What is the primary function of copper in a pot still during whiskey production?

The primary function of copper in a pot still during whiskey production is to remove undesirable sulfur compounds from the distillate. During fermentation, yeast produces various sulfur-containing compounds, such as dimethyl sulfide (DMS) and hydrogen sulfide (H2S), which can contribute to unpleasant aromas and flavors in the final spirit. These sulfur compounds can impart notes of cooked vegetables, rubber, or even sewage, negatively impacting the quality of the whiskey. Copper acts as a catalyst, reacting with these volatile sulfur compounds and converting them into less volatile or non-volatile compounds that remain in the still or are more easily removed during subsequent distillation steps. Specifically, copper reacts with hydrogen sulfide (H2S) to form copper sulfide (CuS), a solid that precipitates out of the distillate. Copper also promotes the conversion of other sulfur compounds into less offensive forms. The amount of copper surface area in the still, as well as the frequency and intensity of copper contact with the vapor, influence the effectiveness of sulfur removal. The shape and design of the pot still, including the presence of condensers and purifiers, are also factors that influence copper contact. Without sufficient copper contact, the resulting whiskey would likely have a harsher and less desirable flavor profile. Therefore, copper plays a crucial role in refining the spirit and producing the characteristic flavors associated with many types of whiskey.