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kkimmes 09-05-2012 04:18 PM

Newbie All Grain Question
I did my second all grain batch the other day. The NB Wee Heavy.
It was running late at night by the end of the brew day and I forgot to measure my gravity before I pitched my yeast and headed to bed.
I did however take a reading with cooled wort while I was doing my boil.
The pre-boil wort SG measured 1.074 with a recipe expected 1.083 SG.

Is there a way to estimate what the post boil SG would have been?

I started with 6.2 gallons when I began my boil and I boiled down to 5.4 gallons.

FWIW, the batch is gurgling away during fermentation. Pretty intense.....

Molybedenum 09-05-2012 04:23 PM

PbG * PbV / V

Should get you the post boil gravity. V is post boil volume, PbG is preboil gravity, PbV is preboil Volume.

kkimmes 09-05-2012 07:48 PM

Umm, I don't think that works.
I get 1.2331 for a SG
1.074 *(6.2/5.4) = 1.2331
If that was the case, I would be high on life and beer :)
Any other ideas, or just don't forget next time.....

Molybedenum 09-05-2012 09:19 PM

Take the 1 off, and just use the decimal portion. "070" would be 1.070, etc.

DocScott 09-05-2012 09:32 PM

1.085 at 5.4 gallons post boil

DocScott 09-05-2012 10:45 PM

This is able to be calculated bc the total gravity of your wort stays constant through the boil. Therefore, V1*gravity1=V2*gravity2.

In your case, V1 is 6.2 gallons, gravity1 is 74 (use the numbers after 1.--- in your read specific gravity) and V2 is 5.4. Solve for gravity2 = 85. Therefore your OG post boil is 1.085

kkimmes 09-06-2012 08:46 AM

Thanks for the help!

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