Here’s a good question, from regular reader Brendan H. which allows me to solicit the opinion of some friends…
Another weird question for you, thinking as I kick a bottle of Cigar Malt.
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.
If so then it might seem wise
to swish the whisky around the top of the bottle to recapture any
vaporous alcohol before opening.
Thanks for the science lesson.
I responded to Brendan…
Theoretically, It COULD.
If it sits for a long time with a bad seal, the alcohol could evaporate…reducing the amount of Alcohol (by volume) in the liquid.
Once the alcohol has entered a gaseous state I don’t think it will recombine with the liquid by swishing…
But I thought I’d ask for input from some of my industry friends…
Chris Morris, Master Distiller, Brown Forman
You are correct. Every time a bottle is opened, a drink poured
out, and the bottle resealed you have created headspace. The headspace
will be filled with evaporate.
Keep doing this and the ever increasing
headspace will continue to sap the alcohol strength from the spirit
(very small amount overall).
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.
Dave Pickerell, Master Distiller, Maker’s Mark
At the risk of being too technical … here goes.
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).
If the bottle is loosely closed … or not capped at all … The alcohol will continue to evaporate and will never reach an equilibrium because it will continue to escape from the open mouth of the bottle into the surrounding air space. Thus, the proof will continue to drop. This also explains why a non-chill filtered whisky bottled at a proof of 86 or greater will eventually cloud up if left for a long time with the cap off or the seal loose. When the product reaches a proof below 86, a chill haze begins to develop, because some of the components become insoluble in alcohol and water mixtures below 86 proof … This haze can be anything from a little cloudy to something akin to river mud.
Mark Reynier, Bruichladdich
When reducing to obtain the desired 46% vol that we like to bottle at, it is notoriously difficult to arrive at the precise
figure because the alcohol strength (in bulk) and at cask strength is so volatile. We have a legal 0.1 variance and a matter of 60 minutes is enough to reduce the strength by 01 or more.
Therefore, even at a reduced volume (a bottle) and strength - and with exposure to air, I imagine that the strength would fall . . . albeit at a stultifyingly slow
The reduced alcohol burn referred to is probably reduced by the rasping cigar smoke in the throat.
Ian Millar, Glenfiddich
First off, why would you have a bottle open so long this could happen??? THAT wouldn’t happen in Scotland!
Secondly, yes – you could lose something in evaporation and the rate of loss would relate to the temperature of the room and was the bottle in direct sunlight or indeed artificial light.
(Never take a chance – store the bottle in a cool dark place, open with good friends and devour with joy).
All the best