Within-Vineyard, Within-Vine, and Within-Bunch Variability of the Rotundone Concentration in Berries of Vitis vinifera L. cv. Shiraz

Abstract

This study characterizes the environmental factors driving rotundone concentrations in grape berries by quantifying rotundone variability and correlating it with viticultural parameters. Dissection of the vineyard into distinct zones (on the basis of vigor, electrical soil conductivity, and slope), vine into orientations to sun (shaded/unshaded), and grape bunches into sectors (upper and lower and front and back) shows the influence of vine vigor, sunlight, and temperature. Occurrence of the highest rotundone concentration was observed in shaded bunch sectors and vines and from higher vigor vines in the southern-facing areas of the vineyard. The highest concentration of rotundone is consistently found at the top and in shaded sectors of bunches, and this correlates to lower grape surface temperatures. Modeling showed that berry temperature exceeding 25 °C negatively affects the rotundone concentration in Shiraz. Both natural and artificial shading modulated the grape surface and air temperature at the bunch zone and increased the rotundone concentration, without affecting other grape berry quality parameters. Thus, temperature and possibly sunlight interception are the main determinants of rotundone in grape berries. Vineyard topography, vine vigor, vine row, and grape bunch orientation influence the level of berry shading and can, therefore, adjust bunch surface and zone temperatures and influence the berry rotundone concentration.

Fortification and Elevated Alcohol Concentration Affect the Concentration of Rotundone and Volatiles in Vitis vinifera cv. Shiraz Wine

“…Siebert, Wood, Elsey and Pollnitz [6] first investigated rotundone recovery rate from grape berries using different extraction methods, and observed higher rotundone recovery (45%-100%) when using ethanol as extraction solvent compared to extractions without ethanol (16%-28%). Based on this, rotundone extraction method used for rotundone quantification was established using 50% ethanol as solvent to extract rotundone from grapes, which is now accepted as the standard rotundone extraction/quantification method [6,10,16,19]. In Ts-day 5 treatment, it would take time for added sugar to be fermented into alcohol after the addition in the 5th day.…”

“…Grapes for the current fermentation trial were collected from a commercial vineyard located in the Grampians wine region of Victoria, Australia ( [15,16,24], packed in styrofoam boxes on dry ice, transferred to the University of Melbourne, and stored at −20 • C before further experiments.…”

“…Rotundone is responsible for the attractive "pepper" character in grape berries and wine, and is especially important for cool-climate Shiraz (Syrah) [6][7][8]. It is possible to manipulate the concentration of this compound in wine by increasing rotundone production in grape berries [8][9][10][11][12][13][14][15][16][17][18][19]. Approximately 10% of the rotundone in grape skins is extracted into the grape berries during fermentation, regardless of starting concentration, so any manipulation that increases the amount of rotundone in grapes will be reflected by an increase in wine.…”

“…It is clear that climate and weather variables are important as rotundone has been observed in Shiraz wine produced from cool-climate wine regions [4]. Large variations in the concentration of rotundone have been observed within vineyards, between vines and within bunch regions, with more rotundone produced in areas having a southerly aspect, higher canopy cover and shading of bunches [16]. These factors explain how lower bunch zone air temperature, lower berry surface temperature, less direct solar exposure and higher precipitation are associated with elevated rotundone production [8,10,16].…”

“…Large variations in the concentration of rotundone have been observed within vineyards, between vines and within bunch regions, with more rotundone produced in areas having a southerly aspect, higher canopy cover and shading of bunches [16]. These factors explain how lower bunch zone air temperature, lower berry surface temperature, less direct solar exposure and higher precipitation are associated with elevated rotundone production [8,10,16]. Higher irrigation together with on-vine drying has been proven as an effective viticultural technique to improve rotundone concentration in the resultant wine [11].…”