As a sommelier and brewer, I have had the opportunity to observe and study the effects of various factors on alcoholic beverages, including bourbon. When bourbon sits out for an extended period of time, several changes can occur, both in terms of taste and appearance.
One of the first things to happen is evaporation. Alcohol, being a volatile compound, tends to evaporate faster than water. This means that if you leave a glass of bourbon out for a while, the alcohol content will gradually decrease. This can have an impact on the overall flavor profile, as alcohol often contributes to the perceived “heat” or “burn” of the spirit. So, if you leave bourbon out for too long, you may notice a milder taste compared to when it was freshly poured.
Another consequence of evaporation is the concentration of certain compounds in the bourbon. As the alcohol evaporates, the remaining liquid becomes more concentrated with other components, such as fatty acids, esters, and other volatile compounds. These compounds can significantly impact the flavor and aroma of the bourbon. For example, fatty acids can contribute to a richer and oilier mouthfeel, while esters can add fruity and floral notes.
However, as the bourbon continues to sit out, a point may be reached where some of these compounds begin to precipitate out and form sediments. This can result in the bourbon becoming cloudy or hazy in appearance. The precipitated compounds can include fatty acids, tannins, and other insoluble materials. This is similar to what can happen when you chill a whiskey or bourbon, causing the fatty acids to solidify and create a cloudy appearance.
It's important to note that the exact changes that occur when bourbon sits out can vary depending on several factors, such as the specific composition of the bourbon, the temperature and humidity of the environment, and the duration of the exposure. Additionally, the impact of these changes on the flavor and aroma of the bourbon can be subjective, as different individuals may have different preferences.
To summarize, when bourbon sits out for a prolonged period, the alcohol content gradually decreases due to evaporation. This can result in a milder taste compared to freshly poured bourbon. Concurrently, the remaining liquid becomes more concentrated with other compounds, which can influence the flavor and aroma. Eventually, some of these compounds may precipitate out, leading to a cloudy appearance. The specific changes that occur can be influenced by various factors and can vary from one bourbon to another.