Calculating the ABV of an Eisbier

[BitterSweetBrews]

I had 6 gallons of beer (Amber Ale) cold crashing after dry hopping in my lager fridge, which was set at about 37 degrees. When I brought it out to bottle (all my Kegs are in use) I was surprised to find a big chunk of ice on the top of the liquid. The bucket was high up, on the compressor hump and I guess the circulating fan I had by the cooling coils in what use to be the Freezer section super cooled the top of the fermenter (I removed what used to be a shelf between the Coils/freezer section and the fridge section).

So I had a dilemma. Do I leave the beer out to thaw or do I take advantage of this and make an EisBier. I was a little concerned about oxidization after melting, so that was one factor. I tasted the unfrozen liquid and it was pretty good, so I decided to bottle it as is. It wasn't a hard decision. So, now I need to figure out what the ABV is.

Here is what I came up with. Please let me know if I am correct.

After the ice melted I was pretty surprised how light/clear it was compared to the rest of the beer.

Before I crashed it and the big freeze the ABV was at 5.6% for about 5.5 gallons of liquid (6 gallons in the fermenter, less about 1/2 gallon of trub or 726 ounces).

So, 5.6% of 5.5 gallons is 40.65 ounces of alcohol.

I now have 4 gallons of liquid or 528 ounces.

Since the same alcohol volume is still in this liquid, I just need to find out what percentage 40.65 ounces of alcohol is of 528 ounces.

40.65/528 = .076989

So my new AVB works out to be 7.7%.

Right?

 

[botigol]

Your volume numbers are slightly off, but should be close enough. I ran this through a Pearson's Square and came up with 7.33%; less than 0.5% discrepancy I would call it good.

 

[ajdelange]

Since the same alcohol volume is still in this liquid....

I don't think you can assume that. In the one Eisbeer that I have actually measured it turned out that the ABV was a couple of percent lower than what one would calculate if it were assumed that pure water froze. This may have something to do with the way this brewer did his freezing and 'ice' removal and it may be the case that you removed less alcohol but the only way to determine the actual ABV of your beer is distillation or gas chromatography.

 

[BitterSweetBrews]

I don't think you can assume that. In the one Eisbeer that I have actually measured it turned out that the ABV was a couple of percent lower than what one would calculate if it were assumed that pure water froze. This may have something to do with the way this brewer did his freezing and 'ice' removal and it may be the case that you removed less alcohol but the only way to determine the actual ABV of your beer is distillation or gas chromatography.

I suppose that this is true about the scientific methods to get a perfect number.

Since the alcohol does not freeze at 30ish degrees I am confident the ice did not have any or much alcohol in it. I did take the ice out and put it in another bucket to measure it. It was not a real solid block and was kind of flaky almost honeycombed. But it did not seem to have any liquid in it. I suppose some could have been trapped which would affect the numbers.

I checked last night and it had melted down to 1 gallon of liquid (not 1.5). I tasted it and it was pretty much lightly beer flavored water, not beer. I sensed no alcohol. Since I had measured the SG and got an ABV before it froze, I feel I had a good number to start with.

So using that figure I would have had 5 gallons if the ice was melted which works out to 36.96 ounces of alcohol AT 5.6%. Plugging this 37 ounces into the formula with 4 gallons of beer, this would work out to 7% using my method.