Introduction
Aging is the most value-added transformation that a rum can undergo while at a distillery or aging cellar. But aging all spirits involves so many variables, that distillers/cellar masters often leave decisions to chance. In this new series, The Rum University and Rum Central will monitor and share monthly data from a single barrel, so that readers can better understand the transformations that rum undergoes while aging.
Different climate conditions around the world affect these transformations in different ways. While the effects are universal, the results presented in this new series will be those from Rum Central’s Florence warehouse, located in Central Texas, USA.
Environmental Parameters
As part of this study, we will be monitoring daily temperature and relative humidity inside the cellar, near the location of the selected barrel.
Physical Parameters
We will also be monitoring physical changes of the rum inside the barrel, including:
- pH
- ABV
- Color and
- Composition
Equipment
The environmental parameters will be recorded using Rum Central’s Amprobe Temperature and Relative Humidity Data Logger, which is configured to log readings hourly.
Once per month we will withdraw a sample from the barrel we selected for this study. The sample will then be analyzed for physical changes using the following equipment:
pH will be measured using a Hanna Instruments Edge pH Meter.
ABV will be measured using an Anton Paar Snap 50 Alcohol Meter.
Color and composition will be recorded using a Thermo Scientific Spectronic 200 Spectrophotometer, with a wavelength range from 340nm to 1000nm.
Sample Spectometer Reading
Expectations
Acidity should increase (pH should decrease) over time, accompanied by a decrease in total volume (due to evaporation) and in ABV (due to esterification) and an increase in wood extractables. The concentration of aldehydes, acids and esters should also increase over time (due to the interaction of the different alcohols with oxygen inside the barrel).
The question is not: will all the things we expect to happen, actually happen? But rather: at what rate will the transformations take place given the environmental conditions inside the aging cellar?
If or when the month-to-month changes are significant, we will also include organoleptic (aroma and taste) assessments, describing the perceived changes when comparing the alcohol in the barrel to an un-aged control sample.
The Barrel
The Rum
The white rum used to fill the barrel is column-distilled, from fermented High Test Molasses (“miel virgen”). The entry ABV into the barrel is 63.43% ABV.
The Barrel (#19-0018)
The barrel is made from White American Oak and it was charred prior to its first use aging Bourbon Whiskey (for 3 years). Rum Central received the barrel shortly after it was emptied and this is its second use.
Most aged rum produced around the world employs ex-Whiskey barrels, thus our decision to use one for this series. Since its first use was only 3 years, the barrel still has a lot of wood extractives to contribute to our rum. These extractives include:
Cellulose - is the most abundant natural polymer on earth. It consists of linear chains of glucose units and remains relatively intact even after wood curing and toasting.Hemicellulose - also known as a “wood sugar” is a two-dimensional polymer comprised of many simple sugars, including: Glucose, Xylose, Mannose, Arabinose, Galactose and Rhamnose.
Lignin - despite the fact that it is also one of the most abundant nature-produced materials on earth, lignin remains one of the least understood. Oak ligning consists of two building blocks: guaiacyl and syringyl. The former is responsible for producing coniferaldehyde, vanillin and vanillic acid, which -especially the vanillin- are easily recognized in cask-condition spirits.
- Oak tannins - these plant polyphenols derive their name from the Latin word tannum, which means “crushed oak bark,” since in early times oak trees served as a major source of tannin for the leather-tannin industry. Tannins improve aged rum’s character by increasing the perception of balance, complexity and roundness.
Got Rum barrel
Join us next month, as we share our observations from the first month of aging at the cellar!