I visited the Bourbon Festival in Bardstown, KY a couple of months back. While touring the Getz Museum and attending an auction where prohibition-era bourbon was up for bid (some that had been distilled as early at 1917), I noticed that many of the older bottles appeared to be as little as half empty. While these bottles were sealed, sometimes in wax, I believe that this apparent loss of was due to slow evaporation over the years. Is this correct? Also, some of the bottles that were quite empty (i.e., about half) looked cloudy. Would this be due to these bourbons not having been filtered (and subsequently subjected to cold temperatures), or is it due to a concentration and subsequent release of some of the soluble matter in the whiskey?
I guess these questions ultimately lead to another question: If these bourbons have been "concentrated" by evaporation, how would they taste? At the auction I attended, they commented that the Van Winkle family had been given a bottle the evening before of one particular brand -- they opened it and let everyone sample some -- and apparently the bourbon was quite good (and different from "modern" bourbon). The bottles they pointed out did not appear to have suffered too much from evaporation (at most 1/4 to 1/3 of the liquid). Is there some sort of event horizon whereupon a bourbon no longer tastes good because it has been concentrated? Or, could the "different taste" of the older bourbons that had evaporated some be the result of some of this concentration (thus indicating a sliding scale of flavor)?
I was just wondering. Being a law student (and on a very fixed income), I didn't really have the resources available to bid on any of these bottles (none going for less than $60-70), but I do have an avid interest in the topic.