What is the secret of what is referred to as mineral wine, such as a «Vin du glacier», a glacier wine from Switzerland’s Valais region, or the «Tracce di Sassi», a Merlot from Ticino that bears traces of sedimentary rock? Can geological flavours from the ground beneath a vineyard give the wine a spicy mineral note? In short, is it possible to taste the stone beneath the wine?

A subjective field of experimentation

There is divided opinion concerning the issue of minerals and wine. According to Rainer Kündig from the Swiss Geotechnical Commission, there are two distinct camps of «believers». «I have talked to winegrowers who are convinced that their wines have aroma components that stem from minerals. But there are others who think that any talk of a taste of stone in the wine is rubbish.» The earth scientists have thus tackled a controversial topic that can even be regarded as a subjective field of experimentation «on the interface between unambiguous geological links and suppositions, between what we feel intuitively and what we are taught, between intuition and hard evidence».

The project with the modest title «Stein und Wein» (Stone and wine) has the ambitious aim of «getting to the bottom of geology as a factor in the Swiss winegrowing regions». Together with a team of 40 authors who are «wine lovers with a background in geology and wine experts with an interest in geology» from across Switzerland, Kündig is working on a comprehensive book that examines and classifies the wine regions by geological subsoil rather than cantonal boundaries.

Iron, manganese and Pinot noir

Willi Finger, another geologist with an interest in wine and member of the editorial team, uses the following example to explain the approach followed by their «wine geology» of Switzerland: «The fundamental question is whether rock and deposits of mineral elements in the subsoil – limestone, gneiss and gypsum or calcium, silicon, sulphur and iron respectively – have an effect on the vine and on the wine. In order to find an answer, we carried out a geological and sensory examination of Swiss wine regions with unusual rock bases as well as their produce.» One example is the vineyard in Sargans at the foot of Mount Gonzen. This is the site of the largest iron and manganese deposits in Switzerland, estimated at 5.5 million metric tons. An ambitious winegrower is cultivating the «quite challenging» Pinot noir grape directly adjacent to the iron mine, which was closed down in 1969. Willi Finger tells us that while no clear note of iron or manganese was detected during blind tasting, there was agreement on the high quality of the wines produced in this region.

Is this due to the special geological make-up at the base of the Gonzen mountain? The two scientists from ETH Zurich assume this to be the case. «There are many factors which indicate that the rock base influences the growth of a vine», says Rainer Kündig. For example, vines absorb the rock’s mineral elements dissolved in the groundwater through their roots. «In fact the earth – as a substrate for the plant – is a product of the weathering of bedrock, combined with biological and geomorphologic processes.»

Some of the vineyards in Zurich are rooted in molasses sediments – debris deposits that were washed from the Alps down into the foothills around 30 million years ago. Later, during the Ice Ages, lots of moraine material from the drainage basin of the Linth Glacier was deposited on top of those. «However, it would be an exaggeration to claim that you can taste these ice age remnants in the wine», says Kündig. «Taste is always a subjective experience.» Willi Finger adds: «Our main objective with the book we are writing is to provide geological expertise regarding one of humanity’s oldest cultural assets.»

In addition to a brief outline of the geological record, a chapter on Switzerland’s geological diversity and a botanical excursus on the origin and spread of the types of grape in the region, the book includes a geological and oenological presentation of ten Swiss wine regions.

Geo-oenological discoveries

The visualizations provided in this special «wine geology» are also fascinating for the reader. The 3D depiction of a topography – a GoogleEarth image of a certain region – is supplemented by superimposing a geological map. This allows even non-expert readers to understand the relationships between stone and wine. For instance, the visualization for the area around the municipality of Fully in Lower Valais shows why the wines from the region might have different tastes. Although they are all cultivated on alluvial fans, the composition of the loose rock material in the individual fans varies because the rock layers piled above the vineyards are different.

«Apart from the transfer of knowledge, we also want to encourage others to make geo-oenological discoveries, to experiment and to sample the taste – for example of the wines from Lower Valais» the two geologists agree. Willi Finger says that while working on the project he was pleasantly surprised again and again by the diversity and quality of the Swiss wines. «The wines from the east of Switzerland didn’t have the best reputation. But nowadays there are excellent wines from Basel to Graubünden, and we also made real finds in the cantons of Uri and Glarus.» Rainer Kündig emphasizes the openness especially of the young winegrowers around the country: «Many of them are interested in scientific connections in the area of wine cultivation or are training at wine academies to become professional wine tasters.» Speaking of a sense of smell and taste: «I hope our book will create an appetite for more. Shall we finish our discussion by comparing «gypsum wines» from the cantons of Aargau and Waadt?»

Book and Event

More information on «Stein & Wein – Die Geologie der Schweizer Weingebiete» (Stone and wine – the geology of the Swiss wine regions), which is expected to be published at the beginning of 2014.
Interested parties can find out more about «Stein & Wein» at the ETH Treffpunkt Science City on 16 November (focusTerra, NO building).