New Insights Into The Relationship Of Wine, Oxygen, And Wine Closures

Bordeaux, France.-Feb 10, 2007 - Vinitech Bordeaux 2006, the most prestigious industry trade show in France, set the stage for a stimulating technical conference on the subject of wine closures and oxygen management.

Sponsored by Nomacorc, world-leading manufacturer of co-extruded synthetic closures, this event provided a forum for the presentation of recent research into the relationship of wine making, oxygen management, and closures.

The reputation of a chateau or brand rests on the ability to ensure that the consumer enjoys each bottle of wine as the winemaker intended. The quality of the wine is subject to many post-bottling factors including oxidation, and reduction. The ability to control these factors is critical and challenging. Depending on the varietal and winemaking style, varying amounts of oxygen are required to provide the optimum wine aroma and texture.

Nomacorc assembled industry leading specialists in winemaking, chemistry, and closures to present and discuss the latest thinking on the relationship of wine, oxygen, and closures. Participants in the Vinitech conference included:

Dr. Laurent Dulau Vinidea, France
Professor Michel Moutounet INRA Montpellier, France
Dr. Vincent O’Brien Provisor, Australia
Dr. Stephane Vidal Inter-Rhone, France
Pierre Dubrion Vignobles James Herrick, France
Dr. Olav Aagaard Nomacorc LLC, US

Following is a synopsis of the presentation of each of these distinguished panellists.

Dr. Laurent Dulau - Vinidea

"Market trends and oenological knowledge of factors in wine quality: all the more reason for controlling O2 from collection of the harvest to the shop shelf."

The changeover in the wine market, during the last 15 years, from supply-driven marketing to demand-driven marketing, means it is necessary for producers to comply with consumers’ expectations and requirements.

Amongst these requirements, today’s consumer, whether from a new or traditional consumer country, is looking for fruity, rounded wines without sensory defects (such as oxidation or reduction).

Wine aromas can be divided into two categories:

• Fermentative aromas, of higher alcohol and ester type, mainly produced by yeast during alcoholic fermentation.
• Varietal aromas specific to the grape and certain grape varieties. Most of the aromas in this second category develop during alcoholic fermentation.
• For example, this could be molecules such as thiols, norisoprenoids, terpenols or pyrazines (Tominaga et al. 1998).

Whatever category they belong to, the aromas are sensitive to both oxidation and emergence of reduction notes.

The example was brought up that the concentration level of the oxygen-sensitive aroma 3-mercapto-hexanol (3MH, providing grapefruit notes to e.g. Sauvignon Blanc, Murat et al., 2001) can be directly correlated to the perceived quality of the wine; the more the better.

The lower the sum of the ranks, the better the wine is deemed.
3 MH = 3 mercapto-hexanol
According to Murat et al., 2001 R 2 = 0.83960 500 1000 1500 2000 2500 3000 050 100150200
Sum of ranks: 3MH (ng/L)

If we want to protect the wine’s quality potential right up to the end consumer, it is therefore advisable to control the level of O2 present in the wine, namely not too much nor too little, bearing in mind that the optimal concentration of O2 varies from one wine to another.

This is a genuinely new challenge for the world wine industry… and for the producers of closure solutions!

Professor Michel Moutounet - INRA

"Oxygen in oenology - general remarks on solubility, dissolution, consumption and oxidation phenomena in wines"

Air is a gaseous mixture chiefly made up of nitrogen and oxygen. Each of these gases exerts a partial pressure on the liquids with which they come into contact. Likewise, each of them may dissolve in the liquid in question. This dissolution is governed by Henry’s law in which the oxygen concentration is:

pO2 = H x C*

pO2 = Partial pressure of O2

H = Henry constant which is the solubility coefficient
C* = Concentration of O2 at equilibrium

H depends on the temperature and nature of the liquid
As such, the molar concentration of dissolved oxygen in a liquid in equilibrium with a gas phase depends on the partial pressure of the gas and its solubility coefficient, which itself depends on the temperature and nature of the liquid. In wine this equilibrium concentration at atmospheric pressure and at 20°C is 6 mg/L for oxygen (otherwise called 6 ppm).

The oxygen concentration in wine is also dependent on its speed of dissolution, i.e.:
Finally the oxygen in wine gets consumed. So the level of oxygen in wine is a meta-stable state that depends on the kinetics of oxygen dissolution in wine and the speed with which the wine consumes the oxygen. In turn, the latter component depends on the wine’s chemical composition and in particular its polyphenolic fraction.

In fact, the oxygen initially reacts with certain polyphenols of orthodiphenol type and transforms them into quinones, which in turn, through a coupled oxidation reaction, may affect various components of the wine:

• Ethanol by transforming it into ethanal
• Other polyphenols
• Certain aromatic molecules such as thiols, for example

Thus, thanks to oxygen, certain reactions that are necessary for a wine’s quality can occur (stabilization of colour via the reaction of anthocyanines with polyphenols, polymerization of certain tannins to lead to less astringengy).

It is advisable to adapt the quantity of oxygen to the redox potential of the wine as to benefit from the positive effects without incurring the negative ones. In future, precise measurement of this potential will be a key element in determining the "O2 potential" of a wine.

Dr Vincent O’Brien - Provisor

"Controlling oxygen in Australian wines"

The main goals of the Australian wine industry are market knowledge, quality control and profitability.

Market knowledge enables the winemaker to adjust the style of wine to best suit the demands of the consumer. Suffice to say, wine quality consistency is of paramount importance once the desired wine style has been determined. For example, using the same harvest of Riesling, it is possible to produce a semi-oxidative style of wine or a wine that is more reductive, depending on the type of market targeted. In addition, recent AWRI studies have shown that the characteristics sought and appreciated by oenologists and consumers are not the same, hence the importance of market knowledge.

Thanks to the focus on quality control, it is possible to reduce the emergence of defects (such as oxidation and reduction). This proficiency in quality control can have an influence of up to 50% on the gross profit generated.

kl. a = coefficient volumique dkl. dk1 = Mass transfer coefficient

Ci = concentration initialeCi initialeCi = initial O2 concentration

C* = concentration de l'OàsaturatiC* l'OàsaturatiC* = O2 concentration at saturation

2a = surface spécifique de l'interface gaz/liquide (m2/m2a ma = specific surface area of the gas/liquid interface e transfert)

As such, it is paramount in the Australian context to produce wines with a defined style that are consistent in quality and free from fault. This involves controlling the oxygen input throughout the production chain, including bottling. Precise studies into bottling conditions and choice of closure are therefore being conducted by Provisor and AWRI.

These studies demonstrate, amongst other things:

• That control of oxygen input following closure is essential for the quality of the wine.
• That depending on the type of wine and its redox potential, the quantity of oxygen which is positive for the wine will vary (Allen Limmer A&NZ Grapegrower & Winemaker 33rd Tech Issue).
• That failure to control oxygen may lead to the emergence of reduction notes or excessive oxidation (Cf. figure 2).
• That the screw cap type closures allow less air and therefore less oxygen to pass through than other closures (Godden et al., NZSC Symposium, 2004).
• That different Oxygen Transfer Rates (OTR) for different closures have an effect on the sensitivity to oxidation of a wine; this sensitivity can be indirectly measured by monitoring the concentration of Free SO2 (Cf. figure 3).
• That variability from one closure to another is significant in the case of most cork closures.

The onus is therefore on professionals to gain better knowledge and assess the oxygen permeability properties and reproducibility of the closures that they wish to use, in order to limit the risks of aromatic deviation of their wines during bottle-ageing.

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