Yield and Quality of Wine Grape Cultivars in Arkansas

A survey was conducted to determine the quality and yield of 15 major wine grape cultivars. Six Vitis vinifera L., three Vitis rotundifolia Michx., and six French-American hybrid cultivars were included in the survey. Fruit maturation was determined by percent soluble solids, TA, and pH measurements. Soluble solids were attained at the expense of acidity and pH. In spite of low soluble solids at acceptable pH levels, pH appeared to be the best parameter by which to monitor maturation and to determine harvest date. Commercially acceptable yields were obtained from all V. vinifera and V. rotundifolia cultivars. Little information is available on adaptability and maturation of wine grape cultivars in Arkansas (15). The % soluble solids and grams tartaric acid equivalent/100 mL (TA) have been the parameters most often used to assess grape maturation in the state. Preliminary evaluation of wine grapes in Arkansas have shown low soluble solids (11,13,15,17), low acidity (15,18), and high pH (15,16,18) in fruit at harvest. Recently, pH has been added as one of the important parameters for monitoring maturation. In wine, pH is important in malolactic fermentation (10), microbial stability (2), taste (2), color stability (9,18,19), stability of soluble grape protein (14), and solubility of potassium bitartrate and calcium tartrate (3,4). Amerine and Ough (1) indicate that wines with a pH above 3.6 may have stability problems. Also, adjustments in pH are more difficult to make than adjustments in % soluble solids and acidity. This study was initiated to evaluate fruit maturity parameters and to determine maturation rates of some of the major wine grape cultivars grown in Arkansas. Yield was also determined because of its influence on quality and cultivar selection (20). Materials and Methods Fifteen cultivars from three species of grapes were monitored during 1979 and 1980. The V. vinifera L. cultivars tested were Cabernet Sauvignon (red), Petite Sirah (red), Pinot noir (red), Gewurztraminer (white), White Riesling (white), and Chardonnay (white). The French-American hybrid cultivars tested were Villard noir (red), de Chaunac (red), Baco noir (red), Villard blanc (white), Aurore (white), and Seyval (white). The V. rotundifolia Michx. cultivars were Noble (red), Carlos (white), and Magnolia (white). The V. vinifera and French-American hybrid cultivars were evaluated in commercial vineyards at Altus, Arkansas, and the V. rotundifolia cultivars were evaluated in a commercial vineyard at Forrest City, Arkansas. The 1979 season was cool and wet, but the 1980 season was hot and dry. Generally, the combined effects of drought. and high temperatures in 1980 produced the most unfavorable climatic conditions for viticulture in Arkansas since 1936 (J. R. Morris, unpublished data). Two replications of each cultivar consisted of three mature, uniformly growing, healthy vines, separated by appropriate guard vines. All data were subjected to analysis of variance and F-tests. Quality data were analyzed as a factorial, and only the interactions of cultivar x sampling date are presented. LSD was used to separate means. Fruit quality determinations: After veraison, fruit samples were collected at an early, mid, and late stage of maturity. Each sample consisted of at least 200 randomly selected berries from each replication which were sealed in polyethylene bags, stored on ice, and transported to the University of Arkansas Food Science Laboratory at Fayetteville where they were immediately frozen for later analyses. At the time of analysis, thawed samples were blended for 30 seconds in a laboratory blender and then placed in a 250 mL beaker which was covered with a watch glass. The samples were then heated for one hour at 85°C in a water bath, allowed to cool, and squeezed through two layers of cheesecloth. The resulting juice was centrifuged for 10 minutes at 2100 g. Percent soluble solids was determined using a Bausch and Lomb Abbe refractometer. A 5 mL aliquot of juice was diluted to 125 mL with deionized H20 and then titrated to pH 8.4 with 0.1 N NaOH to determine acidity. Acidity is expressed as g tartaric acid equivalent per 100 mL. The pH was determined using a Corning (Model 130) pH meter. Yield determination: Following the late fruit sampling, the vines were harvested and individual vine yields recorded. Pruning weight for each vine was obtained in January each year. Results and Discussion In 1979, the highest yielding red cultivars were Noble, Petite Sirah, and Cabernet Sauvignon. Among the white cultivars Magnolia, Carlos, and Villard blanc produced the highest yields (Table 1). The Pinot noir, Noble, and Petite Sirah were the highest yielding red cultivars in 1980. The white cultivars having the highest yields were Carlos and