Here the answer to a question I’ve never wondered about: The last dram from a bottle of Scotch is less potent than the first. The reason? Scientology.
Oops. I mean science.
The Scotch Blog begins with a simple question submitted by a reader:
Does the alcohol content of my whisky decrease as I near the bottom of the bottle?
I ask this because (1) there seems to be less alcohol burn as I wind through the bottle and (2) because alcohol being a light, fairly volatile liquid, could be in vapor form at the top of the bottle and released when I remove the cork.
Kevin, the eminent Scotch blogger himself, runs the question by a number of master distillers and discovers that yes, alcohol burns off of Scotch into the air above. If the bottle stays open a long time, that alcohol evaporates freely into the living room. Even if the bottle is closed, though, the emptier the bottle, the more headspace of air for alcohol to evaporate into. Unseal your bottle and the alcohol goes floating away.
Or as Dave Pickerell, master distiller at Maker’s Mark, says:
If the bottle is tightly sealed, only a relatively small amount of alcohol will evaporate … and then an equilibrium condition will set up where alcohol evaporates and condenses at the same rate and the concentration of alcohol in the vapor state is constant throughout the space…. it will not stratify… The proof in the liquid will remain essentially unchanged. Even if the bottle is opened and partially consumed, and then tightly re-sealed, this same equilibrium will be achieved, and there will be essentially no proof reduction … even as the liquid volume decreases. (Theoretically, there might be a minuscule proof reduction here, but I don’t think you could notice it).
Of course, if you are really worried about losing any of the good stuff evaporating into the air between the booze and the cap, there is a quick solution. Anyone know the answer?
Perry, put your hand down. Let’s give someone else in the class a chance to answer. Anyone? No?
OK, let’s let Chris Morris, master distiller at Brown Forman, answer:
If you desire to return the alcohol vapor to the spirit you would have to chill the bottle to condense it. That of course is not standard storage procedure. I wouldn’t worry about it.
WWW – the Weakening Whisky WoundTable [The Scotch Blog]