Measure alcohol in beer
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FloppyKnockers
Well-Known Member
You need to know your original gravity for the final alcohol reading then OG - FG x 131 = ABV
For example, If my wort (before pitching yeast) is 1.052 and after it's done fermenting I end up with a gravity of 1.010. The difference is 0.042. I multiply that by 131 and I get 5.502 or 5.5% ABV.
For example, If my wort (before pitching yeast) is 1.052 and after it's done fermenting I end up with a gravity of 1.010. The difference is 0.042. I multiply that by 131 and I get 5.502 or 5.5% ABV.
That percentage is likely Brix you can covert from brix to specific gravity and use the above mentioned formula or you can take your original brix - final brix then multiply by .55 to get your abv. So 15brix - 5 brix = 10 brix then 10brix x .55 = 5.5abv
However with a refracometer you have to compensate for alcohol presence, because that will throw your reading off. It's best to use a hydrometer especially for your final gravity readings.
However with a refracometer you have to compensate for alcohol presence, because that will throw your reading off. It's best to use a hydrometer especially for your final gravity readings.
DuncB
Well-Known Member
You can use a formula on your final beer if you get a separate brix reading from the refractometer and a hydrometer.
Useful if you don't know OG or add a load of fermentables after the OG is measured.
Useful if you don't know OG or add a load of fermentables after the OG is measured.
Ok. But if I don't have OG, and just the beer. How do I then measure the alcohol percentage with a refractometer, or what else may be used?
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Not easily. You can estimate what your OG should have been from the recipe, and make some assumptions about a refractometer correction factor to use, but the fact is that we don't actually measure the ABV in our beers. We calculate it. I'm not aware of any instrument similar to a vinometer that will work for beer.
If it was all-grain and you don't know the OG, you can't figure out the ABV with just a refractometer. If it was extract, then you can plug the ingredients into a recipe program and that should be very close.
If you really want to get carried away and you have a very accurate way to measure volume, you could take something like 100 mL of beer, heat it to the boiling point of ethanol (78C/178F) for a while, and then measure the volume that remains. If you do it right (so that all of the ethanol but none of the water evaporates) then the reduction in volume would equal the ABV.
If you have $700 to spend you could buy both of these which I believe will let you calculate the alcohol content of finished beer.
https://www.my-smartref.com/en-us/p...MIovO3u8LLjAMV3EpHAR1zHgq7EAAYASAAEgLBr_D_BwE
https://www.my-smartref.com/en-us/p...MIovO3u8LLjAMV3EpHAR1zHgq7EAAYASAAEgLBr_D_BwE
I will try this: buy different beers with different alcohol%. Measure using a vinometer, when the carbon is gone, and see if I can make a conversion table. If there is little divergence between different beers, it may be usable. The beer will not be wasted.
DuncB
Well-Known Member
You need to get a hydrometer as well as the refractometer.
Put the hydrometer in the finished drink and take reading.
Take a reading with refractometer in brix.
Use this
https://www.vinolab.hr/calculator/alcohol-from-hydrometer-refractometer-en27
Orrrr, buy a cheap breathalyzer, drink one of your beers in 15 minutes, check you're BAC with the breathalyzer.. drink a beer that you think has similar abv, check BAC again, repeat this process until you find a match, or you run out of beers, or you pass out.. do it for science.
My suggestion will be less intoxicating I believe.
And IF I can produce a reliable conversion table, will you then read and use it?
No, I calculate my abv via an Anton Paar easy dens. So I would have no use for it.. but that's just me, maybe someone somewhere would.. charts, tables, spreadsheets, graphs, and so on exist for almost anything one can imagine.
The description of Anton Paar easy dens don't seem to be usefull for alcohol percentage in finished beer.
Or tell me: you buy a 4.6% beer, run it through your Anton Paar, and you get a result of 4.6%.
No. A good old-fashioned hydrometer is more than good enough for my purposes. Your proposed method seems unlikely to work since my understanding is that a vinometer is really only accurate for dry white wines. If a bit of residual sugar throws it off, I can only imagine what all the dextrins (and other stuff) in finished beer will do.
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Won't work. Anyone who has done, or studied, distillation knows that the initial distillate contains both alcohol and water, and as you continue boiling the alcohol content goes down and the water content goes up monotonically.
You could distill until the boiling temp gets to 100°C (212°F, or whatever your local water boiling point is based on altitude), then measure the ABV (using a Tralle hydrometer) and volume of the distillate, calculate the total alcohol volume, and then figure out the dilution level in the original beer. You need to make sure your distillate comes out of the condenser cold, so that you are not losing any alcohol to evaporation.
You can measure the ABV of a simple binary solution of alcohol and water with an appropriately scaled hydrometer, since you don't have any of the confounding compounds (dextrins, proteins, etc.) that exist in beer.
Brew on
I believe that you need both the SmartRef and the EasyDens (as well as the app). Pricey solution, as mentioned above.
I use the Anton Paar easy dens too. Really nice little measuring unit. Measures current gravity. yes, to measure ABV you need an easy ref too - and it can calculate ABV from the two working together (one measuring density / the other a refractometer).
That said... I take my pre-boil and post boil gravity and record it the batch recipe. When I know my OG, and use the EasyDens on the finished beer - I can easily calculate the ABV.
That said... I take my pre-boil and post boil gravity and record it the batch recipe. When I know my OG, and use the EasyDens on the finished beer - I can easily calculate the ABV.
keystonehb
AHA Homebrew Shop of the Year 2025
Based off what I know I do not think this will work. Vinometers, proof and trail hydrometers, "alcohol refractometers", and other type of alcohol testers are affected by sugar content. What this means is that the dryer your beer is the more accurate it is. To accurately do something like this you would need to know the exact sugar % of each beer being tested, and even then it may still not be 100%.
shoengine
Whale Noun Member
Why do you need to know what the alcohol content of something is without having the initial reference? I can understand it for a single beer, I've forgotten to take readings before, but seems like a non-issue for most situations.
In those times I forgot to take readings and wanted to know for purposes of sharing I would just estimate based on either earlier examples or using the raw extract info plus my typical brewhouse efficiency. Not exact, but ballpark is good enough for my homebrewing needs.
In those times I forgot to take readings and wanted to know for purposes of sharing I would just estimate based on either earlier examples or using the raw extract info plus my typical brewhouse efficiency. Not exact, but ballpark is good enough for my homebrewing needs.
I am more interested in how than why. But ok. Other than making beer I am experimenting with buying cheap products containing suger or no sugar, carbonized and not. I add sugar and bread yeast into the bottles, let it ferment 2 weeks, and taste it. It is tedious to go through the OG FG process of each bottle, if it can be avoided.
worlddivides
Well-Known Member
It literally only takes a few seconds. Some of the other methods I've seen proposed in this thread (simply because the OG isn't available) would be far more time-intensive and tedious than simply measuring a gravity sample at the beginning and measuring a gravity sample at the end. If the calculations are too complex, then this will do them for you:
https://www.brewersfriend.com/abv-calculator/
I know there are some people who think checking OG and FG is tedious, but they generally don't care to know what the ABV is.
I could be wrong but assuming the sugar be used is 100% fermentable and yeast has an approximate attenuation level, you should be able to assume your abv% within a couple points, the only variable would be attenuation and you could just take a fg, knowing your sugar to water ratio would give you your og .. for example, dextrose has 42 gravity points per pound per gallon. So if you have 5 gallons of water and add 5lbs of sugar your og will be 1.042 there's no need to take an og reading with a hydrometer if this is how you're going about it.
This article is pretty interesting, although it is about low alcohol beer, as far as using the Anton Paar instruments to determine alcohol content without knowing starting or final gravities:
https://www.williamsbrewing.com/Alcohol-reduction
https://www.williamsbrewing.com/Alcohol-reduction
If using simple sugars, like dextrose (corn sugar) or sucrose, most yeasts will be at, or very close to, 100% attenuation. The attenuation estimates for yeast assume typical carbohydrate profiles of wort, which has significant amounts of more complex sugars like maltotriose and dextrins. Many yeasts can metabolize maltotriose, but some can't, and very few yeasts can metabolize dextrins, so different yeasts will have different attenuation depending on the molecular weight distributions of the sugars in the wort.
The gravity potential of table sugar (sucrose) is 46.2 pts/lb. If you mix 5 lb of sucrose with 5 gal (8.33 lb/gal => 41.65 lb) the resulting °Plato is 100°P * 5 lb / (5 lb + 41.65 lb) = 10.72°P. If we convert that to SG, it equals 1.043. The gravity potential of corn sugar (dextrose mono hydrate) is less than sucrose because 9.09% of the weight is water. So, 1 lb of corn sugar mixed with 1 gal of water will result a solution at 100°P * 0.9091 lb [dry wt] / (1 lb + 8.33 lb) = 9.74°P, which works out to an SG of 1.039, not 1.042.
The true definition of points/lb is: The SG that would be achieved by mixing 1 lb with enough water to make 1 gal of solution. Since the solute (sugar in this case) contributes to the volume, it takes less than 1 gal of water to make 1 gal of solution - it only takes 0.962 gal (7.715 lb) of water mixed with 1 lb of sucrose to make 1 gal of solution. If we then calculate the °Plato is 100°P * 1 lb / (1 lb + 7.715 lb) = 11.4744°P, which has an SG of 1.0462.
The incorrect definition of SG potential in the quoted post is an extremely common misconception, which results from the rather convoluted actual definition of SG potential.
Brew on
Ahh, makes total sense, I didn't account for the volume of the sugar itself. Thanks @doug293cz for clarifying that. I seldom use this process so forgive me for incorrect information. To touch on what you mentioned about attenuation and dextrins, I believe yeasts with STA1 are capable of metabolizing those dextrins. I don't have documentation on that but I read it somewhere on HBT so it must be true.
I saw the winemaker at a nearby winery using some odd looking stainless steel contraption with a little bunsen burner, that measured evaporation of a small sample, and had charts that you plugged in the local barometric pressure and elevation, and he said that's what the ATF required him to use, to prove his ABV claims on wine, rather than just OG/FG math. No idea what it was called, but it looked pretty neat. (this was quite a few years ago), long before I knew anything about gravity and fermenting or anything, so not certain I'm explaining what I remember very well.
Drink a 12-oz glass. If you get snockered, it's about 8%.
keystonehb
AHA Homebrew Shop of the Year 2025
These will only accuratly work if there is little to know residual sugar as the sugar suspension affects the "boil"
