Date of Award
Master of Science
Food Science and Technology
John R. Mount
P.M. Davidson, Ivon McCarty
The production and consumption of wine in the United States has increased about 80% in the last 10 years (Havighorst, 1980). It was not until 1977, however, that the Tennessee State Legislature passed the "Grape Wine Law" which made it legal to produce wine commercially in the state (Cuskaden et al., 1980). Little information was available on the composition of grapes grown in Tennessee and less information was available on the wine produced from these grapes. This study, therefore, was undertaken to first compare the chemical composition of juices and resulting wines of various Vitis labrusca, Vitis vinifera and French hybrid cultivars grown in Tennessee, second to compare the chemical composition of these products with standards of other wine producing areas and third to compare growing regions of Tennessee for wine grape producing potential.
The harvested grapes were transported to the Food Technology and Science's pilot plant in Knoxville and prepared for fermentation. The grapes were destemmed and crushed and samples of juice removed for analysis. The white wine grapes were pressed and the juice placed into one gallon glass jugs fitted with air locks. The °Brix was adjusted to 22.0 with sugar, SO2 was added at 50 mg/l and a standard culture of yeast (Saccharomyces cerevisiae var. Montrachet) was added to each of the cultivars of grapes. The red wine grapes were fermented on the skins for three days and then pressed. Sugar was added to raise the initial °Brix to 22.0, SO2 and yeast were added as above. The juice was allowed to ferment to dryness, racked and samples of wine obtained.
The samples of juice were analyzed for °Brix by table refracto-meter, and glucose and fructose content by a high performance liquid chromatographic procedure. A Waters Carbohydrate Analysis column was used with an acetonitrile:water solvent (80:20 v/v) and a Differential Refractometer detector. The samples of juice and wine were analyzed for pH; total titratable acidity as tartaric acid by titration to pH 8.2 with 0.1N NaOH; tartaric acid content with an HPLC procedure utilizing a u-Bondapak phenyl column, a 0.5% acetic acid solvent containing Waters PIC A reagent, and a Variable Wavelength Absorbance Detector set at 250 nm; tannin, by the non-tannin phenols and total phenol content were determined by the method described by Peri and Pompei (1971) and color using a Hunterlab Color Difference Meter. The wines were also analyzed for alcohol and acetaldehyde using gas chromatography procedure with a flame ionization detector and a carbowax column; and for volitile acidity by distillation and titration as acetic acid.
The °Brix of the juice samples ranged from 10.5 to 18.0 with the east Tennessee grapes being significantly higher (p<0.05) than the grapes from middle Tennessee. The fructose/glucose ratio for the different cultivars varied from 1.22 to 0.92 with all but two of the cultivars having a ratio higher than 1.0.
The pH of the juice samples ranged from 2.70 to 4.00 and the total titratable acidity from 0.43 to 1.22g tartaric acid/100 ml. The east Tennessee grapes were found to be more acidic. The pH and titratable acidity of the wine samples followed the same pattern as the juice samples. The tartaric acid content for both the juice and wine samples were determined to be approximately 60% of the total acid content of the juice and wine samples.
The tannin and total phenol contents in the juice were from 14.80 to 60.76 mg/l and from 89.18 to 184.50 mg/l, respectively. The tannin and total phenol contents in the wine were from 16.51 to 120.23 and from 77.27 to 414.51 mg/1, respectively. The east Tennessee grapes were slightly higher in tannin and total phenol content.
The alcohol content of the wines from the University Experiment Stations averaged 9.35%, indicating that fermentation of sugar to alcohol occurred in the juice. The volatile acidity and acetaldehyde contents were low for all the wines tested which also indicates a desirable fermentation occurred in the juice.
The composition of the grapes indicated several cultivars grown in Tennessee could be used to produce wine. The majority of the cultivars, however, would be more suitable blended together to yield desirable chemical and physical properties. The location that the grapes are grown in Tennessee significantly affects the composition of the juice and wine and therefore must be considered when determining how various cultivars should be blended to produce the more desirable wine.
Nisbett, Harold M., "Composition of grape cultivars grown in East and Middle Tennessee for wine production. " Master's Thesis, University of Tennessee, 1986.