One of the major challenges that global warming poses to viticulture is maintenance of adequate acidity at maturity in white grapes for sparkling winemaking. Today many wine regions are revising their historically-grown cultivars lists, seeking for new, or why not ancient, varieties capable of retaining adequate acidity to produce more appreciated wines. However, criteria for selecting performing genotypes in terms of acidity at harvest are complex. Late veraison and ripening can be inadequate traits, since they do not necessarily reflect a capability of maintaining a minimum grapes acidity with satisfying sugars.
In this biennial work, we compared fruit, must and wines composition of a local, widely grown white grape variety in the Colli Piacentini area (cv. Ortrugo, ORT) with those of a minor autochthonous variety, namely, Barbesino (BRB). ORT and BRB had a similar sugar (TSS) accumulation dynamic, whereas BRB exhibited a delayed loss of titratable acidity (TA). However, BRB, showed a significantly higher malic acid degradation rates (MAdr) from veraison to harvest. Plotting malic acid concentration (MA) against MAdr revealed that the higher BRB MAdr were essentially a smokescreen, since BRB had consistently lower MAdr than ORT for any value of MA < 9 g/L. As a result, BRB wines showed the highest TA, while ORT had the lowest TA and higher pH.
Our data reveal that that MAdr can be a misleading parameter when selecting cultivars for acidity, since an high abundancy of MA could lead to high MAdr, independently by final TA and MA at harvest. Conversely, MAdr should be evaluated as a function of instantaneous MA, to be considered a reliable parameter for identifying genotypes guaranteeing higher acidity. In detail, our data suggest that low MAdr at MA < 9g/L could represent a new benchmark when phenotyping for acidity. Our work demonstrates that currently neglected cultivars could help preserve must acidity, as compared to traditional varieties having early ripening, maintaining the links with terroir and local traditions at the same time.
