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Old 05-10-2012, 01:50 AM   #1
thomasrj
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Default ABV measurement sans hydrometer/refractometer

I hope this is the right spot; I figured the science-minded folks would know how to answer this best. Thanks in advance for your help.

The question:

Is there a (relatively) easy way to determine alcohol content, either %mass or %vol, without using hydrometer or refractometer readings? Related: Can a hydrometer get out of whack and just give erroneous readings?

Here's why:

I recently brewed a milk stout and I don't trust the ABV calculation based on the hydrometer readings. OG was 1.100 and FG was 1.024. By my calculation, this should indicate a touch over 10% by volume. I've had a lot of ten percent beers, and this is not one.

I'm looking for a way to verify this. I'm a grad student so I have access to standard lab equipment/supplies if necessary.

I did a hydrometer calibration check with cool tap water and had a reading of 1.001, which I think is reasonably accurate for a municipal supply of treated surface water.

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Old 05-10-2012, 02:44 AM   #2
Haputanlas
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Can you post the recipe and your volume of wort after the boil?

I have doubts about the 1.10 OG if you weren't anticipating a huge beer.

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Old 05-10-2012, 11:35 AM   #3
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The usual method of determining ABV is to separate the alcohol from the beer by distillation and then measure the density of the distillate whose volume has been adjusted to that of the original beer sample. Gas chromatography is sometimes used and there are special (read expensive) instruments that look at density and NIR absorption of the beer and determine ABV from that.

Accurate determination of the density of the distillate requires that a digital density meter be used (expensive) or that one go through the elaborate steps required in making the measurement with a pycnometer. So I guess the answer is no, there is no simple method.

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Old 05-10-2012, 02:01 PM   #4
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Quote:
Originally Posted by ajdelange View Post
So I guess the answer is no, there is no simple method.
Well, that figures...

It was 6.6 lb of LME and 0.5 lb each of maltodextrin and lactose. I was expecting around 1.064, but I figured the hydrometer couldn't lie. Maybe I just pulled the sample from a thick part of the wort or something like that.

Thanks for the help, guys. I guess in the long run, it doesn't really matter--it tastes good either way
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Old 05-10-2012, 02:20 PM   #5
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Your reading is either due to temp of the sample, stratification of the wort, bad hydrometer or volume. Extract is extract. No way to magically get 34 gravity points

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Old 05-10-2012, 04:28 PM   #6
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Quote:
Originally Posted by thomasrj View Post
Well, that figures...

It was 6.6 lb of LME and 0.5 lb each of maltodextrin and lactose. I was expecting around 1.064, but I figured the hydrometer couldn't lie. Maybe I just pulled the sample from a thick part of the wort or something like that.

Thanks for the help, guys. I guess in the long run, it doesn't really matter--it tastes good either way
I'm assuming this is a 5 gallon batch?
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Old 05-10-2012, 04:45 PM   #7
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Quote:
Originally Posted by thomasrj View Post
Well, that figures...

It was 6.6 lb of LME and 0.5 lb each of maltodextrin and lactose. I was expecting around 1.064, but I figured the hydrometer couldn't lie. Maybe I just pulled the sample from a thick part of the wort or something like that.

Thanks for the help, guys. I guess in the long run, it doesn't really matter--it tastes good either way
At 5 gallons, I calculate that your OG should have been 1.052. With extract it's pretty hard not to hit your numbers.

Assuming your hydrometer didn't "lie" about the FG (1.024), your Alcohol By Volume should be 3.66%.

However, I'm going to assume that your hydrometer did lie and that you're closer to 1.013 FG. If this is the case, you have an ABV of 5%.

Now, I'm making all of that up about the FG, but I'd suspect that this is where your numbers would be if the fermentation actually finished properly. Also, I don't know anything about the yeast you used, so expect +- a few percent.

Note, I feel pretty confident that if you only added the ingredients you mentioned, your OG was close to 1.052. Now, I'd suggest getting a different hydrometer and/or research the proper way to read a hydrometer (Youtube and HBT search). Then you can find out the real FG and hopefully be close to what the real ABV is.
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"There is no strong beer, only weak men"
"Pretty women make us BUY beer, ugly women make us DRINK beer" - Al Bundy
"Give a man a beer, he'll drink for a day. Teach a man to brew, he'll be drunk for the rest of his life."

Primary: Viking Metal, Berliner Weisse
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Bottled: None
Notable Empties: Oaked Black IIPA, BBK I, Red IIPA, Burning Bush, Apophis "The Destroyer", Vanilla Porter
On-Deck: Hobbit Ale, The Titan BW, Ale of Olympus

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