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# Anybody got a good %ABV-%ABW conversion polynomial?

edited January 2018 in General

I'm revisiting a subject I sorta half-ass fixed a while back, but I'd really like a good (or better) answer that I can use in an Excel formula that crops up in much of my ethanol accounting spreadsheets. When last I did this, I fed 20 fairly good %ABV,%ABW pairs into a time-bombed limited (hence the only 20 points) trial version of somebody's curve-fitting program, and got the following:

``````Y=0.06838416+0.769439X+0.002151989X^2-0.00002420972X^3+(2.548199*X^4)(10^-7)
``````

As you can see from that first co-efficient, there will be a .068% error when converting 0%ABV to %ABW ( the answer you get is 0%ABV equals .068384%ABW, and that's bogus.

Does anyone have a better polynomial than my crappy one?

Zymurgy Bob, a simple potstiller

my book, Making Fine Spirits

Tagged:

• edited January 2018

Show-off

;<)

I'm more like I am now than I was before.

• edited January 2018

I have this formula that I have picked up across my web travels

• Thanks so much Richard. I'm betting it'll be closer than what I was using, but I'll test it against that awful TTB Table 4.

@Kapea said: Show-off

;<)

No, I'd be a show-off if I had it right. Must be Richard's the show-off. 8)

Zymurgy Bob, a simple potstiller

my book, Making Fine Spirits

• Richard, after getting polarity wrong on the second term of that polynomial, I corrected it and evaluated it at the 2 values I knew exactly, 0%ABV and 100%ABV. I could see in advance that it'll be correct at %ABV=0, and it was, but at %ABV=100, I got 99.51267. Does that line up with what you've seen?

I still think yours is better than what I had, and I'm inclined to say at first approximation that it's good enough for TTB, but I want to do more testing first.

Zymurgy Bob, a simple potstiller

my book, Making Fine Spirits

• In honesty can not comment. It's what I copied off one of the sites and have never had the need to really use it.

• You should reach out to Meerkat over on ADI.