Tracing down tobacco aromas in aged brandies

I’ve become so accustomed to fermented beverages having flavors completely unrelated to their starting ingredients that I all too easily forget that there’s anything strange about it. And then I introduce someone to wine tasting for the first time and find myself having to explain that, yes, the wine tastes like cherries and no, they don’t put cherries in the wine to get it to taste that way. (But also sometimes that, yes, the wine tastes like oak, and yes, they do put oak in the wine, or wine in the oak, to make that happen.)

Wine and aged brandies, like Cognac, sometimes taste like tobacco. No one adds tobacco to them.* What happens instead is an example of what you could liken to chemical convergent evolution. Brandies can indeed contain odiferous molecules also characteristic of tobacco flavors. But those molecules appear to come from the breakdown of compounds present in grapes, not from any exposure to tobacco (and, needless to say, the tabanones in tobacco don’t come from grape-derived compounds).

Megastigmatrienone is more conveniently called tabanone. Or, more properly, megastigmatrienones are are more conveniently called tabanones, because the designations apply to a group of similar molecules. They seem to show up in wine because carotenoids – the highly pigmented class of antioxidant molecules you’ll recognize from it’s best-known carrot-colored member, beta-carotene – can become megastigmatrienones under appropriately acidic conditions. The precise pathway from grape-derived carotenoids to tobacco aromas remains something of a mystery. It seems that brandies, distilled from grape wine, end up with concentrated amounts of tabanones or precursors which then have an extra chance to develop into tabanones during barrel aging.

That mystery makes all the more interesting a recent study to quantify tobacco aroma molecules in Cognac and Armagnac**. Most of the (many) examples they tested contained some tabanones. Concentrations varied widely, but the Armagnacs averaged higher than the Cognacs and – evidently to everyone’s surprise – the aged rums thrown in for comparison ranked even higher than the Armagnacs. Much higher, in fact, even though the molasses from which rum is distilled doesn’t contain significant amounts either of tabanones or of the identified precursor molecules present in grapes.

So, why is this interesting?

  1. Tobacco aromas in aged spirits are evidently not just coming from molecules originally present in grapes.
  2. The oak barrels used for aging rum, as well as various brandies, probably contributes substantially to tobacco aromas in those spirits by leaching precursor molecules out of the wood and into the spirit and providing favorable conditions for their development.
  3. The researchers behind this study seem to think that their new-and-improved means for quantifying particular variants of tabanones could be useful for distinguishing Cognac from Armagnac, presumably to defend against passing one kind of spirit off as another. Looking at the enormous variation in tabanones between one kind of Cognac and another, or one kind of Armagnac and another, this suggestion seems frankly ridiculous. Chemistry backs up tasting experience: individual bottlings vary dramatically in the presence or absence of tobacco aromas as a defining characteristic. Yes, Armagnacs beat out Cognacs on average, but averages don’t help distinguish individuals when individual variation is so high. A more interesting use of this research, I think, is the starting point it provides for thinking about how barrel-aging adds to tobacco aromas, in spirits and possibly in wines. I suspect that the people who produce these spirits already have a lot to say on that point. Joining their knowledge with some well-placed chemical analyses could improve everyone’s understanding of how tobacco aromas happen and how to manipulate them.

 

* Ewwww.

**Camper English has drawn up a helpful comparison between Cognac and Armagnac at Alcademics.com.

Waste not? Capturing every last bit of aroma potential from fermentation

The aroma of baking brownies arouses two categories of responses. Summary of Category One: “Wow, that smells delicious!” Summary of Category Two: “Oh no, just smell all of that chocolate flavor escaping into the air that won’t be in the finished brownies any more.” This new research is for people who empathize with category two.

As Saccharomyces cerevisiae ferment grape sugars into ethanol, they produce massive amounts of carbon dioxide. Most of that CO2 gas escapes from the top of the fermenting liquid (small amounts remain dissolved in the wine) and, with it, escape wine aroma molecules. One of the two defining features of an aroma molecule is that it’s volatile, which is to say that it evaporates readily; you can’t smell a molecule if that molecule can’t make its way into your nose. (The other defining feature of aroma molecules is their ability to activate sensory receptors; even after a molecule makes its way up your nostrils, it still has to trigger a sensorineural response.) Volatile molecules will escape from a stationary liquid to some degree, but they escape a whole lot faster when the liquid is moving (hence our habitual practice of swirl, then sniff), and even faster still when bubbles forming inside the liquid carry those volatile molecules up from the inside out.

In short, the logic of physics and chemistry have it that a lot of aromatic molecules are lost to the air during fermentation. In theory, those molecules could be captured and deposited back into the wine after fermentation to yield a more aromatic final product.

This idea occurred to a bunch of Italian food scientists, who gave it a try with two sangioveses and a syrah and have published the results in the American Journal of Viticulture and Enology. It seems to have worked pretty well. They attached a condenser to the top of their stainless steel fermentation tanks and collected the vapor rising from the tanks as a liquid that they could then dose back into the wine after fermentation was complete. Which is, of course, precisely what they did. A sensory panel was universally able to identify which wines had received more and less condensate and which had received none at all though, to the study’s detriment, only eight test-sniffers* were involved and they weren’t asked to report on what they thought about the wine’s aromas or on how the wines tasted. 

There’s a certain appealing efficiency to the idea of capturing a heretofore lost byproduct of fermentation – all of those lovely aromas of fermentation, plus a healthy dose of alcohol (the liquid condensates contained about 24% ethanol) – and doing something with them. The condenser itself is a simple apparatus consisting, essentially, of a heat exchanger. Adding the condensate back to the wine is an obvious use for the stuff, but it’s certainly not the only one, and so in effect this is an experiment in increasing our efficient, sustainable use of available resources, like turning vine prunings into biochar or using grapeseed flour as a nutritional supplement. Though, the folks with Category One brownie aroma responses might have a different perspective.

 

*Eight test-sniffers who were described only as “panelists,” and who were therefore most likely  happened to be around the lab when testing needed to happen. Since the panelists’ job here was limited to answering the questions, “which of these wines doesn’t smell like the others?” and “which smells most intense?” it’s not frightfully important whether they were trained sensory testing experts or wine professionals or ordinary-Jane wine consumers. If and when this idea is taken into “which of these wines is most appealing to you?” territory, someone will need to decide whether they care about the responses of wine experts, random occasional drinkers, or both.

A new review of familiar news on grape solids

I’ve just finished reading a (short, I’ll admit) review on the “characterization and role of grape solids during alcoholic fermentation under enological conditions,” and I’m delighted to report that there’s little to report. You’re not missing some manner of fascinating spanking new research on grape solids because you don’t have a subscription to the American Journal of Enology and Viticulture. If you got the picture that solids are important for yeast growth from your favorite old textbook for Winemaking 101, you still have the right picture. Chances are that you’re not doing solids wrong.

The major message about grape solids during fermentation continues to be that solids provide yeast with nutrients they need to survive high alcohol concentrations in low- or no-oxygen environments. With plenty of oxygen, yeast can make the lipids they need to maintain good, strong cell membranes. In the absence of oxygen, they can’t and need to absorb those lipids from their environment. Since a fermenting must doesn’t provide a whole lot of oxygen access, wine yeast need those external lipids. Per the classic “oil and water don’t mix” principle, lipids aren’t very soluble in water. (And per the very nouveau classique cocktail principle of fat washing, we’re familiar with the notion that lipids aren’t very soluble in alcohol, either.) The main source of lipids in a wine fermentation that’s essentially water, then, is the solid part.

Ergo, wine solids → lipids for yeast → strong, healthy cell membranes able to withstand the stress of finishing off the last sugars in that 15% alcohol Napa cab.

A few noteworthy points the authors make along the way to that conclusion:

  • Solids aren’t static through fermentation: small particles stick together into larger particles, and larger particles fragment into smaller particles when rising bubbles of carbon dioxide agitate the mix.
  • Solids may also help yeast by helping to remove carbon dioxide. Suspended particles act as nucleation sites for dissolved gases, allowing CO2 to be carried up and out of the must faster and in turn making the environment less yeast-toxic. This, however, seems to be a minor consideration.
  • The more yeast-assimilable nitrogen (YAN) the must contains, the more solid-associated lipids need to be available to support yeast growth to take advantage of all of that nitrogen.

All of which leaves plenty left for scientists to continue investigating. We still don’t have a good picture of how yeast take up lipids from grape solids, either in terms of the mechanism at the cellular level or in terms of how the dynamics of solids settling and mixing matters. Our understanding of how solids move during fermentation could be more detailed (which sounds like a job for the Champagne physicists who study the science of celebratory bubble movement, though I imagine that the CIVC may have them busy enough on other projects). How solids play with wine aroma is a whole category of interesting questions, and research in that arena might even have something useful – and new – to say to winemakers. In the meantime, the news from the research front is that grape solids are still a matter of the good care and feeding of your yeast friends.