Author Topic: hard time hitting post boil gravity from pre boil  (Read 2598 times)

Offline peter831

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hard time hitting post boil gravity from pre boil
« on: June 25, 2015, 03:47:39 PM »
I have been using this software for a long time, and never really understood how to make adjustments so that the pre boil OG results in the recommended post boil OG.

I am brewing the Citra Double again, 3rd time, great beer, and usually I just don't worry about this but its getting old.

My estimated pre boil gravity is 1.063 and the post boil is 1.083

60 minute boil, starting with 7.5 gallons pre boil and need 5.5 at the end of the boil to go through the chiller.

I cant boil off enough water to raise the gravity 20 units and still end up with 5.25 gal into the fermenter.

is it me?

peter

Offline brewfun

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Re: hard time hitting post boil gravity from pre boil
« Reply #1 on: June 25, 2015, 04:56:08 PM »
Going by the post boil numbers and dividing that up to get the preboil gravity shows 7.25 gallons. Add 4% expansion and you should measure about 7.5 gallons.

From the post boil gravity: 83 * 5.5 = 456.5 gravity points.
456.5 / 63 = 7.246 gallons cold wort, preboil.
Now, add heat expansion: 7.25 + 4% = 7.54 gallons pre boil

So, the math works. Which number is off?

It matters when you take your measurements. Your hot post boil volume is going to be about 4% higher than after chilling. That's close to 5.75 apparent gallons at 205F. Thus, your real boiloff is 1.5 gallons and that will change the math outlined above.

If you're not able to boil off 1.5 gallons, then either lengthen the boil time a little (up to 90 minutes) or reduce the boil off rate to match what your system does.

Always work backwards from the target OG by adjusting your equipment profile to match your actual measurements.
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Offline peter831

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Re: hard time hitting post boil gravity from pre boil
« Reply #2 on: June 26, 2015, 03:00:55 PM »
okay, thanks

I don't seem to be able to hit the post boil number,

maybe I will recalibrate the volumes in my boil keg

thanks again

peter