Experimental Production of Fortified Sweet Wine by Single-Stage Continuous Fermentation. I. Evaluation of Five Strains of Saccharomyces Cerevisiae and Saccharomyces Bayanus

¹ S. Smith & Son Pty. Ltd., Angaston, South Australia 5353
² University of New South Wales, Kensington, New South Wales 2033, Australia
³ University of New South Wales, Kensington, New South Wales 2033, Australia.

The fermentation characteristics of four strains of Saccharomyces cerevisiae and one of Sacch. bayanus were evaluated in a single-stage continuous fermentor with a grape-juice substrate. The fermentor was operated at 4.5% ethanol and 26°C; the productivity of the fermentor under these conditions ranged from 1.2 to 3.4 g EtOH/l/hr, with Sacch. bayanus strain 505 showing the highest productivity. Yeast productivity ranged from 4.2 to 25.4 x 10⁷ molecules EtOH/cell/sec.

The strains flocculated strongly and their cells elongated during continuous fermentation. The quality of the fortified sweet wines, adjusted to 4.8° Brix and 18% ethanol, prepared from all five strains was judged commercially acceptable. No contamination of the fermentation by natural bacteria and yeasts was experienced, although some of the wines prepared from one of the test strains had a strong H₂S-type odor.