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Old 07-22-2010, 12:51 PM   #1
brazedowl
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Default calculating ABV

I've got the general idea of getting the OG and then subtracting the FG and calculating the ABV.

BUT lets say that I get the OG and FG in the primary, and calculate the ABV then rerack onto a significant amount of sugar in the secondary. Do I just measure the OG, measure the FG, calculate again and add the two ABV values?

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Old 07-22-2010, 01:04 PM   #2
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Im not sure how to do it manually. I use Brewsmith - consider getting it or the free 30 day trial. Otherwise if you say what size batch and how much suger I can work out how much your abv will increase.

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Old 07-22-2010, 01:07 PM   #3
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No, calculate the OG as it would have been if you added all of the sugar at the start of fermentation, then calculate the actual final apparent gravity, then use the linear approximation of your choice.

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Old 07-22-2010, 01:18 PM   #4
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This is how I do it.

I always take reading when I rack to the secondary to give me an idea where my brew is. 99.9% of the time fermentation is completed before I rack to the secondary. I use the secondary for dry hoping/ fruits/ flavors. Before I bottle/keg I take another reading, and 99.9% of the time time is still the same as it was when I rack into the secondary.

OG (pre-primary, wort) - FG (secondary/bottling/kegging) * 131 = ABV

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Old 07-22-2010, 01:39 PM   #5
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If I understood correctly. You are asking how to calculate a total ABV if you add more fermentables in the middle, right?

I would take an original, and final before racking. Calculate the difference in gravity points (i.e. 1050-1010 = 0040) Then rack onto your sugar, stir, take another sample and maybe you are at 1020 now. Take you final gravity and say you are back at 1010. So your total sugars would now be 0050 and you could multiply that by .131 to get you ABV. The problem here is that you may not have an even dilution of that sugar. So I would go with taking the normal gravities, then weighing out the amout of sugar and using the fermentable ppg number to figure out how many gravity points it is for your volume (5 gallons).

To calculate the sugars you can use this table to see the ppg http://www.byo.com/resources/grains?gtype=5

So for example if you had 1 pound of dextrose in five gallons you would take 1037/5 or really 37/5 which gives you a little over 7 gravity points for your volume. So that should be the increase that you could add to your OG-FG (before racking) differential.

Not sure if this all made sense, but ask questions if it doesnt.

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Old 07-22-2010, 05:14 PM   #6
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Quote:
Originally Posted by remilard View Post
No, calculate the OG as it would have been if you added all of the sugar at the start of fermentation, then calculate the actual final apparent gravity, then use the linear approximation of your choice.
+1 - A pound of sugar in 5 gallons will add almost exactly 9 points. Add that to your OG, measure your FG once fermentation is complete, and calculate from there.

Also, (OG-FG)*131 over-estimates over about 6% ABV. There are more accurate correlations if you're interested.
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Old 07-22-2010, 08:20 PM   #7
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Quote:
Originally Posted by a10t2 View Post
Also, (OG-FG)*131 over-estimates over about 6% ABV. There are more accurate correlations if you're interested.
Good to know. This is acctually for my blueberry wine. So I have no doubt it'll be up and over 6%
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