What temperature effect results in more astringent and harsh congeners during fermentation?

High fermentation temperatures, often referred to as "hot," lead to the production of more astringent and harsh congeners. This is because yeast metabolism increases at elevated temperatures, leading to a higher rate of chemical reactions. As a result, there is an increase in the production of undesirable byproducts during fermentation, including certain types of fusel alcohols and other congeners that contribute to off-flavors.

In contrast, lower temperatures might slow down fermentation and reduce the production of these harsh congeners, yielding a smoother and cleaner spirit. Moderate temperatures are typically more conducive to balanced fermentation, allowing yeast to thrive without producing excessive undesirable compounds. Room temperature tends to fall into a more balanced range but doesn't necessarily ensure the same level of control over congeners as a cooler fermentation might.

The hot condition significantly influences the flavor profile of the final product, making it essential to manage fermentation temperature carefully in whiskey production to achieve desired taste characteristics.