Die invloed van temperatuur tydens meganiese oes op wynkwaliteit

Project Number
WW 12-16

Project title
Die invloed van temperatuur tydens meganiese oes op wynkwaliteit

Project leader
Steenkamp, J

Project description
Cabernet Sauvignon wines was sensory evaluated during August 2001. Although grapes were hand and machine harvested at three different times of the day, no significant differences could be found in wine quality. As in the previous two years, Sauvignon blanc grapes slowly cooled down from harvest until approximately 7:30 in the morning, after which it began to warm up again until approximately 15:00. Although the average hourly temperatures varied between years, a similar trend was observed. During the first hours after harvest, there was an initial small temperature difference between hand and machine harvested grapes, but this changed dramatically around 12:30. To avoid the detrimental effect which high temperatures may have on wine quality, it is recommended that grapes are picked during the morning and delivered to the cellar as soon as possible. Due to the mechanism on which mechanical harvesters function, the percentage stems present in hand and machine harvested grapes differs highly It should be considered to compensate for the weight loss associated with machine harvested grapes. The sugar concentration in machine harvested Sauvignon blanc grapes was significantly higher than for hand harvested grapes. It seems as if the fans of the mechanical harvesting machine concentrate the must to some degree. Sauvignon blanc vines apparently also reacts quickly to environmental conditions, since the sugar concentration changes during the course of the day and is at its highest at mid-day. The sugar concentration of grapes stayed constant during the post harvest period. The acid concentration of machine harvested grapes was significantly lower than those harvested by hand. This could be as a result of higher temperatures of machine harvested grapes. The temperature during the period from harvesting to delivery had no influence on acid concentration. The pH of machine harvested grapes was invariably higher than for hand harvested grapes. This could also be attributed to higher temperatures of machine-harvested grapes, as well as the longer skin contact to which the grapes were subjected. This theory is confirmed by the fact that there is also a significant increase in the pH of must if it is delivered directly after harvesting. Since it is clear that there is a significant difference in physical, as well as chemical composition between hand and machine harvested grapes, it can be expected that wine quality would also be affected.

Presentation(s)
Steenkamp, J, Van Schalkwyk, D, Rhode, E E and Calitz, F. 2001. The effect of temperature on wine quality of mechanical harvested versus hand picked Chardonnay and Cabernet Sauvignon. Paper presented at the 25th National Congress of the South African Society for Enology and Viticulture.15-16 November, Somerset West. South Africa.

Article
Steenkamp, J. 1998. Riglyne vir die meganiese oes van wyndruiwe, Wynboer, Mnth Feb (p. T2-3)

FinalReport.pdf

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