Definition: By-products from the process of fermentation of alcohol that contribute most of the unique tastes, aromas and colors of each of the different spirits. Congeners are also largely responsible for hangovers: the more Congeners consumed, the higher chances are that one will have a hangover.
Fewer Congeners are removed during the production of darker spirits like brandy, whiskey and red wine which explains their stronger taste and the higher likelihood of a hangover the next day. On the other hand, clearer liquids such as vodka contain the smallest amount of Congeners because of the distillation process. Likewise the cheaper a spirit is, the less it has been processed to remove impurities.