Light Strike

Lightstruck wine, also known as “light strike” or having a “goût de lumière” (French for “taste of light”), is a wine fault that occurs when wine is exposed to ultraviolet (UV) or strong visible light. The chemical composition of wine, including compounds naturally present such as riboflavin and sulfur amino acids, is influenced by the alcoholic fermentation process. This exposure triggers a photochemical reaction that degrades certain compounds in the wine, particularly riboflavin (vitamin B2) and sulfur-containing amino acids like methionine. Riboflavin is primarily produced by the yeast Saccharomyces cerevisiae during alcoholic fermentation.

Light reacts with riboflavin, which is naturally present in wine, to produce volatile compounds, including volatile sulfur compounds. The result is the formation of volatile sulfur compounds that produce unpleasant off-flavors and aromas. The degradation of riboflavin and sulfur amino acids in wine exposed to light leads to the formation of these volatile compounds, which are responsible for the light-struck taste. The effects of light strike are irreversible, and once a wine is affected, its original aromatic compounds and quality cannot be restored.

Light strike is a fault more commonly associated with white and sparkling wines, particularly those in clear or light-colored bottles, though any wine can be affected. The issue gained particular attention in the Champagne region, where producers traditionally used clear bottles to showcase their wine’s color and clarity.

What are the characteristics?

Light strike wine exhibits several distinctive sensory characteristics that make it immediately recognizable to experienced tasters:

Aromatic defects: The most prominent feature is an unpleasant sulfurous smell often described as “wet wool,” “wet dog,” “cooked cabbage,” “boiled cabbage,” “skunky,” “unpleasant smells,” or “struck match.” Some people also detect notes of rubber, burnt hair, rotten eggs, or garlic. These aromas are produced by mercaptans and other volatile sulfur compounds, including unpleasant sulfur compounds, formed during the photochemical degradation process.

Light strike creates unpleasant sulfur compounds, which are responsible for off-putting aromas such as boiled cabbage, drains, and wet dog. Fruity aromas are particularly affected, with the loss of fresh fruit flavors and the dominance of unpleasant smells.

Flavor impact: On the palate, lightstruck wines taste flat, dull, and oxidized. The fresh fruit flavors are muted or completely masked by the off-flavors. There’s often a bitter, unpleasant finish that lingers uncomfortably.

Visual changes: While less obvious than the aromatic defects, extended light exposure can also cause the wine to lose its vibrant color, appearing more brownish or faded than it should. Light exposure can also cause the formation of yellow and brown pigments due to chemical reactions.

The intensity of these characteristics depends on the duration and intensity of light exposure. Wines exposed to direct sunlight for even a few hours can potentially develop noticeable defects of light strike. The degradation of wine quality due to light exposure can happen within hours and is irreversible.

Wines Vulnerable to Light Strike

Not all wines are affected in the same way by light strike. Sparkling wines like Champagne and Prosecco are exceptionally vulnerable to light strike reactions. These bubbly beauties are often stored in clear glass bottles to showcase their sparkle and clarity, leaving them exposed to harmful light. The riboflavin and sulfur compounds in sparkling wines mean that when light hits these components, it can quickly create unpleasant smells and tastes.

White wines such as Sauvignon Blanc and Pinot Grigio are also vulnerable, especially when stored in clear glass bottles. These wines naturally have higher levels of sulfur-containing amino acids that transform when exposed to light. Rosé wines are often stored in clear bottles to highlight their color and, therefore, are also vulnerable. The visual appeal of clear bottles means increased vulnerability to light strike.

Red wines are generally less vulnerable to the effects of light strike. Their higher polyphenol content works like a natural shield, helping to protect wine from light strike reactions. No wine is completely bulletproof; the choice of glass bottles, especially those that are green or amber, offer additional protection.

Winemakers use amber glass or green glass bottles as their first line of defense against harmful light.

How can light strike be prevented?

Wine producers and consumers can take several practical steps to prevent light strike in wine:

Bottle selection: The type and color of wine bottles play a crucial role in protecting wine from light strike. Dark amber bottles block 90% or more of harmful light, making them the best choice for preserving wine quality. Green bottles block upwards of 50% of damaging wavelengths, while clear glass (flint glass) blocks as little as 10%, leaving wine much more vulnerable.

Flint glass is especially problematic for sparkling, white, and rosé wines, which are significantly more likely to be affected by light strike when bottled in clear glass. Using green or amber-colored bottles can significantly reduce the risk of wine faults caused by exposure to light.

Storage conditions: Wine should always be stored in the coolest, darkest part of the house to avoid exposure to harmful light. Keep bottles away from direct sunlight and fluorescent lighting, especially those emitting wavelengths of 200-420 nanometers (UV and blue light), that can trigger light strike. Wine cellars, closets, or dedicated wine refrigerators with solid doors are ideal for storage. Even indirect light exposure over extended periods can cause damage.

Retail display practices: Wine shops and supermarkets should avoid displaying wines under bright lights or in windows where sunlight can reach them. Consumers should avoid buying the first bottle presented and instead choose bottles still in their cardboard box, or select bottles from the back of the shelf in supermarkets, furthest away from the light. Wines meant for window displays should be dummy bottles, not actual inventory for sale.

UV-filtering film: Some retailers and storage facilities use UV-filtering window film or specialized lighting to reduce harmful light exposure while maintaining visibility. Additionally, orange coloured cellophane wrapping, as used by some producers, can filter up to 98% of harmful light and is especially effective for delicate wines.

Packaging innovations: The wine industry is exploring new packaging and lighting solutions to prevent wine faults caused by exposure to light. This includes experimenting with UV-filtering clear glass, alternative packaging like bag-in-box, cans, or opaque materials, and installing LED bulbs in storage areas to reduce UV and blue light exposure.

Quick consumption: Once a bottle is opened and cannot be protected by dark glass, it’s best consumed relatively quickly, especially if stored in a well-lit area.

Conclusion

Light strike in wine is apreventable but surprisingly common wine fault that can significantly diminish drinking pleasure. The distinctive sulfurous, wet wool character that develops from light exposure is one of the most recognizable off-flavors in wine, making affected bottles immediately unpleasant to most consumers. Fortunately, prevention is straightforward: proper bottle selection, storage in dark conditions, and mindful retail practices can almost eliminate this problem.

For wine enthusiasts, understanding light strike characteristics helps identifying faulty wines reinforcing the importance of proper storage, for producers, it underscores why dark glass bottles remain the industry standard despite the marketing appeal of showcasing a wine’s visual beauty. Whether you’re a casual wine drinker or a serious collector, keeping your wines away from light is one of the simplest yet most effective steps in preserving their intended flavor and quality.