The impact of delayed grapevine budbreak on lemberger wine sensory compounds under variable weather conditions

Introduction

Spring freeze events threaten grape production globally ^1–3. As grape buds emerge from dormancy in spring, freezing temperatures have the potential to damage green tissues ^4,5, decreasing yield potential and compromising fruit quality by harvest ^2,6,7. Bud freeze damage may become more frequent if global warming accelerates budbreak without a concurrent decrease in spring freeze events ^3,8. One promising strategy to prevent grapevine freeze damage is to delay budbreak, for example by applying chemical products during dormancy ^7,9,10 or by postponing winter pruning until after budbreak ¹¹. Although these methods are effective at preventing freeze damage, in cool climates with short fruit ripening periods, delaying budbreak has the potential to delay the development of sugars, phenolics, and volatile compounds in fruit, negatively impacting the flavor, aroma, and mouthfeel of finished wines. In this study, we evaluated the impact of two techniques to delay grapevine budbreak on volatile and nonvolatile compounds of Lemberger wines (Vitis vinifera), and we related the impacts on wine composition to consumer perception, over three vintages at a cool-climate site.

This study builds on our past work, where we investigated the effects of applying a chemical spray product and delayed winter pruning on Lemberger budbreak, freeze damage, yield parameters, and basic wine chemistry in 2018 and 2019 ⁷. While we found no differences in basic fruit and wine chemistry by harvest, vines with later budbreak tended to show a delay in berry color change around veraison, assessed in mid-August each year, suggesting a delayed onset of phenolic compounds that went uncharacterized. Furthermore, in the pilot year of that study (2017, unpublished data), budbreak was delayed up to 23 days, over twice as much as the highest delay in 2018 and 2019, which led to an even more extensive delay in the onset of veraison. Due to distinct variations in key phenological stages and seasonal weather conditions over the three years of the study, we expanded our research to understand the extent to which delaying budbreak affects volatile and nonvolatile compounds in wines from 2017-2019.

Here, we aimed to determine how delaying budbreak and the onset of fruit ripening impacts wine chemical composition and whether impacts of delaying budbreak are consistent among years, or if they mainly depend on factors such as seasonal weather. We also evaluated if consumers could detect differences between wines made from vines that experienced a different degree of delayed budbreak and onset of veraison. We hypothesized that, among vintages, seasonal weather metrics would more strongly impact overall wine composition than delaying key phenological stages (i.e., budbreak and veraison), regardless of the extent of delay. However, within each vintage, we hypothesized that if there was still a delay in fruit phenological development at veraison, delayed budbreak treatments would lead to lower concentrations of nonvolatile (e.g., tannins and anthocyanins) and volatile (e.g., terpenoids and ethyl esters) compounds in finished wines, which consumers would be able to detect.