Calculating ABV without OG

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jfkriege

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Is there a way to calculate the abv of a brew without having the OG?

I have both a hygrometer and refractometer. Is there perhaps a way using the FG from the two instruments and calculating from that?
 
If it's an extract recipe, yes, the OG will be easy to calculate. If it's not, then if you know your efficiency you can get a good estimate of the OG, but it may not be exact.
 
if you have a good scale it is pretty easy to do. Measure the final gravity of the beer with a hydrometer. Take a small sample and weigh it. Then dry the sample with gentle heat, removing all the moisture. Then weigh it again - calculate the weight% solids. This will give you your final sugar% (or Final Brix). Send me the two numbers and I will tell you what % alcohol you have.
 
ok mansfield, let me test your skills. my FG is 1.017. I used your dry-out method to find a %sugar of 5.93. So tell me, what is my %ABV?

I already know the answer cuz I measured my OG, I am just wanting to see if you can actually do this.
 
The amount of solids will probably depend somewhat on the ABV and OG (or vice versa) because they both get in there during the mashing process but it seems unlikely that one can provide a reliable estimate of the other.

Putting your recipe into Beersmith or some other software to estimate the OG is probably as close as you can get without sending a bottle off to an analytical lab. Like Damdaman said, if it was from extract then you should know almost exactly how much fermentable sugar you started with.
 
Now that I think about it I'm pretty sure you can get the ABV from the FG and the %age by mass of solids if you know the specific gravity of the solids. I don't know whether that is a known quantity or not. I'm used to doing those kinds of calculations with soils and and air and water, not with beer solids, water, and alcohol. :)
 
This link has a method for calculating ABV without the OG -

"A quite simple way that will give accuracy up to 0.1% is to boil off all the alcohol and substitute by water. This means boiling down to less than a third of the original volume in most cases, it's not that hard to smell if there are alcohols in the vapour. Fill with water so you have your original volume and take the difference in gravity, then look up alcohol content in the table:"

http://www.realbeer.com/spencer/attenuation.html#alcohol
 
The two things that I am wanting to know the ABV for are both wines. If it helps the situation, they have both fermented to dry (0.996).
 
Yorbag,
Sounds like you made a pretty sweet beer - that is a good bit of sugar. So here is my answer: You have a FG of 1.017 and you measure the %sugar to be 5.9 wt% - this means you started with an OG of 1.058 and you have an ABV of 5.4%. My numbers will only be as good as your measurements. What kind of beer is it? How close are my numbers to your measured OG?
 
jfkriege - if you have a good scale go ahead and dry out a sample. For a typical wine with an OG of 1.085 you would have a finished product of 2.6wt% sugar (BRIX) and 11.4% ABV for a final gravity of .998

withak - you are on the right track, need to have a good understanding of sugar effect on SG.

gxm - that is an interesting concept, I need to try it out. I am thinking it is easier to go ahead and dry the sample out and do the sugar analysis -if you have a scale. Also, I don't think all of the alcohol is gone until you almost completely dry it out. However, if you don't have a scale this method would work pretty well.
 
5.9% is not the amount of sugar he started with, it is the amount of solids left in his beer after it ferments (some of which might be sugar). Even if the 5.9% by mass was all sugar it wouldn't give you the ABV because it is the sugar that the yeast didn't eat and he needs to know how much sugar the yeast did eat.
 
Wow, that is incredible. My OG was 1.060, or at least that is what I measured. This was an ESB that I bottled last fall, very good balance even with the high FG.

OK, sounds like we are all perplexed, how did you do this?
 
Haha! Not too shabby! OK, here ya go...

You measured 5.9% sugar in your beer (by drying out a sample and weighing on a lab scale). The SG of 5.9% sugar in water is about 1.023. But for your sample, you measured 1.017. The reason it is lower? Because in additon to sugar and water you also have alcohol. Alcohol reduces the SG, duh. Here is the math:

SG = [0.79 ABW + 1.4 BRIX + (100-BRIX-ABW)]/100

ABV = ABW*SG/.794

It is pretty cool but not something I do very often, kind of a waste of good beer usually. I find it to be very accurate as long as I am careful with the dry-out and weight measures. Also, I don't filter my beer but when I use this dry-out method I always make sure I get a nice sediment-free sample of beer. I hope this helps,
 
BeerSmth has a formula to do it if you have a refractometer. You can take a sample, measure the FG with a hydrometer and the Brix with the refractometer. Enter these two numbers in and use the "Finished Beer ABV/OG" dropdown and it will give you every other value.

Not sure if its accurate or not, never really tried it.
 
Haha! Not too shabby! OK, here ya go...

You measured 5.9% sugar in your beer (by drying out a sample and weighing on a lab scale). The SG of 5.9% sugar in water is about 1.023. But for your sample, you measured 1.017. The reason it is lower? Because in additon to sugar and water you also have alcohol. Alcohol reduces the SG, duh. Here is the math:

SG = [0.79 ABW + 1.4 BRIX + (100-BRIX-ABW)]/100

ABV = ABW*SG/.794

It is pretty cool but not something I do very often, kind of a waste of good beer usually. I find it to be very accurate as long as I am careful with the dry-out and weight measures. Also, I don't filter my beer but when I use this dry-out method I always make sure I get a nice sediment-free sample of beer. I hope this helps,

just thought i'd bump this, going into the kitchen to test right now....seems to come up often enough for a bump.....
 
all these damn things are telling me going from 1.060->1.003 gives me less than 4% alcohol....i'm sorry i bumped it before testing it out.....lol

unless 1 gram dry weight out of 30 gm's cider is not 3.333 BRIX......
 
all these damn things are telling me going from 1.060->1.003 gives me less than 4% alcohol....i'm sorry i bumped it before testing it out.....lol

unless 1 gram dry weight out of 30 gm's cider is not 3.333 BRIX......

Are you aware that the refractometer needs correction whenever alcohol is present? So FG 1.003 reads closer to 6.3 Brix, not 3.3 Brix.

Or conversely, if the two readings that you were able to take are final Brix 3.3 and FG 1.003, then your ABV is about 3.8% and your actual OG would probably have been closer to 1.032 than 1.060.

Lots can go wrong if you don't take alcohol into account, or aren't using the correct equations.

What readings have you actually taken, with what tools? I'm pretty good at the maths.
 
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Are you aware that the refractometer needs correction whenever alcohol is present?

LOL, seriously...i've been here over a year ;)...i don't own a refractometer, i took a 30 gram sample and put it in the food dehydrator till it was dry and got 1 gram....whice would be 3.333 brix right? (being that 1 BRIX is 1 gram sugar in 100 grams water)


i'm not completely sure on OG, i didn't measure and maybe the 4lb's of table sugar i didn't stir in are still at the bottom of the 10 gallons of apple juice....(could be why my ciders are taking so long to finish...something i'll have to think about, might still be a useful experiment)

(and it's bed time, but i think i'll stir it up before hand and see if i feel anything at the bottom)

edit: now the plot thickens, or thins, depending on how you look at it, lol.... i gave the fermenter a good stir and now the hydrometer reads lower then 1...probably .998 or .999 i'll have to dry another sample tomorrow, but all these calcs are telling me ~4%, and with 10 gals of apple juice and 4lb's of sugar i get 1.060 OG...which would put this at 8%
 
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LOL, seriously...i've been here over a year ;)...i don't own a refractometer, i took a 30 gram sample and put it in the food dehydrator till it was dry and got 1 gram....whice would be 3.333 brix right? (being that 1 BRIX is 1 gram sugar in 100 grams water)

i'm not completely sure on OG, i didn't measure and maybe the 4lb's of table sugar i didn't stir in are still at the bottom of the 10 gallons of apple juice....(could be why my ciders are taking so long to finish...something i'll have to think about, might still be a useful experiment)

(and it's bed time, but i think i'll stir it up before hand and see if i feel anything at the bottom)

edit: now the plot thickens, or thins, depending on how you look at it, lol.... i gave the fermenter a good stir and now the hydrometer reads lower then 1...probably .998 or .999 i'll have to dry another sample tomorrow, but all these calcs are telling me ~4%, and with 10 gals of apple juice and 4lb's of sugar i get 1.060 OG...which would put this at 8%

Ah, okay, now I see. So.......... how well do you trust the calibration of your scale measuring grams within a tenth of a gram? And when is the last time you calibrated your hydrometer? As already you're seeing differences of up to 0.005 on your hydrometer depending on when and how you look at it. When you find out the most precise numbers, report back, then we can talk some more. :)
 
Ah, okay, now I see. So.......... how well do you trust the calibration of your scale measuring grams within a tenth of a gram? And when is the last time you calibrated your hydrometer? As already you're seeing differences of up to 0.005 on your hydrometer depending on when and how you look at it. When you find out the most precise numbers, report back, then we can talk some more. :)


didn't realize it needed to be to the tenth of a gram....think it was 30.xx something, to 1.1 maybe, figured rounding would work. hydrometer should be good. Think i'll just get a refractometer, in case i ever need one. (which i might, if i try my hand at making sake again)

edit: just got up, don't remember if i said it, but this is just a fun experiment for me...
 
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Hi, Just to help you guys out with the maths, but you do need Excel !! :)
Here is how to calculate the ABV without the OG and to calculate the OG all from the final specific Gravity (Hydrometer)and the final specific Gravity (Refractometer in Brix)

Put this formula in to Excel cell C2 to give the ABV:

=(277.8851 - (277.4*B2) + (0.9956 *A2) +(0.00523 * A2*A2) + (0.000013*A2*A2*A2)) * (B2/0.79)

Put this formula in to cell D2 to give the OG:

=0.00432*((-400*B2) + (2.512*A2)+400.52)+0.9977

then put the Brix reading in to cell A2 and the Specific Gravity (Hydrometer) in to cell B2.


Make sure you are sober when you take the readings as a small error can result in quite an inaccurate reading, as I found out lol

(Oh the reason I put everything in row 2 is so you can put column headers in row 1 :) )
Enjoy
 
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Without getting in to a debate, I would suggest that you try both formulas out on a known sample and see which one is the more accurate. :)
If you haven't got Excel you could always pick up a calculator .... :)

Cheers Guys
 
or... you can guestimate it based off of others who use the same recipe and adjust if you think your Juice was sweeter or not. Look at Edwort's Apfelwine. It's 2lbs sugar per 5 gal (so 4 for 10).

or... 46 points per pound of sugar (if you know how much sugar was in your AJ (aka if it was store bought).

also beersmith or some computer program like that can estimate it based off of what you used to create the mash.
 
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damn, a double bumped thread! or triple..... ;)


i got a refrac now, and i can say comparing the reading between it and a hydrometer...gives a pretty good ABV reading.....


trying to do it by weight, not so much.....
 
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Or you can just take an OG reading and eliminate the headache lol , jk . Pretty cool using math to figure it out . Heck I usually just drink it .
 
Or you can just take an OG reading and eliminate the headache


wouldn't work for my ciders that i dump 4lbs sugar into....because i don't stir in the sugar thoroughly, and different brands of juice give different gravities....

i'd imagine a no boil extract recipie would have a similar technical problem...in fact i see people having it all the time around here, ;) :mug:
 
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