Identifying the best parameters to determine genotype capability to retain adequate malic acid at harvest and in final wines

Maintaining optimal grape acidity at harvest is one of the most complicated challenges under climate change pressures, especially in early ripening cultivars. Warming trends are compressing vine phenology and fostering berry malic acid respiration. In this work, over four years, we evaluated yield components and fruit ripening in two local varieties in the Colli Piacentini, Ortrugo (ORT) and Barbesino (BRB). Our goal was to evaluate their ability to maintain satisfying acidity at harvest and understand the limits and features of the genetic control over organic acid degradation during ripening. The two varieties exhibited comparable yield and grape total soluble solids (TSS) accumulation dynamics, but BRB showed consistently higher acidity during the entire ripening process in any of the four years. BRB's higher acidity was linked to higher malic acid concentrations. ORT had earlier onset of malic acid degradation than BRB and lower maximum malic acid degradation rates. Malic acid degradation rates were lower in ORT also later in the season, until harvest. However, correlations built between malic acid degradation rates and instantaneous malic acid concentration revealed that BRB had a consistently lower malic acid loss for values of malate < 10 g/L. Our work demonstrates that there is a genetic control over the malic acid degradation rates exhibited at varying malic acid concentrations and higher acidity at harvest can be found in varieties exhibiting low malic acid degradation rates when malic acid is < 10 g/L. Post-veraison berry growth rates could interact with genotype effects. The analysis of the correlation can be used at different scales to identify cultivars retaining higher acidity at harvest.