# Homebrewers Association | AHA Forum

## General Category => Yeast and Fermentation => Topic started by: howlinghound on January 14, 2014, 02:11:08 PM

Title: Calculating correct OG
Post by: howlinghound on January 14, 2014, 02:11:08 PM
OK, so I finished a brewing new batch of Golden Strong (essentially the Zymurgy Nov/Dec 2009 p16 version) and I took an OG measurement of the wort in its undiluted state (straight off the boil and before top-off).

This was because I was mixing the top-off directly into the carboy and didn't want to reach into the final volume for a sample.

Anything wrong with this calculation?  Wort vol = 3.2 gal, top-off = 2.3 gal, total vol =5.5.  The gravity measurement of the concentrated wort was 1.12

((3.2 * 1.12)+(2.3*1))/5.5  = 1.0698 (call it 1.07 for calculated OG).  The recipe as printed shows OG=1.08

Thanks
Title: Re: Calculating correct OG
Post by: Stevie on January 14, 2014, 02:16:00 PM
That's how I have done it in the past.
Title: Re: Calculating correct OG
Post by: Jimmy K on January 14, 2014, 02:16:33 PM
Looks correct to me!

- Sent by my R2 unit

Title: Re: Calculating correct OG
Post by: Joe Sr. on January 14, 2014, 02:42:16 PM
Never thought of doing it that way, but it looks right and I like the approach.

Eliminates the weird readings from stratification of poorly mixed top off in the fermenter.
Title: Re: Calculating correct OG
Post by: dmtaylor on January 14, 2014, 02:54:01 PM
That calculation is correct.  An even easier way to do it is simply knock the 1. off the front of each reading and use "Gravity Units".  For example, 1.120 becomes 120.  So then the math is simply 120 * 3.2 / 5.5 = 70.  Then you put the 1.0 on the front again at the end to get 1.070.  Either way works fine.
Title: Re: Calculating correct OG
Post by: a10t2 on January 14, 2014, 08:53:13 PM
That'll get you close enough for brewing purposes, but it'll be a little bit off because SG doesn't scale linearly with volume. If you convert to Plato (28.75°P) and multiply by the mass fraction (0.6098) it's 17.5°P, or 1.0721 SG.