Incidences of the climate, the soil and the harvest date on Colombard aromatic potential in Gascony

This experiment tries to characterize the role of soil, climate and harvest date on the composition of grape-derivated thiols, 3-mercapto-hexanol (3MH) and 3-mercapto-hexile acetate (A3MH), in the white wines from Colombard varieties in Gascony (South-West of France). A network of 6 plots has been observed since 1999 on different pedologic units. The plots have common agronomical characteristics, plantation spacing (2,900 to 3,500 vines per ha), plantation aging (1985-1990), strength conferred by rootstock (SO4, RSB), soil management (grass covered 1 by 2) and training system (vertical shoot positionning pruned in single Guyot). Meteorological stations are located near the plots. Climatology is characterized by sums of temperatures and rainfalls during the vegetative growth. Vine water status is determined by stem water potential. The results show that it is possible to define 2 major kinds of soil, confirmed by measurement of primary shoot growth rate and his date of cessation growth. Grapes are harvested in 3 times between 40 and 55 days after veraison and vinified on a standart protocol. Grape-derivated thiol rate (3MH, A3MH) quantified in wines is dependant on the vintage conditions. Temperature variables seem to contribute to the presence of sulphur compounds in wines as well as the length of non-cutted primary shoot. An early harvest date does not benefit to increase grape-derivated thiols quantity in Colombard wines. Late harvest wines show better mouth balance and better aroma characteristic when tasted by expert group.