Do high temperature extremes impact berry tannin composition?

Wine growing has proven to be a development opportunity for agribusiness in several new regions of brazil, including the federal district. There are more than ten existing wineries, established in the last five years. Through the double pruning system, which consists of trimming the growing shoots in the summer and positioning the ripening of the fruits in a cooler period of the season, the grapes are sought to ripen more completely. The syrah variety has shown excellent adaptation to this cycle management model.

In interaction with climate and genetic or human factors, the soil is a major component of the viticulture terroir. The mineral composition of the soil influences vine performance and wine sensory attributes. Among the elements that vines take from the soil, nitrogen is the one that has the strongest impact on vine physiology, vigor and grape composition. In addition to its major effect on primary metabolites in berries, nitrogen plays also a decisive role in the secondary metabolism, especially in the production of key compounds for berries quality, like volatile thiols, methoxypyrazines and glutathione (GSH).

Several Uruguayan wineries have begun to produce wines with minimal intervention, to increase the sustainability of their vineyards and wines. These wines are characterized by the minimum intervention in the management of the vineyard, its harvest, vinification, conservation and aging1,2. Sulfur dioxide (SO2) is not used or is used in reduced doses, although chitosan can be substituted or supplemented1. The objective of this research is to evaluate SO2 reduction or replacement options adapted to the production of Tannat red wines with minimal intervention. Vinification of the Tannat grapes with autochthonous yeasts (LN) was carried out during the 2023 vintage.

Climate projections for the future suggest favourable conditions for some wine producing regions, but challenging conditions for others. For instance, temperature increases are likely to shift grapevine phenology, ripening and harvest dates, and potentially affect grape quality and yield.

Climate influence on grapevine physiology is prevalent and this influence is only expected to increase with climate change. Although governed by a general determinism, climate influence on grapevine physiology may present variations according to the terroir. In addition, these site-specific differences are likely to be enhanced when climate influence is studied using farm data. Indeed, farm data integrate additional sources of variation such as a varying representativity of the conditions actually experienced in the field. Nevertheless, there is a real challenge in valuing farm data to enable grape growers to understand their own terroir and consequently adapt their practices to the local conditions. In such a context, this article proposes a framework to site-specifically study climate influence on grapevine physiology using farm data. It focuses on improving the analysis of time series of weather data. The analytical framework includes the synchronization of time series using site-specific thermal indices computed with an original method called Extended Growing Degree Days (eGDD). Synchronized time series are then analyzed using a Bayesian functional Linear regression with Sparse Steps functions (BLiSS) in order to detect site-specific periods of strong climate influence on yield development. The article focuses on temperature and rain influence on grape yield development as a case study. It uses data from three commercial vineyards respectively situated in the Bordeaux region (France), California (USA) and Israel. For all vineyards, common periods of climate influence on yield development were found. They corresponded to already known periods, for example around veraison of the year before harvest. However, the periods differed in their precise timing (e.g. before, around or after veraison), duration and correlation direction with yield. Other periods were found for only one or two vineyards and/or were not referred to in literature, for example during the winter before harvest.