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Old 02-12-2012, 12:49 AM   #1
Jan 2012
Pasadena, MD
Posts: 17

I froze my beer for more alcohol, but since there's less water, the beer is thicker.

The whole point is because alcohol has a lower freezing point than water and vice versa with melting. Since I froze it, I can drip the alcohol out, kinda like Brewdog did with their tactial nuclear penguin beer.

Here's my problem and I'm hoping you all can help me:

My FG was 1.025 and my original ABV was right at 5%, but after I froze it, the beer is WAY thicker and now my new FG is 1.070. So now I can't figure out what the ABV is since the hydrometer went the opposite way. Anyone know how to calculate this??

I tasted it, and it's definitely substantially stronger than before and tastes so much better. I kind of want to do this with every beer I brew just for the heck of it, but if I can't figure out how much alcohol is in this thing I'm going to go insane!!!!!

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Old 02-12-2012, 01:20 AM   #2
Beerrific's Avatar
Mar 2007
Posts: 5,562
Liked 55 Times on 47 Posts

conservation of alcohol:
(5%* the original volume)/(the new volume)=new abv

Given you know the pre- and post-feeze gravity, you need to know the original or current volume.
conservation of sugar:
pre(vol*gravity)=post(vol*gravity) <--- solve this for 1 unknown and sub into the above equation

Assuming it was 5 gallons before freezing:
5*25=x*70...x=1.8.....ummm, maybe you need to mix it up and try taking the reading again.

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Old 02-12-2012, 03:01 AM   #3
Scotty_g's Avatar
Mar 2007
De Pere, WI
Posts: 364
Liked 13 Times on 12 Posts

Did you check the post-freeze gravity when it was still ice cold? You will need to do a temperature correction.

You also concentrated the unfermented sugars. That may be messing with your reading. But I'm guessing it's a temperature issue.
Natural 20 Brewery

Yes, that *is* beer. Water, malt, hops, and yeast mean it's beer. Go ahead and try a glass...

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Old 02-12-2012, 01:59 PM   #4
Aug 2010
McLean/Ogden, Virginia/Quebec
Posts: 9,657
Liked 1604 Times on 1222 Posts

Your prospects of getting a good answer by any method other than distillation are low. The following method is a lot of work but is about the best I can think of short of distillation (or GC).

1. Carefully measure the original extract (OE)*
2. At the completion of fermentation carefully measure the specific gravity.
3. Measure the true extract (TE)** of the beer.
4. Estimate the ABW of the beer from ABW = f*(OE - TE) where f = .48394 + 0.0024688*OE + 1.5609E-5*OE*OE. This is a fit to Balling's table.
5. Determine the weight of the beer either by placing it in a tared vessel on a scale or by converting the 20/20 SG to density (multiply by 0.998203) and multiplying the volume (in Liters) by the density. Make sure you measure the volume at 20 C.
6. Multiply the weight of the beer (kg) by the ABW/100. This is the weight of alcohol
7. Multiply the weight of the beer (kg) by the TE/100. This is the weight of the extract.
8 Subtract the extract and alcohol weights from the total. This is the weight of the water.
9. Freeze the beer but don't allow it to freeze solid. Remove slush as soon as enough forms to facilitate removal and retain it. Keep doing this until you have collected as much slush (which will of course, melt) as desired.
10. Weigh the slush and subtract its weight from the original beer weight or re-weigh the remaining beer.
11. Divide the weight of the alcohol from Step 6 by the new weight of the beer. This is the new ABW.
12. Measure the SG of the new beer. Multiply the ABW from Step 11 by the SG and divide by 0.791(the specific gravity of ethanol). This is the approximate ABV.

Obviously steps 10, 11 and 12 can be done while waiting for more slush to form and one can repeat from step 9 until step 12 indicates a target ABV.

Steps 7 and 8 are optional but their results may be of interest.

This method assumes that mostly water with a bit of extract will be removed as the slush forms. Of course some alcohol will come out with it as well and this is a major source of inaccuracy. The other big source is in the calculation of the original ABW from the Balling table. I've had you go through the additional pain of using true extract difference rather than apparent extract difference in order to eliminate the additional error introduced by deviation from Tabarie's principle (upon which OG - FG methods are based) and included the dependence (through the f factor) on OG which most methods ignore.

If you are willing to accept the Tabarie portion of the error in order to avoid having to do the TE determination (and I wouldn't blame you for that) then obtain the apparent extract (FG converted to P) and estimate ABW in Step 4 from ABW = f*(OE - AE) with f = .39661 + 0.0017091*OE + 1.0788E-4*OE*OE.

*To obtain OE carefully (with a narrow range 20C/20C hydrometer) measure the specific gravity and convert to P = -616.868 + 1111.14*SG -630.272*SG*SG + 135.997*SG*SG*SG
**To obtain true extract measure exactly 100 mL of the beer into a volumetric flask and warm to the temperature for which the flask is calibrated. Using a pipet add or remove beer until the flask is full to the mark at the calibration mark. Quantitatively transfer (this means pour, then rinse with a small volume of DI water then repeat with a second small volume) to a beaker. Slowly evaporate the beaker contents down to around 30 mL. Slowly means in a water bath - not on an open flame. You don't want to cook anything. Transfer quatitatively back to the volumetric flask and make up to the mark, at the calibration temperature, with DI water. TE, in P, is obtained from the specific gravity of this reconstituted (without the alcohol) beer using the same formula as in *.

Reason: Several typos corrected

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Old 02-12-2012, 09:26 PM   #5
Jan 2012
Pasadena, MD
Posts: 17

You guys are awesome! I'm going to try this with my IIPA that I have fermenting. I'm going to take detailed notes of volume and everything I can physically do and see what I can get.

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