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Comment by Xcelerate | Hacker News Reader

So, having a background in chemical engineering, perhaps I’m missing something embarrassingly obvious here and should hand over my degree, but what does adding a few drops of water do to something that has already been heavily diluted with water? Most bourbons are not sold at barrel strength (which is typically around 60-70% ABV), and they are watered down to either “full proof” or somewhere around 45-50% ABV as the last step before bottling. Adding a few additional drops of water beyond this step does not initiate any chemical reactions and just dilutes the bourbon slightly further than whatever level the distillery decided was pleasing to a large number of consumers. At most, perhaps it encourages the drinker to swirl the glass a bit.

What am I missing here?

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Obviously, there are exceptions in every direction and not all whiskeys are made the same, but bourbon is probably a lot closer to "barrel strength" than you think, it's a big part of why older bourbons are generally more expensive (higher proof, lower volume). Most bourbons aren't sold at barrel strength simply because they are blends of multiple barrels.

To my understanding, for bourbon any water added to the product is generally done prior to aging in the barrel. After that most of bottle proof comes from blending different ages of bourbon (because barrel ABV generally increases with age due to the angel's share and other factors) or different barrels of the same age that started at different (water cut) proofs to begin with (depending on the type of bourbon and its age statements).

On the factor of age, it is my understanding 60-70% ABV is expected for something closer to 7-10 year old bourbon and 3-5 years old (which is often the majority) is "naturally" closer to that 45-50% you see in the majority of bottles on store shelves.

I toured a few of the major distilleries in Kentucky last year, and most of them specifically mentioned that water is added after removal from the barrel, even for the less aged ones (of course this is skipped for some of the rarer products, e.g. E.H. Taylor barrel proof or Elijah Craig barrel proof). This is to meet certain product consistency requirements across their brands. I asked if it was the special “limestone water” originally used in distillation, and I believe it was Buffalo Trace that said no, it’s just regular water purified via reverse osmosis.

ABV decreases with age, the angels share is alcohol evaporating before the water.

I think you need to consider it not as a chemist, but as a psychologist.

There is some complicated chemistry that occurs at the liquid-air boundary and is affected by slight dilution.

https://www.nature.com/articles/s41598-017-06423-5

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