Enzymatic Management of High pH Grape Juice and Must & The Effects of Crop Thinning on Grape Yield and Wine Quality

High pH winemaking is a common problem all across the state of Texas. Texas is a warm growing climate with temperatures reaching above 100°F (38°C) during the summer. In warm weather growing climate, such as Texas, grapes ripen more quickly, leading to higher soluble solids and lower acidity. These analytical parameters in grapes at harvest, along with other parameters such as potassium and pH, directly affect the wine made from these grapes. If these parameters fall outside of their desired ranges it can lead to serious quality issues in the finished wine such as instability and undesirable flavors. For the first study, the enzymes glucose oxidase (GOx) and catalase were used as a potential pH lowering pre-fermentative treatment on Tempranillo juice and must. The effects of GOx and catalase were observed and recorded on juice and must chemistry prior to fermentation as well as in the finished wine. Parameters measured on the grape juice and must during GOx treatments include pH, TA, glucose, and gluconic acid. Parameters measured on the resulting finished wine include pH, TA, alcohol %, Free SO2, and volatile acidity (VA). Using GOx with catalase at a rate of 1.0(g/L) was most effective in juice which lowered pH from an average of 4.6 to 3.8, while increasing TA from an average of 3.13(g/L) to 7.86(g/L). The resulting wines had a lower pH and higher TA, but were less alcoholic and did not hold free SO2 as well as the control wines. The effects of crop thinning using a mechanical harvester on grape yield and composition and wine quality was also evaluated. Crop thinning and pruning treatments were carried out on Tempranillo and Mourvèdre grapevines at four different levels: vines pruned to two buds per spur and then shoot thinned and crop thinned using a mechanical harvester (2BFT), vines pruned to three buds per spur and then crop thinned using a mechanical harvester 3 (3BFT), vines pruned at two buds per spur (2B), and vines pruned at three buds per spur (3B). Data was recorded for berry composition at harvest and for the finished wines nine months after bottling. The parameters analyzed at harvest include pH, titratable acidity, Brix, potassium, and yeast assimilable nitrogen (YAN). After the wines spent nine months in bottle, they were then analyzed for pH, titratable acidity, alcohol percentage, free SO2, volatile acidity, malic acid, lactic acid, tartaric acid, and color. The finished wines from the Tempranillo treatments were also judged blindly and scored based on preference by an untrained consumer panel. Scored data by the panelist include wine taste, wine aroma, wine appearance, and wine color. The data revealed that soluble solids (Brix), pH, and potassium were all higher in crop thinned treatments than non-crop thinned treatments for both Mourvèdre and Tempranillo at harvest. The resulting wines from both varieties were also higher in alcohol and redder in color. Data from the consumer panelist showed that the taste of Tempranillo wine made from treatment 2BSFT was most preferred, but not statically preferred from treatment 2B. Crop thinned wines were also statically preferred for appearance and color by consumer panelist