Rum Aging Science2
Series Overview
The January 2020 issue of “Got Rum?” covers in detail the goals of this series, as well as, descriptions of the different equipment being used to collect and measure the data.
November’s Weather
November was considerably cooler than October, the average outdoor high temperature was 69F and the average outdoor low was 46F.
Inside the cellar, the temperature ranged from a high of 75F to a low of 57F.
Temperature for November
The average rainfall in our area (Central Texas) was 2.83 inches, which translated to moderate humidity levels in the cellar. The relative humidity inside ranged from a high of 86% to a low of 24%.
Humidity for November
The Rum
The rum has completed its first year inside the barrel. The natural color extracted from the oak staves has slowly but steadily increased month to month.
From an organoleptic perspective, the rum already has matched or surpassed commercially-available “aged” rums from some craft and large distilleries, many of which have additional caramel incorporated to darken the color.
Samples of rum until December
pH: The rum that went into the barrel had a pH of 7.04. This final reading after 12 months in the barrel is 4.63.
pH of rum for December
As you can see above, the most drastic visual increase of acidity (reduction in pH) took place almost immediately, but the increase in real, titratable acidity was actually more linear.
ABV: The alcohol concentration of the rum in the barrel decreased during the first half of the year and increased during the second. What this means is that, proportionally-speaking, more alcohol vapor left the barrel earlier, and more water vapor left the barrel later. The starting ABV was 63.43% and the final ABV is 63.84%.
ABV od rum for December
Conclusions
Aging rum truly is one of the most value-added transformations a rum producer can take advantage of.
Barrel selection is at the core of this transformation, since it will dictate the availability and type of extractable materials rum will be interacting with.
This full year we’ve monitored the rum inside an ex-whiskey barrel, and we witnessed how much natural color it extracted, and how fast it did so.
We also monitored the pH changes to the rum during this journey and the impact of acidity in flavor creation, mainly in the form of esterification.
We also looked at ABV changes of the rum inside the barrel. Many readers have written with questions about why the ABV went up during the latter part of the summer, and this is a topic that we’ll explore in more detail in future articles.
Are these results typical of all aging warehouses around the world? Probably not. Even if the daily temperature and humidity deltas at our Distilled Spirits Plant in Central Texas are a close match to those experienced elsewhere, the alcohol vapor concentrations and amount/frequency of air exchange in those warehouses would also have to coincide with ours for the results to be the same. Having said all this, the closer the environmental match, the better the data will follow along.
Q: Is the rum ready to be sold after 1 year in the barrel?
A: While the transformation after 1 year of aging is quite noticeable, the rum’s journey has only began! If the distiller is in need of cash, then it would be OK to harvest a few barrels for bottling, but we would recommend keeping as many barrels as possible full, so that they continue to age. These barrels will then sell for much more money than their younger counterparts, handsomely rewarding patience.
January to December rum samples
COMING UP NEXT
The response to this series from craft rum distillers has been overwhelming! Some were not aware of the chemical changes that would take place; others didn’t know about the ABV fluctuations. Those distillers who only had whiskey-making experience were shocked by how little color is extracted from a used barrel, compared to that from new ones.
The questions have steadily poured in and the next steps for us could not be clearer: Rum Aging Science must continue, but the scope needs to be extended to include new barrels and different types of oak as well.
rum aging science questions
Will rum’s chemical changes happen just as quickly in French Oak barrels as they do in White American Oak ones? Will color extraction be different in new barrels, depending on their toast/char level?
These are some of the questions we’ll be exploring in future installments of the new series. So stay tuned and keep the questions coming!