Cultured butter is made in the European-style with pasteurized cream in a churn just like regular butter, but with one added step. After pasteurization, the cream is fermented by adding a carefully selected bacterial culture. The cream rests for one day in a vat to allow the culture to produce a complex blend of flavor compounds. This is the source of the flavor difference between cultured butter and sweet cream, or American-style butter. After the fermentation, the cream is churned into butter.