Effects of post-fermentative cold maceration on chemical and sensory characteristics of Syrah, Cabernet Franc and Montepulciano wines

Climate change and harvest date decisions have led to the evolution of must quality over the last decades. Increases in must sugar concentrations are among the most obvious consequences, quantitatively. Saccharomyces cerevisiae is a robust and acid tolerant organism. These properties, its sugar to ethanol conversion rate and ethanol tolerance make it the ideal production organism for wine fermentations. Unfortunately, high sugar concentrations may affect S. cerevisiae and lead to growth inhibition or yeast lysis, and cause sluggish or stuck fermentations. Even sublethal conditions cause a hyperosmotic stress response in S. cerevisiae which leads to increased formation of fermentation by-products, including acetic acid, which may exceed legal limits in some wines.

Tannin, anthocyanins and their reaction products play a major role in the quality of red wines. They contribute to their sensory characteristics, particularly colour and astringency. Grape tannins and anthocyanins are extracted during red wine fermentation. However, their concentration and composition change over time, due to their strong chemical reactivity1. It is also well known that yeasts influence the wine phenolic content, either through the release of metabolites involved in the formation of derived pigments1, or through polyphenol adsorption2,3.

2,5-Dimethyl-4-hydroxy-3(2H)-furanone (furaneol) is an important aroma compound in fruits, such as pineapple and strawberry, and is reported to contribute to the strawberry-like note in some wines. Several grapevine species are used in winemaking, and furaneol is one of the characteristic aroma compounds in wines made from American grape (Vitis labrusca) and its hybrid grape, similar to methyl anthranilate. Muscat Bailey A is a hybrid grape variety [V. labrusca (Bailey) x V. vinifera (Muscat Hamburg)], and its wine is one of the most popular in Japan. The inclusion of Muscat Bailey A in the ‘International List of Vine and Varieties and their Synonyms’ managed by the ‘International Organisation of Vine and Wine (OIV)’ in 2013 has further fueled its popularity among winemakers and researchers worldwide.

Grapevine berries produce thousands of secondary metabolites of diverse chemical nature that have been largely detailed in the past due to their importance for defining wine quality. The wide Vitis vinifera diversity, resulting in thousands of different varieties well detailed in many studies regarding berries, is still not investigated in vegetative organs, leaves in particular. Deepening knowledge related to this aspect could be of great interest for many reasons (for example the possibility of using leaf extract for pharmaceutical, cosmetic and nutrition purposes) but, above all, for understanding the susceptibility of different grapevine varieties to pathogens.

Bacterial malolactic fermentation (MLF) has a considerable impact on wine quality. The yeast strain used for primary fermentation can consistently stimulate (MLF+ phenotype) or inhibit (MLF- phenotype) malolactic bacteria and the MLF process as a function of numerous winemaking practices, but the molecular evidence behind still remains a mystery. In this study, such evidence was elucidated by the direct comparison of extracellular metabolic profiles of MLF+ and MLF- yeast phenotypes. Untargeted metabolomics combining ultrahigh-resolution FT-ICR-MS analysis, powerful machine learning methods and a comprehensive wine metabolite database, discovered around 800 putative biomarkers and 2500 unknown masses involved in phenotypic distinction.