Following this post, here are a few more observations about beer, molecules, and what the art director can get away with when there are no chemists around!
Hugh Malone is a Belgian IPA produced by the Allagash brewery in Maine, USA, as part of their tribute series. Those of you with a little beer chemistry knowledge will immediately realize/already know that the name of this beer is a play on words that references humulone, the trivial name for a bitter tasting compound found in humulus lupulus (hops).
Very much like Winter Ion by Element Brewing, the label on Hugh Malone sports a molecular representation that looks remarkably feasible. Unlike the molecule on the label of Winter Ion, this one is basically correct, but again (and probably for good reason), the art director has had his way with the molecule.
As you can see from the photograph below (blown up from this source), the molecule plays a prominent role in the advertising.
The first thing that struck me was that there is the potential to think that C21H30O5 is the formula of a side chain that branches vertically upward at the top left of the structure – it’s not. C21H30O5 is actually the molecular formula of humulone.
Secondly, as is often the case, the R group (on the six membered ring) hides a multitude of sins. Of course, the use of R is anatomically entirely acceptable and there is little doubt that its use is to make the molecule more ‘manageable’ in terms of the limited space on the label, but at the same time it’s a shame, since its use hides a certain ‘pseudo symmetry’ surrounding the three side chains. Here’s a screenshot of the ChemSpider record (full ChemSpider record).
Humulone is a pretty interesting molecule, not least of all because of its keto-enol tautomerism and the role that plays in producing a number of different, acceptable representations. ChemSpider lists six when humulone is used as the search term. According to Brewing: Science and Practice by Dennis Edward Briggs, Chris A. Boultona & Peter A. Brookes (p 262), the major tautomer of humulone is not the one shown on the Hugh Malone label.
The ChemSpider record also reminds us of the important role that trivial names play in communicating chemistry in everyday situations. A beer whose name was a play on 5,6-Dihydroxy-4-(3-methylbutanoyl)-2,6-bis(3-methyl-2-buten-1-yl)
Unsurprisingly, given humulone’s relevance in beer chemistry, the Hugh Malone label is not the only place that this molecule turns up in beer culture. I found this picture of a Triumph Brewing coaster, here.
Obviously this molecular representation is a lot less accurate in terms of the structure, with all kinds of perspective issues and even atoms missing. Having said that, it does look as though this was lifted directly from p 20 of Lee W. Jansen’s, Brew Chem 101 but either way it’s still enough to give an organic chemist a touch of heartburn. I wonder if Triumph’s beer is better than their chemistry?
Humulone is usually depicted in a positive light when it comes to beer pop-culture, but in reality it can have a more sinister role to play. Beer folk are familiar with the term ‘skunked’ being applied to beer, and the layman’s understanding of the term can be boiled down to mean the ‘smelly’ or ‘off’ flavors and aromas that can get into beer if it has been exposed to ultra-violet (sun) light. The chemistry of the photochemical reaction starts with humulone, and ends with beer that is not good at all.
Again in Brew Chem 101, Jansen (p 74), suggests that the reaction involves the formation of an isoprene diene radical from humulone that reacts with H2S to yield 3-methyl-2-butene-1-thiol. Other sources say that the reaction is actually between isohumulones (isomers created from humulone during the boiling of the wort in the brewing process), that undergo the photochemical reaction, then subsequently react with sulfur containing amino acids to produce the thiol. PICSE gives a kind of hybrid explanation, where isohumulones are the starting materials that go on to react with H2S to form the ‘skunk’ molecule. In most complex reactions there is seldom one, single, simple explanation, and the truth almost certain sits at some juncture of all of those suggested processes. In any case, the only thing that really matters is that the 3-methyl-2-butene-1-thiol is produced at the end. The ‘skunk’ molecule happens to be a molecule that is much easier to draw, name and get ‘right’ when compared to humulone and I wrote a separate post about it, here. As such, perhaps we should have more beer labels with it adorning them, 99.99% of folk would never know! ;-)