N
A T U R A L T E R R O I R U N I T S
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
_________________________________________________________________________
Terroir and natural terroir units
Terroir
is not a new concept. We know that
the Eqyptians (3000 B.C.) had and 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 catagories, 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 terrior 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.
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 (Sequin, 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, interalia, 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 wine, 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 (1ºC decrease per 100m
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, with day temperature playing the
preponderant role (Kliewer & Torres, 1972). Optimum mean temperature for pigment formation is in the
region of 20 – 22ºC (similar pattern for phenolics) and a mean temperature
range of 20 – 22ºC 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 that 3 – 4m.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, 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 (Sequin, 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 the
regulation of the water supply to the grapevine (Sequin, 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 NTU’s 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 NTU’s 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 & LEVAADOUX, L, 1946. Eléments de Viticulture Génerale.
Ecole Nationale d’Agriculture, Montpellier. 400pp.
CAREY,
VA, 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. Eléments de Physiologie
de la Vigne et de la Viticulture Générale.
Francois Champagnol, Saint-Gely-du-Fesc, France.
351pp.
CONRADIE,
WJ, 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,
BG, 1987. Influence of temperature
on coposition and quality of grapes. Acta
Hort. 206, 23-33.
CROWE,
PR, 1971. Concepts in Climatology.
Longman Group Limited, London. 589 pp.
DE BLIJ,
HJ, 1983. Wine. A Geographic Appreciation.
Rowman & Allanheld, New Jersey.
239pp.
DUBOS,
J, 1984. Importance du terroir
comme facteur de différenciation qualitative des vins.
Bull. O.I.V. 57 (639), 420-434.
DUMAS,
V, LEBON, E & MORLAT, R, 1997. Différenciations
mésoclimatiques 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,
RP, 1989. Wind and its effects on
viticulture. Austr. Grapegr.
Winemaker, March, 16-17.
HANCOCK,
JM, 1994. Geology.
In: ROBINSON, J,
(Ed). The Oxford Companion to Wine.
Oxford University Press, Oxford. 1088pp.
KLIEWER,
WM & TORRES, RE, 1972. Effect
of controlled day and night temperatures on grape coloration. AM. J. Enol. Vitic. 23 (2), 71-77.
LAVILLE,
P, 1993. Unités de terroir naturel
et terroir. Une distinction nécessaire
pour redonner plus de coherence au système d’appellation d’origine.
Bull. O.I.V. 745-746, 227-251.
LEBON,
E, 1993. De I’influence des
facteurs pédo- et méso-climatiques sur le comportement de la vigne et les
caractéristiques du raisin. Application
à l’établissement de critères de zonage des potentialities qualitatives en
vignoble à climat semi-continental (Alsace).
Doctorat en Sciences de la Terre thesis, University of Burgundy. 165pp + annexes.
MORLAT,
R, 1989. Le terroir viticole:
contribution à l’étude de sa caractérisation et de son influence sur
les vins. Application aux vignobles
rouge de Moyenne Vallée de la Loire. PhD
Thesis, University of Bordeaux II. 289pp
+ annexes.
PRESTON-WHYTE,
RA & TYSON, PD, 1988. The
atmosphere and weather of Southern Africa.
Oxford University Press, Cape Town.
374pp.
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,
RE, 1997. South African Atlas of
Agrohydrology and –Climatology. Water
Research Commission, Pretoria, Report TT82/96.
276 pp.
VAN
SCHOOR, LH, 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,
JL & 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.
