The Impact of Bagging Grape Clusters on Grape Ripening and Quality (in Collaboration with VT) (2017)

This study examines the impact of bagging grape clusters during the growing season on grape and wine flavor, chemistry, microbiology, and phenolics. The vineyard uses organic grape growing practices, and the goal of this project was to see if bagging grape clusters would improve disease resistance without negatively impacting grape and wine quality. The bags used were 19x27cm white paper bags with micropores. Corot Noir grapes in one block experienced 4 treatments: 1) not bagged, 2) bagged at pea-sized berries, 3) bagged at berry touch, and 4) bagged at veraison. Because of a prediction of reduced disease incidence in bagged clusters relative to unbagged clusters, and because unbagged, rotting clusters were going to be dropped during the season, green harvesting of the treatment clusters was undertaken on lagging blooming clusters at berry set in order to attempt to keep crop levels similar between treatments. Lagging clusters were also not bagged on treatment rows. Control and treatment grapes were harvested 2 days apart from each other, and the 3 treatments were combined into one must to ferment. Both control and treatment musts received a 10% saignee, both were inoculated with Renaissance Ossia yeast, and all other treatments between wines were equal. Both bins received 2 weeks extended maceration. Bagging clusters might have reduced incidence of black rot, with the earlier bagging treatments being more effective; however, more intensive work is needed to confirm this. The grape treatments generally exhibited slight increases in berry weight and cluster weight, as well as increases in malic acid, pH, and YAN. Juice and wine chemistry was not much impacted, except that acidity was lowered in the bagged treatment. Bagging clusters lowered the microbial content of the juice, although wine was not much impacted. All phenolic and color parameters, in grape and wine, were either reduced or did not change as a result of bagging. 64% of people were able to distinguish the wines in triangle testing, suggesting a statistically significant difference between them (p<0.001). Of those who correctly distinguished between the wines, there was not a major preference for one wine over the other, perhaps slightly favoring no bags. There were strong trends for the unbagged treatments to have higher Overall Aromatic Intensity and higher Acidity. There was a slight tendency for Fruit Intensity to be higher in the unbagged treatments as well.

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