One of wine chemistry’s best parlor tricks is the “what’s that smell” game. Why does your wine smell like raspberries, or turpentine, or mint? If there’s not yet a chemical explanation for how it got there, we can often at least point to a molecule. And as various plays on molecular gastronomy have made clear, pointing to the molecule can be a lot of fun. We can ask where else that molecule pops up and devise creative food-wine combinations, or just marvel at the envirochemical systems that make compounds produced by South African trees pop up in aged red Bordeaux.
Speaking of South African trees and aged red Bordeaux, recent wine chemistry research has identified a molecule best known from the former as the explanation for minty aromas in the latter. A group of (no surprise) Bordeaux wine chemists have concluded that the classic minty-ness some red Bordeaux acquire* can be attached to piperitone, a molecule previously undiscovered in wine but, the European Bioinformatics Institute tells me, is commonly extracted from South African eucalyptus trees.
Along the way, the authors make a second and perhaps more interesting point about how chemists go about pairing up molecules and aromas. A typical method involves gas chromatography-olfactometry: the gas chromatograph separates out the components in a (vaporized) sample, and the olfactometer lets you systematically sniff the components that come out of the chromatograph. The excellent thing about this method is that it lets an experimenter identify the “odor-active” components of a sample. The downside is that you’re smelling and studying each of those components individually rather than investigating how they interact or what difference they make to a wine’s total aroma. Even if the conventional tasting note gives individual aromas as though the OWP** is smelling down a list, smelling is more complex than that. The wine-sniffing nose receives a whole pile of odor-active molecules at once, the brain processes them together, and then our memory and language processing functions arrive at descriptors that probably aren’t one-to-one matches for the molecules that came in at the front.*** At least in theory, a molecule may smell minty without contributing to how we perceive mint in a wine, or vice-versa.
An alternative this article touts is “aromatic reconstitution:” a complex sample (vaporized wine, for example) is separated out into odor-active “fractions” using that gas chromatograph, and the fractions are recombined in their original proportions but with one missing. Meanwhile, other wines naturally lacking the smell-of-interest are spiked with the most interesting odor-active fractions. The recombinations and spiked samples are smelled, and results are tabulated for what smells appear or disappear in association with what fractions. Researchers can then go back to the fractions that matter the most to the smell-of-interest and work out what the heck, molecularly speaking, they’re dealing with. Much to their credit, in this study local Bordeaux wine professionals were pulled in to do the smelling.
All of that (and a lot more, in this very thorough study) let the researchers say that piperitone contributes to the minty aroma of aged red Bordeaux, a much stronger conclusion than saying that piperitone is found in aged red Bordeaux and piperitone smells like mint without directly connecting the two. The piperitone-mint link might have useful consequences of some kind for people with wine aging problems or chefs creating gently eucalyptus-scented lamb roasts, but it’s also one more step toward working out the moving parts of both smell and wine aging. And eventually, that’s going to be more than a parlor trick.
*Including, in this study, a 1998 Pomerol. I mean, it probably wasn’t Petrus, but this still sounds like the researchers enjoyed themselves.
**Obnoxious Wine Professional
***How the brain processes smell is a good deal more complex than I’m making it out to be here, and neuro-sensory-scientists are still working out a lot of the details. Modern science tends to be pretty good at teasing out how representational processes work – how we see, for example – but seems to make a lot less progress with affective processes involving emotion and non-linear, extra-logical processes.