Brewing Wort: Calculating Boil Length for Desired Gravity

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To determine the boil length needed to achieve a specific gravity in home brewing, one must consider the volume of wort, initial specific gravity, desired post-boil specific gravity, boiling temperature, and evaporation rate. The standard boil times are typically 60 or 90 minutes, but calculating the exact time requires understanding the evaporation rate, which is about 20% per hour. While some brewers rely on hydrometers for measuring specific gravity, others may use taste tests for a more subjective assessment. The discussion highlights the importance of these calculations for effective brew day planning. Accurate measurements and calculations can significantly enhance the brewing process.
Ohio Homebrew
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Hello. I am not quite sure this is the correct place for this question so I will apologize now if it isn't. As a home brewer I mash the malt with hot water and collect the runoff (called wort) which contains the sugars needed for fermentation. Most recipes call for a boil length of either 60 or 90 minutes with an anticipated specific gravity at the end of the boil. My question is this, if I know:

The volume of wort collected in gallons
The specific gravity of the wort before the boil
The anticipated specific gravity post boil
The temperature at which the wort boils, 212° F
An evaporation rate of 20% per hour

How long must the boil be to reach the anticipated specific gravity? I'm not too worried about humidity, ambient temperature, elevation, or other external factors, but knowing this could make planning a brew day much easier.

Thank You,

Tom Dible
 
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i don't know, Buckeye Brother
bnut i'll be there to sample any runs...
since we don't have a college ball team these days..

where's Woody?
 
Hi Tom,

I have attempted a few brews before. I have never tried calculate boiling time and such.
I basically use a hydrometer to find specific gravity. I find this the most accurate method considering all the variables, especially brewing from 'scratch'.

I have a friend that is a brewer in a commercial micro brewery. His test for the wort is a pipette of several mm to taste, and hydrometer.

LOL, I think, sometimes the more random variables added into the brew only tend to make it more interesting.

Yes, I also would like to be there to have a 'wee' sample of your run.
 

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