Increasing fermentation reliability and flavour compound formation by wine yeast FINAL REPORT to GRAPE AND WINE RESEARCH & DEVELOPMENT CORPORATION Project Number: UA 00/5 Principal Investigator: Dr Vladimir Jiranek Research Organisation: University of Adelaide Date: February 2003 1 Final Report - February 2003 Project Title: Increasing fermentation reliability and flavour compound formation by wine yeast. Project File No: UA 00/5 Prepared by: Vladimir Jiranek and Jennie Gardner School of Agriculture and Wine, The University of Adelaide, PMB 1 Glen Osmond, SA 5064. Ph: (08) 8303 6651, email:
[email protected] Abbreviations: CDGJM, chemically defined grape juice medium, FAN, free amino nitrogen, HNE, high nitrogen efficiency, PCR, polymerase chain reaction, ?, deletion, HPLC, high performance liquid chromatograph. Background The availability of a variety of wine yeast strains allows the winemaker to have greater control over the characteristics of oenological fermentation. Even so problem fermentations, specifically those which are sluggish or fail to complete are common. With the recognition of the central role of juice nitrogen deficiencies in many of these problem ferments, the use of nitrogen supplements has become widespread and routine. Nevertheless this strategy is not always successful. Nitrogen additions are a valuable tool for prevention and control of stuck fermentations, yet the timing of addition is critical (Bely et al., 1990) and the presence of residual nitrogen might favour microbial spoilage (Henschke and Jiranek, 1993) and formation of a carcinogen, ethyl carbamate (An and Ough, 1991). At any rate it is desirable to reduce additives made to premium wines. Another option for the prevention of stuck fermentation, which has yet to be employed is the use of “nitrogen efficient” wine yeast strains (Jiranek et al., 1991, 1995, Gardner et al., 2002).