Tuesday, September 20, 2011
“total package oxygen” (TPO) in bottled wine
September 19, 2011
What Oxygen Research Means to Winemakers Studies cast doubt on usefulness of free SO2 and dissolved oxygen measurements
by Jim GordonZebulon, N.C.—The world’s leading supplier of synthetic corks decided in 2007 aggressively to commission research about oxygen’s role in wine quality at several international universities. The research yielded dramatic results that not only led Nomacorc, the sponsoring company, to develop new products, but potentially changed the game for winemakers everywhere.
During what was called a media day at Nomacorc headquarters in the countryside near Raleigh, N.C., academics from California, Chile and the company’s own scientific and marketing teams brought journalists from Europe and North America up to date about the research and what it means for winemakers. Nomacorc intended the event to publicize its new Select Series closures, which offer a range of three oxygen transmission rates, and a new software tool called NomaSelector, which helps winemakers calculate their wines’ oxygen needs.
The seminar sessions also stressed:
• Traditional measurements of dissolved oxygen and free sulfur dioxide may be outdated;
• Management of oxygen in wine needs to extend beyond simply keeping it out;
• Different wines have different needs for oxygen;
• Winemakers now have the knowledge to extend their craft into and beyond the bottling line.
Possibly the most fundamental new recommendation was that enologists now should understand what Nomacorc calls “total package oxygen” (TPO) in bottled wine, if they want to protect their wines from too much oxidation or reduction and remain confident about its shelf life: In other words, that it will taste like the winemaker intended when a consumer drinks it.
TPO includes the dissolved oxygen in the wine, the oxygen in the headspace and the oxygen that will enter the wine through the closure over time. While winemakers long have been able to measure dissolved oxygen, and more recently have become aware of closures oxygen transmission rates, the headspace oxygen has been very difficult to measure.
Check oxygen in closed bottles
Nomacorc developed a versatile, easy-to-use oxygen-measuring instrument called NomaSense that helps researchers and winemakers check the percentage of oxygen in juice, must and wine as well as in the headspace while the bottle remains closed. Larger wineries and labs have bought the devices, and according to Nomacorc, at least one major wine university, Geisenheim in Germany, is including this kind of oxygen testing in its best practices protocols.
The basic model of NomaSense costs about 6,500 euros, while a more advanced model that can measure down to the level of trace measurements is about 10,500 euros. Mai Nygaard, Nomacorc’s global business development manager, said that most of the units have been sold in Europe, but that the largest U.S. wine producers, including E. & J. Gallo and Constellation Wines U.S., have purchased and are using them, along with various wine labs.
Nygaard said that data about TPO collected from wineries shows that on average, one-half to two-thirds of the oxygen in bottles is in the headspace, not dissolved in the wine. She said that at bottling, the TPO ranges from 2-6ppm (mg/L); the company’s fastest OTR closure, the Select Series 700, only admits 1ppm over 150 days.
Dr. Stéphane Vidal, global director of enology for Nomacorc, said that the company’s focus now is “all about winemaker intention,” and that winemaker intention is related to shelf life, or aging ability. A winemaker who knows the total package oxygen of his wine at bottling, and can closely control the bottling process, can make smart choices about what closure and OTR rate to select, based on how the winemaker wants that wine to taste at the time it is likely to be opened.
He compared the process to a car staying safely on the road—not veering into the reduction ditch on one side or the oxidation ditch on the other. Another presentation included research results indicating that consumers are good at detecting the effects of oxidation and reduction even if they don’t know the terms and will reject wines in the extreme ranges.
A new standard
Two professors who supervised oxygen research at their universities also summarized their findings. Dr. Andrew Waterhouse heads the Department of Viticulture and Enology at the University of California, Davis. “Now the oxygen measurement is standard,” he said. “You can’t do a study without this.”
Waterhouse and his team studied not just oxygen at post-bottling, but also oxygen’s interaction with the whole winemaking process, including barrels vs. stainless fermentation vessels; lees contact vs. filtered wine; micro-oxygenation and other choices. He summarized his team’s findings as a confirmation that a wine’s composition affects its response to oxygen: Different wines have different oxygen needs.
Dr. Eduardo Agosin of Centro de Aromas, Pontificia Universidad Católica de Chile, studied oxygen levels in must and wine during industrial-scale winemaking. Using the NomaSense technology, he found that oxygen is distributed very unevenly through a large fermenting tank undergoing pump overs: Yeast near the bottom of the tank had almost no oxygen to digest. The rack-and-return procedure produced much more consistent distribution.
Other partners in the Nomacorc-funded research were: Institut National de la Recherche Agronomique at Montpellier in France, the Australian Wine Research Institute and the Geisenheim Institute in Germany.