Effect of light and temperature on 3-alkyl-2-methoxypyrazine concentration and other impact odourants of Riesling and Cabernet Franc wine during bottle ageing

Abstract

3-Alkyl-2-methoxypyrazines (MPs) are grape- and insect-derived odour-active compounds responsible for green and vegetative perceptions in wine, and at elevated concentrations are detrimental to wine quality. We examined the influence of light and temperature during cellaring on MPs and other impact odourants. Riesling and Cabernet Franc wines were supplemented with 30 ng/L of each of 3-isopropyl-2-methoxypyrazine (IPMP), 3-s-butyl-2-methoxypyrazine (SBMP) and 3-isobutyl-2-methoxypyrazine (IBMP), and stored under one of the following conditions: (i) at ambient temperature (22 °C) under fluorescent lighting, (ii) in the dark at ambient temperature, or (iii) in the dark at cellar temperature (12 °C). Additionally, for the light condition, wine was stored in clear, green or amber bottles. MPs did not vary consistently over time under any of these light or temperature conditions. IBMP decreased over 12 month by approx. 30% under all conditions in both Riesling and Cabernet Franc. Acetate esters also decreased with time, regardless of light or temperature conditions, while phenethyl acetate and isoamyl acetate decreased at a greater rate at 22 °C compared with 12 °C. Free and bound SO2 retention was higher in light-excluded conditions and influenced by bottle hue. Measures of browning and phenolic content were also affected to varying degrees by bottle hue and storage temperature. These results should assist winemakers in selecting bottle hues, and assist in selection of optimum storage conditions for preserving wine quality in both retail and cellar environments.