Our latest MW Perspectives essay, written by Cathy van Zyl MW, explores the factors that allow Cabernet Sauvignon to thrive in Stellenbosch, South Africa. Read an excerpt below, and find the full essay in the MW Perspectives section.
A late-budding, late-ripening variety, Cabernet Sauvignon needs warmth to ripen. In Bordeaux, it’s the gravel that plays a major role coaxing the grape to ripeness, warming up quickly in the day and retaining its heat, often well into the night. In climates warmer than the Médoc, well-drained sites with low potential vigor are more important than gravel, per se. Consider the large alluvial benches of Oakville, California, or the terra rossa over limestone of Coonawarra, South Australia.
Stellenbosch, South Africa, lacks these features, yet its Cabernet Sauvignon wines are increasingly acknowledged as being able to stand shoulder-to-shoulder with those from areas long-recognized as classic Cabernet sites. What, then, is it about Stellenbosch that enables these results?
First, Cabernet Sauvignon in Stellenbosch is planted in well-drained soils derived from granite, shale, and sandstone that receive just the right amount of rain (about 600 to 800 millimeters a year) to ensure this noble variety thrives. Second, the vines are exposed to approximately 14 daylight hours in summer and 10 in winter, more than sufficient to fully ripen the grapes. In fact, in contrast to Bordeaux, where poor weather (mostly rain) during the harvest in late summer and early autumn can negatively impact the quality of the crop, vintages in Stellenbosch are largely consistent because the long, warm conditions permit late ripening and it seldom rains, and then only briefly, during harvest season.
Finally, while the average annual temperature in Stellenbosch town is 16.4 degrees Celsius (61.5 degrees Fahrenheit), with temperatures reaching the high 20s (low 80s Fahrenheit) during the summer months (a climate few would describe as cool), the region’s vineyards are sited where they experience “cool sunshine.” This term describes areas that receive consistent long sun exposure without excessive heat accumulation, making them cool compared to surrounding areas yet warm enough for late-ripening varieties. Increased solar radiation paired with cool temperatures has the effect of slowing the ripening process and accumulation of sugars but increasing the production of flavor compounds in grape skins and maintaining acidity. These factors are critical for achieving the ripeness and structure necessary for making high-quality Cabernet Sauvignon wines with elegance, latent power, and cellaring potential.
All the above is only possible because of Stellenbosch’s dramatic—and hallmark—topography. Because of the rapid change in elevation over a relatively short distance—there are just 10 kilometers between the coastal plain at 5 meters above sea level to the Hottentots Holland Mountains at over 1,500 meters—Stellenbosch’s vineyards have numerous and varying slope aspects. These aspects are critical because of their impact on the vineyard’s exposure to various influences. Key among these is wind, including the Cape Doctor in summer, the Berg winds in winter, and the diurnal thermal winds, namely sea, mountain, and valley breezes.
These slope aspects also impact drainage patterns, ventilation, and the sun’s passage over and penetration into vine canopies. The steeper the slope, the more the aspect will affect the ambient temperature in the vineyard itself. Within the canopy, aspect influences soil temperature, which in turn affects root growth and function and, depending on the soil composition, can impact the rate of reradiation. Simply, the steeper the slope, the better the drainage, the warmer the soil, the better the ventilation (which lowers the risk of disease), and the more sunlight (though not necessarily warmth) that can be reflected into the canopy.
Stellenbosch producers know this and select their Cabernet sites accordingly—that is, for as much cool sunshine as they can get.