is there a way to calculate how much water I need to evaporate to reach my OG? - Home Brew Forums

 Home Brew Forums > is there a way to calculate how much water I need to evaporate to reach my OG?

06-16-2013, 11:19 PM   #1
Elysium
Recipes

Feb 2013
Posts: 1,187
Liked 22 Times on 22 Posts

I always check the amount of wort I got before the boil and check the gravity before the boil.

But I am wondering if there is a way ((if there is an equation) to calculate how much I need to boil off to get to my required OG gravity.

I understand that I have wort shrinkage, loss in equipment and trub...but that is irrelevant. I'd just like to know how much liquid I need to boil off to get to my desired OG. There must be an equation.

Thanks.

06-16-2013, 11:22 PM   #2
Revvy
Post Hoc Ergo Propter Hoc

Recipes

Dec 2007
"Detroitish" Michigan
Posts: 40,939
Liked 3212 Times on 1896 Posts

In beersmith it is called the boil off tool. There looks to be some free calculators here.
__________________
Like my snazzy new avatar? Get Sons of Zymurgy swag, here, and brew with the best.

Revvy's one of the cool reverends. He has a Harley and a t-shirt that says on the back "If you can read this, the bitch was Raptured. - Madman

I gotta tell ya, just between us girls, that Revvy is HOT. Very tall, gorgeous grey hair and a terrific smile. He's very good looking in person, with a charismatic personality... he drives like a ****ing maniac! - YooperBrew

06-17-2013, 05:44 AM   #3
IL1kebeer
Recipes

Jan 2013
Inland Empire, CA
Posts: 723
Liked 91 Times on 78 Posts

Multiply your preboil og by your preboil volume. that will give you a your total gravity points. divide that by your target og then you will get the voluime that you need to shrink your wort down to after boil and cooling losses.

Example:

Preboil gravity = 1.055
Preboil volume = 6.5 Gallons
Target OG = 1.065

55 (preboil gravity) * 6.5 (preboil volume) = 357.5 total gravity points

357.5 (total gravity points) / 65 (target OG) = 5.5 gallons

6.5 (preboil volume) - 5.5 (volume after boil and cooling) = 1 gallon

Keep in mind that this doesn't take into account any losses from trub or plate chilllers etc.

And also, like Revvy said, there are many different programs out there that will do these calculations for you.

Elysium Likes This
06-18-2013, 08:47 PM   #4
brewinginnc
Recipes

Dec 2012
Posts: 293
Liked 40 Times on 25 Posts

Gravity calculator at onebeer.net

06-19-2013, 04:54 PM   #5
Elysium
Recipes

Feb 2013
Posts: 1,187
Liked 22 Times on 22 Posts

Quote:
 Originally Posted by IL1kebeer Multiply your preboil og by your preboil volume. that will give you a your total gravity points. divide that by your target og then you will get the voluime that you need to shrink your wort down to after boil and cooling losses. Example: Preboil gravity = 1.055 Preboil volume = 6.5 Gallons Target OG = 1.065 55 (preboil gravity) * 6.5 (preboil volume) = 357.5 total gravity points 357.5 (total gravity points) / 65 (target OG) = 5.5 gallons 6.5 (preboil volume) - 5.5 (volume after boil and cooling) = 1 gallon Keep in mind that this doesn't take into account any losses from trub or plate chilllers etc. And also, like Revvy said, there are many different programs out there that will do these calculations for you.
Thanks a lot for the equation. I have already made a calculator from it using an excel file.

there is one thing I dont understand......

I started with a 1.032 pre-boil gravity and 5.81 gallons of wort. I wanted to reach 1.053....after the boil I was left with 0.8 gallon of trub and 1.5 gallons of wort boiled off. According to the calculator..I should have boiled off 2.3 gallons of wort to get to 1.053, but I got there with 1.5 gallons.
Is it because my system is not flawless or is this because the turb left from the grains doesnt really affect the final gravity. I guess it hardly has water, but mainly the dirt left over form the grains.