Yeast strains used for sake brewing are, in general, difficult to sporulate and incompetent at mating with others.We isolated eight mating-competent mutants from strain Kyokai no.7 and three other strains for ginjo-shu making with the aid of pNN63 and pNN64 plasmids.These plasmids were collstructed by NAKAZAWA et al., (J.Ferment.Bioeng., 78: 6-11, 1994) for the detection of the mating competency of the host cells.With these mating-competent mutants and three haploid strains used in genetic studies, we constructed 21 putative hybrids by crossing, and found that 8 of the 21 isolates are putative triploids and the remaining 13 are tetraploids.To see their hybridity, the putative hybrids were examined for their electrophoretic karyotypes and sporulation abilities.We found that 17 of the 21 isolates are hybrids.The sake brewing characteristics of the hybrid clones were examined on a small scale artificial sake mash, then by 1 kg pilot brewing using five selected isolates.The results suggested that some of the hybrids are superior for sake brewing with regard to their taste and aroma, but none were superior to Kvokai no.7 and no.901 with regard to mash fermentability.
