Did a google on this and came up with "new abv=(original abv)*(original volume)/(new volume)" from another forum. Is this correct? Any help would be appreciated. Thanks guys and gals.
That's the correct calculation. If you have 5 gallons of beer at 10% ABV, 5 x 0.1 = 0.5 gallons of alcohol in the beer. If you then remove 2.5 gallons of water from it, you calculate 0.5/2.5 = 0.16 or 16% ABV. The problem with this calculation is that it assumes what you remove from the beer is pure H2O with no alcohol left behind. As someone who's attempted eisbocks before, its a pain in the ass process and impossible to determine whether or not you've left alcohol behind.
If you take a hydrometer and a refractometer reading, there is plenty of brewing software out there that will take the two values and spit you out an estimated ABV. Combine that with a proportional calculation based on volume loss to ice, and I think you will have a reasonably fair estimate. Assuming you have a refrac, of course.
Thanks to both of you. I found this to be the case last night. I had three frozen quart-sized 9% ziplock bags that were (mostly) full and funneled those down into two 12oz bottles. Each time this eis-alcohol dripped too slow for my liking I put a "fresh" bag-full on. Once I took the ice off and disposed of in the sink I saw that there was plenty of alcohol left judging by the color. It's a mystery as to the exact percentage! Thanks again.
The “real” way to do it is to measure out a precise amount of the beer by volume, capture all of the alcohol through distillation, dilute back to the original volume with water (at the same temperature), and measure the gravity of this alcohol/water mixture. It only takes a few thousand dollars worth of gear: http://www.themadfermentationist.com/2009/07/testing-alcohol-content-of-ice.html in that case the gravity slightly more than doubled while the ABV only increased by 75%. I’ve always wondered if you could do the same thing in reverse. Boil-off the alcohol, dilute back to the original volume with water and see how much the gravity climbs with the alcohol replaced with water. It would be tough to measure with great precision, but it would give you an estimate.
I think it would work. If you heated it very slowly to 180ish, held it there for an hour, then replaced to the original volume with distilled water you could probably get reasonably close. Closer than the ballpark methods usually used anyway.
If you have a good scale and/or graduated cylinder and are willing to use up some precious eisbock you try this at home. Take an initial weight/volume measurement, boil off the ethanol keeping the temp at a balmy 172-176F. Then cool and take a final weight/volume measurememt. ((final/initial)-1)X100%= -ABV/W
By the way, it was your "Apple Jack" video that I am replicating. Although the apple jack part is just a side project. I'm soaking oak spirals in the apple jack and going to dry hop them in the secondary (keg). Russian imperial stout. Should be interesting. Thanks for the video inspiration!
You're welcome. I hope your eising process goes a little more smoothly than mine did. Lots of good suggestions in the comments on that video.
