wein.plus
Attention
You are using an old browser that may not function as expected.
For a better, safer browsing experience, please upgrade your browser.

Log in Become a Member

The somewhat unwieldy term oxygen management describes all measures that influence the extent to which the wine or even the must comes into contact with oxygen. This primarily concerns the various steps of winemaking, but for years now research projects have been looking at how a controlled supply of oxygen via the closure can also positively influence the development of the wine during bottle ripening. The Nomacorc company, manufacturer of plastic closures for wine bottles, is making great efforts in this direction.

Reduction and oxidation as wine defects

The starting point for the research is wine faults that can be caused by too much or too little oxygen contact of the wine. Nomacorc outlines the problem on its website as follows: "Reduction as a result of insufficient oxygenation during winemaking and ageing leads to an increased presence of undesirable sulphur-based components that cause an odour reminiscent of rotten eggs. Certain grape varieties and winemaking styles are more susceptible to reduction than others, and closures that allow minimal amounts of oxygen to penetrate (e.g. screw caps) are thought to support the likelihood of this undesirable reaction occurring. Oxidation occurs when there is too much oxygen in the wine. It leads to changes in colour and aroma. In most cases, oxidation is due to the introduction of too much oxygen during winemaking. It often occurs when little care is taken when bottling. The cause is often closures such as natural corks, which can have leaks or an irregular structure." Nomacorc also refers to an investigation on the occasion of the "International Wine Challenge" 2008, where several thousand wines from all over the world were tasted and judged. There, six per cent of the wines had been identified as defective, with 29 per cent showing reductive and 19 per cent oxidative off-flavours.

The oxygen permeability of bottle caps is tested in the laboratory. (Photo: Nomacorc)

In 2007, Nomacorc launched basic research programmes in cooperation with scientific institutes from seven important wine-growing countries to investigate, according to the company, "the influence of the oxygen permeability of closures on the development of wine after bottling". The focus is on how the oxygen supply through the bottle closure affects the chemistry and sensory characteristics of the wine and how the influence of oxygen during bottling, the nature of the closure and wine development are related. According to Nomacorc, factors such as storage and temperature conditions are also taken into account. The aim of the research projects is to "acquire sound knowledge about wine development after bottling in order to ultimately be able to improve wine quality".

Research shows oxygen influence during bottle ageing

Nomacorc's research partners include the Davis Department of Viticulture and Enology at the University of California, the Institut National de la Recherche Agronomique (INRA) in Montpellier, the Australia Wine Research Institute (AWRI), the Centro de Aromas at the Pontificia Universidad Católica de Chile and the Geisenheim Research Institute. In September 2012, this circle was expanded to include the Dienstleistungszentrum Ländlicher Raum (DLR) Rheinpfalz, the Centro Ricerca e Innovazione (CRI) in San Michele all'Adige and the Universidad de Zaragoza. Each research institute is investigating different specific questions, but it is always about the amount of oxygen that enters the filled bottle through the cap, which is indicated by the so-called Oxygen Transfer Rate (OTR). Journalist Simone Dowé summarises the main research results in an article in the magazine "Getränkeindustrie" (issue 4/2012): "In the research, different production methods were first applied to different grape varieties. Then the scientists exposed the wines produced to different controlled oxygen concentrations, continuously monitoring the oxygen content during bottle storage using NomaSense technology."

NomaSense technology can be used to determine the oxygen content in wine. (Photo: Nomacorc)

NomaSense is a measuring tool developed by Nomacorc to determine the total oxygen content in wine. The analyser measures both the oxygen dissolved directly in the wine and the gaseous oxygen in the air space. The NomaSense method is based on a photoluminescence technology which, according to the company, enables a particularly precise determination of the oxygen content without having to open the bottle. As one of the central research results, Dowé mentions "that a varying oxygen supply during bottle ageing has a resounding effect on aroma development in red wines, especially through the use of closures with varying OTRs. When Grenache, Shiraz, Carménère and Cabernet Sauvignon were studied under different oxygen conditions, the studies proved that OTR is a key factor in the development of red berry aroma." Within two to four years, for example, the researchers were able to identify an "optimal OTR range" based on different aroma profiles of a wine, "within which flavour attributes of red and dark fruits, chocolate and spices develop more strongly".

Controlling wine development via the closure

Dowé goes on to say that the Australian Wine Research Institute concluded that "the aroma, colour composition and sensory characteristics of Shiraz are effectively influenced by the choice of OTR". According to the research results, jam, berry and chocolate notes, for example, are enhanced over a period of 40 months in standard bottles with very low oxygen supply during bottle storage. In red wines, the development of reductive flavour off-flavours during bottle ageing is related to the presence of the sulphur component methyl mercaptan. Other sulphur components such as hydrogen sulphide and dimethyl sulphite also play a role. In the case of the Carménère grape variety, closures with lower OTRs, such as screw caps, led to the formation of reduction aromas, as confirmed by scientists at the Pontificia Universidad Católica de Chile. Conversely, higher OTRs produced more red berry aromas. In Carménère Reserve, on the other hand, wines sealed with closures of a lower OTR had more intense aromas of caramel, purple and dried fruits, while higher OTRs in the closures promoted the formation of berry and tobacco aromas."

According to the article, OTR can further "be used to control the evolution of phenolic compounds during ageing in the bottle". The Institut National de la Recherche Agronomique (INRA) in Paris found that. "In both Grenache red and Grenache rosé wines, colour intensity increased with increasing OTR over two different vintages. The loss of free SO2, flavanols and the conversion rate of anthocyanins to new pigments [...] can also be influenced by OTR, as the study results showed," says Dowé. At the Geisenheim Research Institute, it was discovered "that oxygen management during bottling also shows effects during longer storage - independent of the type of closure. The reason: fluctuations in oxygen content during bottling can change the wine."

The wine is also exposed to the influence of oxygen during bottling.

Plastic closures with individual OTR

The new research partners will also each be involved in the projects with their own focus: DLR Rheinpfalz is focusing on the influences of winemaking and oxygen contact on the sensory and chemical properties of Pinot Noir - before and after bottling. Research at the Italian CRI is to focus primarily on the reaction of different types of wine with oxygen, and the analytical laboratory for aromas and oenology at the Universidad de Zaragoza is concerned with research into oxygen factors that influence wine aroma.

With this research and its results in mind, Nomacorc has developed a range of plastic wine closures that, according to the product description, "ensure a consistent and predictable oxygen supply" and are manufactured using a patented coextrusion process. They consist of a flexible foam core and a sealing, stronger outer shell.

Cross-section through a Nomacorc closure: foam core and outer shell are firmly bonded together. (Photo: Nomacorc)

The closures are designed to allow a precisely calculated amount of atmospheric oxygen to pass through per unit of time, thus enabling a targeted influence on wine development, according to the manufacturer. The "Light", "Smart+" and "Classic+" product lines have a constant, firmly defined OTR, whereby emphasis is placed on a particularly low calculated oxygen input. The "Select Series" closures with four types, which differ in diameter and density, among other things, and are each available in three length variants, allow the wine to mature specifically with different exposure to oxygen.

Screw caps with a special seal

Plastic stoppers, however, are not the only closure option for regulating the oxygen supply in the bottle in a planned way. The company VinPerfect offers a modified screw cap that contains microscopic holes in its closure cap through which air can pass. A special seal is inserted into the aluminium cap, which is a composite of several layers of plastic (polyethylene and polyester, partially coated with aluminium). This seal ensures that a constant, defined amount of oxygen passes through the closure. "VinPerfect combines the reliability of a screw cap with the oxygen permeability of corks, but at a controlled level," says VinPerfect board member Scott McLeod. VinPerfect is also researching oxygen management and advertises that wine producers could use the special screw caps to control the ageing of their wines after bottling: "The closure can be selected to match the amount of oxygen supplied to the intended shelf life of the wine." It is therefore possible to adapt the closure to the intended shelf life of a wine or to determine this via the oxygen permeability of the closure.

Both VinPerfect and Nomacorc thus emphasise that the development and life of the wine can be actively influenced by controlling the oxygen transfer during bottle ageing. According to Simone Dowé, "oxygen management not only contributes to the control of undesirable aroma substances such as reduction and oxidation. With the application of oxygen management strategies, especially with the selection of closures with the right OTR, it is also possible to promote sensory attributes that are appreciated by the consumer. Storable wines can thus also be guaranteed to mature for up to ten years without aroma defects." However, if the closure is used to specifically influence certain aroma characteristics, the wine is not created in the vineyard or even rudimentarily in the cellar, as is practised and propagated by winegrowers who work close to nature - instead, it only takes shape in the bottle, so to speak.

The production of bottle closures with defined OTR requires careful quality control. (Photo: Nomacorc)

Oxygen management unimportant when buying wine

For consumers, on the other hand, the topic of controlled oxygen supply in the bottle is difficult to grasp. "Oxygen management tells the customer at most something about the old saying 'the wine has to breathe', but hardly any customer has a real idea of what is supposed to happen there," says wine merchant Armin Busch of K&M Gutsweine in Frankfurt. When buying wine, the focus is more on practical-functional aspects, such as whether the bottle can be opened without tools. The susceptibility to errors with regard to the risk of cork taint and the image of the closure also play a major role. "Women are more pleased with screw-tops, the bottle opens more easily and you can close it again. White wine, which is drunk young by most customers, is still more readily accepted with screw caps; with red wines, especially those that can or should mature and be stored, people tend to still value the cork," reports Busch. This observation is confirmed by Kai Buhrfeindt, sommelier and owner of the Frankfurt wine restaurant "Grand Cru", who is occasionally told "that for a romantic evening for two in front of the fireplace with a bottle of good red wine, it should rather be the 'popping feeling' with natural cork". So does the consumer not care about possible improvements in the ageability of a wine?

Certainly not, because nobody likes to drink spoiled or stinking wines. But the research results on the targeted oxygenation of wine after bottling are still young and rather little known. The special closures may open up new possibilities for wine producers, but these must not least fit their philosophy, and each closure has its advantages and disadvantages. Armin Busch thinks "that the winemaker should think about oxygen management before bottling, especially with regard to the closure that is then used." Rüdiger Meyer, sommelier and wine consultant from Pähl am Ammersee, also points this out: "Wines with screw caps may not be as reductive as with other closures." Meyer considers closures with predetermined OTR "in principle useful for all" types of wine, "you just have to adapt the winemaking". Wine merchant Busch expresses himself restrictively: "I could imagine that this could be interesting in general for wines capable of maturing. But is it really worth the high production costs?"

From the consumer's point of view, other criteria are more important for wine closures than oxygen management in the bottle. (Photo: DWI)

Effect only after long storage time

This question is justified at least to the extent that a controlled oxygen supply via the closure actually only makes sense for certain wines. "Controlling wine development via the bottle closure is only possible to a very limited extent," says Professor Dr. Rainer Jung, deputy head of the Department of Cellar Management at the Geisenheim Research Institute. "Although the manufacturers of corresponding closures use controlled oxygen management as a sales argument, in this phase - i.e. after bottling - influencing the wine via a firmly defined oxygen supply is hardly relevant." According to Jung, other factors matter, and he explains the connections:

"The wine absorbs oxygen during its entire production process. Already when the must runs off freely, it reacts with the air and turns brown because oxidation enzymes start to act. The brownish colour comes chemically from certain phenolic ingredients that are oxidised. This is a completely normal process and not at all bad - on the contrary, the yeast needs oxygen to multiply and work, and the more yeast there is, the safer the fermentation will be. Fermentation itself is a reductive process (i.e. opposite to oxidation), and the wine becomes light again. If it were left unprotected after fermentation, it would also turn brown again because oxidation would then set in. To prevent the wine from reacting with the oxygen in the air, firstly, the head space in the tank or barrel (i.e. the free space between the surface of the liquid and the upper wall of the container) is kept as small as possible and, secondly, sulphurous acid is added to the young wine. This is used to preserve many foods, and in wine only a comparatively very small amount of 100 to 150 milligrams per litre is used. Sulphurous acid has several effects: It inhibits microorganisms and binds certain substances relevant to taste that cause oxidation notes (such as acetaldehyde). The so-called free sulphurous acid is decisive. It ensures that the wine remains stable because it reverses oxidative reactions. Only when all the free sulphurous acid is bound in the wine does it begin to change aromatically.

The wine is also exposed to atmospheric oxygen during filtration and bottling. During bottling, one can influence the oxygen uptake by the choice of process. Bottling machines where a short tube goes into the neck of the bottle and the wine then runs down the inside wall supply it with more oxygen than machines where a long tube goes almost to the bottom of the bottle and the bottle is filled from the bottom up. But there are also economic reasons for which method is used, because filling with a short tube is faster. After filling, the head space of the bottle is usually inerted, i.e. filled with a gas that shields the wine from the oxygen in the air; this is often carbon dioxide or nitrogen. However, if the head space of the bottle is not inerted, the oxygen remaining there poses a great danger of oxidation. Here is a calculation example: If 100 milligrams of sulphurous acid per litre have been added to the wine, this means 40 to 50 milligrams of free sulphurous acid per litre. If there are 15 or 20 millilitres of air in the head space, the free sulphurous acid is reduced to about 20 milligrams per litre within the first three months after filling, i.e. by about half. And less free sulphurous acid means that the wine will mature faster and thus change aromatically more quickly.

So it is of much greater importance whether the bottle headspace has been inerted than to control the influence of oxygen by the choice of closure. Of course, every bottle closure has a certain oxygen passage, whether calculated or not, and there are very tight and less tight closures. In the bad case, the oxygen passage reduces the free sulphurous acid by about 10 to 15 milligrams per litre in a year of storage, in the good case by only two milligrams per litre and year. However, 90 to 95 per cent of the wines sold in Germany are drunk in the first two years after filling, which means that for the vast majority of wines it doesn't matter at all what the bottle is sealed with, because the effect of the different oxygen passage of the individual types of closure would only become noticeable after a storage period that the vast majority of wines don't even reach."

The storage conditions influence the development of a wine more than the bottle closure.

Jung points out another point: "As soon as the bottled wine is sold, the winemaker can no longer influence its development anyway. The influence of oxygen through the closure is the least of the problems. After the sale, one bottle is on the wine merchant's shelf and gets neon or daylight, another bottle is stored by a wine lover in a cool, dark cellar, a third is kept by a consumer in the cool near the window or next to the heater - and the temperature and, to a certain extent, the light have a much stronger effect on the development of a wine than the influence of air over time. Theoretically, the producer would have to store the wine properly himself and the consumer would only be allowed to buy it ready to drink, but that is not really feasible. If the winemaker leaves the storage of the bottled wine out of his hands or leaves it to chance, the conditions are incalculable, but for the effect of a controlled oxygen supply to take effect, they would have to be as stable as possible."

So, according to Jung, oxygen management via the closure only becomes relevant after several years of storage, and most wines are consumed well before that time. Moreover, with wines that age for so long, the image of the closure type comes before functionality: "If you have a Château Pétrus from 1985, you expect a natural cork in the bottle, nothing else. Whether a plastic or screw cap would promise a more predictable development is completely irrelevant."

To the magazine article "Screw tops are becoming socially acceptable"

To the magazine article "The most common closures

To the magazine article "Winemakers' and associations' opinions on closures"

To the magazine article "No perfect closure for all types of wine"

To the website "Closures in Wine

Related Magazine Articles

View All
More
More
More
More
More
More
More
More
More
More

EVENTS NEAR YOU

PREMIUM PARTNERS