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Cabernet Sauvignon-A Global Exploration Of One Of The World’s Greatest Grape Varieties
The following seminar was presented in London as part of a look at Chilean Cabernet.
Chilean Cabernet Sauvignon
This Global Exploration is a celebration of the great quality and diversity of the noble Cabernet Sauvignon.
It is also recognition of the importance of this variety to the Chile where it has flourished on its own roots for more than 160 years.
Chilean Cabernet Sauvignon is distinctive reflecting qualities conferred by a unique set of terroirs.
In January last year at the first of Santa Rita's South American seminars I attempted to describe Chilean Cabernet Sauvignon,
“Nearly always with a glass staining vibrant colour, opening to fresh aromas of spicy, slightly briary, essence of Cabernet fruit, tinged with an exotic edge of mulberry and cassis.
The ripe fruit sweetness of the middle palate graduates to a plane of definite and serious tannins. This serious terroir driven red wine of a style that can't be produced anywhere else.”
Cabernet Sauvignon - The Variety
In the words of Wine Chile, “Cabernet Sauvignon is Chile's star grape, the king of all reds”, and slightly more prosaically from the wonderfully weighty tome, Winegrapes by Jancis Robinson et al, Cabernet Sauvignon is “the world's best-travelled variety making concentrated, tannic wines for particularly long ageing.”
We now know from the same impeccable source that Cabernet Sauvignon is the offspring of Cabernet Franc and Sauvignon Blanc and that it arrived on the scene in the Gironde sometime before the middle of the 18th century.
Cabernet Sauvignon shares Cabernet Franc as a parent with Merlot and Carmenere and their shared propensity to retain the green character of isobutyl methoxy pryazine (IBMP) probably derives from Cabernet Franc; they have all inherited the green gene.
One of the few recognized vices of Cabernet Sauvignon is that in cool and damp years and cool and damp soils where vine vigour is too great and canopy shades the fruit, the grapes retain IBMP, which reflects in the wine as an herbaceous, tomato vine, green character. Poor old Carmenere inherits the green gene from both sides because its other parent Cabernet Gros is also a grand child of Cabernet Franc.
The sequence of ripening in the Cabernet family also reflects the order of propensity to retain IBMP, which together with phenol, builds up in the lag phase of berry development before veraison. The longer the lag phase the more IBMP and the later ripening the variety and so it goes with Merlot earliest, then Cabernet Franc, then Cabernet Sauvignon and finally and potentially the greenest, Carmenere. It's fortunate we know to grow Cabernet Sauvignon and its siblings in free draining, warm and rocky soils and to leaf strip and expose bunches immediately after flowering which helps limit the accumulation of IBMP.
As well as the potential to exhibit “green characters” Cabernet Sauvignon wines have more colour (anthocyanin), more tannins and more malic acid than the rest of its family and in fact more than most other varieties.
In a seminal cross vintage study of Cabernet Sauvignon, Cabernet Franc and Merlot on gravel, sand and clay soils, Kees van Leeuwen et al identified Cabernet Sauvignon's greater concentration and found,
“The best vintages were those in which the water balance from flowering to harvest was most negative.
The best soils were those on which water deficits resulted in earlier shoot growth slackening, reduced berry size and high sugar and anthocyanin concentrations thereby increasing grape quality potential”.
And from the same author in a paper entitled The Concept of Terroir in Viticulture,
“The best expression of terroir is achieved when the precocity of the grapevine is suited to the local climatic conditions in such a way that full ripeness is reached by the end of the growing season.
For the production of high quality red wines environmental conditions should induce moderate vine vigour, either through moderate water deficit stress or through low nitrogen supply. These conditions are most frequently met on shallow or stony soils in moderately dry climates."
The site terroir should bring the grapes to full sugar, phenol and flavour ripeness between the 10th of September (March) and the 10th of October (April)], where
“the ripening of the grapes occurs in cool conditions at the end of the summer or in early autumn.”
It is important to understand the genetic dispositions and family relationships of Cabernet Sauvignon because it explains why it is so often blended with other less green, less tannic and earlier ripening varieties including Merlot and Cabernet Franc and with varieties unrelated to it and low in green propensity including Malbec, Petit Verdot and Shiraz. Carmenere is not usually a comfortable blending partner with Cabernet Sauvignon, sharing an amplified version of its green vice.
Cabernet Sauvignon Wines and Terroirs
To again quote Jancis et al from “Winegrapes”, Cabernet Sauvignon “has a particularly powerful identity”, “there's a recognizable nobility and stability to its aroma which can vary from blackcurrant to cedar.”
“What is remarkable about Cabernet Sauvignon is that it imprints its identity so firmly on any wine that includes it”, “although it manages to produce great wine in only a small proportion of the hundreds of regions in which it is planted.
The most obvious established candidates are the Medoc, Pessac-Leognan, Penedes, Napa, Bolgheri, Sonoma, Santa Cruz Mountains, parts of Washington State, Puento Alto in Chile and Coonawarra and Margaret River in Australia.”
Terroir, Geology and Soils
The “Global Exploration” of Cabernet Sauvignon we are about to embark upon includes wines from
- The quaternary gravel soils of the Medoc/Pauillac ( Chateau Pontet Canet) and Pessac Leognan (Domaine de Chevalier)
- The quaternary alluvial rock and gravel benches and colluvial fans of the Maipo Alto (Casa Real and Carmen Gold) and the Aconcagua River (Sena) tumbling down from the Andes in Chile,
- A sliver of the sedimentary Pacific sea bed comprised of decomposing Franciscan green stone over fractured limestone on Monte Bello Ridge in California's Santa Cruz Mountains (Ridge Montebello),
- The sandy loam over clay and decomposing granite of the slopes of Stellenbosch in South Africa (Jordan Cabernet Sauvignon),
- The sandy, pebbly loams on tertiary ferricrete of Margaret River (Cullens Diana Madeline) and the clay loams on a quaternary limestone ridge of Coonawarra (Petaluma Coonawarra) in Australia,
- The quaternary alluvial gravels of the hills above Bolgheri (Sassacaia).
- The freely drained soils of the lower slopes of the Havelock Hills, part of the coastal range Pacific seabed marine sediments formed where the Australian tectonic plate meets the Pacific plate on the east coast of New Zealand's North Island
All of these soil and geology matrices are very free draining, of moderate to low fertility and induce the gradient of stress through the growing season that van Leeuwen has identified as being necessary to produce high quality red wine.
As important as the soils and geology are in determining the final quality and style of wine produced, terroir expresses itself primarily through climate the most important parameter of which is the temperature through the vine growing-season.
Heat summation is the sum of all temperature that is useful to the vine through the 7-month growing season. It is accepted that the vine only responds physiologically at temperatures above 10∞C.Summing the temperature above 10∞C for the 7-month growing season accounts for the viticultural warmth of a site or region and for Cabernet Sauvignon's home, Bordeaux, it ranges from 1485∞C days in Graves and Medoc to 1599∞C days in Pomerol.
Cabernet Sauvignon requires more than 1320∞C days to ripen, whereas its blending partners, Merlot, Malbec, Cabernet Franc and Shiraz only require 1260∞C days.
The late ripening Carmenere and Petit Verdot require at least 1380∞C days to reach full maturity.
Our “Global Exploration” of Cabernet Sauvignon includes the variety at home in Graves and Medoc where the heat summation is 1485∞C days, in its very warm South African terroir at Stellenbosch at 2000∞C days and to cooler locations in Hawks Bay, New Zealand, Coonawarra Australia and Santa Cruz Mountains in California at around 1400∞C days. Maipo Alto and Ocoa in the Aconcagua Valley in Chile, Willyabrup at Margaret River in Australia and Bolgheri in Italy are slightly warmer than Bordeaux so there is a spectrum of terroir heat summations against which to examine the quality and style of wines made from Cabernet Sauvignon in our “Global Exploration”.
|Region||GDD (day°)||Diurnal Range (°C)||Growing Season Rain (mm's)||Afternoon Humidity (%)|
|Medoc / Graves||1485||11.4||427||59|
|Ocoa Aconcagua Valley||1685||19.0||40||50|
|San Jose (Santa Cruz Mtns)||1411||9.1||70||49|
Heat summation is the most important parameter of climate contributing to terroir, but diurnal range is also very important.
Because the vine can work for 24 hours in maritime climates with low diurnal ranges (warm night temperatures), the production of colour and flavour is continuous. Sugar is consumed by this 24-hour process but is only produced in the sunlight of the day. Therefore maturity is reached earlier and at lower sugars than in climates with cold nights and high diurnal ranges. At the same heat summation a low diurnal range terroir has cooler days than a high diurnal range equivalent.
Cold nights tend to trap malic acid and green flavours, require the grapes to hang much longer on the vine to obtain physiological maturity and end up at higher sugars and therefore produce higher alcohol wines.
Colours tend to be more vibrant and intense from cold night, high diurnal range terroirs.
In our “Global Exploration” of Cabernet Sauvignon we have diurnal ranges from 19∞C at Sena in the Ocoa region of the Aconcagua Valley to 9.0∞C in the Hawks bay region of New Zealand.
Again we have a spectrum of diurnal range against which to assess and discuss the style of wine produced from the great Cabernet Sauvignon.
All of the wines in our “Global Exploration” of Cabernet Sauvignon are first class expressions of this noble variety and each demonstrates the unique qualities conferred by their very different terroirs.
I hope this explanation of the terroirs involved and the physiological response of the vine to the components of terroir will help in your assessment of these exemplary wines.