Cicerone Certified Beer Server Practice Exam

What must be eliminated to prevent skunking in beer?

1. Exposure to air

2. Exposure to sunlight and fluorescent light

3. High temperatures

4. Using old hops

The correct answer is: Exposure to sunlight and fluorescent light

To prevent skunking in beer, it is crucial to eliminate exposure to sunlight and fluorescent light. When beer is exposed to these light sources, a chemical reaction occurs, particularly involving the iso-alpha acids from hops, which can lead to the formation of 3-methylbut-2-ene-1-thiol, a compound that imparts a skunky aroma and flavor. This reaction can happen quite rapidly, especially in lighter-colored bottles that allow more light penetration. While exposure to air, high temperatures, and the use of old hops can all negatively affect the quality of beer, they do not specifically lead to skunking in the same way that light exposure does. Air can promote oxidation, leading to stale flavors, and high temperatures can accelerate spoilage and other undesirable changes. Old hops may contribute to off-flavors due to loss of freshness or changes in the hop oils, but they do not directly cause skunking. Therefore, the most effective measure to prevent skunking is to ensure that the beer is protected from light.