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Old 07-13-2009, 05:47 PM   #1
BrianCSA
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Default Beer Math Challenge!

So I brewed my first solo beer last weekend. I messed up the OG reading by taking it out of the Mash Tun instead of after the boil. If I supply the facts can you figure an approximate ABV and tell me how you got it?

I gathered an unknown quantity of 1.049 (adjusted for temperature) out of my mash tun. I boiled for one hour (60 minutes) and ended up with exactly 5 gallons of post-boil wort in my fermentation bucket. That wort fermented out at 1.012.

Too difficult? Obviously an exact answer is not possible but I think a good estimate should be feasible.

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Old 07-13-2009, 05:54 PM   #2
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A preboil gravity of 1.049. What do you use to boil with?
If I estimate with my usual boil off and trub leavings I'd guess you were in the neighborhood of about 1.056 OG....

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Old 07-13-2009, 05:55 PM   #3
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I boiled in a 15.5 gallon keg from Sab Co. Have gone from "brewing buddy" to "brewer" so I have to learn to pay much more attention to the details.

Edit: With a 60,000 BTU Hurricane Burner.

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Old 07-13-2009, 06:36 PM   #4
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You are most likely anywhere between 56 and 65 on the gravity. If you boiled the hell out of it then high side, if it was a gentle boil then lower.

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Old 07-13-2009, 09:27 PM   #5
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You ended up with 5 gallons. How much was in kettle before the boil started? If we knew that, it would help a lot.

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Old 07-13-2009, 09:37 PM   #6
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I use a Sabco kettle and live in Oklahoma with similar climate.

If nothing else, I'll provide a guess as to starting boil volume being 6 gallons. My boiler burns off about a gallon per hour in 40 to 50% RH and it's rated about 60k btuh on propane.

What yeast did you use and at what temp did you ferment?

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Old 07-14-2009, 06:54 PM   #7
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Nottingham Yeast and between 65 and 68 degrees.

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Old 07-14-2009, 07:03 PM   #8
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If you got 80% attenuation out of the Nottingham (not unusual, unless you had a lot of unfermentables) then your OG was 1.060. If you boiled off a gallon, then your OG was 1.059; 1.25 gallons = 1.061; 1.5 gallons = 1.064.

I'd call it 1.060

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Old 07-14-2009, 07:30 PM   #9
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(Grav Units 1) x (Volume 1) = (Grav Units 2) x (Volume 2)

We are searching for Grav Units 1. But first we need to estimate boil-off rate. I use a keggle and get about 1 gallon per hour. You could be more or less (I STRONGLY recommend knowing this variable about your brew system and using it to target pre-boil gravity!!!). This is the only estimate we have to make. Let's say 1 gallon boil off per hour.

So (Volume 1) = (Volume 2) + (B.O. Rate) = 5 gal + 1 gal = 6 gal

Back to the original formula:

(49) x (6 gal) = (Grav Units 2) x (5 gal)

(Grav Units 2) = 58.8

or Specific Gravity 2 = 1.0588 or 1.059


Use the method I just laid out or the attenuation method used by previous poster (Flying Horse) works just as well. Either way, since we all are comingin at the same number, it helps verify it. I'd say your OG was either 1.059 or 1.060.

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Old 07-14-2009, 07:41 PM   #10
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Thusly,

(OG 1.060 - FG 1.012) x 131 = 6.29% ABV

I forget where the 131 comes from.

Damned $20 softwares making everything to easy.

Um, Hint, Hint.

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