Quantcast

Oops, measured OG before topping off

HomeBrewTalk.com - Beer, Wine, Mead, & Cider Brewing Discussion Community.

Help Support Homebrew Talk:

CallMeZoot

Well-Known Member
Joined
Nov 24, 2007
Messages
130
Reaction score
3
Oops, I just realized that I took my OG reading from the brew pot, before I added my top off water. Is there a reasonably accurate way for me to adjust my reading?

I don't know exactly how much was boiled off, but I estimate that I had about:

  • 3.5-3.75 gallons of wort after the boil (this is what I took the reading from), and about
  • 1.25-1.5 gallons of top off water.

Pre top-off, my temp-adjusted OG was about 1.062 (which I noticed was suspiciously higher than my software's estimation). How can I adjust this to get the real OG for my 5 gallon batch? (I use BeerSmith -- is there a calculator for this?)

Thanks,
chris.

P.S. It's been fermenting pretty heartily for 48 hours so it's too late to take another OG reading.
 

zoebisch01

Well-Known Member
Joined
Nov 15, 2006
Messages
5,180
Reaction score
11
Location
Central PA
Unfortunately, in this case not really. I say this because you don't have accurate measurements of your water amounts. What you do is simply scale the amount by your liquids, but since your liquid amount is unknown in the worse case you'd be off about 30% I think.
 

Chad

Well-Known Member
Joined
Sep 15, 2007
Messages
1,026
Reaction score
12
Location
Apex, NC
Beersmith has a tool for this. Look on the left side menu, under Tools, click on the Dilution Tool.

Plugging in your estimated numbers gives a range of 1.043 for 3.5gal wort to 1.047 for 3.75gal of wort before topping off.

This tool is also handy if you take readings of each sparge but forget to take a final OG. You can calculate your OG by changing "dilute with water" to "dilute with wort." I've had to do this a couple of times. Very handy.

Chad
 

InkPouchMan

Well-Known Member
Joined
Jan 17, 2008
Messages
76
Reaction score
4
Location
Long Island
Since SG is a measure of density (weight/volume), a weighted average over volume will work. Just multiply your post-boil SG by the post-boil volume, add the volume of the top-off water (since its SG is 1), and divide the whole thing by the full volume:

SG = ( ( 1.062 * 3.5gal ) + ( 1.000 * 1.5gal ) ) / 5gal = 1.0434

or

SG = ( ( 1.062 * 3.75gal ) + (1.000 * 1.25gal ) ) / 5gal = 1.0465
 
Top