Chester Osborn explains how geology makes such a difference to wine
UNDERSTANDING the characteristics specific to a site can help you understand what makes a wine so special, writes renowned winemaker and guest columnist Chester Osborn.
IT’S time for much more subdistrict division, what the French call terroir – the characteristics specific to a site.
Each vineyard produces its own unique wine expression. The main five grape/wine flavour factors are: climate, soil (the top layer), geology, aspect and winemaker.
While there is a relatively narrow range of temperatures in which grapevines will work, inland (continental climate) has more diurnal variation. That difference between daytime and night-time temperatures lifts the aromatic length of the wine, compared with sites close to the sea (maritime). This is quite evident in McLaren Vale.
Sandy soils produce elegant wines, due to their low particulate and micronutrient levels. Heavy grey loam soils give richness and earthy characters. Red loam make rich wines with complexities – like blood.
Geology shows more influence in the older vines. In McLaren Vale, a relatively young 2.4 million-year-old sandstone geology gives many tannin flavour types and strong earth influences. Limestone geologies vary in age but all give a strong block-like tannin.
The goal is minerality. This is where three taste sensations, fruit, acid and tannin, come together as one. Over time minerality opens up to fruit. Mineral links to wine have eluded scientists, but bacteria in similar ground has been linked to minerality flavour. If we can pinpoint the subdistricts that are alike, and fertiliser and irrigation are kept out the way, people will know what they are buying when they buy a particular subdistrict. At d’Arenberg, we have 22 single vineyard wines.
From two vineyards just 1km apart:
Coriole 2014 Lloyd Reserve Shiraz
Planted in 1919 on deep red loam over 650 million-year-old calcarious siltstone, sandstone and limestone. Shows dark fruits, rhubarb and notes of iodine and blood from red soil, the grainy structure of the limestone– and some of the spicy, gritty chocolate of sandstone.
d’Arenberg 2012 The Other Side Shiraz
Planted in 1918 on grey loam over 34-56 million-year-old limestone. Shows intense rich earthiness from grey loam, various loud vibrant shiraz fruits, and tonnes of blocky, chocolate, earthy tannins representing the younger, strongly expressive geology.
Chester Osborn is chief winemaker at d’Arenberg, McLaren Vale