How does humidity affect the proof of a spirit?

Humidity affects the proof of a spirit primarily through the process of evaporation. Spirits are typically stored in barrels or bottles where they can come into contact with the surrounding environment. In a humid environment, the water content in the air is higher. As a result, when a spirit is stored in such conditions, the evaporation rate of alcohol is generally higher than that of water. This leads to a situation where the concentration of alcohol decreases, thereby lowering the overall proof of the spirit over time.

As the alcohol evaporates more rapidly, the remaining liquid has a higher concentration of water, resulting in a lower proof. It's important to note that while heat can also influence evaporation and proof, the specific interaction between humidity and alcohol concentration is crucial for understanding this relationship. This concept highlights the importance of environmental factors on the aging and storage process of spirits, emphasizing that humidity plays a critical role in the dynamics of spirit proof over time.