It's been almost 4-months of side-by-side aging of unaged spirit (white rum, 65% ABV) in new, #4-char, 5-gallon oak barrels, one agitated 24/7 by a Symphony, and the other acting as a control. The goal of this investigation has been to start quantifying differences in chemistry that occur during barrel-aging, with and without agitation, using generally accepted industry testing practices (GC-MS) and known chemical markers. Although the unaged spirit in this study was rum, our primary interest is the impact of agitation on unaged spirit in new-char barrels, more typical of US Whiskey and Bourbon, and the resulting maturation chemical markers that are derived from the barrel and that are believed to play a prominent role in the final sensory profiles of such wood-matured spirits (1, 2, 3, 4).
(Bonus: we've got some good sippers on our hands as well.)
As a recap, the Symphony is a wirelessly powered agitation tool that works from inside a barrel to help promote the interaction of the spirit with both the oak and the headspace. The device is designed to be dropped through a barrel's bung hole and to sit on the bottom of the barrel where it agitates the contents inside.
To get a qualitative idea of the changes occurring during our experiment, a simple snapshot into color change is easy to capture and has also been a useful indicator. Pictures of both the Symphony-aged barrel and the control barrel were taken under identical lighting conditions over the course of three months. The results are shown below. These pictures are a continuation of our previous blog entry, and it's worth pointing out that nothing is added to the spirit and that the pictures in the image below are all taken at cask-strength.
Although coloring is just one of the changes occurring during barrel-maturation, the difference is fairly noticeable between the two barrels after only three months, even in the bottle after proofing-down to 40% ABV.
To dive further into the chemical make-up of the spirits after 3-months of aging, samples were tested at ETS Laboratories for their oak aroma characteristics. This test is performed using GC-MS and provides the concentrations of the main oak-derived sensory compounds present in each sample. The image below shows the results from the testing of the 3-month samples on a radar plot, where the blue lines represent the control barrel concentrations and the orange lines represent the Symphony-agitated barrel concentrations.
With the exception of the furanic compounds (which may themselves undergo further reactions during aging [I've read this somewhere, but still looking for the reference]), all of the compounds tested showed higher concentrations as a result of agitation with the Symphony, with the whisky lactones (cis-, trans-) showing the greatest gains against the control barrel, both testing at concentrations over 2X the control.
A deeper dive into the available literature shows that for bourbon whiskey, at least as of 2008, Poisson and Schieberle had identified six (6) primary odor-active compounds, shown below.
Of the compounds cited above, a look back at the radar plot shows that (30) cis-whiskeylactone (cis-oak lactone) exhibits a 108% increase relative to the control, (36) 4-allyl-2-methoxyphenol (eugenol) shows a 36% increase, and (45) 4-hydroxy-3-methoxy-benzaldehyde (vanillin) shows a 31% increase over the 3-months test. The other three compounds from the Poisson paper were not available for testing with the standard oak aroma panel.
So where does that leave us with respect to "accelerated maturation"? Depends on the maturation marker and the timeframe of interest. Admittedly, we could run more tests to further develop slope plots, and we likely will as we go forward. To be clear though, our goal at Hertzbier has always been to enable a distiller to get more out of their barrel for a given amount of time, "more" being represented by a variety of compounds present at levels greater than would have been possible without agitation with the Symphony, a "given amount of time" being whatever amount is suitable to the distiller and his/her craft and the goals for their product, and "barrel" meaning just that...conventional oak barrels. For example, the follow on work to the Poisson paper above dives into the chemical makeup of two commercial bourbons bottled from two different years, both aged for at least 3 years in new charred oak barrels.
Of particular interest are the levels of whisky lactones, eugenol and vanillin given the available test data. A quick comparison with the published literature would suggest that the 3-months of aging 65% ABV spirit in the 5G barrel with Symphony agitation can enable equivalent (or greater) levels of various oak-derived maturation marker concentrations as found in 3-year aged spirit in new, charred 53-Gallon barrels.
To be sure, this is only a small part of the story. There are over some 300+ compounds that have been identified in wood matured spirits, and we've been looking at no more than 10-15 of them. The ester compounds detailed above in the commercial whiskies need also be considered. Unfortunately our testing hasn't been able to quantify all of those compounds (yet), but instead we've been able to take a snapshot of a couple of esters, ethyl acetate and isoamyl acetate, at both 6-weeks and 12-weeks, as shown.
The ester concentrations above show that the barrel agitated with the Symphony isn't driving these reactions to happen at dramatically accelerated rates when compared to the control barrel, although the relative ester concentrations between 6-weeks and 12-weeks do go up in both cases with the Symphony. Additional testing is still needed to see how changes occur over longer time frames. To more fully understand the bigger picture though, a review of the available literature on the subject leads to a book by Nykanen and Suomalainen which claims that a study of ethyl acetate concentrations in bourbon "had an average concentration of 249 mg/L (249 ppm) in whiskey aged for two (2) years, 369 mg/L (369 ppm) in whiskey aged four (4) years [...]".
So what does it all mean? Well, taking everything presented above and extrapolating out a few months, we should have a spirit that exhibits a large majority of the maturation markers of a 2-4 year aged bourbon after 4 months of aging in a new char, 5G barrel...it'll just be made of rum. It's already a tasty sipper though, we'll see if we can wait another month.
Ready to enhance one of your barrel-aged products? We're rolling out a small number of units for initial testing and feedback. Get your's here.