A stratified sampling approach to investigate the impact of climate and maturity on the aroma and phenolic composition of grenache grapes and wines within the poctefa area

Abstract

Context and purpose of the study. Climate change is affecting wine production and induces a large variability in wine composition between vintages. In most cases, this may take the form of altered precipitation regimes and higher temperatures during maturation which may induce a decoupling between technological and phenolic maturations involving a delay, high sugar concentrations and aromatic defects at harvest. This is particularly observed for Grenache, a cultivar well represented in France and Spain within the POCTEFA Pyrenean foothills. The aim of this study was to investigate during two consecutive seasons the impact of climate and maturity on the aroma and phenolic composition of wines made from this cultivar.

Material and methods. For the main PDO located in Pyrénées-Orientales, Aragon, Navarra and La Rioja growing Grenache, normal climatic data (1981-2010) were collected and used to calculate several bioclimatic variables. Data were treated through k-means clustering analysis to determine three homogenous climatic areas. A stratified sampling approach was used to select 30 Grenache vineyards across Spain and France (20/10), and the three climatic area previously identified (10/10/10). For each site, grape samples were harvested at three time points during maturation, the first one corresponding to a sugar concentration of 21.0 ± 2.0 °Brix (P1), the second one (P2) to 10-14 days after P1, and the third one (P3) to 10-14 days after P2. These grapes were used to determine classical enological parameters, to monitor phenolic composition according to the Cromoenos® method, to obtain a berry volatile fingerprint through SIFT-MS analysis and to produce hydrolyzed mistelle – a model to predict the aroma potential of grapes. At P1 and P2, experimental wines were produced under minivinification techniques to analyze wine aroma composition using gas chromatography techniques and to perform descriptive sensory analysis.

Results. The samples obtained in 2024 are presently being analyzed and the results will be available soon. The findings should emphasize the relative importance of climate and maturity on aroma composition, and enable to determine optimal climatic conditions to avoid the appearance of aromatic defects. They shall also be useful to identify new viticultural regions, especially at higher elevation, more suitable for the future production of faultless wines in a context of changing climate.