Alcohol content

If I let a glass of beer warm to room temp, and the use the hydrometer will it tell me what % the beer is? I had someone ask me after I gave them a bottle.

Nope. For that they would have to take a gravity reading before fermentation as well.

The alcohol scale on a hydrometer is for "potential alcohol" and does not equal the actual alcohol level in a beer.

To calculate the alcohol by volume of a beer is an equation using the Original Gravity and Final Gravity. I do not know what the equation is, I just plug the numbers into an online calculator.

Without the OG or sophisticated lab equipment you can not tell.

og-fg x 131

new2brew1221 said:

If I let a glass of beer warm to room temp, and the use the hydrometer will it tell me what % the beer is? I had someone ask me after I gave them a bottle.

Click to expand...

So the best you could do would be to assume a middle of the road attenuation like maybe 72% and use that to estimate what the OG and therefore the alcohol was. But that would be a very rough estimate. Better than a total guess, but still could be well off.

For instance, a beer that finished at 1.012, if you assume 72% attenuation, OG would be 1.043, for an ABV of 4. But if the attenuation was really 65%, then OG is 1.034 and ABV is 2.9. On the other hand, if the attenuation was 80%, then OG was 1.060 and ABV was 6.3%.

Now, get yourself a liquid cromatograph or something like that and you'll be in business.

Revvy's is the formula I have always seen.

The Coopers formula makes everything 5% or more. Take 1.000 water, ferment and it is still 1.000 water. Divide by 7 and it is still zero. Then add .5. That doesn't make any sense.

bleme said:

Revvy's is the formula I have always seen.

The Coopers formula makes everything 5% or more. Take 1.000 water, ferment and it is still 1.000 water. Divide by 7 and it is still zero. Then add .5. That doesn't make any sense.

Click to expand...

Well, really it makes it 0.5% or more. I agree the result you get from water makes no sense, but not quite as badly as you have indicated.

I don't remember where I saw it, but I use this one:

(OG - FG) x 131.25 =

unionrdr said:

Not in my experience. I've used their formula & got 4.5% as well.

Click to expand...

I think you may have typed it wrong or something. Try it with 1.050 OG and 1.010 FG (fairly common readings). That works out to about 5.2% with Revvy's formula but .5067 with Coopers. What is that supposed to mean?

bleme said:

I think you may have typed it wrong or something. Try it with 1.050 OG and 1.010 FG (fairly common readings). That works out to about 5.2% with Revvy's formula but .5067 with Coopers. What is that supposed to mean?

Click to expand...

I think with the Coopers version you would use just the last 3 digits, without the decimal. i.e. your example would be 50-10 instead of .050-.010.

The coopers one adds 0.5% to account for the priming sugar addition, it's just a rough estimate.

The one that I posted is the one most commonly cited, and used. Whether it's the most accurate or right, almost is irrelevant. Because it's the formula most accepted (and listed by folks like Palmer and Papazian.) Therefore if you are brewing a recipe in a book or on a website, more than likely it was the formula the creator used to determine the abv for his recipe.