Yeasts on Arkansas White Riesling grapes and in musts

Wine makers wanting to know about natural fermentations (i.e., those not intentionally inoculated with yeast starter cultures) are interested in the kinds of yeasts present naturally on wine grapes at harvest and which yeasts gain predominance during must fermentation. This information about Arkansas grapes and naturally-fermented musts is not available. Therefore, the objective of this study was to determine the major yeasts present on Arkansas-grown White Riesling (Vitis vinifera) grapes and in fermenting model musts. Randomly selected clusters of grapes were harvested from three different locations (i.e., three replications) within an experimental vineyard at Fayetteville. Sound berries were removed from the clusters and blended for 2 minutes in sterile blender jars. The slurry (must) was divided into four 225-mL portions and dispensed into sterile 250-mL Erlenmeyer flasks equipped with air locks. Potassium metabisulfite was added as a single dose to must samples to give total SO2 concentrations of 0, 25, 50, or 100 mg/L. The set of flasks, containing each of the four sulfite treatments, was incubated at 13°C and sampled at 0, 5, 10, and 20 days.