The Impact of Terroir
Presentation given by Kees Van Leeuwan, January 2013 (for DUAD)
Several factors are key to quality in wine:
Travel in the vines (density, green harvest etc)
Origin (soil and climate)
the word comes from root 'terre' (earth, soil) but terroir is more than this concept
Natural environment (soil, climate), plus biological factors and human factors.
And importantly they all interact
Terroir = typicity and quality of an agricultural product in relation to his origin
Terroir is delimited (ie there is a spatial notion to it)
Terroir and AOC are connected, but not always on the same scale
Controversial subject in winemaking
Often rejected in new world, or at least accent is put on vinification techniques. More accepted in established regions.
Pluri-discipline subject difficult but not impossible to study scientifically
Proof of the effect: Burgundy
In Burgundy most producers possess plots in different sites
Viticulture and vinif techniques are similar
Quality and typicity of wine produced v different (grands crus, premier crus etc)
Vin de terroir / vin de marque - terroir wines and branded wines
Terroir implies single-vineyard or AOC, limited quantities, excellent traceability
Branded suggests quality from vinification techniques and blending
One is not necessarily superior to the other (eg Penfold Grange is a blended wine from different terroirs, Mouton Cadet AOC wines are terroir wines in theory but are in fact brands made from grapes coming from several producers on large scale. Haut Brion is terroir wine from one limited estate but become brand because so famous)
First terroir studies date from 1960s, by Professor Seguin at Bordeaux, defining terroir and role of water
Terroir is an interactive ecosystem, in a specific place, comprising the climate, the soil and the vines
In 2010, the OIV gave a revised description of terroir:
'Vitivinicole terroir is a concept refers to a collective understanding which develops between a biologically and physically identifiable place and the vitivinicole practises that are applied, which confer distinctive characteristics to the products made there.'
Terroir includes characteristics of soil, topography, climate, landscape and biodiversity'
The role of man:
Wine regions tend to develop near to centres of consumption, near rivers and ports, where other agricultural products have trouble growing, where the habitat is agreeable
Winemaking regions thrive over the longterm where:
Conditions are favourable to wine growing (eg no frost)
Where quality wine production is possible
(eg history of bdx winemaking, from romans to england to the classifications - but geography and economics always in play = why pomerol later than graves and medoc etc)
The grape variety
More than 1000 grape varieties but less than 100 can be considered noble.
But just having a nible variety is not enough -cabernet sauvignon prices vary from 3€ to 700€
variety confers a certain typicity to a product (but only one factor)
Each variety needs certain heat conditions to be able to ripen fully
(these are low for early ripeners such as pinot noir, and high for late ripeners such as mouvedre or nebbiolo)
The Influence of Climate
There is no ideal climate, but influencing factors are rainfall, sunshine and temperature. The important thing is the interaction between the grape variety and the climate.
In any given region, the best wines are obtained from noble grape varieties that just manage to attain ripeness under the local climate conditions - as if ripening too quickly seems to lessen the finesse of great wines (Ribereau-Gayon and Peynaud, 1960)
To produce terroir-driven wines:
- Grapes need to reach full ripeness
- Grapes should not ripen in the full heat of summer, because overly quick ripening limits the accumulation of aroma precursors
- grapes should therefore be chosen to attain their full maturity at the end of the season (between sept 10 and october 10 in northern hemisphere or march in southern hemisphere)
This is true in all AOC wine regions in Europe, where despite v different climates and v different grape varieties, maturity and harvest takes place in sept and oct -because have chosen grapes that best suit these criteria (even if choosing it without knowing why).
Often in new regions, grapes are not always selected that are best for local climate conditions, so use technology to make wine.
But move to cool climate winemaking - recognition of terroir-driven winemaking eg Carneros, Monterey in California, Central Otago in New Zealand, Hobart Tasmania the Finger Lakes in New York state (US), Margaret river in Australia
(nb WSET on cool climate wines in Australia http://www.wsetglobal.com/documents/wineaustralia2012.pdf)
Huglin Index for choosing grapes
(figures range from 1500-2300 with lower being cooler climate / early ripening
1500= muller thurgau
1600= pinot blanc
1700= pinot noir
1900=cabernet sauvignon, merlotm chenin blanc, semillon
2100=cinsault, grenach, syrah
Then have to match up local climate to the needs of the grape.
Influence of Soil
Again, impossible to define exactly what is perfect according to its texture, mineral composition, organic materials it contains and amount of living matter etc
It's a complex environment, and can be defined through its geological origin, its pedological nature, by its components when they are analysed chemically and its agronomic functions.
- Geologically, a soil can be defined through the type of rock/bedrock and its date/origin
- Geology also looks at relief and topology/influence on climate
- there may well be a geological impact on tye final wine, but it is most usually indirect
Eg Chablis vineyard, with the influence of the coquiilles in the soil (and exposition affecting vineyards, grand crus southern facing etc)
Pedological nature of soils
The composition, pedology, of soils doesn't seem to be hugely determinant - great Bdx wines are made on variety of soils (peyrosols, rendosols sur calcaire a Asteries, Calcosols sur Molasses du Fronsadais, Pelosols or Planosols)
BUT, certain soils never made good wine (podsozols sableux/sandy, reductisols, fluvisols)
The typicity of wine is influenced by bedrock and soil type (eg Saint Emilion)
The agronomic approach
Takes into account the interaction between soil and vine
The soil affects the vine through
1) temperature of the root area
2) mineral nutrition (azotes)
3) water reserves/accessibilty etc
- Dry and shallow soils are hotter
- Hot soils mean early bud break and can be one factor of early ripening
- Soil temperature can be a quality factor because it allows grapes to ripen in local regions where climate might otherwise be a problem (eg cabernet sauvignon in the Medoc, cabernet franc in the Loire)
- of all the mineral elements in soil, azote levels have the strongest influence (nitrogen)
- vines are often poor in azote, as it is strongly affected by soil parameters such as:
- Organic matter within the soil
- Temperature of the soil
- Aeration of soil
- Soil humidity
Azote nutrition is part of the overall picture of terroir
Effect on wine quality:
Poor azote status is favourable to red wines (phenolic compounds are richer)
At least a moderate level of azote is needed for aromatic white varieties such as sauvignon blanc (important to increase aroma precursors but also levels of glatathione, important to guard against premox)
(basically high nitrogen/azote = high yields)
Nb interesting study by Olivier Tregoat on soils, rootstocks and soils in 7 prestigious Bdx vineyards
http://www.oliviertregoat.com/Soils_rootstocks_and_grapevine_varieties.pdf (we can assume these are the first growths plus cheval blanc and petrus, 400ha of vines, 500 vineyard plots)
Effect of richness of soils on other minerals has less of an impact - except extreme cases such as major excess of potassium (K) which can affect the pH of wine.
But other than that, v little evidence to suggest other minerals have a determining affect on terroir-effect.
The calcium (Ca) has an indirect effect because it does affect soil structure and organic matter
Depends on climate, soil, system of working the soil and vegetal matter.
Prof Seguin studied hydric regime in 60s in Bordeaux, showed regular but low water supply important quality impact.
Hydric constraint encourages an early stopping of vine growth
Hydric constraint limits the size of the berries
Sugar levels are higher if there is moderate hydric constraint
Hydric constraint reduces malic acid levels in grapes
Phenolic compounds increase with hydric constraint
... But severe hydric constraint limits aroma precursors in sauvignon blanc
In great terroir for red wines:
- The grape variety is chosen according to climate that allows late-season ripening
- Vines suffer moderate to high hydric constraints (either the soil is dry and not irrigated) or water-retaining capacity is low
- if water is not limited, azote (nitrogen) supply must be low
= need one limiting factor
Best soils for quality red wine are shallow (Saint Emilion) or gravelly (Medoc)
Can also produce high quality wines with severe water stress as long as yields are very low (eg rhone valley old grenache)
Best soils for quality white wine have more regular water supply than that for reds. Variety still needs to be chosen for late-season ripening. Azote supply needs to be moderate but not too low.