Hydrometer calculation - Home Brew Forums

 Home Brew Forums > Hydrometer calculation

09-26-2011, 02:00 AM   #1
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Aug 2011
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Hi All, I have 5 L. batch show mead and just was racked from primary to the secondary on last Saturday.
It has been fermented in the primary 30 day with ingredient below.
Honey, water, yeast energizer, dry wyeast Red Star Premiere cuvee.
The OG is 1.103

I did hydro test and the letest gravity is came down to 1.011.
So my question is how to calculate the alcohol volume in this batch.

OG = 1.103
Latest = 1.011

09-26-2011, 04:22 AM   #2
OneCerebralSamurai
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Jan 2011
Desert, USA
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I use the calculator on this site:

http://www.brewersfriend.com/abv-calculator/

Make sure you check the button for the "Alternate" equation as it gives more accurate results, particularly at higher OGs.

Your numbers come out to 13.26% abv

BTW – the "standard" equation on the site is ABV = (og – fg) * 131.25

The "Alternate" (better) equation is ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

09-26-2011, 05:45 AM   #3
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Aug 2011
Bangkok, Bangkok
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Thanks!!!

09-26-2011, 02:37 PM   #4
MedsenFey
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Jan 2010
Florida
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Quote:
 Originally Posted by OneCerebralSamurai I use the calculator on this site: http://www.brewersfriend.com/abv-calculator/ Make sure you check the button for the "Alternate" equation as it gives more accurate results, particularly at higher OGs. Your numbers come out to 13.26% abv BTW – the "standard" equation on the site is ABV = (og – fg) * 131.25 The "Alternate" (better) equation is ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)
Actually, the alternate equation looks like it gives erroneous reading that are seriously too high. If you use the fundamental chemistry as outlined HERE the calculation will give you a little above 12%.

As a example of where this "improved" equation breaks down, try assuming a high-gravity fermentation with SG 1.135 and FG 1.000. If you plug that in the equation, you get an ABV of 20.21%. The standard equation give you 17.72%. Using the methodology outlined on howstuffworks, you get 17.94, and if you use a calculator like vinocalc you get 18.6. In order to arrive at 20.21% you have to assume that there is 100% conversion of the 354 grams per liter of sugar into ethanol and that is simply unrealistic. While all of these calculation are estimates, and can be off due to amount of alcohol scrubbed off through entrainment with CO2 (a bigger percentage at high temps) and due to amounts converted into other things like glycerol and higher alcohols, this "improved" formula is just more "off" than some of the others.

Having run some high gravity batches like this, I have measured the ABV using spirit indication with fine scale hydrometers and once sent a sample to a lab, and at a starting gravity of 1.135 I've never measured 20% ABV.

Medsen

09-26-2011, 02:46 PM   #5
iaefebs
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West Coast, MI
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Those SG and FG numbers when ran on BeerSmith shows 12.3% ABV

09-26-2011, 03:26 PM   #6
OneCerebralSamurai
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Jan 2011
Desert, USA
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Quote:
 Originally Posted by MedsenFey Actually, the alternate equation looks like it gives erroneous reading that are seriously too high. Medsen
I've seen several conflicting equations, but my limited experience is that the “alternate” equation is the most consistent with what I've seen. The “potential alcohol” chart that came with my hydrometers match very closely with the results of this equation (which leads me to conclude hat they used this equation, or a similar one, to create the chart).

Also, although very imprecise.... I usually use ec-1118 which is supposed to crap out close to 18% abv. In every batch I've made, this yeast craps out very close to what the equation indicates is 18% (+/- a bit). (I treat my yeast very nicely with nutrient, energizer, and aeration.)

09-26-2011, 04:15 PM   #7
OneCerebralSamurai
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Jan 2011
Desert, USA
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Quote:
 Originally Posted by iaefebs Those SG and FG numbers when ran on BeerSmith shows 12.3% ABV
The explanation I have heard, and it may be completely wrong, is that simple equations that are valid for beer are good estimates for the OG ranges of beer (1.040 – 1.070). Supposedly, these simple equations fail at higher OGs (I usually start my meads around 1.140), and hence the “more complex” equations were developed.

Maybe this is all wrong – Medsen says his brews have been chemically analyzed and that the high OG equations are not accurate.

It seems to me that the best we can do now (short of chemical analysis) is to have a “guess” as to what the abv is with an uncertainty of somewhere around +/- 2%. In the long run, I guess it doesn't make any difference – a good brew is still a good brew. I'm an analytic “numbers guy”, so I like to play with equations and numbers.

09-28-2011, 03:44 PM   #8
cyclejones
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Apr 2011
Los Angeles, CA
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if you have an iphone there's also an alcohol calculator app

09-29-2011, 12:55 AM   #9
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Aug 2011
Bangkok, Bangkok
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Quote:
 Originally Posted by cyclejones if you have an iphone there's also an alcohol calculator app
OK I'll find that app, thanks!!

10-19-2011, 03:14 AM   #10
calicojack
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May 2011
montgomery, al
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someone needs to come up with the "correct" method of doing this long handed. you can not always depend on technology to do things for you.