Distribution of 3-Isobutyl-2-methoxypyrazine across Rachis Components of Vitis vinifera Shiraz and Cabernet Sauvignon

Abstract

Rootstock can signifcantly alter the concentration of methoxypyrazines (MPs) in the bunch stem (rachis) of Vitis vinifera L. cv. Cabernet Sauvignon and Shiraz, which has implications for winemaking and wine style. Te distribution of MPs across the rachis is an important consideration, but such information was not available. Tis study aimed to address this research question by comparing MP concentrations in diferent rachis components throughout grape maturation and in the absence of ambient light. Shiraz and Cabernet Sauvignon bunches were sampled throughout development, segmented into four components (peduncle, top rachis, bottom rachis, and pedicel), and 3-isobutyl-2-methoxypyrazine (IBMP) was quantifed in each. For both cultivars, IBMP showed a negative correlation with grape maturity, with concentrations in pedicel at harvest being signifcantly higher than other rachis components. Additionally, light exclusion signifcantly increased IBMP concentrations in all rachis segments. Te concentration of IBMP varied signifcantly between diferent rachis components. Te greatest concentrations were measured in the pedicel, which also contributed the largest proportion among the components to total rachis by weight. Due to elevated IBMP concentrations in rachis and the difculties in excluding matter other than grape from a fermentor, the presence of pedicel during fermentation could produce Shiraz and Cabernet Sauvignon wines with higher concentrations of MPs, thereby potentially increasing vegetal sensory characteristics.