Incubator initiative: Is berry shrivel in Cabernet Sauvignon influenced by climate and does this potentially affect characteristics of the resulting wine?

Abstract

Berry shrivel is a phenomenon of weight loss in berries during the late ripening stage attributed to dehydration and loss of berry cell vitality that results in losses of yield, quality and profitability. However, virtually nothing is known about shrivel in Cabernet Sauvignon (CAS) and, importantly, the effects of shrivelled fruit on grape/wine composition and quality. During the 2017-18 season, the influence of leaf removal, vine water status and row orientation (E-W vs N-S) was assessed on late season berry shrivel in CAS in the Coonawarra viticulture region. Leaf removal resulted in higher canopy and bunch zone light interception and temperature while reduced irrigation levels resulted in lower soil and vine water status, and lower berry weight and yield. Reduced irrigation also negatively affected berry cell vitality resulting in a higher incidence of bunches with shrivelled berries. E-W oriented rows had a higher incidence of shrivelled fruit as well as lower berry weight and yield compared to N-S rows; this was attributed to the higher vine water stress in the E-W rows. The E-W rows generally had higher soluble solids in the fruit. Sensory analysis of the wines revealed that inclusion of shrivelled fruit contributed to higher dark and overripe berry characters with some oxidised notes; these negative descriptors were exacerbated with vine water stress.

Summary

Climate change in South Australian viticultural regions has resulted in higher growing season temperatures leading to compressed vintages, critical water scarcities, particularly late in the growing season, and altered fruit composition and wine quality that is redefining the regional wine styles of certain cultivars. Manifesting from these altered environmental conditions is an increased incidence of berry shrivel, a phenomenon associated with cell death in the mesocarp.

In this study, we investigated the dual effects of elevated bunch zone temperature (via bunch zone leaf removal) and vine water stress (via 50% deficit irrigation) on the incidence of berry shrivel in Cabernet Sauvignon (CAS) in Coonawarra. Furthermore, the effect of varying proportions of shrivelled fruit 

in the must was assessed viz. wine chemical composition and sensory quality, using an expert panel of tasters.

Leaf removal around the bunch zone was effective in increasing canopy porosity and bunch temperatures by ~ 2 °C. Leaf removal did not impact either soil or vine water status. There was no effect of elevated temperature on berry cell death. Yields as well as the proportion of shrivelled bunches on each vine were similar, indicating that basal leaf removal and higher bunch temperatures do not have an impact on berry shrivel. There was no impact of leaf removal on basic fruit composition parameters.

Vine water stress had a significant impact on the incidence of berry shrivel. Water-stressed vines had similar canopy microclimate, leaf and bunch temperatures, porosity and LAI values to non-water stressed vines. Water stress resulted in higher cell death in the berries, with a significant effect of row orientation. Yield components were not severely impacted by water stress, but significantly smaller berries were observed in the high water stress treatments, particularly in vines with leaf removal. Basic fruit composition was similar between water stress treatments except for anthocyanins, which were higher in the water stressed vines.

Row orientation affected canopy microclimate: higher ambient temperatures and VPDs were observed in the N-S block during the warmest days. This was consistent with the leaf and bunch surface temperatures measured in that block with differences of up to 5 °C observed. N-S rows had higher canopy porosity, soil moisture, and vine water status, i.e. less water stress, compared to the E-W rows. E-W rows also resulted in higher levels of berry cell death at harvest, particularly when water stress and leaf removal treatments were applied; this was not observed in the N-S block. Higher cell death could have resulted from the higher levels of vine water stress in the E-W block. Although neither yield nor berry weight differed between the two blocks, the E-W block had significantly higher amount of shrivelled fruit compared to the N-S block. Must soluble solids, pH, colour and YAN were significantly higher in the E-W block. Wine composition had a similar trend to must composition; the E-W block had higher pH, colour and hue, malvidin glucoside, caffeic acid, quercetin, as well as higher ethanol and volatile acidity. Certain volatile compounds were higher in the N-S block including IBMP. The proportion of shrivelled fruit used for winemaking affected wine composition. Higher proportions of shrivelled fruit resulted in wines with higher anthocyanin and quercetin concentrations but also higher IBMP.

Wine sensory analysis using a modified DA procedure with an expert panel of tasters revealed that addition of shrivelled fruit to the must increased the perception of dark, jammy and oxidised characters, while clean fruit had greater red berry and green character. Vine water stress, higher in the E-W rows compared to the N-S rows, exacerbated the incidence of shrivel and likely also the proportion of berries on each bunch that were shrivelled, consequently increasing the jammy and cooked fruit characters observed in the wines