Estimating ABV of freeze concentrated brew?

[FatDragon]

I've read a number of threads and articles, but I'm still a bit unsure of how one gets a halfway decent estimate of the strength of freeze-concentrated beer without a lab report. Calculating the total alcohol that went in against the total volume out doesn't really work because you're not getting 100% of the alcohol in the runoff. Hydrometers are useless because we've concentrated sugars as well as alcohol so there's no telling what the adjusted OG of the brew would be either. I've read that freezing temperature plays a part, but that should only impact whether or not the beer will freeze, not necessarily the strength of the runoff as it starts to melt, right?

Moving on from hypotheticals, I froze 1.5L of barleywine almost a week ago and bottled the runoff yesterday. I'm wondering if someone can help me work through my data and anecdotal evidence to try and get a decent estimate. Here goes:

Data:
Volume in: 1.5L
Volume out: 0.4L
OG of original beer: 24.5 plato
FG of original beer: 3.0 plato
ABV of original beer: 12-13.2% (depending on how you calculate a beer of this size. I call it 12.4% as a compromise)
FG of concentrated beer (for laughs): 6.0 plato
Freezing temp: ~ -18C/0F
Runoff time: ~25 minutes

Anecdote:
The leftover ice had significantly less color after runoff and the concentrated beer was darker than the original beer, though not way darker. Small tastes of the beer were definitely stronger both in flavor and ABV than the original barleywine, though it didn't taste different, just stronger.

I don't need a lab report or an absolute number, but I would be interested to see if anyone has a good method to ballpark a number to toss out when I share it.

 

[MaryB]

Could weigh it then use a thermometer and bring the temp up to the boiling point of ethanol. Boil at that temp until it quit reducing(it will evap some water but slower than the alcohol, temps will start to rise when all the ethanol is gone). Weigh the leftovers and do the math final weight/beginning weight ti get percentage lost. Ethanol boils at 173.1f so bring to that temp and hold it there by lowering the burner, if it drops below bring the burner up a bit again. You don't want to boil the water so keep a close eye on this and remember, the fumes driven off ARE flammable! Only need to do this to a cup of the beer.

 

[FatDragon]

Having collected 400 mL, I'd be killing most of my harvest for a result of questionable accuracy. Looks like I'll just share my sipper and tell people it's a bit stronger than they're used to.

Oh, and after the ice melted in the bottle, it turns out it's still got a lot of color - hard to tell with ice... Maybe I'll try a boiloff experiment with some of that and do some mathemagic to get an estimate for the concentrate.

 

[FatDragon]

Could weigh it then use a thermometer and bring the temp up to the boiling point of ethanol. Boil at that temp until it quit reducing(it will evap some water but slower than the alcohol, temps will start to rise when all the ethanol is gone). Weigh the leftovers and do the math final weight/beginning weight ti get percentage lost. Ethanol boils at 173.1f so bring to that temp and hold it there by lowering the burner, if it drops below bring the burner up a bit again. You don't want to boil the water so keep a close eye on this and remember, the fumes driven off ARE flammable! Only need to do this to a cup of the beer.

Update: I tried using this method with some of the leftover beer that stayed in the ice when I ran off my ice-barleywine. It's just not a viable solution. Keeping that low a thermal mass at a specific temperature on a home cooktop just doesn't work, and the water that evaporates off below boiling temperatures is not negligible. At my (arbitrary) endpoint, I had evaporated more weight of liquid than the original ABW% of the beer before freezing, and there was still some alcohol evaporating off (by the smell of it). This opens me up to the possibility that my ice-barleywine might not be much stronger than it was before freezing, but mostly it just affirms my expectation that this method just doesn't work as theorized.

 

[MaryB]

I would think a candle or sterno pot and an adjustable lab stand to control the heat would be needed for that tiny of an amount.

 

[FatDragon]

I would think a candle or sterno pot and an adjustable lab stand to control the heat would be needed for that tiny of an amount.

That might have helped, as would a more suitable vessel - the thick-bottomed saucepan over a gas stove left hot spots where different parts of the beer were at vastly different temperatures (+/- 20 degrees F). A beaker over a candle might have worked out better, but even at 173 F you're going to have water evaporating so I'm not certain it would work out anyway. I think it's a viable way to make (mostly) non-alcoholic homebrew but not so much for measuring ABV.

 

[timdillon36]

I have only tried this once with apple cider. I did the freeze thaw in multiple steps over the course of a week or more. I started with 5g in a plastic water bottle and froze that for ~24 hrs, then thaw and drain for 8-12. About 4g went back in the freezer and then thaw again.

I wasnt really worried about the amount of time it took or how many times i had to freeze and thaw but i tried to let it thaw extra each time so i wasnt wasting much alcohol. When i got it down to about 3q it wouldnt freeze anymore. I guessed it to be about 30-35% based on not freezing at -10°f but i could be off because of sugar content beeing concentrate as well.

A word of caution. This is very strong and i considered it apple brandy and drank it with a mixer. If i drank more than one or 2 of these drinks in a night i would have a killer hang over. I attribute that to the temp getting high during fermentation and rather than trying to age the fussuls out i froze concentrated them in.

Im not sure how to dump the heads and tails when freezing.

 

[bkboiler]

i've been looking into this too to make a doppelbock and then an eisbock (as a repeat batch hopefully improving the second time around).

assuming you have og and fg numbers of the beer going into secondary, then you chill to 32F for cold conditioning. i was under the impression that you just measure the weight of the ice that remains in the fermenter after you freeze concentrate then rack away the eisbeer? I'd imagine you'll have to pour the melted water into a separate vessel to weigh it and "compensate" by estimating how much beer your left behind when racking out of the carboy. that should be a reasonable correction.
forgive me if i've overlooked something obvious, i've only done some quick research thus far as brew day for this is about a month away.

 

[FatDragon]

i've been looking into this too to make a doppelbock and then an eisbock (as a repeat batch hopefully improving the second time around).

assuming you have og and fg numbers of the beer going into secondary, then you chill to 32F for cold conditioning. i was under the impression that you just measure the weight of the ice that remains in the fermenter after you freeze concentrate then rack away the eisbeer? I'd imagine you'll have to pour the melted water into a separate vessel to weigh it and "compensate" by estimating how much beer your left behind when racking out of the carboy. that should be a reasonable correction.
forgive me if i've overlooked something obvious, i've only done some quick research thus far as brew day for this is about a month away.

I'm not sure if I'm reading you correctly, but when you freeze concentrate you're not getting every drop of alcohol out of the ice and indeed you may be leaving a significant portion of it behind, so concentration factor doesn't really work for estimating ABV of your ice beer.

 

[Jokester]

I've been poking around doing this sort of thing starting both with a commercial beer, as well as over fermenting that beer with amg and yeast etc.
If I start with an 8-8.5% brew or a hyper ferment brew -
I can get that to freeze up @ -3 to -5 F home freezer.
Then I attempt to concentrate it to 1/3-1/4th the volume.
I'm shooting for a low carb beer tasting liquor.
I'm pretty sure 1/3rd-1/4th the carbs end in the final concentrate.
Pretty sure most of the ethanol is in the concentrate.
Pretty sure methanol if any is split 50-50.
Fusels are mostly left in the ice.

See when the melt off is done, the ice that's left behind has a similar color to the beer, maybe a shade lighter, however any sediments or other bits are wholly left trapped in the ice.
The ice also has a very porous structure. That makes me think the ethanol (lowest melting point) is all out even from the middle of the bottle (my bottles are those 2l fruit juice bottles so its not as deep as a gallon milk jug) methanol (higher melting point than ethanol) is likely still split 50-50, and fusels which are higher melting point than both are mostly trapped in the ice.

Carbs - well these are water soluble and alcohol soluble - almost to equal degree, I'd say this is split in the ratio of liquid - aka 33% means 33% of the carbs are in the melt off.

Hop oils and hop flavors - These are oils, they prefer ethanol as a medium to swim in. That makes the hop oils end in the concentrate. That's why it actually tastes more like the base beer than the beer itself LOL.

Anyway that's been my observations. Be careful and dont throw it back like my friends wife did cos he didn't tell her it was a 25-30% alcohol beer (yea he mixed a bit of the beer back into it for carbonation and it just tasted so much like the base beer, she knocked a few back and went kablooey)