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.