Oxygen in Unexpected Places

Example of measuring oxygen pick-up using NomaSense oxygen analyzer. Photo Credit: Nomacorc

Jason Diefenderfer is a careful man, when it comes to oxygen management. The winemaker at Hope Family wines, in Paso Robles, California, which produces brands like Liberty School, Treanna and Austin Hope, pays attention to every step and makes sure his approach is custom-tailored to each wine he makes. “We have five wineries, five different philosophies. Different styles mean different approaches, even though the wines are made largely the same way.”

This tweaking can make a great difference, of course: the final wines will be affected when more or less oxygen is allowed to reach the grapes and must, depending on factors like the condition of the grapes at crush (pH, Brix, tannins, etc.), varieties (aromatic vs non-aromatic whites, for instance), or even the way the pressing was handled (free-run juice is handled more gently than a harder press).

Diefenderfer is particularly careful post-fermentation, doing rackings and bottlings under nitrogen, using argon to protect some white wines, and being as careful as possible during pumping. “There’s always going to be some exposure, but you want to minimize it at particular times,” he adds.

Minimizing oxygen ingress at later stages is sound prevention. As a wine consumes dissolved oxygen (DO), antioxidants present in the wine (whether natural or added) will be lost, and countermeasures like extra SO2 additions may become necessary. Also, if there is a high level of DO in a wine, at the moment of bottling, this can result in premature oxidation, ruining all the hard work that came before.

Knowing where it all comes from
To make sure everything is okay, on that front, Diefenderfer also takes a lot of measurements. Measuring dissolved oxygen, especially before and after more active phases like racking or pumping, helps him understand what is going on at these stages and whether he should adjust practices or not. To perform these measurements, he uses the NomaSense sensors, which he appreciates for its ease of use. “Using these meters allows you to test where the oxygen ingress happens,” he explains.

This can be crucially important. When a wine reacts with oxygen, the dissolved oxygen is consumed fairly rapidly. A few days after performing an operation, DO levels may well have gone back down significantly, giving the impression that everything is fine when, in fact, oxidation did take place and may have affected the wine significantly. Measuring immediately before and after those more active moments can reveal significant spikes in DO, and thus show that adjustments in handling may be required.

After all, you can sometimes find oxygen where you don’t expect it. For example, when Diefenderfer monitored wines before and after applying crossflow filtration, a process he expected to be pretty much airtight, he found that significant amounts of additional DO appeared, in certain cases.

After looking carefully at the filtration equipment, he discovered that a particular seal found itself under negative pressure, in certain cases, and wound up letting air in when that pressure built up. He retrofitted the seal area, putting wine over the point of entry. That way, when negative pressure happens, wine gets sucked into the filtration system, and not air.

That moment of problem-solving made him all the more a partisan of careful monitoring at every step of the winemaking process, when it comes to oxygen management. Reality isn’t always in line with assumptions. “You always learn something new”, he concludes.

[Photo: Example of measuring oxygen pick-up using NomaSense oxygen analyzer. Credit: Nomacorc]

About the Author

Rémy Charest is a Quebec City-based journalist, writer, and translator. He has been writing about wine and food since 1997 in various Canadian and American print and online publications, includijng Le Devoir, Le Soleil, Coup de Pouce, EnRoute, Palate Press, Punch Drink, WineAlign and Châtelaine, and has been a regular radio columnist for Montreal's CJAD and CBC/Radio-Canada. He is additionally a wine judge for national and international wine competitions, notably the National Wine Awards of Canada and the World Wine Awards of Canada organized by WineAlign.

Rémy Charest Photo Credit: Jason Dziver

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