Terroir and natural terroir units

Terroir is not a new concept. We know that the Egyptians (3000 B.C.) had an understanding of the importance of the interaction between the environment and the vine as they built artificial hills in the flat Nile Delta and divided their wines into five categories, partially based on the origin of the product (Falcetti, 1994).

Georgic authors (200 B.C. – 200 A.D.) underlined the role played by the environment in viticulture both at a macro and microscale and the importance of choosing the site according to the cultivar to be planted (Falcetti, 1994). This concept has formed the basis of many geographical indication systems, not the least being the Wine of Origin System in South Africa.

A natural terroir unit (NTU) is a unit of the earth’s surface that is characterised by relatively homogeneous patterns of topography, climate, geology and soil (Laville, 1993). It has an agronomic potential that is reflected in the characteristics of its products, resulting finally in the concept of terroir. A terroir, therefore, is defined as a complex of natural environmental factors that cannot be easily modified by the producer. With the aid of various management decisions, this complex is expressed in the final product, resulting in distinctive wines with an identifiable origin. The terroir cannot be viewed in isolation from management and cultivation practices, although they do not form part of the intrinsic definition.

The above definition of a terroir determines the way that we study and identify viticultural terroirs. No single environmental component of the terroir system can be studied in isolation, rather the full complex of factors must be taken into account. There will always be two steps for a terroir study. Firstly, all the relevant natural factors (such as aspect, altitude, geology, soil type, effective soil depth, water supply to the vine, etc.) must be identified and characterised in order to identify relatively homogeneous NTUs. Secondly, the response of the vine on the NTUs and the organoleptic properties of the wine originating from these units must be determined over a period of time so that the NTUs that result in a similar product can be grouped into viticultural terroirs.

Wynboer - February 2002 - Natural terroir units: What are they

Terroir studies usually focus on wine character or style rather than quality, but a good terroir is considered to be one that ensures a slow but complete maturation of grapes with a certain regularity in quality of the product from vintage to vintage (Seguin, 1986).

Why is it important to study natural terroir units

As seen above, the identification of NTUs will form the first step of any terroir study that, in turn, is important for, inter alia, the following reasons:

The identification of viticultural terroirs is considered to be of international importance and the Office International de la Vigne et du Vin (OIV) has passed a resolution (Anon., 1993) requiring terroir identification and characterisation in all wine producing countries.

The concept of terroir stresses that winemaking begins in the vineyard. Although there are many factors affecting the final wine character and style, a stable set of environmental features (the terroir) forms the basis of the viticultural ecosystem.

There is growing interest in the origin of wines and in single vineyard wines. The identification of terroir units with specific application to viticulture is an important step in meeting the consumer challenge and penetrating an important market. Terroir studies are, therefore, of commercial interest.

Demarcation of areas of origin should be based on the terroir concept. Terroir studies are important to provide a scientific basis to such a system in order to maintain its integrity.

Terroir studies enable producers to better understand their vineyards and to improve their product. A map of NTUs is of greater use for planning purposes than a soil map alone, as it combines all the factors having an effect on viticultural production.

How does the identification of natural terroir units aid the wine producer

In order to better understand how a map of NTUs can be of use to the wine producer, it is necessary to look at the interaction of each of its components with wine quality and character.

Topography: The effect of topography on temperature variability (above and below ground) can be considered to be one of the main factors affecting the quality of grapes (Gladstones, 1992). Topographic effects on climate can be indirect, due to drainage, exposure to wind, drainage of cold air, or direct, due to the immediate effects of the change in the incidence of the sun’s rays on the earth’s surface (Crowe, 1971).

Altitude, aspect and inclination of the slope are of the most important landscape attributes affecting the climate of the vineyard (mesoclimate) (Dumas, Lebon & Morlat, 1997). Increasing altitude tends to result in decreasing temperature (1C decrease per 100 m increase for dry air; this value will be lower for water saturated air; Preston-Whyte & Tyson, 1988), but this effect can be alleviated by an increase in radiation, warmer soil surfaces, poor ventilation and movement of cold and warm air (Dumas et al., 1997; Gladstones, 1992).

Slope aspect affects temperature via sunlight interception, as well as exposure to winds and rainfall (Schultz, 1997). Topographic variability results in an open or closed landscape, affecting air movement in an area and sunlight interception (Lebon, 1993). Terrain morphology, due to its constituents of slope inclination and slope shape, affects temperature variability and soil water drainage. Convex landscape forms will generally result in less day-night temperature variation in comparison to concave forms (Branas, Bernon, & Levadoux, 1946), while concave slopes often result in accumulation of soil moisture and nutrients at the foot of the slope (Schultz, 1997).

Climate: A variety of mesoclimates can be identified in a hilly or mountainous region as a result of topographical effects on various climatic elements. Large bodies of water also have a modifying effect on temperature due to their temperature inertia, resulting in the reduction of both the diurnal temperature range and the contrast between minimum and maximum temperatures (Gladstones, 1992). Temperature is probably one of the most important parameters affecting the grapevine as it has an effect on almost every aspect of the vine’s functioning (Coombe, 1987). High temperatures will result in slightly higher sugar contents, up to a temperature threshold. Malate contents will be lower, while tartrate contents will be little affected. Potassium contents will increase, affecting the wine pH. The effect of night temperatures on anthocyanin synthesis appears to be partially dependent on the contrast between day and night temperatures, with day temperature playing the preponderant role (Kliewer & Torres, 1972). Optimum mean temperature for pigment formation is in the region of 20-22C (similar pattern for phenolics) and a mean temperature range of 20-22C in the month of ripening is optimal for physiological ripening in grapes and for the synthesis of colour, flavour and aroma compounds (Gladstones, 1992).

Relative humidity has an effect on the photosynthetic rate when the soil water supply is limited (Champagnol, 1984) and it has been shown that low relative humidity values and high temperatures result in high berry pH values, as well as reducing the growth and yield per unit water transpired (Gladstones, 1992). High relative humidity values can, however, increase disease incidence.

Wind has both positive and negative effects for viticulture. Strong winds in spring and early summer can injure new growth and young bunches, as well as reducing fruit set. Moderate winds of higher than 3-4 m.s-1 can result in closure of stomata in the leaves resulting in inhibition of photosynthesis (Hamilton, 1989). Air circulation, however, prevents high relative humidity and excessively high temperatures from developing in vine canopies. In areas where the soil has a potential for high vigour, strong winds may be conducive to quality by limiting the vegetative growth of the vine.

Geology: There is little literature on the relationship between geology and wine, although a paper on this subject has recently been published in the Wynboer (Wooldridge, 2000). Geology forms an integral part of the eco-geo-pedological sequences used by Morlat (1989) and Lebon (1993) in their identification of basic terroir units in the Loire Valley and Alsace, respectively, and is considered by Dubos (1984) to be one of the most important static components of the terroir complex affecting character and quality of the final product. According to Hancock (1994), geology potentially has both direct and indirect effects on wine character and style and includes the effects of the underlying parent material, the resulting soil physical and chemical characteristics and variations in topography. It contributes to the physical properties of soils, affecting in turn the water supply to the vine. Underlying rocks can also significantly affect water supply to the vine, depending on soil depth and penetration by the vine roots. Soils originating from different parent material often have distinctive chemical compositions. Van Schoor (2001) proposed a possible effect of minerals, e.g. quartz and clay fraction kaolinite. However, the most significant effect of geology appears to be through its contribution to soil physical properties (Seguin, 1986).

Soil: The effects of soil on wine character and style are probably one of the most widely debated topics in viticulture. Soil has a definite effect on the quality of wines under the same climatic conditions but the effect is not consistent over seasons, indicating an inter-relationship between soil and climate (Saayman, 1977; Conradie, 1998). Although soil characteristics such as soil colour, temperature and chemical composition definitely play a role in the effect of soil on the growth pattern of the vine and, consequently, wine character and quality, the most convincing indications are that the main effect of soil type is through its physical properties and, more specifically, through the regulation of the water supply to the grapevine (Seguin, 1986). This must be considered in conjunction with the meso- and seasonal climate. Deep soils without chemical or physical restraints for root development will promote a well-developed root system with a high degree of buffering against climatic extremes (Van Zyl & Van Huyssteen, 1979) and contribute to constancy of the product across vintages, irrespective of the seasonal climate – the hallmark of a good terroir. But, not only does soil temper climatic extremes (such as drought and high temperatures), climate and climate-dependant factors are some of the most important parameters affecting the formation of soil (De Blij, 1983). Soil distribution can, therefore, often be related to landscape positions within a certain geological formation.

Synopsis

From the above discussion it is clear that the NTUs integrate environmental factors affecting wine character and style and that it is impossible to determine the effect of one factor without taking the other components into account. A map of NTUs is, therefore, a vital tool for a producer/ co-operative cellar/viticultural consultant to aid in the understanding of the reaction of the vine to the environment, and the style and character of the resulting wine. By linking existing block data and knowledge based on personal experience to the map, it becomes a powerful predictive tool for planning of new vineyards, as well as for planning agricultural practices. It will also aid a winemaker in his planning of the harvest and in his decision about which grapes to combine for fermentation.

The example of the Bottelaryberg-Simonsberg-Helderberg winegrowing area

A map of natural terroir units has been compiled for an area of approximately 25 000 ha to the west and south west of Stellenbosch (Fig 1).

The relatively complex topography of this area and its proximity to the Atlantic Ocean, with the resulting interplay of sea and land winds, provide many different environments for viticulture (Carey, 2001), which are well represented by the identified NTUs. These NTUs integrate aspect (taking radiation differences and effects of dominant winds into account), altitude, terrain morphology (crest, midslope, footslope, valley bottom), broad soil description and geological parent material. These factors provide a wealth of environmental information and are an important basis for studying the environmental effects on the vine phenology and production and wine character. As mentioned above, NTUs form a platform for further studies on the interaction between the environment, the vine and the resulting wine and a database of viticultural, climatic and wine related data. This goal is pursued on plots situated in close proximity to a weather station and on various landscape positions. Results from these studies will form the topic of future publications.

Literature cited

ANON., 1993. Commission I: Viticulture. Resolution VITI 2/93. Criteria for differentiating and delimiting vitivinicultural zones and regions and examination of the role played by natural and human factors. Bull. OIV. 751-752, 734.

BRANAS, J, BERNON, G & LEVADOUX, L, 1946. Elements de Viticulture Generale. Ecole Nationale d’Agriculture, Montpellier. 400 pp.

CAREY, V A, 2001. Spatial characterisation of natural terroir units for viticulture in the Bottelaryberg-Simonsberg-Helderberg winegrowing area. M.Sc. Agric Thesis, University of Stellenbosch. 90pp + annexes.

CHAMPAGNOL, F, 1984. Elements de Physiologie de la Vigne et de la Viticulture Generale. Francois Champagnol, Saint-Gely-du-Fesc, France. 351pp.

CONRADIE, W J, 1998. The effect of soil and climate on the character of Sauvignon blanc wine. In: Proc. SASEV Congress, November 1998, Cape Town, South Africa.

COOMBE, B G, 1987. Influence of temperature on composition and quality of grapes. Acta Hort. 206, 23-33.

CROWE, P R, 1971. Concepts in Climatology. Longman Group Limited, London. 589 pp.

DE BLIJ, H J, 1983. Wine. A Geographic Appreciation. Rowman & Allanheld, New Jersey. 239 pp.

DUBOS, J, 1984. Importance du terroir comme facteur de differenciation qualitative des vins. Bull. O.I.V. 57 (639), 420-434.

DUMAS, V, LEBON, E & MORLAT, R, 1997. Differenciations misoclimatiques au sein du vignoble alsacien. J. Int. Sci. Vigne Vin. 31 (1), 1-9.

FALCETTI, M, 1994. Le Terroir. Qu’est-ce qu’un terroir Pourquoi l’etudier Pourquoi l’enseigner Bull. O.I.V. 67, 246-275.

GLADSTONES, J, 1992. Viticulture and Environment. Winetitles, Adelaide. 310pp.

HAMILTON, R P, 1989. Wind and its effects on viticulture. Austr. Grapegr. Winemaker, March, 16-17.

HANCOCK, J M, 1994. Geology. In: ROBINSON, J, (Ed). The Oxford Companion to Wine. Oxford University Press, Oxford. 1088pp.

KLIEWER, W M & TORRES, R E, 1972. Effect of controlled day and night temperatures on grape coloration. Am. J. Enol. Vitic. 23 (2), 71-77.

LAVILLE, P, 1993. Units de terroir naturel et terroir. Une distinction necessaire pour redonner plus de coherence au systeme d’appellation d’origine. Bull. O.I.V. 745-746, 227-251.

LEBON, E, 1993. De l’influence des facteurs pedo- et misoclimatiques sur le comportement de la vigne et les caractristiques du raisin. Application  l’etablissement de critres de zonage des potentialits qualitatives en vignoble climat semi-continental (Alsace). Doctorat en Sciences de la Terre thesis, University of Burgundy. 165 pp + annexes.

MORLAT, R, 1989. Le terroir viticole: contribution  l’tude de sa caracterisation et de son influence sur les vins. Application aux vignobles rouge de Moyenne Valle de la Loire. PhD Thesis, University of Bordeaux II. 289pp + annexes.

PRESTON-WHYTE, R A & TYSON, P D, 1988. The atmosphere and weather of Southern Africa. Oxford University Press, Cape Town. 374 pp.

SAAYMAN, D, 1977. The effect of soil and climate on wine quality. In: Proc. Int. Sym. Quality of the Vintage, February, Cape Town, South Africa, 197-208.

SEGUIN, G, 1986. ‘Terroirs’ and pedology of wine growing. Experientia 42, 861-873.

SCHULTZ, R E, 1997. South African Atlas of Agrohydrology and -Climatology. Water Research Commission, Pretoria, Report TT82/96. 276 pp.

VAN SCHOOR, L H,2001. Geology, particle size distribution and clay fraction mineralogy of selected vineyard soils in South Africa and the possible relationship with grapevine performance. M.Sc. Agric Thesis, University of Stellenbosch. 113pp.

VAN ZYL, J L & VAN HUYSSTEEN, L, 1979. Die indeling van gronde volgens potensiaal vir wyndruiwe met spesiale verwysing na die Bo-Bergriviervallei. Wynboer July, 46, 55-61.

WOOLDRIDGE, J, 2000. Geology: A central aspect of terroir. Wynboer December, http://www.wynboer.co.za/recentarticles/1200geology.php3.

* Sections of this paper presented in partial fulfilment of the M.Sc. Agric. (Viticulture) degree at the University of Stellenbosch

About the Authors:

V A Carey1*, E Archer2 & D Saayman3

1. ARC Infruitec-Nietvoorbij, Stellenbosch.
2. Department of Viticulture and Oenology, University of Stellenbosch, Matieland.
3. Distell, Stellenbosch.
*Present address: Department of Viticulture and Oenology, University of Stellenbosch, Matieland. E-mail: vac@sun.ac.za.

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