Copper Stills in Alcohol Distillation
Stills play an essential part in alcohol distillation by vaporising and isolating low-strength alcoholic compounds from other liquid components, and then coming in contact with copper surfaces which catalyze chemical reactions that remove undesirable odours and flavours, leaving your spirit with an inviting bouquet and taste that leaves it smooth on the palate.
Copper is an extremely reactive metal that reacts with molecules in alcohol vapor to form complexes that break down volatile sulphur compounds like Dimethyl-di-sulfide (which smells of rotting vegetables) into Sulpher dioxide and Ethyl Acetate which have fruity aromas reminiscent of apples or pears.
Copper has long been used in distillation as it acts as an effective filter by binding aldehydes to its surface and binding with them so they are discharged through copper sulphate in the spent wash. Copper also acts as an attractant and binding agent in that certain compounds – like aldehydes – cling onto it, acting like an attractant to attract or attract other compounds onto itself, such as aldehydes. Finally, when used as a form of filtration it also attracts and binds other molecules such as aldehydes are then discharged along with copper ions or oxide layers and discharged as part of the spent wash with copper sulphate discharged with discharge of any spent wash wash water discharged.
Size and shape of stills play an integral part in producing quality new make spirits. A widening neck of a copper still gives rising vapours more surface area to interact with, producing lighter new make spirits than one with narrower walls or narrower neck.
Copper stills can be costly to operate due to their need for thick walls that can withstand the stresses and strains associated with distillation processes, while their maintenance requires frequent repairs due to rapid oxidization. As a result, many distilleries opt for hybrid stills wherein some components of the still are made from stainless steel rather than pure copper, providing greater control of copper contact.