To record the effects of prolonged culture storage on the sugar tolerance of Zygosaccharomyces rouxii and Z. bailii, the fermentation behavior of three freshly isolated strains in four different glucose broths (aw values; 0.963, 0.936, 0.909 and 0.858, respectively) was compared with that of the same strains after 2 years of storage (a) on high-sugar agar slants with repeated subculturing and (b) in Biomalt (liquid malt extract) without subculturing. The trials with stock strains resulted in large reductions of both ethanol yield and production rate. Cells stored in liquid malt extract showed a slightly faster and stronger fermentation than cells maintained on agar slants. Therefore, for storage of osmotolerant culture collections use of natural liquid products such as Biomalt, without subculturing, is suggested.
1Present address: Fermentation Microbiology Laboratory, Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139.
2Department of Food Science.
3Department of Mathematics.