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.

Whey proteins for reducing astringency: If it works for tea…

Important note: The following story should NOT lead you to conclude that you need to stop drinking wine if you generally avoid dairy. Please see the comments at the bottom of this post, this post on wine allergies (and why you probably don’t have them), and this post on gluten in wine.

Short: The main protein in whey, a voluminous byproduct of cheesemaking, might be a good (and cheap) fining agent for reducing astringency in red wine, but it’s going to need a lot more testing, and I’m (very) suspicious.


Many people* add milk to black tea because it softens the harsh edges of what is so often an unfortunate cup of broken orange pekoe. The combination works because a milk protein, β-lactoglobulin, binds tannins. This was news a few years back because adding milk reduces astringency, but not nutrition value (unless you’re fine-filtering your tea after adding milk, and I can’t imagine you are). Whey protein-bound tannins won’t bind to your salivary proteins to dry out your mouth, but still work as antioxidants in your body.

Adding β-lactoglobulin from whey protein might for essentially the same reasons be useful to decrease the astringency of red wine. Casein, another milk-derived protein, is routinely used for wine fining. The benefit of making the switch is cost. Casein ends up in cheese. β-lactoglobulin ends up in the whey left over after making cheese. Ergo, the cheese-eating world has more β-lactoglobulin sitting around than casein, body-builders’ post-workout protein shakes and the occasional bottled whey beverage notwithstanding.

This is one of those so obvious and sensible-sounding ideas that I’d be inclined to think: surely someone’s already tried this and found that it doesn’t work or everyone would be doing it already. Still, a quick search of the scholarly literature suggests that no one has, publicly, though this study from 2007 found that β-lactoglobulin binds well to resveratrol.**

The chemists behind this just-published study found that β-lactoglobulin reduced astringency about as well as gelatin, gram for gram, at least for the random cheap French merlot they tested. Even better, β-lactoglobulin worked about as well as a combination of β-lactoglobulin and casein.

If you’re waiting for the catch(es), here they are:

  • β-lactoglobulin shouldn’t work as well as gelatin on the basis of established knowledge about tannin-protein interactions. Tannins bind best to big, loosely folded proteins with lots of an amino acid called proline. Tannins bind less well to small, balled-up proteins. Gelatin (and some major salivary proteins, coincidentally) are loosely folded and proline rich. β-lactoglobulin is small and balled up. The authors make a gesture toward figuring out why β-lactoglobulin still works by quantifying the concentration of total protein-precipitable tannins and a few specific, important tannin molecules in the wines before and after treatment with gelatin, β-lactoglobulin, or the β-lactoglobulin-casein combination. Those tests confirmed that β-lactoglobulin is binding tannin molecules, but also that they’re binding weakly.
  • This weak binding seems to involve groups of tannin molecules strung together. β-lactoglobulin doesn’t do a good job of binding to individual tannin units (monomers) hanging out in the wine on their own.
  • These authors only tested whey protein with one red wine (the random French merlot), and only measured astringency by chemical approximations, not with real swirling and spitting tasters. So I’m suspicious. Surely, the idea of using whey protein for wine fining has occurred to at least one food processing house or winemaking supply company with the resources to test the theory out on their own, on many different wines, with their in-house sensory panels doing the tasting. If it worked, whey protein would be on the market. If it didn’t, they might well not broadcast the news. And – forgive me this, because excellent research can come from unlikely places – the authors are from the University of Reading in the UK and the National University of Rosario in Argentina, neither of which is a hot bed of groundbreaking wine research. That’s not to say the researchers aren’t good, but it is to say that they might not have ideal access to the accumulated wisdom of the field.

An interesting idea. Unlikely to be the next wine chemistry success story, but an interesting idea.


*I add milk to black tea on rainy days because the aroma evokes England and memories of a childhood I never actually had of drippy days shut up inside with endless tea and books in a British country house. I can tell you this because it has rained here every day for more than a week.

**I think that at least the general idea that β-lactoglobulin binds to wine tannins might be buried in this 2011 masters thesis conducted at Massey University in New Zealand, but I’ll be honest: I didn’t have the patience to read the whole thing carefully enough to find out.

Playing the “what’s that smell” game with aged red Bordeaux

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.