Selection and screening of yeasts for Sauvignon Blanc wines
Marie-Charlotte COLOSIO, Institut Français de la Vigne et du Vin, France
Sauvignon Blanc is one of the most widespread, popular and aromatic varieties throughout the world. Characterized by particularly strong but also very sensitive varietal flavors such as polyfunctional thiols whose perception thresholds are very low; winemakers are looking for more and more balanced fruitiness and greenness coming from the fermentation process in order to maximize consumer’s attraction. The choice of the yeast strain as well as the fermentation parameters are crucial to achieve their goal. This work presents a full study from the screening of a yeast bank collection towards genetic (IRC7 gene expression) and phenotypic (H2S, SO2, volatile acidity productions…) features to the characterization of the best strains through several lab- and micro-scale vinifications (aromatic and sensory attributes), dry yeast quality tests (E2U™ process) then extensive field trials. The results showed that there was first a strong correlation between the zygosity of the short or full-length allele of IRC7 (IRC7S or IRC7L) and the capabilities of the strains to release thiols, especially the 4-mercapto-4-methylpentan-2-one (4-MMP) imparting box tree, passion fruit aromas. Very different potentials to produce undesirable compounds in addition to acetate and ethyl esters were as well observed and lead to the selection of a IRC7L/IRC7L strain (A) mainly promoting all aromatic thiols and complex ethyl esters.
Influence of yeast strains and fermentation parameters on Sauvignon Blanc aromatic profiles
Nathan WISNIEWSKI, Fermentis, France
The study of the strain (A) in comparison with a IRC7S/IRC7S strain(B) showing a high acetate ester production capability through different fermentation temperature and nutrition regimes was performed. It clearly highlighted a higher release of thiols as well as a lower concentration of acetate esters at high temperature (i.e. 18°C vs 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 the release of 4-MMP by the strain A when the initial temperature was 18°C then lowered to 12°C after 3 days. This latter temperature regime was rated among the best ones as minimizing defects and maximizing the concentrations of most of the aromatic compounds what was judged very positively during a preliminary tasting. Strain A was then produced and dried through the E2U™ process and its viability and population were evaluated under very different rehydration conditions interms of media and stirring regimes. It showed a high resistance in all circumstances. Finally, 32 field trials in 6 different countries completed the characterization of this strain and confirmed its suitability for thiolic varieties with complex fruity notes (especially towards exotic, citrus and white fruits), a high crispness and overall good balance and persistence in mouth.