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Home Brew Forums > Home Brewing Beer > Extract Brewing > calculating OG
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Old 11-02-2009, 07:44 PM   #1
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Default calculating OG

So, I used a recipe formulator (beer recipator) and calculated an OG of 1.066. When I brewed, I took a reading from the kettle, then after racking to the primary I had to top-off with 0.75 gallons of water.

Reading was at 1.072. So, is this formula correct for calculating real OG?

[4.25(1.072) + 0.75] / 5

because that equates to 1.0612, which is a bit lower than expected OG.

I used 7 lb of DME in a 6 gallon boil. I did leave some behind in the kettle, for the trub. Is this where my missing gravity is?

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Old 11-02-2009, 09:21 PM   #2
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Beersmith comes up with 1.061 so I'd say your math is pretty dead on. I'm assuming your doing a 5 gallon batch. It sounds like you left...lets say a half gallon of wort in your pot and then added .75 gallons of water.... That would lower your OG. I usually just dump everything into the primary and then worry about top-off. Either way... the beer will come out fine. .005 won't be a deal breaker...

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Old 11-02-2009, 09:31 PM   #3
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I do the same as Hammy, especially when I'm doing an extract brew. No real reason to worry about leaving much behind in the kettle. I just pour it all through a large kitchen strainer to get most of the hop gunk out. It's not like you're having a ton of hot break from extract and some cold break is good for the ferment if you're doing ales.

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Old 11-03-2009, 04:45 PM   #4
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I did probably leave 1/2 gallon. I have one of those funnels with a fine mesh, and it got clogged pretty early on with hop material, and so I took the funnel out and siphoned straight into the carboy. I didn't want to have orange peel and trub material in the primary for a month, so i stopped it early.

i just bought a cane screen, so hopefully I can pull more out next time. Thanks!

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Old 11-03-2009, 07:35 PM   #5
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I make 6 gal batches, with a 5 gal boil, and add 1 gal to the primary. I always seem to come up short on my OG. I would like to be able to measure the OG in the kettle, and account for the added gallon of water. That way I can add some more DME to get it up if necessary. So my math says that 1 of 6 gallons is 17%. So I can assume that the OG needs to be 17% higher? So lets say my OG should be 1.068 for a 6 gal recipe. Then, my 5 gal wort should be 68(1.17) or 1.079.... Does this seem right guys?

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Old 11-03-2009, 07:41 PM   #6
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The easiest way? Use software like Beer Smith and enter a recipe for 6 gallons. Then change the batch volume to 5 gallons and leave everything else the same. That should tell you what your OG should be if you finish your boil with 5 gallons and top up with a gallon of water.

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