Privateer Rum’s Maggie Campbell on Barrel Aging Science – Tropical or Otherwise

The “Wonk” in Cocktail Wonk refers to digging deep to understand
as much as possible about spirits and cocktails. Many of the stories here involve the chemistry
of aging, as well as the different elements in a spirit – water, ethanol, and
other compounds such as
esters, aldehydes and higher (heavier) alcohols
. It’s these compounds that
give spirits their aroma flavor. Each spirit has its own ratios of these
compounds, thus making that spirit taste different than any other spirit. The
set of aromatic compounds in a spirit are impacted by many processes, including
fermentation, distillation, and barrel

There was recently a Facebook post about rum and the aging
process. Within the comment threads was a discussion of tropical aging, and
whether the high angel’s share (evaporation from a cask) slowed down after the
first few years. I’ve heard Caribbean distillers mention that their evaporation
rate was higher in the first few years, but I couldn’t pinpoint why. Luckily, Privateer
Rum’s Maggie Campbell, who I’ve written about previously,
wrote a very compelling comment in that thread which helped my understanding.

I felt that rather than have Maggie’s words be lost in the
sands of Facebook time, they should live on in a more permanent, visible form. I
asked Maggie for permission to reprint her comment here, with slight
reformatting for clarity and unrolling some of her abbreviations.

Maggie wrote:

Tropical aging does have more angel share. A certain amount of this also relates to the tradition for higher entry proof in the Caribbean ((proportionally more alcohol that readily evaporates) – but of course consistent 85 °F days is [also] a factor. And many more unique characteristics affect tropical aging beyond that.

It is well studied in formal industry study programs that the molecules that will readily volatilize in ambient conditions evaporate off in the first few years of aging and is related to the cellar conditions.

 Essentially what can turn into a vapor in those conditions does, and what is left behind are the molecules that do not as easily vaporize. What is left behind are heavier, longer chain molecules that may need more energy or specific conditions/structural changes of oxidation etc. to continue to evaporate. It does not magically stop of course; evaporation still happens. It does however slow down on the following years noticeably – everywhere, not just tropically.

But again humidity, consistency of temperature, and many other factors play into the unique expression of tropical aging. And of course, entry proof intersects with the rate of these chemical changes (higher proof – slower, lower proof – faster – due to stability) as well as temperature (higher temps – faster, lower temps – slower).

Clearly there is much more to this conversation than what I’ve covered here but this is part of one aspect.