How to calculate FG? - Home Brew Forums

 Home Brew Forums > How to calculate FG?

10-09-2008, 01:23 AM   #1
Fireguy
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Sep 2008
Midwest
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I know I have had a few questions recently, but I have been wondering how to calculate my gravities? If my OG is 1.071, what can I expect for my FG? and how or what equation do u use to get it? I hope im posting this in the right forum....since its on cider i thought why not? thanks folks

10-09-2008, 01:27 AM   #2
Yooper
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In order to guestimate the FG, you have to know the probable or likely attenuation of the yeast, or the ABV threshold of the yeast. For example, montrachet will probably go to 14% in a healthy fermentation. Or, in a beer, you can plan on 75% attenuation for Nottingham yeast.

Most wine yeasts will take anything under 1.100 totally dry, depending on ingredients.
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10-09-2008, 12:53 PM   #3
Tusch
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To give numbers to Yooper post, with almost any wine yeast, you can expect anything from 1.100 or lower to go all the way to between 1.000-.990 generally
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10-09-2008, 05:43 PM   #4
Pogo
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Fireguy -

If the Original Gravity (OG) of your batch is 1.071, and the Final Gravity (FG) turns out to be, say, 0.998.

To estimate the Alcohol By Volume (ABV), simply subtract the FG from the OG, and multiply the result by 131.

(OG - FG) X 131 = % ABV

1.071 - 0.998 = 0.073 X 131 = 9.563 % ABV

Pogo

10-09-2008, 10:08 PM   #5
lapaglia
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Quote:
 Originally Posted by Pogo Fireguy - If the Original Gravity (OG) of your batch is 1.071, and the Final Gravity (FG) turns out to be, say, 0.998. To estimate the Alcohol By Volume (ABV), simply subtract the FG from the OG, and multiply the result by 131. (OG - FG) X 131 = % ABV 1.071 - 0.998 = 0.073 X 131 = 9.563 % ABV Pogo
Slight OT.
I always used this for final ABV.
OG-FG/7.36*1000 = %ABV
1.071 - 0.998 = 0.073 / 7.31 = 0.00998 * 1000 = 9.98 ABV.

Forget the fact that its a little more math. I have seen both formulas use. Is there a way to tell which is better or closer to the actual?

In addition the "Joy of Homebrewing" (AKA the BIBLE as some people say) says the equation is og-fg x 105, as brewmonkey says og-fg x 131.

Fermcalc says OG 1.071 - FG 0.998 = 9.9 %ABV
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10-09-2008, 11:50 PM   #6
Fireguy
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Midwest
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Thanks folks!!! that is exactly what I need to know. Guess Ill just have to wait till it stops fermenting to know for sure.

10-10-2008, 06:47 AM   #7
Pogo
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lapaglia -

Thanks for opening my eyes a little bit.

I've been totally unaware that there was more than one way to compute ABV.

Maybe someone with access to a refractometer will test their SG readings and verify which method is superior.

Thanks for the class!

Pogo

10-10-2008, 11:30 AM   #8
lapaglia
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Quote:
 Originally Posted by Pogo lapaglia - Thanks for opening my eyes a little bit. I've been totally unaware that there was more than one way to compute ABV. Maybe someone with access to a refractometer will test their SG readings and verify which method is superior. Thanks for the class! Pogo
No problem, now the real thing is to figure out which it the most accurate for what we are doing. Its possible all the methods are as accurate as the next one as its all approximate readings. Hopefully someone smarter than I am has the answer.
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