PHOTO OXIDATION OF LUGANA WINES: INFLUENCE OF YEASTS AND RESIDUAL NITROGEN ON VSCS PROFILE

Abstract

Lugana wines are made from Turbiana grapes. In recent times, many white and rosé wines are bottled and stored in flint glass bottles because of commercial appeal. However, this practice could worsen the aroma profile of the wine, especially as regards the development of volatile sulfur compounds (VSCs). This study aims to investigate the consequences of exposure to light in flint bottles on VSCs profile of Lugana wines fermented with two different yeasts and with different post-fermentation residual nitrogen.

Wines were produced with a standard protocol with Turbiana grapes with two different yeasts. During the alcoholic fermentation of the must additions of inorganic or organic nitrogen supply were made. Wines were bottled in inert conditions in flint bottles and exposed for 30 days to light at controlled temperature of 20°C. Subsequently the VSCs profile of the wines was analyzed using GC-MS techniques. Wines were then subjected to the sorting task sensory analysis.

The VSCs profile analyzed showed significant differences for carbon disulfide, methanethiol, dimethyl sulfide and dimethyl trisulfide. The variability given by the yeasts leads to statistically significant differences only for diethyl sulfide and dimethyl disulfide. Regarding the differences given by the residual nitrogen, the samples in the transparent bottles with higher residual nitrogen showed a greater increase of sulfur compounds. Wines with a higher organic residual nitrogen showed significant differences for carbon disulfide, methanethiol, dimethyl sulfide, diethyl sulfide and dimethyl disulfide. Linear correla-tions were found between residual nitrogen in wines and carbon disulfide, methanethiol and dimethyl sulfide. The sensory analysis sorting task highlighted the formation of two main classifications made up of wines with a low residual nitrogen and wines with a high residual organic nitrogen. This study showed the great impact of light exposure in transparent bottles has on the aromatic and sensory quality and how the post-fermentation residual nitrogen, especially for organic nitrogen, in the wines can worsen this qualitative deterioration. This underlines the impact of the presence of residual nitrogen on the stability of the wine during maturation, placing the attention on the dose of nitrogenous nutrition introduced during alcoholic fermentation. The choice of yeast strain seems to have an influence, albeit minor, on the development of VSCs compounds in wines exposed to light.

ACKNOWLEDGMENTS: The present work was supported by Laffort, France.