Winemakers have many issues to worry about as they turn grapes into wine, and it’s helpful to have a checklist to help make the process less risky and less variable. But is it possible to set specific values for oxygen management throughout the process, from crush to bottling?
Nomacorc enology department researcher Maurizio Ugliano does suggest one value for where a wine should be at bottling, the end of the process. The value is referred to as Total Package Oxygen (TPO), and it’s a combination of the dissolved oxygen in the wine (DO) and head space oxygen (HSO), the amount present in the space between the closure and the surface.” That total amount is what the wine has access to after bottling operations; 2 mg/L or below is what we recommend.”
That figure, he quickly adds, is a recommendation, not a hard number that must absolutely be hit. “If people are getting satisfying results with 4 mg/L, it’s not as if we’ll argue with them. If they don’t see variations and issues, that’s quite fine. However, it would be a good idea for wineries to know their number and stick to it, and be able to refer to that value in case something doesn’t seem quite right. ”
To Each (Wine) Its Own
Oxygen pickup happens at a lot of times and places throughout a winery, whether in the press pan, when a bung is opened on a barrel of aging wine, or during rackings and pumpings. In some cases it might have desirable effects, in others not. It depends a lot on the individual wine—White or red? Which grape variety or varieties? High or low acid? How tannic?—and on the winemaker’s objectives and stylistic preferences.
In a presentation about oxygen demand in wine, Bordeaux researcher Nicolas Vivas, an authority on barrel aging, pointed out that there is no intrinsic, fixed number for a given wine. “A wine doesn’t have any needs, any requirements. It isn’t asking us for anything. (…) Even if it’s going reductive, it’s not that it needs oxygen, it’s just living its life. On the other hand, winemakers and wine buyers have ideas about what they want to achieve, and how wine should show to be appreciated and sold.”
Ugliano agrees, adding another metaphor to the mix: “It’s a bit like the amount of salt you add to the soup. Soup doesn’t need salt to become soup. The amount of salt has to do with your taste and the type of soup you’re looking to serve.”
How you make the soup—or the wine—will vary according to the ingredients you use. Ugliano points out, for instance, that when making Muscadet, the grape used (Melon de Bourgogne) has a lot of small phenolic compounds that can oxidize easily and very differently from Chardonnay, which has a different set of phenolics. A red wine with big tannins is a different beast, as it has more sturdy structures to face oxygen ingress. Syrah tends to be reductive, while Grenache tends to be oxidative, as many winemakers will tell you—and so on.
Moments That Count
Whatever the wine, certain rules of prudence apply in oxygen management. The later you are in the process in the winery, the more careful you should be. In those later stages, excess introduction of oxygen will be more dangerous, especially for white wines.
Additionally, the most risky moments are also the most active ones: rackings, pumpings, blending, and all operations linked to bottling. Making sure your stainless steel tanks are airtight and your barrels are well closed and topped up is important too, but it’s when liquid is moved around that the real trouble can hit.
In those active phases of winemaking, how much oxygen ingress is too much? Again reluctant to give arbitrary, one-size-fits-all figures for oxygen management, Ugliano points out that “In the case of a wine transfer, people might want to avoid any oxygen pickup greater than 0.5–1.0 mg/L. It’s not that 1 mg/L can be harmful in itself, but since there are usually many transfers in the life of a wine, adding 1 to 2 mg/L at each transfer may result in a wine that comes out a bit tired at the end of the process, or perhaps needing a bit of extra SO2, which could have been avoided with more careful oxygen management.” The more transfers you’ll make, the more you should limit the amount of oxygen ingress at each step.
Don’t Be Random
To know what is actually going on, it becomes essential to measure oxygen levels present in the wine at various times, especially before and after wine transfers, to evaluate pickup levels at each of these steps. In the reality of everyday winery operations, perfection may not be attainable, but consistency may be more important anyway. “You’re looking to reduce the random factor, says Ugliano. If you have a pump that isn’t the most airtight, but you’re aware of it and you try to manage it carefully, that might be as good as or better than if you have the perfect equipment but fall outside of the standards you’ve set because you’re not handling things carefully enough.”
In other words, set a protocol that gets the wines where you want them—and stick to it. “If you’re hitting all your targets and the wines are showing the way you want them, it’s good. If you’re not, you need to start measuring,” he concludes.