Study of oxygen impact on aroma and mouth-feel allows winemakers to better judge optimum oxygen transfer rates (OTR) for closures
LONDON (May 24, 2007) – Nomacorc, the worldwide leader in the growing alternative wine closure category, revealed the latest results of its ground breaking, post-bottling chemistry research at a company-hosted interactive seminar at the London International Wines and Spirits Fair. The session, attended by wine experts from around the world, explored the impact of oxygen on the evolution of bottled wine.
The Nomacorc research team – led by Malcolm Thompson, Olav Aagaard, Stéphane Vidal, Denis Sergent, and Jean-Baptiste Dieval – demonstrated how closures with a differing oxygen transfer rate (OTR) affect wine evolution in the bottle. Using a Sauvignon Blanc from the Bordeaux region and a Shiraz from the Barossa Valley in Australia, the research team analyzed the performance of each type of wine using three different closures that allowed low, medium and high OTR.
Wines were stored for one year under identical controlled conditions, and OTR values were measured using a Mocon Oxtran analyzer, according to ASTM F1307-02, which is a standard industry methodology. Applying enological analyses (free and total SO2, color and other factors) and tasting panelist descriptors (olfactive, gustative and mouth-feel), Nomacorc researchers concluded that each closure type led to differences in wine development.
The Sauvignon Blanc with the low OTR closure, which provided the least amount of oxygen to the wine, demonstrated the highest degree of fruit preservation but was accompanied by the presence of reduced notes. The bottle with higher OTR was less fruity but free of reduced character defect.
The Shiraz with the low OTR closure presented both bitter and astringent characteristics. The medium OTR closure was the best balanced and least bitter, and also had rounder tannins. The wine with the high OTR was found to have more bitterness but lowest astringency.
Nomacorc's research also revealed how winemakers can use this knowledge of oxygen sensitivity to more effectively control wine development. Olfactive sensory descriptors can be translated into chemical classes of molecules, which – once identified – can be assessed based on their sensitivity to oxygen. This scientific knowledge allows winemakers to better judge which closure OTR should be optimum for the intended wine development.
While some aromas are sensitive to oxygen, others are essentially unaffected. Nomacorc has created a classification system that groups the various aroma classes – mercaptans, volatile sulfur compounds, terpenes, norisoprenoids, esters, higher alcohols, volatile phenols, pyrazines and anisoles – with respect to their sensitivity toward oxygen. Using this classification system, it is clear that Sauvignon Blanc aromas belong to the oxygen-sensitive class (mercaptans) and thus benefit from low oxygen exposure. The reduced characters of the Sauvignon Blanc (volatile sulfur compounds) are found under anaerobic conditions, and contact with oxygen will lower their concentration.
Based on this knowledge, the winemaking style can and should influence closure choice. For example, when using a reductive winemaking style, which can maximize the presence of fruity notes but at the risk of producing reductive characters, a winemaker can use a closure with a somewhat higher OTR to lower the risk of obtaining reduced notes while still preserving the fruity character of the wine.
In the Shiraz example, oxygen influences the gustative and mouth-feel sensations, also known as bitterness and astringency. These sensations are attributed to the tannin molecules in the wine, where bitterness is correlated to the smaller tannin molecular structures (monomers and oligomers) and astringency is attributed to the longer-chain molecules (polymers). Tannin molecules are highly reactive and constantly changing in size, often breaking into smaller pieces or reacting with each other to form longer molecules. This depolymerize-repolymerize attribute of tannins leads to a broad range of molecules of differing sizes, which all influence the wine's bitterness and astringency. Moreover, tannins can undergo cross-polymerization reactions mediated by acetaldehyde. Interaction with oxygen can rapidly lead to both increased bitterness as well as softening of the tannins.
This knowledge explains the reaction of the Shiraz to the various types of OTR closures. In the case of the wine with the low OTR, both bitterness and astringency were noted. With the medium OTR, adequate oxygen was available – resulting in lower wine astringency. Bitterness, although still present, was noted as being far less than in the low-OTR example. The high-OTR Shiraz presented the least amount of astringency, but the wine was higher in bitterness because of small-bridged tannin structures.
Nomacorc will continue to explore post-bottling chemistry and oxygen transfer topics through its state-of-the-art, proprietary, advanced sensory research laboratories. This important research is also conducted through ongoing strategic relationships with world-renowned institutions such as the Australian Wine Research Institute (AWRI), University of California at Davis Department of Viticulture and Enology, French Institut National de la Recherche Agronomique (INRA), and Geisenheim Institute, Germany.
About Nomacorc
Nomacorc is the worldwide leader in the growing alternative wine closure category. Dedicated to technological innovation, Nomacorc manufactures its portfolio of products using a patented co-extrusion process. As a result, Nomacorc closures provide consistent, predictable oxygen management and protect against off-flavors due to oxidation, reduction or cork taint. Nomacorc products are available through a vast network of distributors and sales agents on six continents. With more than 400 employees worldwide and state-of-the-art manufacturing facilities in the United States and Belgium, Nomacorc currently produces closures at the rate of nearly 2 billion annually. For more information, visit nomacorc.com.
