GEOLOGY, CLIMATE AND WINE QUALITY - SOME OBSERVATIONS FROM THE VINEYARDS OF THE WESTERN CAPE PROVINCE, SOUTH AFRICA

This paper will attempt define if wine quality may be linked to geology or climate in South Africa’s winelands. A range of highly rated wines was identified from prominent local wine tasting events. The cultivars Chenin Blanc, Chardonnay, Sauvignon Blanc, Cabernet Sauvignon, Merlot, Shiraz and Pinotage were used. Only the top rated wines were selected, 713 in all. These came from 352 sources, for example wine estates or distinct blends from large producers.

Once the grape source had been identified, the geology was defined. As identification of each vineyard block would have proved time-consuming, a farm scale analysis of the geology was undertaken. Granite was the most common rocktype. This was not unexpected, granite being the most significant rocktype in the main quality wine regions of South Africa. However shale based bedrock showed interesting variations. Chenin and Sauvignon Blanc showed the lowest granite percentage and strongest shale component. In contrast Shiraz and Cabernet Sauvignon showed the highest granite and lowest shale percentage. Merlot had the highest proportion of shale of the red varietals. These observations compare with some of those in France. For example top Merlots are associated with argillaceous rocks in Pomerol and Shiraz with granitic rocks in the Rhone Valley. The results indicate that rocktype influences may exist in South Africa’s vineyards.

The wine distributions against regional degree-day figures were also studied. Chenin Blanc appears to prefer warmer conditions than Sauvignon Blanc. This contrasts with the cool climate Loire valley of France where both thrive. Skewed distributions of Chardonnay and Sauvignon Blanc may result from lack of plantings in suitable locations. Merlot and Pinotage distributions appear to peak at cooler levels than Cabernet Sauvignon and Shiraz. A parallel exists with France where Merlot ripens earlier than Cabernet Sauvignon in Bordeaux, and Shiraz is associated with the hotter Côte du Rhone region.

As the wines used represent the top of the quality range for the seven varietals, some initial conclusions on the suitability of individual rocktypes and climatic conditions can be drawn. The study has also shown that wine tasting results could provide a valuable source of data in the understanding of terroir.