Light Struck – Know Your Off-Flavors


Light-struck off-flavor, also known as skunked flavor, refers to an undesirable taste and aroma resembling skunk spray or wet cardboard in home-brewed beer. It occurs when beer is exposed to ultraviolet (UV) light, causing a chemical reaction that produces compounds responsible for the off-flavor. Understanding its characteristics, causes, and prevention methods can help home brewers produce beer free from light-struck off-flavors.


The aroma associated with light-struck off-flavors is often described as skunky or reminiscent of wet cardboard. It can be quite pronounced and overwhelming. The skunky aroma can mask or interfere with the intended aromatics of hops, malts, or other ingredients in the beer.


The flavor of light-struck off-flavors reflects the aroma, presenting skunky or cardboard-like notes on the palate. It can range from subtle and barely noticeable to strong and highly objectionable. Light-struck flavors can significantly affect the overall taste profile and enjoyment of the beer.


The primary cause of light-struck off-flavors in home-brewed beer is exposure to ultraviolet (UV) light. This exposure triggers a chemical reaction between light-sensitive compounds, typically derived from hops, and sulfur-containing compounds in the beer. This reaction results in the formation of off-flavor compounds resembling skunk spray.

Prevention: To prevent light-struck off-flavors in your home-brewed beer, consider the following measures:

  1. Light Protection: Shield your beer from UV light by using amber or dark-colored glass bottles, which offer better light protection compared to clear or green bottles. Alternatively, consider using opaque containers such as stainless steel kegs or aluminum cans.
  2. Light Exposure Minimization: Minimize the exposure of your beer to direct sunlight or other sources of UV light during the brewing, fermentation, and packaging processes. Store your beer in a dark or shaded area to avoid light exposure.
  3. Rapid Packaging: Package your beer promptly after fermentation is complete to minimize the time it spends in contact with light. Exposure to UV light is cumulative, so reducing the exposure time helps mitigate the risk of light-struck off-flavors.
  4. Proper Storage: Store your packaged beer in a cool and dark environment, away from sunlight or fluorescent lighting. Maintain consistent temperature conditions to avoid fluctuations that can trigger light-induced off-flavors.


Light-struck off-flavors can be an unwelcome characteristic in home-brewed beer, impacting both aroma and flavor. By understanding its description, aroma, flavor, causes, and prevention methods, home brewers can take proactive steps to protect their beer from light exposure and avoid light-induced off-flavors. By focusing on light protection, minimizing light exposure, prompt packaging, proper storage, and regular quality control, you can produce high-quality beer free from the interference of light-struck off-flavors.

Al Ingel

Al Ingel is a seasoned and accomplished home brewer with a brewing journey spanning 14 years. His passion for the craft has translated into numerous medals and best of show awards. Al's expertise extends beyond personal success, as he has collaborated with local breweries, seeing his creations enjoyed by the community. Al has generously shared his knowledge by mentoring home brewers, refining their techniques and enhancing their beer quality.

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