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.

8 thoughts on “Waste not? Capturing every last bit of aroma potential from fermentation

  1. Scrubbing and capturing as a condensate seems a fresh approach but ducting vapors from the top of one tank into the bottom of another in series has been around for a long while. At 24% abv, their “condenser” could be called a cold still? Imagine what one could do with Muscat or Malvasia….

    • Yep. “Nose to tail cooking,” so to speak, is becoming quite the rage all over the place. Even if some part of me rails a bit at the idea that we need to squeeze maximum economic value out of everything, using what we have doesn’t seem a bad thing at all when I put it that way.

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  3. I believe very slow fermentation achieved by lowering the temperature of the primary fermenter to a point where the yeast is just barely working, thus generating little turbulence, would accomplish essentially the same goal. Although admittedly this would add additional time and cost to the process.

  4. You see this effect in rotary fermenters. The cooling jacket gives an unintended consequence to provide a condenser of sorts.
    Likewise open fermenters give about 1% less alcohol yield over closed ferments.

    I’m talking reds of course .

  5. Now this is interesting, to a chemical engineer! Cooler fermentation should reduce the stripping effect due to lowered volatility of the odour molecules. Refluxing the ferment with a condenser is nice, but might recapture less desirable species – some stuff you want to remove. I once tasted a wine on the cusp of aldehyde oxidation and it was (ahem) aldehideous. A demister might be less interventionist as it would only return liquid droplets that ‘belonged’ in the fermenter. Lower must weight will mean less CO2, less stripping, and perhaps more generous aroma profile (cool climate riesling?) BTW I like your Blog!

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