Soil sommelier: Slate

Your monthly guide to the soils grapes love

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Slate is prominent in the regions of Mosel, Saar and Ruwer. Vines grow along the Mosel river and its tributaries on severe, steep slopes of blue, grey and red slate, which has a lot of useful properties besides adding to the beautiful landscape of the area.


Uses

Winemakers use the rocky soil as a heat store for their grapes, which comes in particularly useful in the early spring and late summer when temperatures aren’t as high as neighbouring winemaking regions. Slate retains heat from the sun remarkably well, and keeps the vines’ roots warmer for a longer period of the year. This means a longer growing season and, ultimately, riper grapes.

Slate is also really bad at holding moisture, which is ideal in the Mosel, Saar and Ruwer regions where it can average up to 100mm of rainfall each month. In Mosel particularly, the mornings can be damp due to mists rising from the wide river, so allowing residual moisture to drip from leaf and grape onto a fast-draining rocky slope is essential to avoid mildews and moulds taking up residence in the vineyard.


Terroir

Have you ever licked a fragment of slate? Give it a go. 

Slate has an ozonic, petrichor-ish sort-of flavour, given off by the minerals in that stone. Seriously. It’s seen by some winemakers as just as important as the grapes in their vineyards, creating what’s known as “stony minerality” — the vines have to send their roots much further into the soil to retrieve the nutrients they need, giving them much more contact with the slate below.

This minerality offers complexity and freshness to fruit-forward wines, and can create elegance and structure where there might have been low acid (Rivaner) or intense aromas (Riesling) to contend with.


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