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Author Topic: Alternate abv calculators  (Read 5645 times)

Offline Iliff Ave

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Alternate abv calculators
« on: November 02, 2018, 01:39:27 pm »
Any reason to use the alternate equation for higher abv beers? I get almost a full percentage point more using the alternate equation for a 1.093 og beer.
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Offline Robert

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Re: Alternate abv calculators
« Reply #1 on: November 02, 2018, 02:08:42 pm »
The relationship between change in real extract and alcohol just isn't linear, it varies with original extract across all beers, no matter the gravity.  But AFAIK it's pretty simple to approximate:  ABW=[0.8192(OE-AE)]/[2.0665-(0.010665OE)]  That's the formula I've always used for all beers.  Is that what's now called "alternate?"  Is it the standard? Or is there another one out there now?
« Last Edit: November 02, 2018, 02:19:38 pm by Robert »
Rob Stein
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Offline Iliff Ave

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Re: Alternate abv calculators
« Reply #2 on: November 02, 2018, 02:23:14 pm »
According to some sources:

Standard:
ABV = (og – fg) * 131.25

Alternate:
ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

I get 9.3% abv with the standard and 10.1% abv with the alternate

Apparently the alternate may be more accurate for higher abv beers. I'm too dumb to know what is better or more accurate. One of my apps is standard and another appears to use the alternate. I guess I will just send it to the lab.

« Last Edit: November 02, 2018, 02:28:59 pm by goschman »
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Offline Robert

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Re: Alternate abv calculators
« Reply #3 on: November 02, 2018, 02:38:32 pm »
Well, that second one obviously accounts for difference in OG, and the first one just assumes a linear relationship.   I'm way too lazy to figure out if the second is just a restatement of the one I know.  But anything accounting for different OG would be more accurate for all beers, so if your calculator gives you a choice, why not always use the alternate? 
Rob Stein
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Offline Iliff Ave

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Re: Alternate abv calculators
« Reply #4 on: November 02, 2018, 02:46:54 pm »
Well, that second one obviously accounts for difference in OG, and the first one just assumes a linear relationship.   I'm way too lazy to figure out if the second is just a restatement of the one I know.  But anything accounting for different OG would be more accurate for all beers, so if your calculator gives you a choice, why not always use the alternate?

I don't know hence the post. Beersmith seems to use the standard equation from my experience.
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Offline joe_meadmaker

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Re: Alternate abv calculators
« Reply #5 on: November 02, 2018, 02:51:44 pm »
It's math time.  I opened Excel and dropped the two formulas in with a range of original and final gravities.  The OG values I used were 1.100, 1.090, 1.080, ... down to 1.020.  I set the final gravity for everything to be 1.000.  Here are the ABV results:

Standard formula:
1.100 - 13.1
1.090 - 11.8
1.080 - 10.5
1.070 - 9.2
1.060 - 7.9
1.050 - 6.6
1.040 - 5.3
1.030 - 3.9
1.020 - 2.6

Alternate formula:
1.100 - 14.2
1.090 - 12.6
1.080 - 11.0
1.070 - 9.5
1.060 - 8.0
1.050 - 6.6
1.040 - 5.2
1.030 - 3.9
1.020 - 2.5

Assuming these equations are accurate, it looks like the standard would be good up through about 1.060.  Once it gets up to 1.070 they start to split.  I think as Robert stated, the alternate should be good to use all the time.

Offline Iliff Ave

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Re: Alternate abv calculators
« Reply #6 on: November 02, 2018, 03:19:41 pm »
Thanks guys
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Offline Robert

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Re: Alternate abv calculators
« Reply #7 on: November 02, 2018, 03:57:09 pm »
Thanks, joe_meadmaker, for doing the math for us, the math-challenged and lazy.  I still wonder if my weight/°P based formula is effectively the same as the alternate SG version given here.  But I don't wonder enough to actually do any math.   
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Offline joe_meadmaker

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Re: Alternate abv calculators
« Reply #8 on: November 02, 2018, 05:29:03 pm »
Robert, here's the results from your equation.  But take this with a grain of salt because there have been a lot of conversions with the numbers.  I first found a website to convert the test gravity readings to OE and AE.  I then also needed to convert the ABW results to ABV.  For which I used a linear equation, even though the relationship isn't linear.  It was the only one I could find that gave results that made sense.

ABW=[0.8192(OE-AE)]/[2.0665-(0.010665OE)] converted to ABV:
1.100 - 13.5
1.090 - 12.1
1.080 - 10.7
1.070 - 9.4
1.060 - 7.9
1.050 - 6.6
1.040 - 5.3
1.030 - 3.9
1.020 - 2.6

So from that, the formula you have also appears to pull away from the standard as OG goes up, but not as much as the alternate formula.  Who knows which one is actually more accurate?  These equations are always advertised as an "approximate ABV" anyway.  I think any of these are close enough at the homebrew level.

Now it's time to RDWHAHB!

Offline Robert

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Re: Alternate abv calculators
« Reply #9 on: November 02, 2018, 06:07:07 pm »
Yeah, the formula I have (Greg Noonan was my source a couple of decades ago, and I'm sure I saw the same in something by George Fix too) is definitely an approximation, I suspect precision requires a regression equation.  What's probably the key thing here is that the digression starts at the same point, and tracks closely, so I'd bet both equations are approximating the same "real" formula.  And also, most importantly, it does suggest that up to a pretty high gravity,  the inevitable errors in your gravity readings will be far more significant than the errors in your chosen calculator.  Thanks again, cheers, enjoy your evening.

(In my equation things probably go pear shaped right off the top.  That 0.8192 is an approximation of the relationship between real attenuation and apparent attenuation.   Another nonlinear relationship,  I believe.   The SG equation is obviously doing the same, differently. )
« Last Edit: November 02, 2018, 06:31:28 pm by Robert »
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Offline ynotbrusum

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Re: Alternate abv calculators
« Reply #10 on: November 02, 2018, 08:16:57 pm »
I’m glad that some of you guys took classes in college that were where I stopped, or way beyond where I stopped.  I trust your calculations and in no way suggest that I can follow them.  I rarely care significantly what my final gravity is, but I appreciate that you guys do, and that is cool with me.  Thanks for being the keepers of the gate, fellows!
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Offline txbrewingbm

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Re: Alternate abv calculators
« Reply #11 on: December 21, 2018, 06:18:23 am »
Yes, it is important to calculate the ABV – Alcohol By Volume. Fans of highly alcoholic beers are well aware of what ABV means—or at least that a beer with an ABV above 10% has the potential to leave you with a buzz before the first pint's finished. Determined with an instrument called a hydrometer. abv calculator is a handy one-stop tool for determining the final ABV percentage of your fermented beverages. To determine the ABV, simply measure the Original Gravity (OG) of your wort or must on the day you made it and then measure the FinaGravity (FG).

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Re: Alternate abv calculators
« Reply #12 on: December 21, 2018, 06:31:03 am »
One of the greatest articles ever written on brewing calculations:

https://www.homebrewersassociation.org/attachments/0000/2497/Math_in_Mash_SummerZym95.pdf

This article first acquainted me with many of the more thorough versions of common brewing calculations.

Offline dmtaylor

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Re: Alternate abv calculators
« Reply #13 on: December 21, 2018, 07:31:33 am »
The relationship is non-linear.  I learned almost 20 years ago that the 131.25 factor is a farce, that at low alcohol the factor is closer to 128 and at high alcohol it's closer to 133 or 134.  Forget the effing .25, that's ridiculous.  The result is good to 2 sig figs at best.

So.... for a 1.093 beer finishing at approximately 1.023, just for example, I'd use a factor of 133, which by the old linear equation would give (1.093 - 1.023) * 133 = 9.3%.  But maybe that factor should be 134.  If so, then it's 9.4%.  Meanwhile...

I'd have a hard time believing any "alternate" equation that told me the ABV is >10% unless the FG was much lower than my example of 1.023.
Dave

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Offline Robert

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Re: Alternate abv calculators
« Reply #14 on: December 21, 2018, 04:55:17 pm »
One of the greatest articles ever written on brewing calculations:

https://www.homebrewersassociation.org/attachments/0000/2497/Math_in_Mash_SummerZym95.pdf

This article first acquainted me with many of the more thorough versions of common brewing calculations.

Thanks for the link, Big Monk.  Now I've got a refinement of the first term (approximation of RA) in my old equation (post #2.)  So now I'll go with ABW = [OE - (0.8114*AE + 0.1886*OE)] ÷ [2.0665 - 0.010665*OE].  Still an approximation but a better one.

(Edited for numerous bungles.)
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« Last Edit: December 21, 2018, 06:57:33 pm by Robert »
Rob Stein
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