No abstract

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.

No abstract

In recent years, studies have reported the positive influence of non-Saccharomyces yeast on wine quality. Many grape varieties under mixed or sequential inoculation show an overall positive effect on aroma enhancement. A potential impact by non-Saccharomyces yeast on volatile and non-volatile compounds should benefit the flavor of Riesling wines. Following this trend, four separate sequential fermentations (using the non-Saccharomyces yeasts Torulaspora delbrueckii, Metschnikowia pulcherrima, Pichia kluyveri, and Lachancea thermotolerans with Saccharomyces cerevisiae) were carried out on Riesling must and compared to a pure culture of S. cerevisiae. Sequential fermentations influenced the final wine aroma. Significant differences were found in esters, acetates, higher alcohols, fatty acids, and low volatile sulfur compounds between the different trials. Other parameters, including the production of non-volatile compounds, showed significant differences. This fermentation process not only allows the modulation of wine aroma but also chemical parameters such as glycerol, ethanol, alcohol, acidity, or fermentation by-products. These potential benefits of wine diversity should be beneficial to the wine industry.

Most wine aroma compounds, including the varietal fraction, are produced or released during wine production and derived from microbial activity. Varietal aromas, typically defined as terpenes and thiols, have been described as derived from their non-volatile precursors, released during wine fermentation by different yeast hydrolytic enzymes. The perception of these minority aroma compounds depends on the chemical matrix of the wine, especially on the presence of majority aroma compounds, such as esters or higher alcohols. Strategies aiming to reduce the production of these masking flavors are on the spotlight of enology research as a way to better define varietal standard profiles for the global market. Using a natural white must from Verdejo variety (defined as a thiol grape variety), here we describe the analytical and sensorial impact of using, in sequential inoculations, a selected strain of Metschnikowia pulcherrima, in combination with two different Saccharomyces cerevisiae strains. An increase in the levels of the thiol 4-MSP (4-methyl-4-sulfanylpentan-2-one) over its sensory threshold, together with a decrease in higher alcohol production, was observed when M. pulcherrima was used. This has an important impact on these wines, making them fruitier and fresher, always preferred by the sensory panel.