Is this Whiskey getting better?...
By Alex Gillham
A topic much debated amongst Whiskey forums is the apparent aroma and taste changes that occur the longer a particular bottle has been open. Many stating that bottles tend to “open up” up to a point, and then oxidise or “flatten” out but no real explanation has ever been provided. Could it be that our palates become familiar with a particular whiskey, desensitised almost, so that going back to it time after time reveals small nuances we’d not noticed previously? Or are there chemical changes occurring which are altering the profile? As a Bourbon lover with an Analytical Chemistry background this is something I’ve long wanted to investigate on a molecular level, to see if any Chemistry is happening within the bottle that can account for the perceived changes over time.
Given all the comments on the British Bourbon Society Group page, the BBS Whistlepig 10 year old Rye private barrel pick was a prime example of a Whiskey that seemed to open up and improve the longer the bottle was open. It was also the first Whiskey I was lucky enough to own 2 identical bottles of so I couldn’t pass up the opportunity to dabble in a little science…
My mission was 2-fold; determine by blind tasting panel whether the contents of the two bottles had a noticeable difference. Secondly, using analytical methods, compare the aroma profiles of the two bottles to see if any differences can be detected.
I first had to make sure the first bottle had been open long enough, and was empty enough, for any differences to become noticeable. Drinking the Whiskey was hardly a chore, it’s a great pick and I’ve always been a fan of Whistlepig. The hardest part was drinking it slowly enough and ensuring there would be enough left to fulfil the panel sampling requirements. I waited until the bottle had been open for 6 months, a predicted sweet-spot where any anticipated “opening up” should have become apparent. The storage of the open and unopened bottles was identical; they sat next to each other on my living room shelf.
The experiment I devised would form 2 parts;
i) Blind olfactive assessments by an expert panel consisting of 6 BBS members.
ii) Analytical comparison of the aroma profiles the two bottles.
To ascertain if there was indeed a consumer-noticeable difference between a fresh bottle and one that had been open for 6 months, a blind panel would be presented with three 15mL samples in a triangle test format; two samples from one bottle and one from the other labelled A, B and C. All sample sets were configured randomly. It should be noted that the open bottle was approximately half full when the samples were taken and the samples taken from the fresh bottle were immediately after it the seal was broken.
An expert panel consisting of 6 (including myself) experienced Bourbon drinkers was selected to carry out the assessments. The panel were asked to assess each of the three samples and select which they believed to be the odd one out. They were also asked to provide any tasting notes and comment on the differences they perceived. No other information was provided to the panelists at this time. None of them had a clue what I was up to but I was providing them with some [pretty good] free Whiskey so all were compliant and willing to participate. My blind tasting set was administered by my wife.
1. Dave: Did not select the odd one out
2. Nev: Correctly identified the odd one out. Tasting notes stating that the older bottle had more kick and zing to it whereas the fresh bottle was duller tasting.
3. Chris C: Did not select the odd one out
4. Tommy: Did not select the odd one out
5. Clayton: Correctly identified the odd one out. Chris preferred the open bottle and found it spicier, sweeter and “excellent”. The fresh bottle was “dull and lacked depth and punch”.
6. Me: Did not select the odd one out
Analytical Methodology: (Slightly boring bit)
I adopted an analytical technique called Headspace (HS) Solid Phase Microextraction (SPME) for this analysis. It’s a technique commonly used to profile volatile organic compounds in many different matrices across many industries. For this analysis a 1cm SPME fiber coated with a mixture of phases (in this case PDMS/Carboxen/DVB) was selected for its broad selectivity. A 50mg aliquot of each sample was weighed into a septum-capped headspace vial. The fiber is exposed to the headspace of a sample for 10 minutes after an initial sample equilibration period of 10 minutes at 70˚C. The volatile compounds from the sample headspace are adsorbed onto the fiber phase and then are thermally desorbed into the inlet of a Gas Chromatograph (GC) in pulsed splitless mode for 2 minutes. The inlet is set to 250˚C which ensures all compounds are transferred from the fiber to the GC inlet. The pulsed splitless injection ensures all volatile materials are focussed onto the column providing good peak shape. Within the GC is a 30m analytical column which separates the mixture into individual compounds (the chromatography bit) which are then detected by the Mass Spectrometer (MS). Blanks were run before each sample to eliminate any carry-over.
The chromatogram below shows the old and the new whiskey profiles overlaid. The black trace being the “open for 6 months” bottle and the blue trace being the freshly opened bottle:
As you can see from the above chromatogram, the two overlaid chromatograms appear identical, like the same sample had been run twice. Even when zoomed right in on the low-level components; little difference can be observed between the two profiles showing that they are compositionally identical and no reactions/degradation had occurred to any of the aroma compounds detected.
Ethanol aside, a total of 36 aroma compounds were detected in the Whiskey, which is more than I was expecting! The table below details those compounds and lists their relative percentage abundance. The analytical method used does not detect water and so the Ethanol level appears higher than the actual proof of the Whiskey- before anyone gets excited about it being an 85.5% hazmat! Also, the % abundance of the other aroma compounds will appear exaggerated but I’ve quoted to provide some idea of the proportions of the compounds present. What we’re really looking for in this study is differences between the two samples.
Many of the compounds identified were Esters, a group of compounds used widely in the flavour industry but also naturally occurring in wines and spirits. Iso Amyl Acetate, for example, gives the characteristic banana flavour to foamy banana sweets. It’s most likely accountable for the “banana bread” notes associated with such whiskies as the 1792 Full Proof or Crown Royal Northern Harvest Rye. Other compounds detected that have aromas more characteristic of American Whiskey are Vanillin and 4-Ethyl Guaiacol which provide the sweet vanilla and smokey/char notes so prominent in American Whiskey.
There are other more sophisticated analytical techniques for Whiskey profiling capable of providing a more comprehensive analysis but HS-SPME-GCMS seemed to work quite well in this project and detected a good array of compounds.
To demonstrate that the analytical method was sensitive enough to pick out differences between Whiskies I analysed a Jim Beam Double Oaked Bourbon sample that I happened to have at work from a previous project using the exact same method. The chromatograms below are as follows (Black: Whistlepig, Blue: JB DO).
Clear differences can be seen between the two Whiskey profiles. Phenyl Ethyl Alcohol (sweet floral honey-like aroma) and Vanillin (the main constituent responsible for the aroma of vanilla pods) were seen to be higher in the Jim Beam Double Oaked Bourbon than in the Whistlepig Rye. Most of the other aroma compounds detected were more abundant in the Whistlepig.
Having only two of the six panelists correctly select the odd one out in a triangle test would usually be considered statistically inconclusive as you’d expect one in three to guess it correctly. That’s what makes the comments so valuable. Both panelists that correctly selected the odd one out stated that the freshly opened bottle was “duller” and the 6 months open bottle had more “zing and punch”. Both sets of comments completely support the “opening up with time” theory.
As for the 4 panelists that failed to detect any difference between a freshly opened bottle and one that was allowed time to “open up”; I suspect this effect isn’t as noticeable to some consumers as others.
The analysis showed zero difference in chemical composition between the two bottles which tells us that there is no chemistry occurring in the bottle - not within the first 6 months anyway. So the perceived opening up must be due to something else. I’m pleased I’ve investigated the aroma profile differences between two identical Whiskies but would still like to understand this “opening up” effect.
I can hypothesise that when a Whiskey bottle is corked, equilibrium exists between the Whiskey and the enclosed air (headspace) above it. When the bottle is fuller, very little headspace exists and so the majority of the volatile materials will stay in the liquid. The more of the bottle you drink, the larger the headspace volume in the bottle becomes and every time the bottle is opened those aroma compounds that build up in the headspace are released. In theory, this would mean your Whiskey would be getting less flavoursome the longer it was open, right? The most volatile and most abundant component in the whiskey is Ethanol. In the case of the BBS Whistlepig; 57.8% of the whole bottle is in fact Ethanol, closely followed by water. Therefore, surely it will be Ethanol that will move into the headspace first and saturate it, as it’s more volatile and more abundant than the aroma compounds. If we lost some Ethanol from the Whiskey every time you opened the bottle, you effectively increase the concentration of the other aroma compounds, or allow them to come to the fore. Perhaps this is what is behind the “opening up” phenomenon?..
Maybe comparing Ethanol levels can be my next experiment…
Special thanks to the expert panel (Chris Neville, Dave Hoolickin, Tommy Gan, Chris Coleman and Chris Clayton) and to my employer who has allowed me the freedom to be creative in the Labs. Thanks also to Bobby and Aaron, who nearly made the expert panel but drank the samples before they got them home!
Thanks for reading.
BBS Member since August ‘17