboil efficiency was 75%. From my postboil measurements, my efficiency appears to be 70% which is about what I average. I don't know if the small change I made may have increased the efficiency or not.

Any thoughts? Should I just use my preboil gravity to calculate my efficiency?

Offline denny

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Re: preboil vs postboil gravity
« Reply #1 on: January 20, 2014, 03:05:16 PM »
If you want to know your mash efficiency, use the preboil gravity.  If you want to know your brewhouse efficiency, use post boil into the fermenter.
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Offline goschman

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Re: preboil vs postboil gravity
« Reply #2 on: January 20, 2014, 03:19:58 PM »
Okay. I suppose I should be tracking my mash efficiency instead of my brewhouse efficiency which is what I have been doing.

Offline klickitat jim

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Re: preboil vs postboil gravity
« Reply #3 on: January 20, 2014, 04:44:46 PM »
I only track brew house, IMO easier. I'd track mash efficiency if I was worrying about keeping a CFO happy, or if my mash efficiency was too high. All I care about is close repeatability. I also don't have 11 pallets of cans with an ABV printed and TTB looking over my shoulder

Offline ynotbrusum

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Re: preboil vs postboil gravity
« Reply #4 on: January 20, 2014, 07:26:15 PM »
Mash efficiency is helpful in deciding things like adjusting crush, comparing grains for a particular recipe and the like.  Brewhouse efficiency for me is less important between the two, but mine is typically in the low 70's, which I accept given my system.  YMMV, of course.
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Offline erockrph

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Re: preboil vs postboil gravity
« Reply #5 on: January 20, 2014, 07:44:39 PM »
Brewhouse efficiency is a bit easier, but with the amount of hops I use, preboil is my best gauge for measuring consistency. Plus, I'd prefer to know if I'm going to need to adjust my gravity as early on in the process as possible.
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Offline amh0001

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Re: preboil vs postboil gravity
« Reply #6 on: January 20, 2014, 08:16:36 PM »
You can use this to figure out your efficiency.

http://www.brewersfriend.com/brewhouse-efficiency/

Beer Smith uses Brewhouse in the eff field.

Also to figure out how much you boiled/changed gravity use this:

http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

Hope that helps. I use these all the time

Offline klickitat jim

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Re: preboil vs postboil gravity
« Reply #7 on: January 20, 2014, 09:27:20 PM »
I use brewers friend too. Works great for me since I'm android only. Very handy

Offline HoosierBrew

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Re: preboil vs postboil gravity
« Reply #8 on: January 21, 2014, 06:12:16 AM »
Brewhouse efficiency is a bit easier, but with the amount of hops I use, preboil is my best gauge for measuring consistency. Plus, I'd prefer to know if I'm going to need to adjust my gravity as early on in the process as possible.

+1.  I measure preboil so I can adjust if need be as well.
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Offline goschman

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Re: preboil vs postboil gravity
« Reply #9 on: January 21, 2014, 09:30:47 AM »
Thanks everyone. I use Beersmith for approximating volumes, gravities, etc.

I guess I am just baffled at how my post boil volumes are extremely inconsistent. That is what makes it hard to use brewhouse efficiency. If my post boil volumes were always the same like my pre boil volumes than I would be more inclined to do so. My burner is always set to the same level and the amount of hops I use in the boil really doesn't vary much. I guess I am just confused...

Offline hoodie

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Re: preboil vs postboil gravity
« Reply #10 on: January 22, 2014, 09:42:41 AM »
In my experience, if you don't stir the wort well before taking a reading you can get different results.

Offline Slowbrew

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Re: preboil vs postboil gravity
« Reply #11 on: January 22, 2014, 10:02:23 AM »
I am probably doing it incorrectly but I take my "Pre-boil" reading right after the hot break.  I've always assumed the wort was thoroughly mixed at that point.

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Offline HoosierBrew

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Re: preboil vs postboil gravity
« Reply #12 on: January 22, 2014, 10:03:56 AM »
I am probably doing it incorrectly but I take my "Pre-boil" reading right after the hot break.  I've always assumed the wort was thoroughly mixed at that point.

Paul

+1.  Same here.  Turbulence of the boil seems to mix things more uniformly.
Jon H.

Offline goschman

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Re: preboil vs postboil gravity
« Reply #13 on: January 22, 2014, 10:26:02 AM »
I make sure that I take my samples after mixing the wort thoroughly. I do not however take my preboil reading after the hot break but right after collecting the second runnings.

Offline dkfick

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Re: preboil vs postboil gravity
« Reply #14 on: January 22, 2014, 10:37:44 AM »
Possible reasons for a lower post boil volume than expected:
1) Hops absorb wort
2) Trub left behind that used to be in the pre-boil wort
3) Wort shrinkage during cooling.

I think the above 3 reasons could easily account for 0.4 gallons 'missing'
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