Dry Cork Wine: Understanding Oxygen Transfer and Storage

Protecting your cellar's value and drinking pleasure means understanding how a dry cork wine impacts oxygen transfer and wine quality. Research by Chanut et al. (2023) highlights that the glass-cork interface is a major pathway for oxygen entry into bottled wines. Storage conditions can significantly alter its barrier properties. The intrinsic oxygen diffusion coefficient of the cork stopper alone remains stable over 24 months. The presence of model wine, however, can nearly double the total oxygen diffusion coefficient at the bottleneck-stopper system within three months at 20°C. That shift happens primarily by favoring transfer at the glass-cork interface. High storage temperatures, such as 35°C or 50°C, further exacerbate this. Chanut et al. (2023) detail significant oxygen transfer or even leakage at the interface.

How does cork drying affect wine quality?

A drying cork can compromise your wine by allowing oxygen to enter the bottle. That ingress leads to oxidation and potential spoilage. Some degree of humidity is necessary to keep cork enclosures from drying out. If a cork dries out, it can permit oxygen to enter the bottle. That oxygen fills the ullage space and can cause the wine to spoil or oxidize. The Australian Wine Research Institute (AWRI) also states that humidity is important. Wines under natural closures can dry out. Leakage can occur if the air is too dry (AWRI: transport and storage).

The ingress of oxygen can lead to various oxidation-type faults, particularly in white wines, according to AWRI: wine faults and taints. Whites are more sensitive to oxidation than red wines. They carry a lower content of natural antioxidant phenolic compounds. Sensory characteristics of oxidation range from a dulling of the aroma to "cardboard," "straw," and "hay-like" aromas. In extreme cases they progress to "sherry-like" and "madeirised". Acetaldehyde is a compound associated with oxidation. At levels above 125 mg/L it can impart odours described as "over-ripe bruised apples," "stuck ferment" character, or "sherry" and "nut-like" characters (AWRI: wine faults and taints). Acetic acid, perceived as the odour of vinegar, can also increase. Acetic acid bacteria convert alcohol to acetic acid in the presence of oxygen. A concentration greater than 0.7 g/L counts as detrimental, according to AWRI: wine faults and taints.

Does bottle orientation matter for cork moisture?

The traditional belief that storing bottles horizontally keeps the cork moist is not consistently supported by recent research regarding oxygen transfer. Most wine racks are designed for horizontal storage. The idea is that the cork remains in constant contact with the wine and does not dry out. However, a study by Chanut et al. (2023) tested microagglomerated corks in two storage positions: vertical (cork in contact with vapor phase) or horizontal (cork in contact with liquid phase). Neither position significantly influenced oxygen transfer through the cork itself or at the glass-cork interface over a 24-month aging period at 20°C. The values of the total oxygen diffusion coefficient for the two storage positions were similar on average, according to Chanut et al. (2023).

Earlier studies have offered mixed results. Mas et al. (2002), cited by AWRI: transport and storage, investigated the impacts of different alignments on bottles sealed with six different closures for white and red wines. They found that, as a general rule, after 24 months, wines stored upright had higher yellow/brown colour than those stored horizontally. The differences were not significant. This study showed higher oxidation for upright samples sealed with agglomerated cork stoppers. White wine samples carried elevated acetaldehyde levels from the 3-month mark onwards (AWRI: transport and storage). Conversely, Skouroumounis et al. (2005) is also cited by AWRI: transport and storage. That work found little effect from bottle orientation, horizontal or upright. The chemical composition and sensory properties of a wooded Chardonnay and Riesling wine held across a 60-month period.

For Champagne and other sparkling wines they tend to age better if kept upright. This is because the internal pressure from trapped carbonic gas provides sufficient humidity and protection from oxygen. The Comité Interprofessionnel du Vin de Champagne (CIVC) recommends storing Champagne on its side in a cool, dark, draft-free place with generous humidity. The bottles should have no direct exposure to sunlight, noise, or excessive vibration.

What role does temperature play in cork integrity and oxygen transfer?

Temperature is a critical factor in maintaining cork integrity and controlling oxygen transfer. Higher temperatures significantly increase oxygen ingress. Wine is highly susceptible to temperature changes. Prolonged exposure to high temperatures can spoil wine or cause it to develop off-flavors.

Research by Chanut et al. (2023) specifically investigated the effect of storage temperature on microagglomerated cork stoppers in contact with model wine (horizontal position). Their findings indicate:

• 20°C: Oxygen barrier properties remained unchanged over 24 months of aging.
• 35°C: Total oxygen transfer did not significantly increase for up to 9 months. Beyond this duration, a significant transfer at the glass-cork interface began to occur. This temperature is "easily reached during bottle shipping," Chanut et al. (2023) note.
• 50°C: A "tremendous oxygen transfer occurring at the glass-cork interface" was noticeable even from 3 months. It accentuated further after 6 months, to a value approaching the diffusion coefficient of oxygen in the air. That indicates "leakage at the glass-cork interface" (Chanut et al. 2023). This could be due to a partial melting of the paraffin and silicone surface treatment on the cork. The liquid:solid ratio increased from an estimated 6% at 20°C to 19% at 35°C and 41% at 50°C (Chanut et al. 2023).

General wine storage guidelines reinforce the importance of temperature control. Most experts, such as Jancis Robinson, recommend constant temperatures between 50 and 59 °F (10 and 15 °C). Excessive storage temperatures have a marked effect on shelf life, according to AWRI: transport and storage. They cause rapid aging and significant deterioration. Marais (1986), cited by AWRI: transport and storage, observed faulty flavors and decreasing overall quality after 12 months of storage at 30°C. Temperatures exceeding 40°C can induce visual and sensory changes in a wine in a matter of days (Ough 1986, cited by AWRI: transport and storage). In general, any storage place where the temperature exceeds 25°C for long periods and 40°C for short periods can affect wine quality (Ough 1992, cited by AWRI: transport and storage).

Thermal cycling, where temperature varies significantly, should also be avoided. It can lead to wine leakage or cork movement due to thermal expansion (AWRI: transport and storage). This physical damage does not necessarily imply compromised wine quality. It still affects appearance and marketability, according to AWRI Technical Note TN09. For more on managing cellar conditions, explore our guide on how to store wine.

How do humidity and light affect bottled wine?

Humidity and light are significant environmental factors that can impact wine quality and cork performance over time.

Humidity: Maintaining appropriate humidity levels is crucial for wines sealed with natural corks. Some humidity is required to prevent cork enclosures from drying out. If the cork dries, it can allow oxygen to enter the bottle, potentially spoiling the wine. The AWRI: transport and storage concurs, noting that "wines under natural closures can dry out and leakage can occur if the air is too dry." Jancis Robinson, suggests 75% humidity as ideal. Definitive research on an optimal range is limited. Conversely, excessive humidity can damage wine labels, hindering identification or reducing potential resale value. Alexis Lichine, however, maintains that low humidity can still be detrimental to premium wine quality. The risk is the cork drying out. For a detailed look at fill levels, see our guide on wine ullage levels explained.

Light: Direct light exposure can negatively impact wine by reacting with phenolic compounds, leading to "wine faults,". Light-bodied white wines are most vulnerable and are often bottled in tinted glass for protection. Light exposure can affect wine taste through the production of volatile sulfur compounds, known as "lightstruck" flavour, according to AWRI: transport and storage. Dozon and Noble (1989), cited by AWRI Technical Note TN09, tested still and sparkling white wines in green glass. Those wines developed lightstruck flavour after 31.1 hours and 18 hours of exposure to fluorescent lamps, respectively. The same wines in clear glass developed this fault much faster, after only 3.3 hours and 3.4 hours. Sensory assessment of affected wines showed a decrease in "citrus" aromas. It also showed an increase in "cooked cabbage," "corn," "wet wool/wet dog," and "soy/marmite" aromas (AWRI Technical Note TN09). Direct sunlight provides significantly more UV-A radiation than fluorescent lamps. Exposure to it is likely even more detrimental (AWRI Technical Note TN09). Light can also exacerbate copper instability in susceptible white wines, leading to haze (AWRI Technical Note TN09).

What are the signs of a compromised cork or wine fault?

Recognizing the signs of a compromised cork or wine fault is essential. It protects both your investment and your drinking pleasure. Visual and sensory cues can indicate issues with your wine.

Visual Signs of Compromise: The AWRI: transport and storage identifies several visual indicators of heat damage:

• Leakage of wine.
• Closure damage.
• Wine travel or seepage on corks.
• Increased ullage.
• Label damage.

These physical signs do not always mean the wine quality is affected, according to AWRI Technical Note TN09. They do, however, impact marketability. Understanding the saturation to ullage chain can help you assess these visual cues.