Soil sommelier: chalk
Your monthly guide to the soils grapes love
Wednesday 25 May 2022
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Chalky soil is something you’d normally consider to be integral to the wines of Loire, Champagne—even the south of England. White, dusty and highly prized for its “stony minerality”, it’s a type of soil that drains easily and is therefore perfect for growing vines on top of.
In Puglia, the chalk is hidden, but it’s definitely there. Layered under a stratum of deep red oxides that give the region its rusty colour, the chalk lays where deep roots can find it, silently filtering the cooler seasons’ rainwater deep into the ground or away from the vineyards into nearby rivers and out into the blue Aegean sea.
“Hard” chalky soils are alkaline, meaning that they have a pH of 7.1 or above. Tom Stevenson, an expert in Alsace wines (a region packed with exciting geological attributes!), points out that “High-pH (alkaline) soils, such as chalk, encourage the vine’s metabolism to produce sap and grape juice with a relatively high acid content.” The vine itself compensates for the lack of acidity in the soil, therefore creating acidic grape juice. And you know what that means—delicious, acid-forward wine!
Chalk subsoil never changes, unlike the topsoil above it. In Puglia, the fertile terra rossa can easily erode over time or be washed away by flash floods. The chalk remains below, reached into by the main arterial roots of the vines, providing ideal drainage and, equally crucially for grape vines, forcing organic matter to decompose rapidly and locking up nutritional manganese and iron within its molecular structure. There is no real goodness in calcium-rich chalk; in fact, chalky soils can cause plants to struggle and become nutrient deficient. Those grapes have to work for every morsel of goodness, creating smaller yields of higher quality grapes suited especially for winemaking.
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