The complicated business of recreating a wine aroma

How wine aroma happens is both very simple and very, very complicated. The simple version: molecules capable of leaving from the surface of the liquid (or carried up to the liquid in the tiny gas bubbles that make sparkling wine sparkle) are carried through the air up to our nostrils where those molecules meet sensory receptors that, when bound to the right kind of molecule, trigger a “smells like” response in our brain. Hence why we swirl and sniff: swirling encourages aromatic molecules to leave the wine; sniffing encourages those molecules to travel into our noses. As you’d expect, the complicated version elaborates on what kinds of molecules are capable of leaving the wine — of moving from the aqueous phase to the gaseous phase, we’d say — and what has to happen between an aroma molecule and a smell receptor for a message to be sent, and how activating a receptor turns into a perception of “smells like” in our conscious minds. But it’s actually even more complicated than that, because molecules that aren’t aromatic and that don’t ever leave the wine for the air influence what we smell, too.

A new study of the aromas of two different Australian shiraz (shirazs just doesn’t look right to me) is a good example of what it takes to make up a wine’s nose.

Wine — talking all wines collectively, not any one in particular — involves at least 800 or so different aroma compounds. The strategies used to figure out that sort of thing, and to analyze the aroma composition of specific wines, are all fundamentally based on separating out all of the many different molecules a wine contains. A common way of doing this is with gas chromatography which, to put it simply, separates molecules by the differences in how they interact with specific solvents. How long it takes a particular molecule to let go of the solvent — its “retention time” — is unique, so seeing a molecule’s retention time is as good as knowing the molecule’s name…at least when someone else has already done the meticulous work of correlating the two. Of those 800-some-odd wine aroma molecules, we can actually only name something like 10-20%. But we know the rest exist, because we can see their retention-time fingerprint pop up on the chromatography results. Even better than gas chromatography, for wine aroma purposes, is gas chromatography-olfactometry, which takes the apparatus for chromatography and adds a smelling port so that scientists can sniff the separated-out molecules as they come up in turn. In the case of the Australian shiraz, the gas chromatography came up with about 100 “odorants,” but the consensus among sniffers was that only about half of those actually smelled like anything. Of those, for only 27 or 28 were their concentrations in the wines high enough to theoretically be detectable (they exceeded their odor threshold). It took 44, added to a wine-alcohol-acid-sugar base, to make something that credibly mimicked the original wine.

Then the researchers asked their trained sensory panel to do something interesting: sniff  the aroma + base wine-like synthetic and the same mix minus one of several key aroma compounds with the goal of identifying which molecules contributed to which perceived smells. The details get long-winded, but the final message stands out. Removing non-aromatic constituents changed aroma perceptions — sometimes more intense, sometimes less, depending on the aroma and the other molecules involved — even when the key aroma compounds themselves were left untouched. And some very obviously smelly compounds present in the wines in quantities far above their odor thresholds had a much smaller impact on wine aroma then their high concentrations would make you think.

In other words, wine aroma isn’t as simple as just pairing up odiferous molecules and their corresponding smells. And we can’t yet predict how or why wine will smell the way it does from first principles. Synthetic wine, then — or at least synthetic wine that replicates real wine — is going to take some time, and a lot more sniffing.

Sensory speculations on the Riedel Coca-Cola glass

The wine news is making hay this week with specialty glassware maker Riedel’s newest custom glass shape designed for Coca-Cola. While the process for selecting the glass sounds pretty empirical — a panel tried Coke out of a bunch of prototype glasses and chose the one they liked best — I can’t help but wonder about the sensory chemical logic behind the design. There’s no sense in being pretentious about this: even if Coke is a mass-produced beverage and a cultural and health nightmare, it’s still very sensorily complex (and unquestionably popular).

The glass recapitulates the wide-shouldered hourglass shape of the old-fashioned glass Coke bottle. That’s simple brand congruity: only the shape of the glass opening and the upper bowl affect the glass’s sensory properties in terms of directing aromatics to the nose and affecting how the liquid hits the palate. The dynamics of how Coke behaves in a glass will be wildly different than wine, with the possible exception of a sweet sparkling. Coke has bubbles, which actively convey volatile aromatics into the head space above the glass. It’s extremely high in both sugar and acid (phosphoric, as opposed to tartaric, malic, and lactic in wine) and contains caffeine, none of which should have a significant affect on aroma save insofar as the sugar increases viscosity. How that compares with the viscosity of wine, where alcohol and glycerol (and sometimes sugar) are responsible for viscosity, I’m not sure.

A spokesperson from Riedel says that the top of the glass is the same shape as the Riedel O-series Sauvignon Blanc glass, which immediately sent me on a search for methoxypyrazines and thiols (two prominent characterizers of Sauv Blanc) in Coke.

No joy, and no surprise: methoxypyrazines are responsible for green bell peppery notes, thiols for various tropical fruit and grapefruit-y aromas. It’s been a while since I had Coke, but I’m pretty confident that neither bell pepper nor passionfruit feature prominently in its flavor profile, even if its citrusy notes are easily agreed-upon. The Open Cola Project recipe, which we might reasonably expect to be in the right ballpark, calls for orange, lemon, and lime oils along with cassia (Chinese cinnamon), nutmeg, coriander, and lavender, and a lot of sugar and acid and caramel color.

From a theoretical perspective, then, I’m going to guess that the glass emphasizes Coke’s spritely and refreshing citrus aromatics first and foremost, leaving the sweet caramel/vanilla and spicy notes to bring up the rear. That testers would prefer that effect is congruent with the famous 1980’s and ’90’s Coke vs. Pepsi trials, which showed that Pepsi tended to win out in sip tests — both because it was sweeter and because it has a heavier initial citrus impression — but that Coke had more lasting fans — because it was less sweet, because Pepsi’s citrus tends to fade after the first few sips, and because Coke has a more robust caramel backbone.

On that basis, the glass should either be really good for a rum-and-coke — if you’re using cheap, sweet rum and want to maintain the refreshing balance of the drink against the extra sugar and body — or really bad for a rum-and-coke — if you’re using decent rum and want to play up the sweet/vanilla/barrel aromas.

If I get hold of a glass, I’ll test the theory — this is worth one small exception to my long-standing boycott of Coca-Cola (as well as Pepsi and a number of other food mega-companies) as a response to the company’s massive funding of campaigns against mandatory labeling of GMO-containing foods (and I can’t stand the stuff in any case). But I’d love to know what characteristics the glass brings out, and to play with fresh vs. flat, ice vs. no ice.

What’s next? A gin and tonic glass? A raw milk glass? An orange juice glass? A Pepsi glass? Tea glasses are apparently in the works, but I can only hope that they’ll differentiate oolong from lapsang souchong from pu ehr.