Freeze resistant bakers' yeast

A diploid hybrid yeast strain having fermentative ability on non-sugar bread dough and freeze resistance, produced by the steps comprising:

• (1) germinating the spores of the following two yeast strains:
• (a) a first diploid strain of Saccharomyces cerevisiae which has a non-freeze fermentative ability on non-sugar dough of at least 140 ml, wherein said non-freeze fermentative ability is qualified by measuring the amount of carbon dioxide generated when the first diploid strain is allowed to ferment non-sugar dough for 2 hours at 30.degree. C., and
• (b) a second diploid strain of Saccharomyces cerevisiae which has a residual fermentative ability rate on non-sugar dough of at least 80%, wherein said residual fermentative ability rate is quantified by preparing a first and second batch of non-sugar dough containing the second yeast strain, said batches being equivalent, fermenting said first and second batches at 30.degree. C. for 60 minutes, freezing said second batch at -20.degree. C. for 7 days and then thawing at 30.degree. C. for 30 minutes, fermenting said first and second batches at 38.degree. C. for 60 minutes and measuring the carbon dioxide generated for each batch;
• (2) recovering haploid yeast strains from said germinated first and second diploid strains, respectively;
• (3) conjugating said haploid yeast strains;
• and
• (4) selecting from said conjugation a diploid hybrid yeast strain having a non-freeze fermentative ability on non-sugar dough of at least 140 ml and a residual fermentative ability rate, using non-sugar dough, of at least 80%, wherein said diploid hybrid yeast strain is a biologically pure culture of Saccharomyces cerevisiae having all the identifying characteristics of FTY-3 (FERM BP-2326).