Rebel Brewer Giveaway!
 Home Brew Forums > Determining OG from the Pre-Boil Gravity?

02-12-2007, 12:13 AM   #1
jcarson83
Feedback Score: 0 reviews

Recipes

Join Date: Jun 2006
Location: Springfield, MO
Posts: 942
Liked 11 Times on 7 Posts

 Determining OG from the Pre-Boil Gravity?

Anyone know how to estimate the original gravity of your wort by taking a reading before the boil off?

EX:
My 7 gallons of wort is 1.065. If my final volume is 5.5 gallons what is my OG?

__________________

02-12-2007, 01:56 AM   #2
ajf
Senior Member
Feedback Score: 0 reviews

Recipes

Join Date: Oct 2005
Location: Long Island
Posts: 4,580
Liked 88 Times on 82 Posts
Likes Given: 37

Assuming you boil down to exactly 5.5g, and transfer the whole 5.5g to the primary, then your OG would be (1.065 - 1.000) * 7 / 5.5 + 1.000 = 1.083.
Unfortunately, the transfer to the primary will not normally be 100% efficient, and to estimate your OG you will have to estimate the amount of wort lost during the transfer. Assuming you lose x gallons, the formula would be modified to
OG = (1.065 - 1.000) * 7 / (5.5 + x) + 1.000, so if you lose 2 pints it would be
(1.065 - 1.000) * 7 / ( 5.5 + 0.25) + 1.000 or 1.079

-a.

__________________

02-12-2007, 11:14 AM   #3
newfie
Feedback Score: 0 reviews
Recipes

Join Date: Jun 2006
Location: Halifax, NS
Posts: 40

hey ajf , i'm not sure what gets left behind will change the grav. when you boil off to the 5.5 gal volume, won't the wort all have a grav of 1083 (including the 2 pts). So the 5.5 gals(less 2 pts) will have a grav of 1083 as will the 2 pts left behind?? Otherwise, the grav of the 2 pts left behind is going to be pretty darn high ( apply conservation of mass theory here).
hey maybe i'm seeing this wrong.... i'm interested in sorting it out though ....
in my own head ....
brewfie

__________________

Last edited by newfie; 02-12-2007 at 11:17 AM.

02-12-2007, 12:56 PM   #4
ajf
Senior Member
Feedback Score: 0 reviews

Recipes

Join Date: Oct 2005
Location: Long Island
Posts: 4,580
Liked 88 Times on 82 Posts
Likes Given: 37

Yes, if you boil down to 5.5g, you'll have a gravity of 1.083, but if you leave 2 pts behind, you will end up with only 5.25g in the fermenter (still at 1.083)

-a.

__________________

02-12-2007, 01:41 PM   #5
jcarson83
Feedback Score: 0 reviews

Recipes

Join Date: Jun 2006
Location: Springfield, MO
Posts: 942
Liked 11 Times on 7 Posts

Thanks for the help guys. Those things really bug the hell out of me until I figure them out (or someone else does.

__________________

 Quick Reply Message: Options Quote message in reply?
 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post snailsongs General Techniques 5 03-05-2009 04:42 PM GFrank All Grain & Partial Mash Brewing 7 02-25-2009 10:15 PM Kaiser All Grain & Partial Mash Brewing 17 02-10-2009 04:07 PM hagbardceline All Grain & Partial Mash Brewing 3 10-17-2008 05:31 AM Sherpa FE All Grain & Partial Mash Brewing 3 07-07-2008 09:06 PM