Protecting Your Cellar: Understanding Wine Storage Light

Wine storage light is a real threat to a fine wine collection. Protecting yours from light exposure is critical to preserving its quality and value. Light can significantly impact a wine's sensory properties. It leads to what is known as 'lightstruck' flavour, according to the Australian Wine Research Institute (AWRI). This off-flavour results from the production of volatile sulfur compounds, as Maujean and Seguin (1983) demonstrated. A study by Dozon and Noble (1989) found that still white wines in clear glass developed a statistically significant level of lightstruck flavour after just 3.3 hours under fluorescent lamps. Wines in green glass took 31.1 hours. For sparkling white wines, the difference was similar: 3.4 hours in clear glass versus 18 hours in green glass. These findings underscore the importance of dark glass bottles. A dark storage environment safeguards your wine too.

How does light damage wine?

Light exposure can adversely react with phenolic compounds in wine. That creates "wine faults" and changes a wine's flavour and aroma. The 'lightstruck' flavour is caused by the formation of volatile sulfur compounds. Maujean and Seguin (1983) believe those compounds are derived from sulfur-containing amino acids such as methionine and cysteine. Riboflavin, or vitamin B2, is present in low levels in wine. It undergoes photo-activation when exposed to light at wavelengths of 370 nm and 440 nm, according to the AWRI. That initiates these reactions.

The Dozon and Noble (1989) study exposed still and sparkling white wines in green glass to fluorescent lamps. It observed lightstruck flavour after 31.1 hours and 18 hours respectively. Wines stored in clear glass developed a statistically significant level of this off-flavour much faster. Still wines took only 3.3 hours, and sparkling wines 3.4 hours. Sensory assessment of these affected wines indicated a decrease in 'citrus' aromas. It also showed a rise in 'cooked cabbage', 'corn', 'wet wool/wet dog', and 'soy/marmite' aromas, as detailed in AWRI Technical Note TN09.

Fluorescent lamps can cause damage. Direct sunlight poses a much greater risk. A 36 W fluorescent lamp with an illuminance of 400 lux provides approximately 14 mW/m2 of UV-A radiation. Full sunlight delivers 60,000 mW/m2 of UV-A radiation, according to Gordon Watson (pers. comm. in AWRI Technical Note TN09). This means direct sunlight provides 4286 times the amount of UV-A radiation as fluorescent lamps. Sunlight also offers a continuous distribution across the visible and ultra-violet spectrum. Fluorescent lamps show discrete peaks instead. Exposure to direct sunlight is therefore likely more harmful to wine quality than exposure to electric lighting systems.

Light exposure can also worsen copper instability in susceptible white wines. That leads to haze. The AWRI recommends that white wines containing a concentration of copper greater than approximately 0.5 mg/L are likely to be susceptible to copper haze. In such cases, protection from light will only delay the inevitable. This is why you often see Champagne and rosé wines shipped in dark glass bottles. Dark glass protects them from light-induced faults. You can learn more about why Champagne and rosé ship in dark glass. This is particularly relevant for iconic producers like Dom Pérignon and Cristal.

What are the ideal conditions for wine storage?

The conditions under which bottled wine is stored play a major part in how a wine ages and evolves sensorially, states the AWRI. Light, humidity, and temperature are the three factors with the most direct impact on a wine's condition. Ideal storage conditions minimise fluctuations in both temperature and humidity. They also protect bottles from light, vibrations, and odours, according to the Comité Champagne. For a comprehensive overview of optimal conditions, consult our guide on how to store wine.

Does bottle orientation matter for storage?

For most still wines, storing bottles on their side is a common practice. Most wine racks are designed this way. The traditional thinking is that this orientation keeps the cork in constant contact with the wine. That stops the cork drying out. However, studies have yielded mixed results on the impact of orientation for still wines. Mas et al. (2002) found that after 24 months, wines stored upright had higher yellow/brown colour than those stored horizontally. The differences were not significant. Skouroumounis et al. (2005) investigated Chardonnay and Riesling wines over 60 months. They found that bottle orientation (horizontal or upright) had little effect on their chemical composition and sensory properties.

More recent research by Chanut et al. (2023) investigated the evolution of oxygen transfer through microagglomerated cork stoppers. The test used miniaturized bottle systems with model wine. The study compared two positions. One was vertical, with the cork in contact with the vapour phase of the model wine. The other was horizontal, with the cork in contact with the liquid phase. Position did not influence the oxygen transfer through the cork or at the glass-cork interface over a 24-month period at 20°C. This aligns with findings from Lopes et al. (2006) and Hirlam et al. (2019), who also reported no significant effect of storage position on oxygen transfer.

For Champagne and other sparkling wines, the advice differs. Champagne is often recommended to be stored upright. The internal pressure from the trapped carbonic gas provides enough humidity and protection from oxygen. Caterer Magazine claimed that a Comité Interprofessionnel du Vin de Champagne (CIVC) study found Champagne stored on its side aged more quickly. Corks lost elasticity, and oxygen seeped in. However, the Comité Champagne's official website states that bottles "can be stored upright or on their sides" in a cool place. It asks for a constant temperature of between 10 and 15°C, with high and constant humidity between 60% and 80%, protected from light, vibrations, and odours. The Comité Champagne further recommends storing Champagne "on its side in a cool, dark, draft-free place" with "generous humidity" and "No direct exposure to sunlight, noise or excessive vibration."

How does temperature affect wine and its closure?

Temperature control is a critical consideration in wine storage. Excessive storage temperatures have a marked effect on the shelf life of bottled wine, according to the AWRI. They cause rapid ageing and significant deterioration. Marais (1986) observed faulty flavours 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 only a matter of days, as Ough (1986) noted. In general, any storage place where the temperature exceeds 25°C for long periods or 40°C for short periods can affect wine quality, according to Ough (1992). Prolonged exposure to temperatures above 77°F (25°C) can spoil wine. It can also cause off-flavours described as raisiny or stewed. Conversely, wine that gets too cold can freeze and expand. That pushes the cork out or cracks the bottle, which allows more oxygen exposure.

Temperature swings can also cause adverse chemical reactions. Repeatedly moving wine from a warm room to a cool refrigerator is one example. The rate of chemical reactions in wine approximately doubles with each 18°F (10°C) increase in temperature. Amon and Simpson (1986) recommend storing bottled wine with the cork in contact with the wine in a cool (15-20°C), dry location. Most experts, including Jancis Robinson, recommend constant temperatures between 50 and 59°F (10 and 15°C). Tom Stevenson speculates that 52°F (11°C) may be ideal. Karen MacNeil recommends around 55°F (13°C) for wine intended for ageing. Wine can be stored at temperatures as high as 69°F (21°C) without long-term negative effect. Professor Cornelius Ough of the University of California, Davis, believes wine can withstand exposure to 120°F (49°C) for a few hours without damage.

A study by Chanut et al. (2023) specifically investigated the impact of temperature on oxygen transfer through microagglomerated cork stoppers in miniaturized bottle systems with model wine. They found that the oxygen diffusion coefficient of the cork stopper alone was not modified, regardless of storage temperature, over 24 months. However, the total oxygen transfer, which includes transfer at the glass-cork interface, was significantly affected by temperature:

• At 20°C: The oxygen barrier properties of the bottleneck-cork system remained unchanged over 24 months.
• At 35°C: Total oxygen transfer did not increase significantly for up to 9 months. Beyond this duration, a significant transfer at the glass-cork interface began to occur. This temperature is noted as one "easily reached during bottle shipping."
• At 50°C: A tremendous oxygen transfer at the glass-cork interface was noticeable within the first 3 months. This phenomenon further accentuated after 6 months, reaching a value approaching the diffusion coefficient of oxygen in the air, indicating leakage at the glass-cork interface.

Two things could explain the increased oxygen transfer at higher temperatures, according to Chanut et al. (2023). One is a partial melting of the paraffin and silicone surface treatment agent on the cork stopper. The other is a modification of the stopper's mechanical properties. The study estimated the liquid:solid ratio of the coating product to be 6% at 20°C, increasing to 19% at 35°C, and 41% at 50°C. This suggests that the coating becomes more fluid at higher temperatures. That may compromise the seal. For more on how fill levels relate to condition, see our guide on wine ullage levels explained.

What role does humidity play in wine storage?

Humidity is important for wines sealed with natural corks, according to the AWRI. Too dry an environment can cause corks to dry out and leakage to occur. If a cork begins to dry out, oxygen can enter the bottle. It fills the ullage space, and the wine may spoil or oxidise.

However, excessive humidity can also damage wine labels. That may hinder identification or hurt potential resale value. Jancis Robinson notes that 75% humidity is often cited as ideal. She adds that there is little significant research to definitively establish an optimal range. Tom Stevenson recommends against storing wine in a refrigerator. The refrigeration process often includes dehumidifying, which can quickly dry out corks. Matt Kramer cites a French study. It claimed that the relative humidity within a bottle is maintained at 100% regardless of the closure used or the orientation of the bottle. Conversely, Alexis Lichine contends that low humidity can still be detrimental to premium wine quality. Corks may dry out. Lichine recommends spreading half an inch of gravel on a wine cellar floor and periodically sprinkling it with water to maintain optimal humidity. For climate-controlled wine storage, moderate humidity levels between 55% and 75% are maintained. That avoids these problems and assists in optimum wine development conditions.

What about vibrations?

Anecdotal information suggests that vibrations contribute to the accelerated ageing of wine, with adverse effects. This remains a research area with relatively little data. A study found that vibrations of different frequencies have their own distinct effect on the chemistry of wine. The study concluded that "Vibration could be used to accelerate the ageing of wine, but in most cases, this may lead to negative effects on wine quality. Therefore, to store red wines with limited changes in physicochemical properties, vibrations should be minimized."

Here is a summary of recommended storage conditions for still and sparkling wines:

Factor	Still Wine Recommendations	Sparkling Wine Recommendations
Temperature	Constant, between 50 and 59°F (10 and 15°C), per Jancis Robinson and most experts	Constant, between 10 and 15°C (Comité Champagne)
Humidity	75% often cited as ideal; climate-controlled storage holds 55% to 75%	High and constant, between 60% and 80% (Comité Champagne)
Light	Protect from light; lightstruck flavour appeared after 3.3 hours in clear glass versus 31.1 hours in green glass (Dozon and Noble 1989)	Protect from light, with no direct exposure to sunlight (Comité Champagne); 3.4 hours in clear glass versus 18 hours in green glass (Dozon and Noble 1989)
Vibration	Minimise vibrations	Protect from vibrations (Comité Champagne)
Bottle orientation	Traditionally on the side; Skouroumounis et al. (2005) and Chanut et al. (2023) found little effect of orientation	Upright or on their sides (Comité Champagne)