Assessment of color adsorption by yeast using Grape Skin Agar and impact on red wine color

Aim: Evaluating Saccharomyces cerevisiae strains for their color adsorption aptitude by using Grape Skin Agar in order to protect the phenolic compounds responsible for the color of red wines; proposing a suitable and innovative medium to be included among the tests currently used for wine strain selection. Methods and results: The strains were identified by fluorescence-Internal transcribed spacer (f-ITS) PCR and PCR-Restriction fragment length polymorphism (RFLP), confirmed by sequencing of ITS fragment, and tested for the parameter “aptitude to adsorb polyphenolic compounds” on the innovative chromogenic medium Grape Skin Agar. Laboratory-scale fermentations were carried out in must with and without SO2. The SO2 determined a decrease in tint, color intensity, and total polyphenol content. The strains M2V CHU7 and M2F CHU9 produced wines with the lowest color intensity, with and without SO2, respectively. By contrast, the strains M2F VUP4 and M2V CHU1, with and without SO2, respectively, produced wines with the highest color intensity, and therefore, they could improve the production of red wines. Conclusion: The study highlights great variability and significant differences among strains in regard to their aptitude to modulate wine color. Grape Skin Agar should be a useful medium to be included in the selection tests currently performed for S. cerevisiae strains. Significance and impact of the study: Our study confirms that yeast strains can modulate the chromatic properties of red wines according to their aptitude to adsorb polyphenols, as tested on Grape Skin Agar. Combining colored polyphenolic compound adsorption assay on Petri plate and laboratory-scale fermentation trials provides an effective way to test yeasts for their capability to improve the chromatic quality of the wines.