The present invention relates to a method for selecting a strain of an organism capable of improved consumption of a mixed substrate comprising two or more carbon sources as compared to a reference strain of the organism, which method comprises: growing a population of the reference strain of the organism in the presence of the two or more carbon sources, wherein the number of generations of growth of the said population on each of the said carbon sources is at least about 50% of the number of generations of growth on the carbon source most preferred by the organism; and selecting the resulting strain of the organism, thereby to select a strain of the organism capable of improved consumption of a mixed substrate comprising the two or more carbon sources as compared to the reference strain of the organism. The invention also relates to strains of organisms selected using such a method. Strains of organisms identified using the selection method may be used in fermentation processes in which a mixed substrate is used.