Importance of polyfunctional thiols on semi-industrial Gew\uc3\ubcrztraminer wines and the correlation to technological treatments

Thiol compounds responsible for tropical fruit associated aroma have been extensively studied over the last 20 years. The occurrence of their non-aromatic precursors in grapes and musts is reported largely mainly for the cultivar Sauvignon Blanc. The presence of these thiols as precursors or free molecules in grape, juice, and wine has been reported in several different varieties, suggesting that they are more or less ubiquitous both for Vitis spp. and interspecific hybrids. The biosynthetic pathways resulting in these compounds are yet to be completely elucidated, but, in the meantime, industry needs to improve technological knowledge to better manage winemaking steps to enhance the variety-dependent aroma of wine. In this work, we studied the implications of the use of grape skin tannins\u2014rich and poor in thiol precursors\u2014 on the final content of 3-sulfanylhexan-1-ol (3MH) and its acetate (3MHA) in wine and the effect in terms of sensory appreciability. The evaluation of 36 vinifications carried out in a semi-industrial scale permitted us to prove that only a tannin originally rich in precursors (High), when added to juice at the beginning of fermentation, enhanced both the concentration of precursors in the juice and the final concentration of aromatic thiols in the resultant wine. The 3MH and 3MHA developed as a consequence of the juice supplementation with tannin High and increased pleasantness and typicality of Gew\ufcrztraminer wines. A later supplementation with tannin High at the end of the alcoholic fermentation was sensorially not effective

Oxidative stress response and nitrogen utilization are strongly variable in Saccharomyces cerevisiae wine strains with different fermentation performances

We used RNA-sequencing (RNA-seq) to analyze the expression profile of four vineyard strains of Saccharomyces cerevisiae having different fermentation performances. The expression profiles obtained in two steps of the fermentation process were compared with those obtained for the industrial wine strain EC1118 and for the laboratory strain S288c. The two strains with low fermentation efficiency, namely, S288c and the vineyard strain R103, exhibited markedly different expression profiles when compared to the other four strains. We also found that the vineyard strains P283 and P301 are characterized by a high expression of the transcription factor Met32p in the first step of the fermentation. Met32p, in coordination with the Hap4p transcription factor, determined the over-expression of the genes involved in the respiration processes, in the response to oxidative stress and in the sulfur amino acids biosynthesis. These combined actions are likely to increase the level of antioxidants whose protective effect could contribute to improve the fermentation process. Gene expression and phenotypic data revealed that the vineyard strain P301 has low nitrogen utilization in comparison to the other wine strains, combined with high fermentation efficiency. Analysis of the genes involved in fermentation stress response revealed a lower expression in strains characterized by low fermentation efficiency, particularly in the first fermentation phase. These findings evidenced the high variability of transcriptional profiles among different wine yeast strains and clarify their connection with complex phenotypic traits, such as the fermentation efficiency and the nitrogen sources utilization

Effects on varietal aromas during wine making: a review of the impact of varietal aromas on the flavor of wine

Although there are many chemical compounds present in wines, only a few of these compounds contribute to the sensory perception of wine flavor. This review focuses on the knowledge regarding varietal aroma compounds, which are among the compounds that are the greatest contributors to the overall aroma. These aroma compounds are found in grapes in the form of nonodorant precursors that, due to the metabolic activity of yeasts during fermentation, are transformed to aromas that are of great relevance in the sensory perception of wines. Due to the multiple interactions of varietal aromas with other types of aromas and other nonodorant components of the complex wine matrix, knowledge regarding the varietal aroma composition alone cannot adequately explain the contribution of these compounds to the overall wine flavor. These interactions and the associated effects on aroma volatility are currently being investigated. This review also provides an overview of recent developments in analytical techniques for varietal aroma identification, including methods used to identify the precursor compounds of varietal aromas, which are the greatest contributors to the overall aroma after the aforementioned yeast-mediated odor release