Thiaisoleucine Resistant Mutants in Saccharomyces

Four presumably dominant thiaisoleucine resistant mutants of a brewing strain of Saccharomyces carlsbergensiswere previously shown to produce more D-amyl alcohol than the parent strain when grown in synthetic minimalmedium with aeration. In the present work an increased production of o-amyl alcohol was also found infermenting wort under brewing conditions resulting in a beer with an altered ratio between D-amyl alcohol andisoamyl alcohol. The synthesis of 2,3-pentanedione plus its precursor, a-aceto-a-hydroxybutyrate, was generallyhigher in the mutants. The mutants showed a somewhat lower rate of increase in cell concentration duringfermentation than the parent strain. With respect to other analytical data and taste, the three mutants isolatedafter moderate mutagenesis did not show deviations outside the range of the parent. One mutant obtained from amore heavily mutagenized culture deviated in several respects.