Terroir Australia - What Terroir Australia does

What Terroir Australia does

Terroir Australia , as its name implies, is firmly grounded in the concept of terroir. Part of the rationale behind that are the observations, repeated over many years of experience as a field geologist, that:

Soil type - more accurately, soil composition and texture - are controlled to a large extent by the composition of the underlying "parent material" (rock/weathered rock, alluvium, scree, wind-blown silt or sand, etc.);

Native vegetation (its density, height/vigour, and species mix) usually reflects the underlying geology.

The degree to which the vegetation cover changes from one rock type (and soil composition) to another ranges from very weak and subtle - even nil in some tropical environments - and depends upon:

Differences in composition, texture and structure between adjacent rock types;

Climate.

Effect of geology and soil on vegetation

In very general terms, vegetation contrast increases - not unexpectedly - with increasing contrast between rock types and, of course, soil compositions. It also increases in a very general sense with increasingly dry, and with increasingly cold, (excluding polar) climates.

	Variation in vegetation cover with rock type - Clare Valley, S.A.

			The image (left) is an example - from one of Australia's better-known wine-producing areas - of the influence of geology on native vegetation. The darkest bands of vegetation, with the largest, tallest trees, are on deep red-brown clay-rich soils overlying dark grey dolomitic shale and dolomite. Shaly rocks containing no dolomite but various amounts of quartz have a paler, thinner soil cover and a thinner, lower vegetation cover. Rocks composed predominantly of silt or sand-size quartz grains have the thinnest, palest, "meanest" soils and sparsest vegetation cover (palest bands; commonly grassy). Some "bands" contain abundant acacias, while adjacent ones contain few or none; there are numerous other vegetation differences.

Geology, soil, and grapevines
It seems logical that if geology and soils can exert marked influences over the many species in a native vegetation ecosystem, they should affect the growth and characteristics of a single plant species such as Vitis vinifera - the wine-grape vine - when it is planted over an area containing various rock types and/or soil compositions.

France
The French have long believed that this is so, and nowhere more so than in Burgundy (Bourgogne). Aside from all the disputation about the influences of vignerons and winemakers on the vines and wines of the Côte d'Or (the most northerly and most famous part of Bourgogne), there is clear evidence in the wines themselves that the geology and soils of those hallowed slopes produce year after year the same underlying characteristics, regardless of maker.

The predominant soil of the northern Côte d'Or, the Côte de Nuits, is shallow (~30 cm), variably stony, red-brown clay overlying limestone (darker, orange to tan colours in map reproduced below). Pinot noir is almost the sole wine product of this area, and "Nuits" reds are characteristically firm, restrained or "backward", relatively tannic, deep coloured, and long lived. The French often refer to them as "masculin".

In the southern part of the Côte d'Or, the Côte de Beaune, limestones are replaced by marl (calcareous mudstone or siltstone) and marly shale (paler orange and buff colours on map above) as the main rock types, and the soils are thicker, paler, and more "sandy" (or silty) than those typical of the Côte de Nuits. The Côte de Beaune is best known for chardonnay, but it also produces some excellent pinot noir (for example, Pommard and Volnay). Beaune reds are typically more aromatic, forward or "soft" and supple than those of Nuits, less tannic, commonly a little paler, and less long lived. Not surprisingly, the French call such wines "feminin".

A greater contrast exists between the wines and the geology & soils of the Côte d'Or and of southernmost Burgundy - Beaulolais, respectively. The geology of the better vineyards of Beaujolais (the Villages) is dominated by granitic rocks and "sandy" soils; there is little of the sort of limestone or "marl" found in the Côte d'Or. Through centuries of "trial and error", it has been found that the grape variety that does best here is not pinot noir, not chardonnay, but gamay - the grape responsible for the seductive red wine of Beaujolais.

Italy
Another well-known example of the effect of geology and soils on wine is to be found in the Piemonte region of Italy. Nebbiolo grown in the La Morra-Barolo area, which is underlain by calcareous marl (silty mudstone containing calcium carbonate), produces Barolo that is aromatic, soft and "fruity", and ages relatively quickly. Rocks underlying the area of Castiglione Faletto and Monforte d'Alba, to the east, include a relatively high proportion of sandstone, which results in less fertile, more free-draining soils. Barolo from this area is usually firmer, more intense, and longer lived than the typical Barolo of La Morra (Robinson, 1994).

Australia
Coonawarra is probably Australia's best-known example of the influence of terroir - its geology and soil components in particular - on vines and wine. The famed narrow strip of terra rossa soil that is the "core" of Coonawarra and consistently produces the best wines is distinctive in both geological and soil terms.

The Coonawarra terra rossa; is underlain by a geological formation known as the Padthaway Formation, which consists of silty to sandy sedimentary rocks that are variably calcareous (calcium carbonate bearing) and variably ferruginous, along with minor amounts of "fresh-water limestone". Along the terra rossa strip, this sedimentary rock is particularly sandy, ferruginous (iron-rich), and calcareous (it is possible that the "strip" was once an off-shore sand bar in a shallow, muddy sea or large lagoon). These properties result in a soil that, because of its relatively free-draining nature and calcium carbonate content (both sand and calcium carbonate content enhance soil drainage properties), and its high iron content, is red-brown in colour, and contains a layer of re-deposited calcium carbonate (i.e.,calcrete, which has been mistakenly identified as "fresh-water limestone" by some) at the level of the winter water table. The red-brown "terra rossa" soils are represented by the red colour in the map reproduced below.

COONAWARRA WINE REGION

The pink tones represent brown to "black" calcareous (calcrete-bearing) clay soils (calcarosols and vertosols) formed on muddier, less sandy parts of the Padthaway Formation; the green, mid blue and deep blue tones adjacent to the red terra rossa represent "black", heavy, clay-rich, non-calcareous soils that are notably poorer in potassium than the terra rossa and the brown to black soils (pink tones); and the yellow tones represent sandy soils, generally overlying yellow-brown mottled clay. The white line is the boundary of the Penola Land System as mapped by the South Australian Department of Agriculture. The Penola Land System equates with the terra rossa, and is approximately equivalent in distribution to the terra rossa as identified in the image above.

Vines grown on soils to the west and east of the terra rossa strip tend to be more vigorous and to produce higher fruit yields and wines of lesser quality than vines grown on the "terra rossa" (and the best-drained areas of "pink", "green", and "blue" soils adjacent to the terra rossa). Red-brown soils that overlie limestone (Gambier Limestone) to the east of the Naracoorte Range (the dark band that runs through the top right corner of the image) are superficially similar to the Coonawarra terra rossa. However, these soils are quite distinct in composition from the terra rossa, containing about 50% less potassium and different clay mineral(s); they are now included in the Wrattonbully Wine Region, as distinct from Coonawarra.

In the Hunter Valley, the best shiraz commonly comes from vineyards on reddish soils that have formed on volcanic rocks and sedimentary rocks poor in quartz sand. In contrast, the best sémillon, the variety for which the region is rightly famous, generally comes from vineyards on paler-coloured sandy soils, rich in quartz grains, which have formed on sandstones.

The Margaret River region of Western Australia produces some of the country's best chardonnay and cabernet/ cabernet-merlot. What is commonly regarded as Australia's best chardonnay comes from vines growing on sandy, gravelly soils formed on geologically "young" alluvial deposits. Nearby, the cabernet and merlot that produce probably our best cabernet blend come from vines growing in reddish-brown soils formed on ancient (Archaean) granitic gneiss (granite-like rock containing abundant dark Fe-Mg-bearing minerals that are aligned to give a finely layered appearance) and ferricrete (a fairly hard surface layer of usually gravelly material cemented by iron oxide and/or hydroxide and/or hydrated hydroxide) of Tertiary age (a few millions, to tens of millions, of years old).

THE Terroir Australia "BOTTOM LINE"

Great wine requires not just great winemaking, but also the best possible sites
with soils that are the best possible for the grape varieties concerned.

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