There are a number of complementary factors – and perhaps almost as many competing theories – about what makes a red wine resistant to oxygen, meaning how well and how long it will keep its aromatic profile after the bottle is opened, or how long it will keep when it is laid down in the cellar. While there is no magic bullet or single determining factor, certain elements are seen as more important than others, notably acidity and phenolics.
Since aging wine is essentially a process of slow oxidation, it seems important to make sure all the necessary elements are present in sufficient amounts to slow down that process as much as possible – at least, when trying to make a vin de garde, made for longer-term aging. However, what are sufficient amounts of these components and how do they interplay? The answers are quite complex, and there are examples that defy expectations.
For instance, it could be assumed that a lower pH and higher acidity would be an indispensable element in ensuring that a wine can age for many years if not decades. But some wines run contrary to that expectation.
“Take the 1947 Cheval Blanc, for instance”, points out Jean Hoefliger, winemaker at Alpha Omega in Napa and Monteverro, in Tuscany, who has also made wine in Bordeaux and in his native Switzerland. “It’s from a very hot year, the pH is somewhere around 3.9, so the acid is low and it was made from very ripe grapes. Yet it’s seen as one of the best ones ever made, and by all reports, it is still tasting fine to this day.”
Of course, this is a bit of reasoning through extremes: a 47 Cheval Blanc is the exception, not the rule. Not all ultra-ripe wines at a pH close to 4 will be able to keep going for over 60 years.
Hoefliger recognizes that the acidity level is an important part of a well-structured wine made for aging, generally speaking, but he argues that it may not be quite as important when other conditions are present, in a way that can compensate for lower acid. “Alcohol levels and especially tannins play a very big role as well. In Napa, I don’t need acidity in the wines in the same way that I did in Switzerland, for instance, because I have these enormous tannin structures.”
When a wine is in contact with oxygen, the so-called “oxydation cascade” starts, eventually leading to obvious oxidation. Tannins and other phenolic components like anthocyanins are rapidly involved in this series of reactions – in certain ways “intercepting” the oxygen before it can affect other elements in the wine. Therefore having higher amounts of those components would logically mean more oxygen resistance, just because of quantity. But there are other factors at work, like the type of tannins and phenolic compounds. And here again, oxygen is a key element. Just as an example, when tannins and anthocyanins react together in the presence of oxygen, wine color becomes more stable during aging, another key feature of long-lasting wines. While the general interactions are understood, the specific mechanisms that make this possible in an individual wine remain largely unknown, as far as chemical reactions and interactions go. Why does it remain so mysterious? First of all, phenolic compounds interact with a mind-bogglingly high number of different compounds, and bind – and sometimes recombine – differently under various conditions involving pH, the presence or absence of oxygen, the length of polymer chains (which can vary over time) and the types of tannins (from stems, skins or seeds or even oak).
Vinification methods can also intervene. Aging a red wine in barrel, for instance, will not only introduce a certain amount of oxygen in the reactions, influencing the formation of polymer chains in many components, but also introduce aldehydes from the toasted wood, which will modify the way the polymer chains build themselves.
Micro-oxygenation is also known to have a great influence on the way tannins form – and how they feel on tasting. The debate on the effects of micro-ox on the aging potential of a wine, on the other hand, is still raging in winemaking circles.
More recently, a number of studies have also shown that by using closures allowing defined oxygen ingress, wine tannin profile can actually be further ‘sculpted’ in the bottle, so that the winemaking process can actually continue post-bottling.
In any case, phenolics and tannins should be carefully taken into account, as well as their interaction with oxygen during winemaking and their effects on long-term oxygen resistance in a finished wine. Whether you are making a red wine accessible for short-term drinking or a cuvée for the ages, they are a key element in the wine’s personality and style.