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.
Most of the vineyards planted on the northern slopes of decomposed granites of the Simonsberg in Stellenbosch are warm sites, and the fact that Cabernet is a late-ripening variety is almost its undoing. The saving grace is the relatively large difference between daytime and nighttime temperatures during the growing and ripening seasons here, which allows the vineyards to cool down sufficiently to retain acidity and helps to moderate sugar buildup.
Data from Warwick Estate pertaining to the last three harvests (2020, 2021, and 2022) show that there is a difference of roughly 10 to 11 degrees Celsius (18 to 20 degrees Fahrenheit) between the average daytime and average nighttime temperatures. The diurnal difference on the slopes of the Simonsberg is exacerbated in the leadup to harvest and results in cool fogs being drawn in at night over the warmer landmasses so that the vineyards of Warwick Estate, Kanonkop Wine Estate, and their neighbors are shrouded. “The fog acts as a little fridge, helping to maintain the acids and [delaying] the heat uptake in the day,” says JD Pretorius of Warwick.
The challenge is to allow the pyrazines to degrade without picking up too much sugar. To do this, Warwick’s row direction is east-west, with the sun tracking the row most of the day. Also, the ridge on which its Cabernet is planted is higher in the north than in the south, giving a helping hand (altitude) to those higher up.
Stellenbosch producers can also find relatively cooler sites using elevation. The average elevation in the Stellenbosch district is 136 meters above sea level, but the hillside slopes and foothills of its mountains are gentle enough to allow Cabernet vineyards to be planted as high as 250 meters, and in a few cases to 500 meters.
As temperature falls (all other things being equal) by roughly 0.6 degrees Celsius (1.08 degrees Fahrenheit) for every 100 meters climbed, producers with the opportunity to plant on higher slopes amplify the benefits of planting on slopes with southerly or south-easterly aspects.
In the Jonkershoek Valley, producers like Stark-Condé and growers favor spots that have higher altitude to catch the sun because of the closeness of the mountains that surround the valley on three sides. The Groot Drakenstein Mountains to the east throw shadows over the vineyards in the morning, and to the northwest, the Simonsberg blocks most of the glow of the afternoon sun. Oldenburg Vineyards (facing northeast) and Bartinney Wine Estate (facing north-northeast) are planted at around 350 meters above sea level to catch as much sun as possible. Given all this, one might imagine that Cabernet here struggles to ripen, but it doesn’t: it just takes its time, with harvests beginning two to three weeks, sometimes longer, after those elsewhere in Stellenbosch.
Yet another cooling influence is a vineyard’s proximity to the ocean, whose impact extends as far inland as sea breezes. At latitudes around 33°S, South Africa is far narrower than South America or Australia, and thus the majority of its wine-growing regions are largely under the influence of maritime air. As a result of the prevailing ocean surface and the land/sea ratio, South Africa’s coastal wine region experiences cooler conditions than the latitude might suggest compared to other wine regions at similar latitudes, especially those in the northern hemisphere.
It’s widely believed there’s a sweet spot for Cabernet Sauvignon on the north-facing slopes of the Helderberg somewhere between 200 and 400 meters above sea level, depending on the aspect. This puts the vines in the east-west wind tunnel formed by the warm air rising off the land as it heats up during the day, drawing in the cool air off False Bay just a few kilometers away.
Most of the slopes in the Greater Helderberg face north and west, and the prevailing wisdom for row direction is northwest-southeast. To minimize physical damage to the vines from wind speed, and to catch a little more sunlight and open the canopy on the southern side of the vine, plantings on the middle slopes at places like Ernie Els and Alto are going in at east-southeast by north-northwest.
Higher up, for example at Waterford, where the Cabernet Sauvignon vineyards are at between 300 and 400 meters, there’s a different school of thought. Here, earlier plantings were north-south, but more recent vines have been planted at east-west to allow the easterlies to go straight through. Also, the upper slopes of the Helderberg are warmer at night than the valley floor, although there’s always a cool breeze through the vineyards.
Stellenbosch is home to a handful of producers whose vineyards are protected from the wind and, as a result, their style almost bucks the trend for the area. In the Greater Helderberg at Rust en Vrede, for example, the Cabernet vines are at just 85 to 135 meters above sea level in a depression below Guardian Peak and Ernie Els. The resulting wines are slightly broader than others from the Greater Helderberg—having, by necessity, traded tautness for richness—but no less fine or less ageworthy.
Thelema, in the Simonsberg-Stellenbosch ward, has southerly aspects at different elevations between 370 and 410 meters, where the wind is not a consideration. Tucked around a corner, in a small depression, it has certain protection.
What’s important in the more northerly reaches of the Simonsberg-Stellenbosch, as in many of the other wards, is the way the Cape Doctor wind operates. At Uitkyk and Delheim Wines, planted between 320 and 480 meters above sea level, the highest and coolest area in this corner, it will barrel through the vineyards, often damaging the vines at crucial points in their ripening.
At Kanonkop, where the vineyards are lower down and at least 2 degrees Celsius (3.6 degrees Fahrenheit) warmer, the wind is less destructive. It is slower and doesn’t gust as much—average wind speed in Stellenbosch is around 15 to 19 kilometers per hour, but the Cape Doctor can reach 160 kilometers per hour. Here, the wind does its job of cooling down the grapes without the damage or stress. This is one of the reasons why one of Cabernet’s parents, Cabernet Franc, with its shorter ripening period, does well here in the heat and intensity of its growing season.
On the southerly and relatively flat outskirts of Stellenbosch town, vineyards are often sheltered from the Cape Doctor and can, on days when other sites are being cooled down by the wind, experience slightly higher temperatures. It therefore takes careful control and vigilance in the vineyard to ensure the ripening grapes don’t accumulate sugars too quickly.
Canopy management and vine orientation can help to protect vines in locations that might otherwise be too warm. A saving grace at Blaauwklippen Wine Estate is careful canopy management and site selection; newer vines are planted on Tukulu soils, which contain a relatively high percentage of clay (upward of 55%) and are therefore cooler.
On the other side of the R44, Kleine Zalze has a mostly south-facing aspect, which mitigates some of the heat, but it has reconsidered its approach for all new plantings. The east-west row direction advocated years ago provided for too much exposure on the slope. Northwest by southeast is by far the better option, and all new vines are being planted accordingly. The estate is also fine-tuning its shoot positioning and pruning regimes, which means physiological ripeness at lower alcohols, with less time spent on canopy management.
While Stellenbosch can generally be described as a warm grapegrowing area, its topography and proximity to the ocean, in combination with the seasonal winds and ocean currents, create numerous microclimates boasting “cool sunshine.” These areas deliver the climatic conditions critical for making high-quality Cabernet wines, and Stellenbosch is receiving growing attention for the excellence of these wines.
Carey, Victoria A., et al. “Viticultural Terroirs in Stellenbosch, South Africa. Spatialisation of Viticultural and Oenological Potential for Cabernet-Sauvignon and Sauvignon Blanc by Means of a Preliminary Model.” Journal international des sciences de la vigne et du vin 43, no. 1 (2009).
Carey, Victoria A., et al. “Viticultural Terroirs in Stellenbosch, South Africa. The Identification of Natural Terroir Units.” Journal international des sciences de la vigne et du vin 42, no. 4 (2008).
Great article. South Africa is an incredible, complex area of valleys and coasts.