Impact of climate on tartric acid metabolism of Ugni blanc berries: comparing of two vintages with climatic conditions contrasting

Abstract

The acid component of berries is an essential criterion for the quality and preservation of distillation wines of Cognac. It must be high enough to protect wine during the storage phase, awaiting distillation. Climate change observed in the Cognac region for several years impact on the acid component of the Ugni-Blanc berries with a slight decrease in malic and tartaric acid content. If the metabolism of malic acid is well known, that of tartaric acid is still poorly documented in particular as regards the impact of weather conditions and the effect of temperature. By comparing the biochemical characteristics of berries (two parcels) of two vintages with climatic conditions contrasting (on 2011: early, hot and dry, and on 2013: later, with a rainy and cool spring), our study highlighted the influence of these conditions on the acid composition and the metabolism of tartaric acid of the berries. The enzymatic activity of L-idonate dehydrogenase (the last known enzyme involved in the synthesis of tartaric acid) is modulated by climatic conditions during the herbaceous growth phase of the berry, inducing a more or less significant accumulation of this acid. Enzymes involved in the synthesis of tartaric acid are thus regulated by the temperatures at the beginning of season inducing a modification of the metabolic pathway of the tartaric acid and the acid component of the Ugni-Blanc berries. The mechanism of regulation will be discussed in a perspective of global warming and adaptation of the cultural practices to prevent a too important drop in the total acidity of musts, and afterward, of wines.