Impact of Mechanical Harvesting and Optical Berry Sorting on Grape and Wine Composition

Abstract

The impact of mechanical harvesting, optical berry sorting, and their possible synergistic effect on grape and wine composition was investigated. Pinot noir grapes from the Russian River Valley American Viticultural Area were harvested by hand, by a standard bow-rod mechanical harvester, or by a mechanical harvester with a Selectiv’ Process on-board. For each harvest method, half of the grapes were unsorted and half were optically sorted at the winery. The grapes, wines at bottling, and wines after three months of bottle aging were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC), ultraviolet-visible spectroscopy (UV-vis), and headspace solid-phase microextraction (HS-SPME) gas chromatography mass spectrometry (GC-MS) for color expression and phenolic and aroma profiling. The machine-harvested grapes had higher levels of β-damascenone, linalool, β-myrcene, and α-terpinene, potentially caused by glycosidic hydrolysis triggered by berry damage during harvest or from induced synthesis as a wounding response. In general, differences in wine composition attributable to harvest method were diminished or eliminated by optical sorting. The machine harvester with the Selectiv’ Process on-board led to wines with the most phenolics, although these differences may have been decreased or eliminated had the grapes been crushed before fermentation as the wines were produced by whole-berry fermentation. Descriptive sensory analysis conducted on wines three months after bottling determined that the wines made from hand-harvested fruit had significantly greater tropical fruit aroma, while wines made from optically sorted treatments had less hue saturation. With only two significant differences among the 18 aroma, taste, and mouthfeel attributes tested, it was concluded that all treatments led to wines of similar character.