van Zyl, S., Department of Viticulture and Enology, Stellenbosch University, Private Bag X1, Matieland (Stellenbosch), South Africa Department of Viticulture and Enology, University of California, 595 Hilgard Lane, Davis, CA, 95616, USA Current address: Department of Viticulture and Enology, California State University, 2360 East Barstow Avenue, Fresno, CA, 93740, USA, South Africa