Available at: https://digitalcommons.calpoly.edu/theses/206
Date of Award
MS in Agriculture - Crop Science
Horticulture and Crop Science
Influence of Crop Load on Fruit Composition Using Pinot Noir Grapes
Patrick G. Phelan
The two seasons for this trial were conducted in 2002 and 2003 at Bien Nacido Vineyard in Santa Maria, California. The trial consisted of pinot noir wine grapes clone 2a, grown on 101-14 rootstock. There were eight treatments with a control consisting of 25 vines per treatment, and 50 vines for the control.
The primary objective of this research experiment was to conduct different vine balance procedures and compare them to the amount of wine phenolics. The vines were altered with two procedures. First was crop yield; fruit thinning altered the treatments by providing four different crop loads and a control. The treatment levels were signified as one ton, two ton, three ton, four ton, and control. The second procedure was timing of fruit thinning. Four different crop loads were split in half giving rise to eight treatments and a control. With four of the treatments the fruit was dropped post-bloom, and the other four treatments were dropped at seventy five percent veraison. Equal amounts of early and late thinning were combined and made into wine which gave four different crop load wines and a control wine. This process was done in 2002 and repeated in 2003. Additionally, other vine growth parameters were analyzed to determine the role that crop load and timing of thinning had in their development.
Seven variables were analyzed from prunings, clusters, juice, and wine samples. They consisted of berry size, cluster weight, titratable acidity, pH, total soluble solids, phenolic profile
(consisting of eleven components), and shoot weight. The results indicated that the following were statistically significant: (1) titratable acidity was significantly different between the 2002 and 2003 growing seasons, (2) total soluble solids showed a significant difference between the early fruit thinning versus the late thinning, (3) berry size in 2002 showed a statistically significant effect of drop date on the mean caliper size, (4) in 2002 the berry size also showed a statistically significant interaction between drop level and drop date, (5) berry size in 2003 showed a statistically significant effect of drop level on the mean caliper size, (6) in 2003 there is also a statistically significant effect of drop date on the mean caliper size, (7) again in 2003 there is a statistically significant interaction between drop level and drop date, (8) cluster weights in 2002 showed a statistically significant relationship between drop level and average cluster weight, (9) in 2002 cluster weights also showed an effect of the time of fruit drop on the average cluster weight, (10) cluster weights in 2003 showed a statistically significant relationship between drop level and the average cluster weight, (11) pruning weights in 2002 showed a statistically significant relationship between drop level and average shoot weight, (12) pruning weights in 2003 showed a statistically significant relationship between drop level and average shoot weight and finally, (13) of the eleven phenolic components measured, five differed significantly by year but not across the five treatments.
Information derived from this experiment suggests that the site is a high vigour location according to Robinson and Smart’s yield to pruning weight ratio. With this in mind we find that TA and pH were not a significant factor, but soluble solids (brix) ascertained a higher degree of brix with the late drop treatment. We conclude this to be an effect of both the high vigour site and more uniform fruit drop. In 2002 and 2003, we find a significant interaction between drop date and berry size with a late drop producing the smallest berries on average. Cluster weights varied between 2002 and 2003 and the results were inconclusive. Shoot weights along with harvest totals concluded a high vigour site. The one ton level in 2002 had a significantly higher average shoot weight than the three ton level (p<.001), four ton level (p=.006), and no fruit drop control (p<.001). There is also a significant relationship between drop time and average shoot weight in 2002 (p<.001), and 2003 (p=.049) with the late fruit drop being followed by a lower shoot weight. This significant relationship expressed that an early drop increased the shoot weight which contributed only more vigour to an already high vigour site. The ratio of yield to pruning weight for 2002 gave us a range of .39 to 1.78, and in 2003 the range was .32 to 1.36 concluding a high vigour site. The phenolic profile expressed a statistical difference by year, but was most likely caused by a varying fermentation temperature or different climatic conditions in 2002 and 2003.