As part of its continuing research efforts in the field of oxygen management, Nomacorc has been working with a number of research partners around the world. The complementary expertise of these partners has helped Nomacorc gain a better understanding of many topics, including wine phenolics, oxidation chemistry, wine aroma chemistry, wine metabolomics, applied enology, and sensory science. Here’s a conversation with one of these partners, Dominik Durner, professor at DLR Rheinpfalz’s Weincampus Neustadt, in Germany, who has been heading a project on the effects of oxygen on red wines at various stages of winemaking.
Can you give us an overview of the research projects you’ve been working on with Nomacorc?
It’s about the understanding of oxygen changes in red wines, and about controlling these changes. We have a lot of chemistry on paper about this, but there is still a huge need for understanding of how to control oxygen-induced reactions. There is certainly something like an oxygen sweet spot in winemaking, and we need to find out which wine needs which amount of oxygen under specific circumstances.
Can you describe the experiments you’re running to find this out?
We are running experiments with various oxygenation regimes in juice, during alcoholic fermentation, after alcoholic fermentation, after malolactic fermentation, and after bottling, with the use of different closures. So we have the whole process of winemaking, and storage afterwards, to work on variations in oxygen ingress. We also work with different grape varieties and run different winemaking operations—like different maceration times or cold soaks—and we try to combine them with various oxygen regimens.
How far along are you with this project?
We started the collaboration with Nomacorc in 2011. Around that time, we also got two liquid chromatography mass spectrometry machines, which we use to find out which substances increase or decrease in the wine with exposure to oxygen. Now, we’re trying to quantify. When we started, it was a 1-year project that was 100 percent funded by Nomacorc, and after that it became a governmental project with 90 percent public funding and 10 percent coming from the industry. It’s now a four-year project that will go on until 2016.
Are there any specific substances that are more significantly affected, from what you’ve seen?
We are mainly focusing on the phenolic profiles. We are notably looking at changes in the sensory profile, and how they correlate with changes in the phenolic profile.
The focus is often on risks or potential problems, but I imagine you’ve also seen positive aspects of exposure to oxygen?
There are many positive effects of oxygen on red wines: high color intensity and color stability, softer tannins and less reductive notes—or no reductive notes at all.
Have there been any surprising results at this point?
Many surprises. For example, it looks like too much oxygen at the early stages of alcoholic fermentation could result in an excessive growth of yeast population that is bigger than the available nutritional capacity of the must, which results in an increasing risk of H2S development. Vice versa, if the oxygen is introduced late in wines that have been elaborated under reductive conditions, it can be detrimental for color and longevity. We definitely need to find the right time and right amount for introducing oxygen during winemaking and after bottling.
These observations reveal a paradox: We would tend to think that if a wine has received only little oxygen in the early stages of winemaking, it would need more oxygen afterwards—after bottling, for instance. Or wines with high oxygen ingress during winemaking would need less oxygen during storage. But it looks like it’s the other way around. When we have wines that have high content of polymerized tannin-anthocyanin structures from oxygen exposure during winemaking, they perform better under more permeable closures, like the Select Series 500 or 700 from Nomacorc. They need small amounts of oxygen over the long term. If they are under tight closures, the wines feel very closed, on a sensory level, and the tannins don’t show well. So if we’re using micro-oxygenation, for instance, we should avoid reductive closures.
That could seem a bit counterintuitive. Can you give an example of how that works?
If you have a wine that is made very reductively, whether white or red, the wines will have precursors for creating acetaldehyde. If you store these wines with a permeable closure, then acetaldehyde will have a greater tendency to form, which can result in oxidative aromas or fast decreasing SO2 levels. Reductive winemaking entails being reductive from the beginning to the bottle. Vice versa, if you’ve allowed oxygen to come into contact with your young wine, you may use a closure that will allow continued contact with oxygen.
Find out more about Nomacorc’s research partners around the world here.
Photo Credit: Wine Folly