When is a light-exposed beer most susceptible to skunking?

A light-exposed beer is most susceptible to skunking within the first few minutes of exposure to light. This rapid sensitivity occurs because certain compounds in hops, particularly iso-alpha acids, can react with ultraviolet (UV) light. When beer is exposed to light, particularly sunlight or fluorescent light, these compounds can quickly degrade, resulting in the formation of mercaptan, which gives the beer a "skunky" aroma and flavor.

This reaction is particularly pronounced in lighter-colored bottles, which allow more light to penetrate compared to darker bottles designed to protect the beer from light exposure. Therefore, minimizing the time that beer is exposed to light, especially in the initial moments, is crucial to preserving its intended flavor profile.