Author Topic: Calculating correct OG  (Read 356 times)

Offline howlinghound

  • Cellarman
  • **
  • Posts: 27
    • View Profile
Calculating correct OG
« on: January 14, 2014, 07:11:08 AM »
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

Offline Steve in TX

  • I spend way too much time on the AHA forum
  • ********
  • Posts: 2921
    • View Profile
Re: Calculating correct OG
« Reply #1 on: January 14, 2014, 07:16:00 AM »
That's how I have done it in the past.

Online Jimmy K

  • Official Poobah of No Life.
  • *
  • Posts: 3604
  • Delaware
    • View Profile
Re: Calculating correct OG
« Reply #2 on: January 14, 2014, 07:16:33 AM »
Looks correct to me!

- Sent by my R2 unit

Delmarva United Homebrewers - President by inverse coup - former president ousted himself.
AHA Member since 2006
BJCP Certified: B0958

Offline Joe Sr.

  • I spend way too much time on the AHA forum
  • ********
  • Posts: 2889
  • Chicago - NORTH SIDE
    • View Profile
Re: Calculating correct OG
« Reply #3 on: January 14, 2014, 07:42:16 AM »
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.
It's all in the reflexes. - Jack Burton

Offline dmtaylor

  • Senior Brewmaster
  • ******
  • Posts: 1320
  • Two Rivers, WI
    • View Profile
Re: Calculating correct OG
« Reply #4 on: January 14, 2014, 07:54:01 AM »
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.
Dave

"This is grain, which any fool can eat, but for which the Lord intended a more divine means of consumption. Let us give praise to our Maker, and glory to His bounty, by learning about... BEER!" - Friar Tuck (Robin Hood - Prince of Thieves)

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3545
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Calculating correct OG
« Reply #5 on: January 14, 2014, 01:53:13 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.
Beer is like porn. You can buy it, but it's more fun to make your own.
seanterrill.com/category/brewing
twomilebrewing.com