Abstract: PURPOSE OF WORK: To elucidate the mechanisms of high performance by soy peptides during yeast fermentation in low temperature stress conditions and to identify a type of soy peptide that is suitable for yeast fermentation at low temperatures during brewing. The growth of a tryptophan auxotrophic yeast strain in a medium containing soy peptide (SP) was compared with that in a medium containing an equivalent composition of free amino acid mixture. At low temperature (10 ?C), the cells grew in the medium containing SP but not in the medium containing the free amino acid mixture. Free tyrosine and phenylalanine inhibited the uptake of free tryptophan at low temperatures whereas most of the tyrosine and phenylalanine were present as oligopeptides in SP. The cells could transport free tryptophan without being inhibited by free tyrosine and phenylalanine at low temperatures in the medium containing SPs. Soy peptide-AM that lacks free tyrosine and phenylalanine was more effective in promoting cell growth compared with a highly hydrolyzed version.