Napa Valley College Fall 2001
Paper for the class:
Effects of Terroir on
Cabernet Sauvignon Wine Character
1871 Mt. Veeder Rd, Napa, Ca.
The Terroir of a vineyard consists of a myriad of factors but, the most significant are:
The dominant philosophy among wine growers today is to allow the terroir to dictate the best grape to grow and the wine to be made from those grapes. This philosophy is closely linked to the idea of appellations. In France with its rich history of winemaking the terroir has had a chance to make its preferences known and the various appellations have existed since 1850. Infestations of phyloxera and mildew introduced from the United States in the 1850s forced a move to the use grafting and phyloxera tolerant rootstocks but, in the last 100 years little has changed in France allowing the terroir to reveal its preferences in trials and experiments carried out by vintners looking for the best wines these regions could produce.
The effects of terroir on wine have not been widely studied probably due to the large number of factors involved says Gerard Seguin the Bordeaux enologist. His definition of a quality terroir is one in which vines and the land are matched such that the grapes are able to mature completely at a slow pace. However, some marketers for the sake of differentiating the various appellations and creating what I would call "terroir equity" have not hesitated to describe the effects of terroir within Napa valley. Because of the absence of objective data much of this paper will be based on such marketing text.
Napa Valley Terroir Effects
A good description of the geology of Napa Valley appears in [Livingston 98]. The valley runs from North to South where the Napa river empties into San Pablo Bay. The climate gets hotter going from the south end around Carneros to the North End at Calistoga. A cross section of the valley would reveal concentric rings of rock with the valley floor consisting of clays and fine grained sediments deposited by erosion from the hillsides. Farther up the hillsides Volcanic ash is exposed and finally near the peaks of the Vaca mountains on the east and the Mayacamas mountains on the west very old marine sediments are exposed.
Livingston describes wines from the mountaintop vineyards as inky and tannic compared to wines with softer tannins and ripe fruit flavors from the mid valley benchlands. The source of this conclusion is not discussed. Smith in contrast states that the upper valley with its more porous soils produces more tannic wines.
In Rod Smiths Napa Valley Primer he describes the essential characteristics of the Napa Valley terroir. First he describes the variance of Terroir in Napa as being large, larger than the variations you would find across the Medoc or the Cote dOr but, not larger than the variations you would find across all of France. Wilson highlights the fact that France has some of the largest variance in Geology for its area that you would find anywhere in the world.
Smith also describes the valley as consisting of raised seabed and volcanic elements. The mountain Mayacamas and Vaca mountains on either side of the valley were formed by plate compression. Napa is unusual in that it is wider and at lower elevation than many of the other stream etched valleys in the coastal range, probably due to decompression at some time that pulled the Mayacamas and Vaca mountains apart lowering the valley between them almost to sea level.
Soil varies along with the geology going from porous well drained soils with low water holding capacity in the North to slower draining clays in the South valley. Volcanic soils are more common toward the north, Howell Mountain and Diamond Mountain and their alluvial fans. The south valley has more of the upturned seabed character, sedimentary clays interlaced with shells and sand. These generalizations should be recognized as such. There are actually 10 different alluvial fans in the valley each of which has its own unique properties. He points out that the climate interacts with the soils in that it changes how the rocks and sand are weathered to produce the soil. This produces additional variance in the terroirs of the valley.
Climatically the Napa Valley is an ideal place to grow grapes. It is half way between the coast where the California current produces a very cool climate and the central valley with its very hot climate. This gradient of temperature produces prevailing on-shore breezes. There is a temperature cycle throughout the growing season with a period of a few days. The variance of this cycle is the dominant reason for the characteristics of a particular vintage from a given vineyard. He shows a graph of hourly temperature for a couple days in August which demonstrates that the variance in weather from day to day is much larger than the variance in weather along the valley, in this case between Oakville and Carneros. Calistogas temperature in the summer is generally 10 degrees higher than the city of Napas.
Smith then goes on to make some generalizations about the character of wines across the valley. He starts with a qualification that for single plots winery style can have more effect than the land and many of the wines are blends which tend to wash out the distinctions of any one location.
He says that Carneros with its cool temperatures and more clayey soils produces Cabernet which is "dark colored with broad fruit and soft tannin". Going up valley where the climate is warmer and the soil is alluvial fans, the wines are "less overtly fruity with more defined tannins and focused intensity".
In the mid valley morning sun vineyards give "bright, high toned wines with leaner tannin and brilliant cherry-like flavor". Afternoon sun vineyards on the east side of the valley like Stags Leap have a "ripe berryish redolence and distinctively soft supple tannins." It is not clear to me what the difference is between a lean tannin and a soft supple tannin.
He says more about the tannins getting stronger toward the north as a result of thicker grape skins coming from drier soils and increasing heat. Drier soils are an unlikely cause since most of the vineyards in Napa valley are drip irrigated. Still the amount of stored water in the soil accessible to the vines for at least the first part of the growing season will be different.
He states that midway up the valley the volcanic and marine soil influences are balanced which results in the most balanced Cabernets coming from this region of the valley. Wines here can also have a "fine herbaceous character". Going further north the tannins scale up further to a kind of "soft chewiness and the blackberry fruit deepens". The increased temperatures and rockier soils and more altitude produce denser more concentrated wines with brawny tannins and tobacco-like tones in the fruit.
Of mountainside wines he says there is an added concentration of fruit which produces a "juicy sensation on the palate". The tannins are also more leathery than in valley wines. Mountain wines show the same gradient in quality from South to North as on the valley floor, increasing in weight and density from South to North. Mt. Veeder wines have "brighter fruit with an herbal intensity" compared to Diamond Mountains "firmer, riper wines with more black cherry flavor."
It should be kept in mind that Smith wrote the web content referenced here for the purpose of stimulating wine consumers to come to Napa Valley. However, he references at least one scientific study which is the paper by Noble.
Other data comes from a map in the visitors center at Domaine Chandon stating that the shale soils of Mt. Veeder produce a steely taste in the wine there.
One option is to go and taste the effects of Napa terroirs yourself. This is possible at a semi-weekly tasting at Franciscan Oakville Estate called "The taste of Terroir where four local Cabernet Sauvignon wines highlighting the differences in the Napa appellations are tasted. I will report the results of this tasting in an addendum to this paper after I attend 12/6/01.
Figure 1. Napa Valley Appellations
Terroir Effects in Bordeaux
In the Medoc region of Bordeaux, Cabernet Sauvignon is the dominant varietal though it is normally mixed with minority fractions of Cabernet Franc and Malbec. There is a strong gradient of style and quality as one goes from the city of Bordeaux Northwest along the peninsula between the Gironde river and the Atlantic Ocean known as the Medoc. The Medoc has a mild climate due to estuary and ocean on either side of it. There are forests that shield it from winds off of the ocean.
According to Stevenson the wine is mild and very plain just Northwest of Bordeaux, gaining character in Margaux and reaching an optimum in the middle region which includes St. Julien, Paulliac, and St.-Estephe. Beyond St. Estephe to the tip of the peninsula, Pointe de Grave, the wines quickly become coarse and one dimensional. According to Wilson the vineyards which produce the best wine in this mid region of the Medoc such as First Growth vineyards Lafite Rothschild, Mouton Rothschild and Latour have a very deep growing zone (30 ft.) and good drainage. They tend to be at slightly higher elevation (50-80 feet) on top of gravel mounds and have a base of fossiliferous, sandy marl and St. Estephe limestone which aid in drainage.
Chateaux Margaux is closer to Bordeaux but still is in the First Growth class. It is not a true gravel mound vineyard according to Wilson. It sits on bedrock with only a thin veneer of gravel. Wilsons explanation for the high quality here is the variety of flavors that come from a half dozen different plots that make up the chateau. Blending by the vignerons is supposedly the magic.
Wilsons conclusion after looking for a correlation of the Classes of Bordeaux wines to their geology is that the higher their elevation the better the wine. In this region higher elevation means more gravel and hence deeper growing zones and better drainage. Higher elevation may be as little as 60 ft. Interestingly the Medoc on the West side of the Gironde was not planted until more than 1000 years after the east side of the Gironde because it has many marshes and was thought not to be suitable for vineyards by the Romans. The East side of the Gironde, Bourg produces good but, not great Bordeaux wines.
Figure 2. Regions of the Medoc and its geology Courtesy Wilson98
A brief look at Australian terroirs in Sothebys Wine Encyclopaedia quickly leads to the conclusion that the variance of terroirs is at least as large as terroirs across the United States or France and is not easy to generalize. I think both Australia and the U.S. will take some time, perhaps 50-100 years for the factors in these terroirs to stabilize as they have done in France.
The parallels between the Medoc and Napa valley are evident in that both areas are of comparable scale and both show a gradient of Cabernet Sauvignon quality from end to end with the south being more mild and ordinary compared to the North which produces heavier, more tannic wines. The middle regions in both cases produce the best balanced wines. The geology in the two regions is totally different, limestone based in the Medoc vs. Volcanic and seabed rock in Napa. However, both areas have good drainage over gravel bases and likely a deep growing zone. It would be interesting to see if different rootstocks have been used in Napa to compensate for differences in the soil and climate to achieve comparable quality.
Over time a particular wine will emerge from a terroir which is better quality than any other wine that might be produced there. Appellations follow too soon after to add perceived value to the wines from that region whether or not that value exists. Winemakers in this region of course strive to improve, differentiate and protect the reputation of their appellation because it is brand equity which people are willing to pay for. But in a new appellation ownership changes rapidly and there are always producers who detract from the quality expected, effectively diluting the appellation equity. The French have done the best job of defining and protecting their "terroir equity", with the Growth classifications enumerating the quality of wines from individual gravel mounds within the Medoc. Napas 9 appellations are all relatively new, less than 30 years old while the French Chateau classification system has been around for more than 150 years. French wine quality is significantly more consistent than U.S. quality as a result and in spite of more variances in weather during the growing season there. With dry conditions in California and the use of irrigation water uptake can be much more precisely controlled in California.
A blatant example of creating terroir equity is the website by California Properties of the Napa Valley Online, http://www.napavalleyrealestate.net/Vineyards/appellations1.html. In this case they are promoting the appellations to increase the perceived value of land rather than the wine that comes from this land. Notably the author doesnt even know how to spell Cabernet Sauvignon correctly.
Finally I would say that the effects of terroir are still very ill understood which is just to say that the vitaculture and winemaking are not exact sciences. A multitude of factors make up terroir and the output of the process which is influenced by terroir is equally complex as is the human sensory system by which the output of this process is judged. Suffice it to say winemaking will remain an art for sometime to come though companies like Enologix may soon put at least the composition of wine and first order sensory evaluation into a quantitative framework.
Smith, Rod, "Wine Making: Terrain and Terroir", A Napa Valley Primer http://www.napavintners.com/wines/terrain.html in three parts. Napa Valley Vintners Association Website.
Wilson, James E. Terroir, University of California Press, Berkeley, Wine Appreciation Guild, San Francisco, copyright 1998.
Stevenson, Tom, The New Sothebys Wine Encyclopedia, DK Publishing Inc.,
New York, New York, 1997.
Noble, A.C. and Elliott-Fisk, D.L. , 1990 Evaluation of the effects of soil and other geographical Parameters on Wine Composition and Flavor: Napa Valley, Ca. pp37-45, Actualities Oenologiques 98, 4 Symposium International dOenologie: Dunod. 567pp Couldnt acquire a copy.
Livingston, John, "The Geology of Fine Wines" , California Wild, fall 1998; -http://www.calacademy.org/calwild/fall98/wines.htm
The Taste of Terroir, Thursday and Sunday 11:00am at Franciscan Oakville Estate Visitor Center. Four Cab tasting which highlights Terroir effects. www.franciscan.com/vc.html
Soils data for Napa Valley, http://www.ca.nrcs.usda.gov/mlra/NapaSS/index.html