Trials with machine harvested sauvignon blanc: the importance of grape transport time and temperature

Abstract

It is well known that free varietal thiols, in particular 3-mercaptohexanol (3MH) and 3-mercaptohexyl ace-tate (3MHA), are important constituents to the aroma of New Zealand Sauvignon blanc wines. This along with the popular practice of machine harvesting in New Zealand were the motivation for the following two pilot studies.
Firstly, it was examined if the presence of 3MH and 3MHA could be influenced by a change in transporta-tion time of machine harvested grapes. This came about as it was noticed that some Marlborough wineries process grapes incoming from multiple growing regions. Here, the thiol precursor contents, Glut-3MH and Cys-3MH, of 21 lab scale wines were examined after experiencing different simulated transportation times (0, 1.5, 3 and 4.5 h).

Results suggested that significant (p < 0.05) increases in the amount of Cys-3MH and Glut-3MH for some of the treatments associated to longer transportation times was possible. However, after fermentation while some of the experimental wines did not display any significant difference between the transportation times trialled, others displayed an opposite (downward) trend for the presence of 3MH and 3MHA across the increasing time points.

Secondly, as machine harvesting can occur throughout the day and night, of which atmospheric changes in temperature are anticipated, it was hypothesised that the skin contact taking place due to the nature of the machine harvesting can occur at different temperatures. For this study a holding period of 2h was chosen to represent the transport time of harvested grapes to a processing winery while the grape holding tempera-tures investigated were 6, 15 and 24 °C. Cys-3MH and Glut-3MH were quantified both before and after the different temperature treatments of the machine harvested grapes. ANOVA and Tukey HSD did not reveal any significant (p > 0.05) differences in thiol precursor levels before the 2h holding period. However, after this time a significant difference (p < 0.05) between the 6 and 15°C for both Cys-3MH and Glut-3MH was established. Following fermentation, the levels of 3MH and 3MHA were also quantified and revealed similar levels of these thiols between all of the experimental wines with no significant differences (p > 0.05) detec-ted between the holding temperatures investigated.