Sour cream, crème fraîche, and buttermilk are indigenous to relatively cool western and northern Europe, where milk spoils more slowly and was often left overnight toseparate into cream for buttermaking. The lactococci and Leuconostoc species that produce them are “mesophilic,” or moder-ate-temperature lovers that probably first got into milk from particles of pasturage on the cows’ udders. They prefer temperatures around 85ºF/30ºC but will work well below that range, and develop moderate levels of lactic acid during a slow fermentation lasting 12 to 24 hours.