The physical aspects of Sangiovese terroir: Brunello di Montalcino DOCG

Brunello di Montalcino, as is the case for fellow DOCG Vino Nobile di Montepulciano, falls fully within the boundary of Chianti’s Colle Sensei DOCG. That is not all that the two regions share; they are also both sources of high-quality Sangiovese wines. I have previously described the physical characteristics of  Vino Nobile de Montepulciano and will conduct a similar exploration of Brunello di Montalcino in this post.

Brunello di Montalcino DOCG’s wine production zone is largely coincident with the borders of the commune of the same name. The region extends over 2450 ha of a square-based hill whose lowest point is 150 m, rising to 630 m at its peak.

The climate is Mediterranean with moderating effects from the sea (40 km away), the surrounding rivers, elevation, and Mt Amiata to the southwest. The climate zones run from north to south. (According to Monty Waldin (Brunello: The many crus of Montalcino, Decanter, 3/19/15), 30 - 35% of Brunello is sourced from the cooler grounds north of the town (yielding paler Brunellos) with the remainder from the warmer south (darker colored, more overtly fruity, savory wines)). Precipitation occurs mostly in the spring and late autumn with average annual rainfall of 700 mm. There is potential for snow at elevations above 400 m. Steady winds allow for the growth of healthy vines while the presence of Mt Amiata to the southwest provides a barrier against storms and hail.

Landscape and Soils

The continued eastward movement of the Northern Apennines has resulted in the creation of a number of long (up to 200 km), narrow (up to 25 km wide), NE – SW-oriented structural depressions on the western side of the mountains in the Tuscany region. These depressions are bounded by normal faults along the margins and subdivided into basins by transfer zones/faults.

Source: Brogi, et al., 2013, Figure 1.

The Siena-Radacofani is one such basin (Past works have referred to them as two separate basins but recent scholarship have "highlighted a common structural evolution, with tectonic features extending from one basin to the other" (Martini and Aldinucci, November 2017).). It is bordered to its left by the pre-Neogene (pre-23 million years ago (mya)) bedrock of the Montalcino Ridge and the Neogene-Quaternary (23 mya to present) magmatic rocks of Mt. Amiata, and to its right by the pre-Neogene bedrock of Mt Cetona and the Cetona Ridge. 

The pre-Neogene rocks of the basin are primarily composed of two superimposed thrust units (Martini, et al.):

·       Tuscan Unit

o   Lower portions range in age from Triassic (252.2 mya) to Oligocene (33.9 mya)

o   Exposed rock consists primarily of shelf components and turbiditic, poorly cemented sandstones (Macigno)

·       Ligurides

o   Range in age from Cretaceous (146.5 mya) to Eocene (33.8 mya)

o   Consists primarily of basinal silaceous limestone and argillaceous limestone (marlstone).

Source: Martini, et al.

The Siena-Radicofani Basin began to form on the pre-Neogene substrates during the middle Miocene and “a thick sedimentary pile accumulated mainly during the early Pliocene." The turbiditic sandstone associated with the Tuscan Unit of pre-Neogene rocks appears to be the major contributor of sand for the basin. Other substrate rocks contributed pebbles, limestone cobbles, metamorphic detritus, and some sand.

The basin emerged toward the end of the Early Pliocene and, after a general uplift, no younger sedimentary record is apparent. Magmatism has affected the southern portion since the early Pliocene and volcanic eruptions occurred during the Pleistocene (1.8 mya – 10,000 years ago). The chart below shows the impact of post-Paleogene depositional activity on the Siena sub-basin and surrounds, to include, specifically, Montalcino.

The following charts display the soils composition in Colli Senesi and its major sub-zones. While Colli Senesi and Nobile di Montepulciano are dominated by marine sands, Brunello di Montalcino shows conglomerates as the major soil type while Chianti Classico shows marly limestone and marls and turbidites.

Source: Table 1, Bonini and Sani 2002

In an effort to gain an even finer definition of Brunello wines, a sub-zoning proposal (spearheaded by wine writer and educator Kerin O'Keefe) -- with the nomenclature and relative characteristics indicated in the chart below -- has been advanced.

But all hands are not on board with this proposal. According to Waldin, "Vineyards zoned in less highly regarded spots may be penalized by the media and then by the marketplace." In a blog post, Stefano Cinelli Colombini, owner and winemaker at Fattori dei Barbi, states that sub-zoning only works on paper, given the diversity in Montalcino vineyards. In a response to one of the comments on his post he notes that, in mapped areas, soil and geography stays constant but weather and things associated with humans are changeable. "You cannot make a reliable map of quality areas," he says. 

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