Anne Flesch, Etienne Dorignac,* and Marie-Charlotte Colosio (IFV Nantes)
*Fermentis, 137 rue Gabriel Peri, 59170 Marcq-en-baroeul, France (e.dorignac@fermentis.lesaffre.com)

Sauvignon blanc is characterized by particularly strong but also very sensitive varietal flavors such as polyfunctional thiols, which have very low perception thresholds. The choice of yeast strain and fermentation parameters is crucial to achieve winemakers’ goals. This work presents a full study, from the screening of a yeast bank collection for genetic (IRC7 gene expression) and phenotypic (H2S, SO2, and volatile acidity production) features, to the characterization of the best strains through several lab- and microscale vinifications (aromatic and sensory attributes), and then extensive field trials. There was a strong correlation between the zygosity of the short or full- length allele of IRC7 (IRC7S or IRC7L) and the capability of the strains to release thiols, especially 4-mercapto-4-methylpentan-2-one (4-MMP), which imparts box tree and passion fruit aromas. Very different potentials to produce undesirable compounds in addition to acetate and ethyl esters were also observed and led to the selection of a IRC7L/IRC7L strain (A) that primarily promoted all aromatic thiols and complex ethyl esters. The study of this strain in comparison with a IRC7S/IRC7S strain (B) with a high acetate ester production capability through different fermentation temperature and nutrition regimes was performed. It clearly highlighted a greater release of thiols and lower concentration of acetate esters at high temperature (18°C versus 12°C) and
confirmed the importance of the nitrogen catabolite repression regulation system in yeast. The supply of ammonium at yeast inoculation indeed drastically lowered and even blocked release of 4-MMP by strain A when the initial temperature was
18°C, then lowered to 12°C after three days. This latter temperature regime was rated among the best for minimizing defects and maximizing the concentrations of most aromatic compounds and was judged very positively during a preliminary tasting.

Funding Support: Lesaffre-Fermentis Institut Français de la Vigne et du Vin, Nantes- France