Jessica Noble, Olivier Teuf, Gordon Specht, and Anne Ortiz-Julien*
*Lallemand SAS, 19 rue des Briquetiers, 31702 Blagnac, France (ajulien@lallemand.com)

Varietal thiols are key compounds of the fruity character in white wines. 3MH, its acetate, A3MH, and 4MMP are among the most-represented thiols, typical of varieties such as Sauvignon blanc or Colombard, but also contributing to the complexity of numerous others. Varietal thiols are present in the must as combined inodorous and non-volatile precursors and are released by yeast enzymatic activity. The precursors and pathways involved are not all known, but the carbon-beta-sulfur lyase family has been identified to be responsible for a significant part of this conversion. However, all yeasts are not equal in their capacity to release varietal thiols. It has been demon­strated that different alleles of the gene IRC7, encoding for a beta-lyase with a high affinity for cys-4MMP, are responsible for huge variations in the volatile thiol release efficiency. We identified a yeast strain from our collection that possesses one copy of the allele encoding for the most efficient version of Irc7p. We implemented a sporula­tion-based strategy to generate a new strain homozygous for this allele, thus express­ing a full potential for volatile thiols release. This new yeast produced very high levels of 4MMP and other volatile thiols in wines and resulted in complex aromatic profiles with more vegetal character and citrus, yellow, and exotic fruit notes.

Funding Support: Lallemand SAS