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Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > How to calculate PreBoil Gravity
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Old 07-26-2012, 03:01 PM   #1
BrokenArmBrewing
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Default How to calculate PreBoil Gravity

I've been stuck with some pretty bad efficiency lately, and I'm trying to hone on what might be going wrong. I use QBrew software, but it doesn't calculate PreBoil gravity. Any Ideas how to calculate this???

I'm thinging if I miss this, I could always boil down a quart or so more. Less volume is not what I'd like but . . .


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Old 07-26-2012, 03:10 PM   #2
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Try this: http://www.brewersfriend.com/brewhouse-efficiency/
Take a sample once you have your full preboil volume. Make sure to mix it if you do any sparging to get an accurate reading.

Also adjust for temperature (Temp adjustment calculator: http://www.brewersfriend.com/hydrometer-temp/)


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Old 07-26-2012, 03:22 PM   #3
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Ok thanks. Working thru mash out right now
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Old 07-26-2012, 03:26 PM   #4
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Nice, whatcha brewing?

If you're low on your supposed SG, you can use a gravity adjustment calculator (http://www.ahomebrewlog.com/gravity_adjustment/ ), but you'll need DME on hand. If it's not off by much, no biggie, RDWHAHB!
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Old 07-26-2012, 03:34 PM   #5
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Well It was supposed to be a Terripan Rye Pale Ale, but someone forgot to order the magnum hops -_- So, Amarillo for the bittering instead . . . Oh Well
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Old 07-26-2012, 03:55 PM   #6
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pre-boil volume = 8 gals
pre-boil gravity = ??
post-boil volume = 6 gals
post-boil gravity = 1.050

So, to calculate pre-boil SG for a 1.050 target OG would then be:
(post-boil volume/pre-boil volume) x (post-boil gravity -1) =
(6/8) x (1.050-1) = .75 x .05 = 0.0375 +1 = 1.038 rounded up

I think
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Old 07-26-2012, 04:30 PM   #7
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I worked that link....looks like i was at 70% efficiency ..... I don't know how to get it better . . . . bigger mash tun?? There's one a 10 gallon at Lowe's now for 40 bucks....I work there, so it may suffer some "missing pieces" for a better price ...lol...don't need that spigot any way
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Old 07-26-2012, 04:36 PM   #8
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Spend $30.00 and get a decent refractometer, and you won't have to calculate anything. They are perfect for preboil gravity readings!
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Old 07-26-2012, 04:38 PM   #9
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70% efficiency is good using a cooler tun (anything between 60-75% is good/normal). I use a 10 gallon cooler for my tun and its perfect for my 5 gallon batches. I did a brew last weekend that had 20lbs of grain and 8 gallons of strike water, with a little room to spare even (though not much...)! What size batches are you doing?
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Old 07-26-2012, 04:41 PM   #10
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5's. Had just enough room for strike water and 14 lb grain bill


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