A thermotolerant alcohol-producing yeast strain, Kluyveromyces marxianus IMB3 was shown to grow on sucrose (10% [w/v]) containing media at 45-degrees-C. Under such conditions the organism reached stationary phase within 20 hours and yielded ethanol concentrations in the region of 33g/L. During growth on sucrose containing media the organism was found to produce a cell- associated activity capable of hydrolysing sucrose. This activity was shown to have a Km of 5.0mM when sucrose was used as the substrate. In addition the enzyme was shown to have a pH optimum of 5.0 and a temperature optimum of 50-55-degrees-C and under those conditions the enzyme was shown to be relatively thermostable.