van Rensburg, P., Department of Viticulture and Oenology, Stellenbosch University, Private Bag X1, 7602 Matieland, Stellenbosch, South Africa. Institute for Wine Biotechnology, Stellenbosch University, Private Bag X1, 7602 Matieland, Stellenbosch, South Africa. Distell, P.O. Box 184, Stellenbosch, 7599 South Africa., South Africa