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Effects of mechanical harvesting on 'Sauvignon blanc' aroma

Herbst-Johnstone, M., Araujo, L.D., Allen, T.A., Logan, G., Nicolau, L., Kilmartin, P.A.
Acta horticulturae 2013 no.978 pp. 179-186
acetates, antioxidants, bottles, fatty acids, flowers, grapes, hexanols, juices, mechanical harvesting, odor compounds, odors, terpenoids, thiols, wines, yeasts
Higher quality wines are usually associated with hand-picked grapes. However, we have shown that higher concentrations of the varietal thiols 3-mercaptohexanol (3MH) and 3-mercaptohexyl acetate (3MHA) are often formed in ‘Sauvignon blanc’ wines produced from machine-harvested grapes, although much lower concentrations were found in wines made from heavily pressed juices low in protective antioxidants. At the same time, the fruity aroma of ‘Sauvignon blanc’ wine is also dependent upon concentrations of various esters and higher alcohols, methoxypyrazines and terpenes. For this trial, grapes and juice were sourced from five locations in Marlborough and at five stages during the harvesting process, and fermented in 750 ml bottles using the same EC1118 yeast strain. These included grapes picked by hand immediately prior to mechanical harvesting, samples taken directly from the mechanical harvester, as the grapes arrived at the winery hopper, along with commercial free run and 1 bar pressed juices. Analyses of aroma compounds were subsequently undertaken by GC-MS. Several aroma compounds showed similar concentrations regardless of the harvesting point, including the methoxypyrazines, fatty acids, terpenes, ethyl esters, higher alcohols and their acetate esters. By contrast, the C6-alcohols, such as hexanol and cis-3-hexenol, and their associated acetate esters, were present at very low concentrations in wines made from hand-picked grapes, but at higher concentrations in wines made from machine-harvested fruit, particularly from heavily pressed juices, and can be expected to contribute “green/grassy”, “flower” and “bourbon” aromas to these wines.