Jessica Noble,* Marion Bastien, Anthony Silvano, and Anne Ortiz-Julien
*Lalemand Oenology, 19 Rue des Briquetiers, 31702 Blagnac, France 
(jnoble@lallemand.com)

Volatile thiols are a well-known family of aroma compounds that, even at low levels, can have a significant affect on the fruity quality of wines. 3MH, 3MH-A, and 4MMP are some of the more well-known aromatic thiols. These compounds confer grapefruit, passion fruit, and boxwood notes in thiolic white and rosé wines when revealed from their odorless form. However, thiol precursors are now known to be present in important red grape cultivars (e.g., Syrah, Cabernet Sauvignon, Merlot, Pinot noir). When revealed, the descriptors used to describe the same thiolic compounds in red wines are black fruits, red fruits, and spice. The aromatic profile of thiols in red wines is complex and is thought to be due to interactions between thiols and other molecules, such as terpenes and esters.

The enzymatic action of yeast is essential to cleave the non-volatile, odorless precursors and release the volatile, aromatically active thiols. Using a cell division approach, we selected a new Saccharomyces yeast with the full potential for thiol revelation due to its highly efficient β-lyase enzyme activity. This enzyme activity is due to the yeast possessing the correct form of the IRC7 gene. The sequence of the IRC7 gene is not identical among all yeasts. Some yeasts have a truncated version of this gene, missing 38 base pairs. This version encodes a non-functional enzyme. Other strains can have a point mutation, close to the enzyme’s active site, which has a strong negative effect on its activity.

For maximum β-lyase activity, the yeast must possess the right combination of the gene, which is the long, unmutated form (IRC7L/L Ref/Ref). This new yeast strain shows very significant thiol revelation, well above average concentration, with a very significant increase in aromatic freshness and black and red fruit notes.

Funding Support: Lallemand Oenology