How to get ABV?

[jpowelle5]

I know, I know - this question has been asked 100+ times and yet here it is again... (-:

I am a newbie and want some clarification. I understand how to take the OG reading before pitching the yeast; I understand how to take the FG reading after full fermentation.

After some diligent research I also now know that unless you adjust those readings based on the temperature you are taking the readings you will have incorrect data.

Question #1 - What is the correct calibration for hydrometers? Is it 1.000 at 59F or 1.000 at 60F or 1.000 at 68F? I have seen all three.

Question #2 - How do I calculate ABV? Again did diligent research and found a variety of methods, online calculators, simple math equations, ect. Which one is correct?

I.E. OG - FG / 0.00738 or OG - FG * 129 or OG - FG * 131

Here is my OG based on taking the reading at 75F and using calibration of 59F for the hydrometer: reading was 1.060 adjusted to 1.062 based on temperature correction.

Here is my FG based on taking the reading at 68F and using calibration of 59F for the hydrometer: reading was 1.022 adjusted to 1.023 based on temperature correction.

Here is what I think the ABV is base on different calculation:
5.28 or 5.03 or 5.10

See where I am coming from? Thanks in advance for any insight into the correct way to (a) take the hydrometer reading & (b) determine ABV.

Jp

 

[ohiobrewtus]

I always use (OG - FG) * .131, so

(60-23) * .131 =

37 * .131 = 4.85%

 

[BeehiveBrewer]

You get ABV by adding more extract! ; )

 

[remilard]

The reason you are finding multiple formulae is that they are all approximations and all assume that abv is a linear function of the difference in specific gravities (it is not). The multiples are all different and are chosen to be exactly correct in some circumstance. The further you get from that circumstance, the less accurate the approximation.

George Fix posted a somewhat more accurate and tedious method on HBD.

HOMEBREW Digest #880 Wed 13 May 1992

Note that specific gravities are used exclusively in the wine literature and percent extract (eg degrees plato) in the brewing literature. Often formulas given in terms of gravities are derived from the wine world and when we are using linear approximations to non-linear phenomena this can be problematic.

 

[brewthunda]

Is BrewCalcs.com reliable? BrewCalcs: Free Homebrewing Calculations

The beer I'm drinking now (souped up Dead Guy clone) had an OG of 1.064 and a FG of 1.010.

Using the 131 method, I get 7.074% ABV
Using BeerCalcs.com, I get 7.4%

[Update: using the Georg Fix method, I get 7.12% . . . so one more to add to the pile - which is correct?]

That's a pretty significant deviation in my book. What's the story?
Until I know the answer I'm just going to keep telling people that the ABV is 7.4% because it sounds more kick ass.

 

[jpowelle5]

That was my point exactly? Which is correct. I think i am with you. I am going to use the highest ABV until someone tells me other wise...

JP

Is BrewCalcs.com reliable? BrewCalcs: Free Homebrewing Calculations

That's a pretty significant deviation in my book. What's the story?
Until I know the answer I'm just going to keep telling people that the ABV is 7.4% because it sounds more kick ass.

 

[Bob]

Which is correct? Re-read Remilard's post, please.

[waits patiently] Hmm, hum, hmmmm...Finished?

The correct answer is, "All of them". Honest. He wasn't lying or deliberately obfuscating when he wrote that all of the formulae are approximations in different ways.

In my opinion, the least inaccurate is Fix's. Note I didn't write "most accurate"; it's not. But out of the various OG-FG*X formulae, it's not too shabby.

And really, fellas, if you're talking about 7.25 vs. 7.4% by volume, what you really want to know is the correct formula to determine the amount of angels able to dance on a pinhead. Now, if the formulae were giving a +/- 2% discrepancy - like 5% vs. 7% ABV - I'd say go nuts with this discussion. But 7.25 vs 7.4% is within each formula's margin of error, which makes the discussion of which is accurate patently ridiculous. The only real way to determine exact ABV is through extensive labratory methods which you probably haven't the equipment to perform.

My advice? Pick the formula that's easiest for you to remember, or gives you a fudge factor or whatever. If it makes you feel better to use the higher ABV, go for it. Just know that you don't need to be sweating so much over the differences between such inaccurate approximations. It's really not necessary.

Cheers!

Bob

 

[jpowelle5]

All I really care about is that I made beer... Looks like beer, smells like beer, tastes like beer - it must be beer and I had fun doing it.

I'm not saying it is the best beer I have ever tasted but it was MY beer.

It was more curiouristy than anything else. How to use a hydrometer accurately and all. I guess I will just use the hydrometer to know if the beer has fermented or not.

Use the 59F as my calibration to adjust the OG/FG for temperature and use the simple math of OG - FG * 131 that should give me something if asked at the local pub.

Thanks to all for posting.

JP

 

[bob1852]

I read somewhere that older hydro's are calibrated at 60*, but newer ones are calibrated at 68*

 

[Zenman]

so i settled on the OG-FG/.00738 using this method the ABV seem to come in low for the style, which I have attributed mostly to me possibly getting off SG readings since I am doing 2 gal partial boils and maybe the water/wort isn't mixed completely despite stirring to aerate it.

Anyway doesn't really matter I guess other than my wife wishing the ABV was higher, and non HB are always incredulous, they assume the point of HB is to make 10% bud clones or at least strong 'bathtub' beer (or why am i bothering, right?).

Guess this stirred up my curiosity, how do the micro's do it, are they not regulated in some way to accurately label it, etc. Or is it very loose and Utah kids itself with requiring the low ABV on beer and the rest is a nod and wink to being 'close'...

 

[remilard]

Guess this stirred up my curiosity, how do the micro's do it, are they not regulated in some way to accurately label it, etc. Or is it very loose and Utah kids itself with requiring the low ABV on beer and the rest is a nod and wink to being 'close'...

Gas chromatography, smaller breweries will hire this out and it is typically only done say once a month, not batch to batch. A brewery with a gas chromatograph will probably do alcohol as well as flavor compounds on every batch since the marginal cost of the tests is fairly small if you have the equipment.

 

[DuckAssassin]

jpowelle5,

As for your hydrometer, if you no longer have the instructions that came with it, or it doesn't say directly on it what the temp you should use is, I would suggest you calibrate it yourself. Get some distilled water and figure out at what temperature it reads 1.000. That is the temperature you should take your readings at or correct your readings to. All of the ones I have had use 60*F, but even then, some are not entirely accurate and you have to adjust. The one I currently use reads .001 high, so I just cool my sample to 60* and subtract that when I take a measurement.