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Old 06-17-2013, 12:19 AM   #1
Elysium
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Default is there a way to calculate how much water I need to evaporate to reach my OG?

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.

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Old 06-17-2013, 12:22 AM   #2
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In beersmith it is called the boil off tool. There looks to be some free calculators here.

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Old 06-17-2013, 06:44 AM   #3
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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.

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Old 06-18-2013, 09:47 PM   #4
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Gravity calculator at onebeer.net

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Old 06-19-2013, 05:54 PM   #5
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Quote:
Originally Posted by IL1kebeer View Post
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.
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