It almost seems wrong to do so, but in theory anyway, would it be possible to take a normal ABV beer and evaporate off most of the alcohol and create a low ABV beer?

-Of the techniques that the big guys use for the creation of low ABV beers, evaporation really seems the only way to accomplish this at home; I know I can change the recipe to come up with a less fermentable and lower ABV RECIPE, but I'm really asking about taking a "normal" beer that's already fermented and bringing it up to ethanol evap temp (78 Degrees C) and just evaporating off most of the ethanol.

-How long would it take to evaporate off most of the alcohol in a 4.5% ABV beer?


A question for AJDelange or any other super geeks: What method could be used before and after holding the beer at 78C to determine how much alcohol was boiled off/ what the new final ABV is?


Thanks,
Adam

I've never tried to remove alcohol from beer (other than for analysis) an so don't have any experience to pass on. I do remember a long discourse in HBD on using low pressure (from an aspirator connected to a corny keg IIRC) rather than high temperature (which give the beer a "cooked" quality). The main problem the guy had was foaming (again relying on memory) but I expect he'd have that with heating too.

The part of the question I can answer has to do with measuring alcohol content. Unfortunately there is no practical (by which I mean within the reach of homebrewers) way to do this. For normal beer strength the usual method is measure a volume of beer precisely and add about half again as much water to it and then distill over nearly the original volume of beer leaving about half the original volume in the distillation flask. The receiver, which is the volumetric flask in which the sample was originally measured out, is then made up to the original volume with DI water and now contains a volume of water/alcohol solution of the same strength (by volume) as the beer. The specific gravity of this is measured. The problem is the measurment of the specific gravity. In the wine industry a Tralle hydrometer can be used but these are just not accurate enough for the low alcoholic strength of beer (the marks are too close together at the low conentration end). A big brewery uses a oscillating U-tube densitometer, which is probably worth more than your car, to do this. The determined home brewer can make these measurements with a pycnometer but the process is laborious and does require, in additition to the distillation apparatus, the pycnometer itself (a little over $100) and a good analytical balance. If a well maintained good one can be found at surplus then this method comes within the realm of possibility for the home brewer. If you want the details of the pycnometer procedure ask and I'll post them.

For low alcohol beer the basic problem (that a low percentage alcohol solution in distilled water doesn't differ much in specific gravity from water itself so that the difference is hard to measure) just becomes more acute. Consequently for very low concentrations the sample is dosed with NAD+ in the presence of alcohol dehydrogenase which converst the alcohol to acetaldehyde and then acedaldehyde dehydrogenase is added to the mix which converts the acetaldehyde to acetic acid. Both these steps reduce the NAD+ to NADH and the concentration of NADH in the solution is thus proportional to the amount of alcohol. NADH concentration is measured by UV absorption so a UV spectrophotometer is required. Plus the kits containing buffers, the enzymes and NAD+ are expensive, have to be shipped refrigerated and have very short storage life.

Another method is gas chromatography - again out of reach for most home brewers with the exception being those that work in or have access to someone who works in a lab.

I was afraid you were going to say something like this...

Refractometers are "thrown off" by the presence of Ethanol and there are widely available formulas for determining the actual gravity of a final beer sample when the ABV and refractor reading (starting gravity and current finished gravity) are known. -I was hoping that if I knew the OG, FG, Refractometer reading of the FG, and then new FG of the final sample with some ethanol evaporated off that it would be possible to solve for the difference in ethanol between what I'll call the "Original Final Gravity" (Pre-ethanol evaporated) and "Final Final Gravity" (Post-ethanol evaporated)....

Theoretically feasible, or non-starter? (Why? -Is the issue just that the gravity difference between the "with ethanol" and "without" ethanol samples would be so small that it would require some super accurate refractometer, the likes of which simply don't exist or at least not within a home brew budget? -If this is the case wouldn't it be unnecessary to adjust the refractometer readings due to the presence of ethanol in the first place?)

(Assumption: All gravity readings are taken at the calibration temp of the refractometer or have the ATC function.)


Edit: I found a reference that stated that the formula used to do this conversion can be found in the CRC Handbook of Chemistry and Physics ("Concentrative Properties of Aqueous Solutions: Conversion Tables", 69th Edition Table 88 Sucrose... If anyone happens to have a copy...


Thanks,
Adam

Are you trying for just a low ABV or are you looking to make a NA beer? If you are going for NA, holding the beer just above the ethanol boiling point would drive off the majority of the alcohol, leaving you with a beer with little alcohol remaining. This doesn't get around the cooking part however. As AJ said, low pressure would allow for alcohol removal without needing to increase the temp as much, but that will also change your eth vaporization point.

It's really a purely theoretical question; I'm not planning on actually doing this and I'm not really even focused on whether or not it would work (I'm certain enough that it would work.("It" being the evaporation of the ethanol.). -I'm really interested in how you could calculate/ test the ABV before/after or the ABV difference.

I'm also curious just how long it would take to boil off the majority of the ethanol.
--If you're only brining the beer up to 78C (172.4F) and only need to do it for a couple of minutes the darkening of the beer would be minimal (i'd have to carb it all over again, though). --And if the time it takes to boil off x% ABV is unknown, and I have a way to measure before/after ABV I could figure out this one, so the two questions ARE sort of related.


Adam

Spiderwrangeler,

On an unrelated note: how the heck did you create a gluten-free WIT beer?!??? Have the recipe/process posted somewhere?
(Did you avoid barley and wheat or did you use an enzyme that will break down the gluten, or what?)



Adam

I think I found what I was looking for! (Excited!)

http://www.musther.net/vinocalc.html#alcoholcalculation

This particular calculator allows you to take the SG with a hydrometer, and the refractometer reading of the same sample and estimate the ABV! I'm curious how accurate it is, but it certainly seems like an estimate is at least possible.

Now I want to validate this with a beer but none of my precious homebrew so I'll have to pick up a 6 pack of cheap stuff around 5% ABV.

-I can take take 1 can and leave it alone and just measure the specific gravity as-is with a hydrometer and refractometer and plug it in and see if the calculator agrees with what is written on the outside of the can, then I can bring the beer up to 79-80C and hold for 5 minutes, take a sample and chill it back down to 60F and take 2 new measurements. (I won't get to this this week or next week but the 2nd week of April looks good!)


Adam

It was a 'wit' in terms of what I'm trying to get out of it flavor-wise, you can find it here
http://www.thebrewingnetwork.com/forum/viewtopic.php?f=6&t=21073&hilit=gluten