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Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Inaccurate OG...any other way to calc %alcohol?
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Old 12-06-2012, 06:15 AM   #1
ayupbrewing
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Default Inaccurate OG...any other way to calc %alcohol?

In the mayhem of making my first batch on Sunday the OG reading had to be taken quickly and because of froth I couldnt take an accurte reading.....i was more concerned with the rest of the process. Is there another technique I can use to calculate % alcohol once its finished?

Thanks.

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Old 12-06-2012, 06:20 AM   #2
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Was it an AG or an extract batch??

If it was an extract it should be really easy to establish your OG.

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Old 12-06-2012, 06:38 AM   #3
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It was extract. OK, so how? I mean retrospectively?

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Old 12-06-2012, 06:40 AM   #4
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White Labs has a kit, but it'll cost you.

http://www.whitelabs.com/lab/alcoholtestkit.html

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Old 12-06-2012, 06:46 AM   #5
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Exactly! Thats what I thought....not so easy retrospectively Thanks

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Old 12-06-2012, 07:06 AM   #6
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You need a refractometer.

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Old 12-06-2012, 07:07 AM   #7
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Quote:
Originally Posted by ayupbrewing
Exactly! Thats what I thought....not so easy retrospectively Thanks
Extract will have a specific and known gravity. If a known amount of that extract is dissolved in a known amount of water, the OG can be calculated very precisely, without any need to measure it.

When brewing all-grain, or simply just not knowing how much water and extract were used (which would be incredibly sloppy), there is another method. It requires taking a FLAT sample of the finished beer, and measuring the OG using a hydrometer AND the (uncorrected) OG using a refractometer, and then doing a bit of math.

People who use a refractometer frequently find the unknown variable of the *corrected* FG, by calculating it using two known variables - the OG and uncorrected FG. That equation can be rearranged to figure out a different unknown variable, the OG, if the two other variables are known... in this case, both the corrected and uncorrected FG (the hydrometer and the refractometer measurements, respectively).

Similarly, one could also rearrange the equation to determine the uncorrected FG if both the OG and corrected FG are known, but as you can probably tell, there's no real point to doing so.
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Old 12-06-2012, 10:10 AM   #8
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Quote:
Originally Posted by ayupbrewing View Post
It was extract. OK, so how? I mean retrospectively?
Let us know the weights/volumes of extract and any sugar, or any other fermentables, you used plus the exact volume of wort that went into your fermenter and we should be able to work out your Original Gravity.

Or, alternatively, you could input the details into a recipe calculator, such as beer calculus, and get the result.
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Old 12-07-2012, 05:39 AM   #9
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So i actually got the recipe from hopville/beer calculus and see that the OG should be 1.068, but it gives a range presuamable because things might not always go perfectly etc. SO i was just wondering how close to 1.068 I was since i missed it.
Thanks though.

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Old 12-07-2012, 05:43 AM   #10
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Emjay: Thanks.So im pretty good with equations but your description left me a little confused. If i take a gravity of a finished beer is that not FG rather than OG as you said - if i read your post correctly, I have a refractometer at work so I could do this calc if I could follow it better. Thanks

Ayup!

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