Experimental wine bottle tracks oxygen moving through the cork - Ars Technica

Overview

Experimental wine bottle tracks oxygen moving through the cork

The small bit of air in the bottle sees oxygen and other chemicals move in and out.

Details

Most people perceive a cork in a bottle of wine as a simple plug meant to keep the liquid in and the outside world out. In the recent study published in Science Advances, a team of French scientists demonstrated the cork is way more than that. By regulating the oxygen transfer into and out of the wine bottle, it works almost as another ingredient.

“Twenty years ago, our group focused on the oxidation and aging of wine and all its parameters,” Thomas Karbowiak said. “Oxygen diffusion through cork stoppers is one of these parameters.” Karbowiak is a chemist at the University of Burgundy, France, and the senior author of the study.

Oxidation is one of the key drivers of wine aging. A slow, limited ingress of oxygen helps wine mature, smoothing out harsh tannins and bringing out an aromatic complexity. But when too much oxygen gets into the bottle too quickly, it can make the wine stale, brownish in color, and unpleasant to drink. That’s because it will also react with alcohol and phenols in the same process that makes a cut apple turn brown.

The problem with trying to study this is that, in a standard 750 ml wine bottle, the volume of liquid and the thickness of the glass make it difficult to accurately isolate, monitor, and measure real-time oxygen kinetics without introducing external air or disrupting the internal environment. “The real bottle of wine is a complex system. We wanted something simpler and easier to understand,” said Julie Chanut, a researcher at the University of Burgundy and lead author of the study.

To bypass this issue, the team designed a custom experimental rig they called the miniature bottle system. “The idea was to see what mechanisms are at work in this system,” Chanut said.

The setup consisted of small glass vials designed to mimic the standard cylindrical geometry of a commercial wine bottleneck. Each vial was sealed using scaled-down cork stoppers ranging in length from 6 to 42 millimeters; the interior could be precisely loaded with either gas or a specific volume of model wine. The reduction in the total volume of both the liquid and gas phases artificially amplified any oxygen concentration changes that occurred. The system acted as a chemical magnifying glass that enabled the scientists to precisely measure extremely subtle physical and chemical mechanisms like outgassing through the cork or the reactions at the interface between the cork and the wine.

Armed with their miniature bottle setup, the team loaded half of the vials with wine, left the other half empty, sealed them with the selection of different length corks, filled them with sensors, and left them for 18 months to age. It turned out the oxygen dynamics in the vials was way more complex than a simple, steady leak through the cork.

During the experiment, the researchers learned there are four stages of oxygen transfer through the cork, which starts the moment a cork is rammed into a bottleneck. The first phase lasted for the initial 15 days after the vials were corked. “It was an equilibration between the liquid phase of the model wine and the gas phase,” Chanut said. There are differences in the gas content between wine that had been aged in sealed containers and the small bit of air that gets trapped and pressurized by the insertion of the cork. In the experiment, the oxygen dissolved in the liquid phase in the vials escaped back to the gas phase.

The second phase that followed, though, was where things got a little more surprising. Chanut’s team observed that, during the first six months, the majority of oxygen that was getting into the wine wasn’t coming from the outside environment. The oxygen, it turned out, was coming from the cork itself, diffusing out of the microscopic spaces in the cork’s cellular structure. The cork was basically outgassing into the bottle.

Three factors contribute to the overall oxygen levels, which change over time.

This was also where the researchers found the first differences between their samples—vials sealed with longer corks were getting more oxygen because the bigger corks contained more oxygen than the short ones.

The moment the cork became an ingredient rather than just a seal came around four months into the experiment, when it began to chemically interact with the wine.

In the vials where the model wine was left in contact with the cork, the liquid began to act as a solvent, extracting phenolic compounds from the cork. These compounds included gallic acid, ellagic acid, and protocatechuic acid, all of which started bleeding into the wine. Once there, they acted as chemical scavengers that, catalyzed by trace metals like iron and copper, reacted with the oxygen released from the outgassing cork. The process caused a noticeable decrease in the wine’s oxygen content—the cork was effectively deploying chemicals that consumed the oxygen it had previously released.

Eventually, after 15 months, the wine settled into the fourth, long-haul phase. Here, oxygen from the outside environment steadily and slowly permeated through the cork. In the 18th month, at the end of the experiment, the team noted that in vials sealed with longer corks (above 30 millimeters), the rate of oxygen transfer during this last phase was so low that the change was barely noticeable.

“Because we used model wine in the experiment and focused on oxygen transfer, we didn’t do any tasting tests,” Karbowiak said. But oxygenation does matter for taste and, Karbowiak claims, the team is already getting a lot of interest from both wine makers and cork manufacturers.

“Wine is a very particular case of a product without a shelf life. So, the question is, ‘When should I drink my wine?’” Karbowiak said. “And actually, we are not able to answer this question.” His team hopes that obtaining detailed data on how specific types and dimensions of stoppers manage wine’s oxygenation after bottling may one day enable wineries and cork manufacturers to solve this problem. But there’s much more we need to learn before we get there.

In the future, Karbowiak’s lab wants to focus on quantifying the exact balance and interplay between the four oxygen transfer mechanisms they discovered. While the team isolated the individual phases, determining how they work with different types of corks and varying environmental aging conditions remains unknown.

Also, because cork is an inherently variable biological material, scientists want to examine how its properties change over several years of storage. For Karbowiak and his team, the goal is to develop methods to evaluate a wine’s initial oxidative potential so that winemakers can pair a specific vintage with a stopper that guarantees desired taste at a precise future date. “We need to know how much oxygen the wine should contain when it is optimal for tasting,” Karbowiak said. “If you have that information, you can select the stopper you need for the right preservation over a specific period of time to pinpoint the moment your wine is at its best.”

Science Advances, 2026. DOI: 10.1126/sciadv.aed 3023

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Key Takeaways

Experimental wine bottle tracks oxygen moving through the cork
The small bit of air in the bottle sees oxygen and other chemicals move in and out
Most people perceive a cork in a bottle of wine as a simple plug meant to keep the liquid in and the outside world out
“Twenty years ago, our group focused on the oxidation and aging of wine and all its parameters,” Thomas Karbowiak said
Oxidation is one of the key drivers of wine aging