Effect of soil type on Sauvignon blanc and Cabernet-Sauvignon wine style at different localities in South Africa

The wine producing regions of South Africa are characterized by climatic diversity. The Coastal Region has a Mediterranean climate, with a mean annual rainfall of c. 690 mm, whereas the Breede River Valley has a semi-arid climate with an annual rainfall of less than 300 mm.
Although irrigation is increasingly practiced, rain-fed vineyards are still commonly encountered in the Coastal Region. Wine styles differ in these vineyards. These differences are due, amongst other factors, to variations in climate and topography. They are also influenced by variations in soil type, notable with regard to water-holding capacity. In contrast to the Coastal Region, all grapevines in the Breede River Valley are irrigated. Under these conditions, in which the effects of soil type, and of water holding capacity, are moderated by scientific irrigation, wine style may be expected to be mainly affected by climate.
The aim of this investigation was to quantify the effect of soil type on wine style in rain-fed Sauvignon blanc and Cabernet Sauvignon vineyards in the Coastal Region, and in irrigated vineyards of the same cultivars in the Breede River Valley. Two experimental plots, representing different soil types, were identified within each vineyard. Experimental wines were prepared separately for each soil type.
Results showed that the styles of Sauvignon blanc, and of Cabernet Sauvignon wines from the Coastal Region, and from the Breede River Valley, were affected by both climate and soil type. The effect of soil type was moderated, but not entirely eliminated, by scientifically scheduled irrigation.