So you think you know wine? Chances are you could be surprised by all the things we’re only starting to understand and quantify in its extraordinarily complex chemistry.
To be convinced of that, there is nothing like a couple of days at the Advances in Wine Research symposium, which was part of the American Chemical Society’s annual meeting in San Francisco. The big takeaway? There is always plenty more to learn.
Over the course of three days (August 10-12), over thirty researchers presented papers covering a wide range of topics: effects of temperature on wine conservation and aging (aka why you should not keep wine bottles in your kitchen); possible methods for chemically “fingerprinting” wines to understand why grand cru wines age well; measurable effects of terroir (soil, aspect, altitude…) in the biochemical profile of wines; and even everything you wanted to know (and then some) about the dynamics of “CO2 diffusion coefficient in champagne wines.” The sessions were attended by many leading researchers from Europe, North America, Australia, and New Zealand, as well as some of the people who apply these principles on a practical level within wineries.
And on the oxygen side of things…
Within this three-day full-on immersion in wine science, one entire day of conferences on August 12, organized with financial support from Nomacorc, focused entirely on the influence of oxygen on wine quality. Simply said, topics were divided into two great categories. First, measuring and quantifying the implications of oxygen exposure for wine quality. Second, identifying how various chemical components present in wine interact with oxygen. Many people might feel that these topics are old, but in reality there was all sorts of surprises, starting with the fact that, well, you shouldn’t really protect grapes and wine from oxygen during the winemaking process, not even in the case of white wines.
For instance, Paul A. Kilmartin, from the University of Auckland, pointed out how machine-harvested sauvignon blanc actually produced higher levels of precursors to desirable aromatic components than hand-picked grapes, potentially leading to more aromatic wines. A cascade of oxidative reactions taking place in the must seems to be at the origin of this phenomenon something that contradicts the general view that gentler is always better at harvest. Dominik Durner, Professor at DLR Neustadt, in Germany (who is working in collaboration with Nomacorc on some of his oxygen-related research), explored the complex interactions between oxygen levels and anthocyanins, various polymerized components and acetaldehyde, to show how oxygen could do things like improve color density, but also result in browning and loss of resistance to oxidation.
The relationship between oxygen exposure and color intensity was also at the heart of a presentation on rosé wines by Véronique Cheynier, from the Université de Montpellier, who pointed out that relatively higher oxygen exposure in rosé winemaking led to higher color intensity, as flavylium forms of anthocyanins increased (forms that are more stable, notably). Her research results also pointed out that too much oxygen could lead to loss of anthocyanins.
Cheynier and Durner’s research held out a theme common to many presentations: a need for finding the right balance in the amount of oxygen allowed in wines at various stages, and the fact that choosing higher or lower levels of oxygen ingress often result in certain trade-offs between one set of components and another. “What’s the best combination of time and oxygen? That’s the million dollar question,” said Vicente Ferreira, a Spanish researcher from Universidad de Zaragoza, who is also a Nomacorc research partner, as he presented a study on the factors leading to the occurrence of oxidative and reductive aroma compounds in a selection of Spanish wines.
Balance was also at the heart of a presentation by Stéphane Vidal, global director of enology for Nomacorc, on “Critical oxygen levels affecting wine aromas.” In it, he described the effects of higher and lower levels of closure oxygen ingress on aromatic components like thiols or beta-damascenone, and how interactions with components like glutathione or quinones, under various conditions, can affect the direction a wine takes towards oxidative or reductive characters. Surprisingly, among the many wine sensory attributes that are affected by oxygen, fruity aromas seem to be the most responsive, and not reduction or oxidation, as one would have imagined. For his part, Maurizio Ugliano, enological research manager at Nomacorc, discussed the use linear sweep voltammetry to assess grape and wine capacity to resist oxidation. The idea of this approach is to identify the amount of oxidizable components (notably, phenolics) in a variety or a wine to help assess how they should be handled in the winery. Monitoring the presence and evolution of these components could provide useful tools to winemakers, as they try to make sure their wines end up where they are supposed to. A great way to showcase the bridges between fundamental research and practical applications that, in the end, will be enjoyed by wine lovers all over the world.