[wideminded]

The "sour beer," known as "wash," is then run successively through a pair of heated stills, bulbous at the bottom, narrow at the top, with a swan's neck extending down to a coiled copper pipe in a tank of cold water that converts the resulting vapor back into liquid. The first part of the run (the foreshots) and the last (the feints), both full of impurities, are eliminated.

I'm not much of a drinker, but I have always been curious about the distilling process. If I understand the description correctly, whiskey must be composed entirely of volatile compounds. And these must tend to be driven off at varying rates so that the composition of the final whiskey changes as it is collected. Is it necessary to add water to adjust the proof or does that all come throught the tube?

[SLB]

I have my asbestos suit on - as I couldn't stand scotch! In my days of bellying up to the bar nothing was finer than a little Kentucky Bourbon. But scotch? Eccccccchhhhhhhhhh

Actually nothing beats a glass of mint ice tea.

[the bottle let me down]

Whisky is typically 60% or so alcohol when it goes into the casks for aging. The composition changes due to slow evaporation during the aging process. When the time comes for bottling, the whisky is diluted with water to the desired alcohol content--usually 40-45% (80-90 proof). Often, there is also a cold filtration process.

Interestingly, the distilleries will also sell casks early on in the aging process to indepedent bottlers who can then choose when and how to bottle the product. More here. (If you have enough money you can do this too. See, e.g., here. Note: I've not done this.) Independents often bottle at "cask strength," i.e., not adding water. Such products are often 50-55% alcohol.

[tortoise]

And these must tend to be driven off at varying rates so that the composition of the final whiskey changes as it is collected. Is it necessary to add water to adjust the proof or does that all come throught the tube?

The different parts of the distilled spirit will contain different mixes of volatiles, but they are collected in the same place and so you end p with a single consistent mix of everything that came out of the distillation column. Different scotchs have different proofs when they go into the barrels, which is typically around in the 100-105 proof area. There are some chemicals that are solved in the alcohol which can precipitate during the filtration and dilution process that occurs before bottling.