Steyn, P.L.2022-01-122022-01-1219/8/20211993*http://hdl.handle.net/2263/83241Dissertation (MSc (Agric))--University of Pretoria, 1993.The aim of this study was to investigate methods of obtaining yeast strain(s) with improved fermentation rates compared with industrially used yeast strains. The criterion was that strains had to ferment molasses faster than the control strain (Y1085) when tested in a standard laboratory scale molasses fermentation test. A technique for pre-screening large numbers of yeast strains with improved fermentation rates before testing them 1n the molasses fermentation test was developed and proved easy and reliable. The isolation of ethanol-, osmo- and thermo-tolerant Saccharomyces yeast strains with increased fermentation rates from natural sources was attempted. 369 yeast strains were isolated and evaluated 1n the Preliminary Test. With the Preliminary Test 179 strains were selected. Forty strains performed similar or better than the control strain in the Preliminary Test. Fourteen strains had improved fermentation rates ranging from 1% to 13% 1n a standard laboratory scale molasses fermentation test compared with the control strain. Ten of these which had more than 3% improvement over the control strain had potential for future evaluation and possible use in the industry. The improvement of the fermentation rate of yeast strains with classical genetic techniques, hybridization and mutations, and methods for the selection of hybrids and mutants suitable for ethanol production, were investigated. 1018 hybrids and mutants were obtained. Sixteen strains tested over a period of 16 months showed limited improvement. The percentage improvement in the fermentation of molasses after 50 hours compared with that of the control strain ranged from 0% to 5,9%. This was lower than the improvement obtained with the isolated yeast strains. From the results it appears that isolation of strains from natural sources, especially sugar mills, remains a viable option for obtaining "new" yeast strains for ethanol production.en© 2021 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.UCTDYeast strainsethanol productionDissertation