Slate / Blue Devonian Slate (Mosel: Heat Absorption; Petrol in Aged Riesling)

The Mosel's slate dates to the Devonian, about 400 million years ago, when a primeval ocean covered today's Mosel country and sediment layers several kilometres thick built up on its floor. When the ancient continents Gondwana and Laurussia collided, that ocean was pushed together between the plates and its floor compressed under enormous pressure and high temperatures; the sediments became slate, which folded up into a mountain range, the Rheinisches Schiefergebirge. About 15 million years ago the ancestral Mosel began to shape the landscape: as the slate uplands rose, its once broad, straight bed cut deeper and grew more winding. Half of the region's vineyard area (no year given) lies on Devonian slate in blue, grey, brown and reddish shades, often so finely layered that it can be broken by hand, and the rock weathers easily. The Lower Mosel, or Terrassenmosel, between Zell and Koblenz differs: there quartzitic sandstones with silt and clay slate make up most of the soils. The roots of the vines penetrate deep into the ground to seek water and minerals.

• Origin: Devonian ocean sediments, compressed under enormous pressure and high temperatures when Gondwana and Laurussia collided, became slate
• Colour and texture: blue, grey, brown and reddish; often so finely layered it breaks by hand; the 400-million-year-old rock weathers easily
• Soils by sub-region: clayish slate and greywacke in the lower Mosel, Devonian slate in the steep sites of the middle Mosel, primarily shell limestone in the upper Mosel; the Saar's soil is predominantly dark Devonian slate, with diabase, a rock of volcanic origin, in some sites
• Ürzig exception: rhyolite, a volcanic rock of entirely different origin, occurs only within the boundaries of Ürzig on the great Mosel bend; the Würzgarten's soil is red weathered slate with a high rock content, its vivid colour from high iron concentrations

The protected valley location makes the Mosel one of the warmest climates in Germany, and the steep slate slopes above the rivers store the sun's heat during the day and release it again at night. Local growers know that Riesling can be ripened only on the sunniest south- and south-west-facing sites, steep enough and close enough to the river to benefit from its function as mirror, on porous slate soils that drain away the region's frequent surplus rainfall and "retain daytime heat to act as night storage heaters". Slate's heat storage is a considerable advantage in cool autumn nights. At site level, the dark soils of stony weathered Devonian slate in the Bernkasteler Doctor serve as an additional heat store while securing water supply through their water-holding capacity.

• Heat storage: steep slate slopes store the sun's heat by day and release it at night
• River as mirror: the best sites face south or south-west and sit steep enough and close enough to the river to benefit from its function as mirror
• Slope: the Doctor faces the Mosel at up to 70 percent and the Würzgarten's Riesling grows on slopes up to 80 percent steep
• Drainage: porous slate soils drain away the region's frequent surplus rainfall

TDN (1,1,6-trimethyl-1,2-dihydronaphthalene) has been called 'delicious' but 'undesirable' in excess, because it can give a kerosene-like aroma in some wines, depending on the age of the wine and individual preference. It is an important part of the bottle-aged bouquet of Riesling, with levels up to six times higher than in other varieties. Free TDN is generally not present in significant quantities in grapes or juice. Its formation depends on carotenoids, which build up in the early stages of fruitset and break down from veraison onwards into C13-norisoprenoids; these, including compounds that give rise to TDN, may attach to sugar molecules, forming a slow-release flavour reservoir from which TDN can emerge during storage. Sun exposure is by far the most studied and accepted contributor to TDN; concentrations increase with bottle age, and more acidic wines have been shown to develop TDN more quickly than others. This TDN research, from a 2012 Australian Wine Research Institute report, addresses Riesling generally; it does not attribute TDN to slate.

• Formation: grape carotenoids break down from veraison into C13-norisoprenoids, including the compounds that give rise to TDN, which can emerge during storage
• Detection: a 2012 study revised the sensory detection threshold, once believed to be 20µg/L, to 2µg/L, and 50% of the population should be able to perceive (but not necessarily recognise) TDN in most Riesling wines
• Vineyard factors: TDN and its precursors increase when grapes are exposed to sunlight and warm temperatures; early harvesting and shading berries are two management strategies
• Bottle factors: concentrations increase with bottle age; in one study, samples stored at 30°C showed considerably higher increases than those stored at 15°C; cork and synthetic closures absorbed more than 50% of the TDN over two years in bottle, while wines under screwcap did not lose any

Devonian slate dominates the steep sites of the middle Mosel, the Bernkastel district that runs from Briedel to Trier. Most of the region's vines stand here, on 5,518 hectares (no year given), and the soils of the steep slopes consist largely of weathered slate. Klüsserath, Trittenheim, Piesport, Brauneberg, Bernkastel, Graach, Wehlen, Zeltingen, Ürzig and Erden lie along this stretch. A series of sundials stands high on the dark slate cliffs of the Middle Mosel around Bernkastel-Kues; the Wehlener sundial was erected in 1842 by the vineyard's owner, Jodocus Prüm, and the site took its name from it around the year 1900. Further north lie the steep red slates of Ürziger Würzgarten and Erdener Prälat. On the Saar, between Serrig and Konz, the soil is predominantly dark Devonian slate.

• Wehlener Sonnenuhr (one of Selbach-Oster's own sites): a steep, purely south-facing slope opposite Wehlen; medium to large Devonian slate chunks in the topsoil over a subsoil of weathered slate with a little loam
• Bernkasteler Doctor: faces the Mosel at up to 70 percent above Bernkastel's old town, turning from southwest to south; dark soils of stony weathered Devonian slate with a high share of fine earth; soil listed as blue and grey slate; 130 to 190 metres
• Ürziger Würzgarten: a south- to southeast-facing amphitheatre opposite Erden; red weathered slate with a high rock content, listed as red volcanic and slate soil; slopes up to 80 percent; 110 to 220 metres
• Saar: vineyards between Serrig and Konz, often on the south slopes of side valleys; predominantly dark Devonian slate, with diabase in some sites

The components of the easily weathering slate enrich the soil, and the Mosel's regional wine body links them with Rieslings it calls as mineral here as nowhere else. Mosel winemakers produce fine, fruity wines with an enormous depth of flavor and a relatively low alcohol content. Many Saar and Ruwer wines reach barely 8 or 9% alcohol yet are capable of ageing extremely well, thanks to their intensely fruity acidity and mineral-layered extract, and the Middle Mosel produces some of the valley's most complete, longest-lasting wines.

• Minerality: slate's components enrich the soil and are linked with Rieslings that the regional wine body calls as mineral as nowhere else
• Fruit and depth: fine, fruity wines with an enormous depth of flavor
• Alcohol: a relatively low alcohol content, with many Saar and Ruwer wines at barely 8 or 9%
• Ageing: Saar and Ruwer wines capable of ageing extremely well; the Middle Mosel produces some of the valley's most complete, longest-lasting wines

Selbach-Oster, based in Zeltingen, picks all the grapes of a parcel together regardless of ripeness, pressing and vinifying them together, an approach the estate presents as giving an unvarnished picture of the terroir; its parcels include Anrecht (in the Zeltinger Himmelreich), Schmitt (in the Zeltinger Schlossberg) and Rotlay (in the Zeltinger Sonnenuhr). VDP member estates working the Doctor include Schloss Lieser (Thomas Haag), Wwe. Dr. H. Thanisch (Erben Thanisch) and Geheimrat J. Wegeler (Gutshaus Mosel), and in the Würzgarten Reichsgraf von Kesselstatt and Dr. Loosen. One leading wine reference names, as sources of the Mosel's best-value Kabinett and Spätlese wines from individual sites, producers including J J Prüm, Selbach-Oster, Dr Thanisch, Dr Loosen, Fritz Haag, Egon Müller and Zilliken.

• Selbach-Oster (Zeltingen): whole-parcel single-pass picking for its Anrecht, Schmitt and Rotlay parcels; Anrecht has flaky Devonian slate in the subsoil, and the Zeltinger Sonnenuhr's topsoil is coarse Devonian slate over weathered clay slate
• Bernkasteler Doctor: VDP member estates Schloss Lieser (Thomas Haag), Wwe. Dr. H. Thanisch (Erben Thanisch) and Geheimrat J. Wegeler (Gutshaus Mosel)
• Ürziger Würzgarten: VDP member estates Reichsgraf von Kesselstatt and Dr. Loosen
• The same best-value Kabinett and Spätlese list also names Clemens-Busch, Grans-Fassian, Reinhold Haart, Heymann-Löwenstein, von Kesselstatt, Schloss Lieser, Carl Loewen, Max Ferd Richter, St Urbans-Hof and Van Volxem, among others

Primary sources (Deutsches Weininstitut / Wines of Germany, Moselwein e.V. at weinland-mosel.de, the Australian Wine Research Institute, the VDP, and Selbach-Oster for its own sites): https://www.winesofgermany.com/our-regions/growing-area/72/mosel, https://www.weinland-mosel.de/de/die-region/wurzeln-geologie, https://www.weinland-mosel.de/de/die-region/die-teilregionen, https://www.awri.com.au/wp-content/uploads/Sept-Oct-2012-AWRI-Report.pdf, https://www.vdp.de/de/die-weine/weinbergonline/lage/4129-wuerzgarten, https://www.winesofgermany.com/our-regions/highlight-of-wine-culture/361/the-sundial-vineyards, https://www.vdp.de/de/die-weine/weinbergonline/lage/4032-doctor, https://selbach-oster.de/lagen/. Secondary sources: https://www.jancisrobinson.com/learn/wine-regions/germany/mosel, https://www.decanter.com/wine-travel/the-middle-mosel-for-wine-lovers-520200/. Last verified 2026-10-04