I met on the spot in 2016 in Beaujolais an extraordinary woman named Isabelle Letessier, a soil scientist by profession, but above all passionately busy reading the bowels of the Earth like others the maps of the sky. A soil specialist who launched, in 2009, a telluric cartography among 14,500 hectares of vineyards and more than 300 types of soil concealed in this magnificent region located between Mâcon in the north and Lyon in the south.
Nearly 15,000 auger surveys (an instrument for taking underground cores) and 1,000 pits dug two meters deep later, the lady completed a painstaking job which, in April 2018, saw Beaujolais labeled “Geopark World of UNESCO”. We will certainly not blame Isabelle Letessier for lacking sagacity or for being a superficial woman!
Are we staying on the surface of things or, more seriously, is the incredible local pedodiversity where blue stones and golden stones, pink granites, clays and pebbles, schists, saprolites and other microdiorites jostle enough to justify the relationship between the vine and the wine? “The soil is a fragile heritage built over millennia”, she confided recently, while specifying that “the soil is none other than a stack of pedological horizons whose structure differs from that of the parent material, because it was acquired under the effect of interactions between mineral and organic constituents”. This, over a period of several million years.
Multifaceted explanation
Understanding the real effects of terroir on wine is much more complex than one might imagine, even if this same terroir remains, in the words of his colleague Nicolas Besset, “a human invention”. To dig a little deeper, we asked a simple question for a complex answer based on our own viticulture in Quebec: “We are identifying the soils and subsoils to define areas suitable for growing vines in Quebec. Is this soil identification operation really important to us and, if so, why can’t the vines, whether from here or elsewhere, be planted anywhere with results that would positively confirm or not that the soil/varietal/climate/terroir adequacy works? “Let’s try an explanation by leaving the floor to the soil scientist…
“Planted anywhere, it still seems daring to me, dear Mr. Aubry, who, I understand, tries a little to provoke me! I would tend to place in the first place the analysis of all the climatological aspects which make it possible to define a range of reasonable grape varieties, i.e. the sum of temperatures, the risks of frost, the climatic conditions more or less “favorable” to mildew and to other diseases, the distribution of rain vis-à-vis the water route of the vine, to arrive at the desirable establishment of the progressive constraint during the ripening period, the dream of any winegrower…” Goes for the weather, but as As the lady points out, “there are also many interactions/feedbacks between soils and current, future, but also past climates”. Yes, but still?
“Some soils naturally heat up faster (colour, stoniness, drying), others drain better, some store 40 liters per square meter, others 400!… and all this inevitably has an impact on the grapes, the yields , maturities and aromatic balances. If the soil/climate correlation seems a little more obvious, what separates us, besides the climate at home in Quebec, from the Beaujolais vineyard, is elsewhere, while the continents were or were not covered with ice, as Isabelle Letessier points out: “The long duration of weathering of granites, for example, allows in Beaujolais or Côtes-du-Rhône the formation of thick and surprising alterites, even on steep slopes. These alterites (or saprolites) contribute enormously to the functioning of soils in temperate regions that have not been covered by ice caps. But the climatic zones which only “deglaciated” about ten thousand years ago (as I suppose in Quebec) will be very different, because the ice caps have the power to plane the alterites and also the old soils . The contribution of these alterites to the functioning of the soil will therefore be very different. »
The pedologist concludes that the current climatic upheavals “will never replace the tens or hundreds of thousands of years spent altering the hard rocks and changing the soils, keys to the functioning of many vineyards”. She invites us in Quebec to explore and identify “as precisely as possible”, because, as she so rightly mentions, quoting Albert Camus: “Nothing is given or promised in fact, but everything is possible for those who agree to undertake and risk. »