Effects on Red Wine Quality of Removing Juice before Fermentation to Simulate Variation in Berry Size

Abstract

Red wines were made from harvests of 9 grape varieties by removing or adding 10% free-run juice before fermentation on the pomace. This procedure was used to simulate variation in berry size without change in berry composition, and its justification is discussed. Berry size varied about ±60% among normal berries harvested from single plots of grapes of each of 5 varieties. Since two harvests of the same variety differed by 46%, the ±10% range in berry weight chosen for experiment appears to be within common variability. The wines produced covered a wide range of nondefective red wine composition. Significantly higher potassium content, pH, flavonoid content, anthocyanin content, aroma rating, red color rating, tannin (astringency) rating, and overall quality were found in direct correlation with decreased berry size or juice content. Comparison of chemical with sensory analysis indicated that in wines averaging about 1500 mg/l flavonoid (as gallic acid) a difference in flavonoid content of 268 mg/l did and 165 mg/l did not make a sensorily significant difference. Similar comparisons with anthocyanin pigment and visual color are discussed. Statistical analyses of the data are also discussed. Removal of juice apparently slightly lowered the efficiency of extraction of substances from the grape skin. Compositional changes were more nearly linear than sensory ratings of the resultant wines. The visual color of wines simulating large berries was higher than anthocyanin content would predict and was attributed to the lowered pH and other compensating factors. Also discussed are other sensory effects and some possibilities of capitalizing in vineyard management upon the increased red wine quality related to smaller berry size.