Grape quality: Research on the relationships between grape composition and climatic variables

The first step in order to develop an optimal QC system (quality control), must be the assignment of a qualitative value to grapes, just prior to crushing at the winery. Quality depends on all levels of production from climatic conditions to transformation methods, in enological industry. The aim of this research was exploring the influence of climatic factors on grapes compositive variables under the assumptions that the other factors were constant. The grape analysis was made considering the grapes taken by a centralised winery located in north-east of Italy in a region called Friuli Venezia Giulia from 1990 to 1993. The number of grape samples taken was 3.475. The analytical variables measured were: Babo degrees (B), total titratable acidity (g/1), and pH by means an automatic analytical station. The climatic variables were determined by automatic multisensor machines of regional climatic network (ERSA). Climatic variables were assessed using several bioclimatic indexes i.e. Ribereau-Gayon one. The results have been treated by some exploratory data analysis techniques such as fuzzygrams, linear regression (ordinary least squares) and robust regression (least absolute value), searching any relationships among bioclimatic indexes and composition variables (Babo degrees and total titratable acidity). There were no significant relationships between temperature (and relative indexes) and composition variables, but there were relationships between cumulative rain (and relative indexes like Ribcreau-Gayon index) and total titratable acidity. By using all this information we have computed a global quality index of grapes based on climatic condition (cumulative rain) of the viticultural season.