Feeding the horses on another warm dry day, the recurrence of a contemplation enters my thoughts. Glancing up the hill to the rocky hillside field that grazes said horses I wonder if this warm weather becomes part of the Irish climate we could consider ripening grapes on these rocky hillside slopes. Vines are, after all much happier on poorer soils, producing more concentrated fruit when struggling for survival. Vines like any other plants and beings work harder on the success of future generations when their environment is not entirely sustaining. But these contemplations are just a prelude, an introduction to an insight on soil and its effect on the vine and resultant wine.
“It is impossible to establish any correlation between quality of wine and the soil content of any nutritive element… if there were such a correlation it would be easy, with the appropriate chemical additives, to produce great wine anywhere.”
An observation by Dr Gerard Seguin, an influential professor in the study of soil and terroir, that exemplifies the lack of understanding still sitting behind discussions on the roots of quality in a bottle of wine.
Seguin states that the physical characteristics of soil predominate as the main influence over grape and wine quality, discounting climate as the major factor. Advances in Science have recently concluded similar findings.
Water and soil, a symbiotic relationship. Top terroirs have soil with the capacity to release water when the vine needs it, the famous blue clay mounded in the middle of the vineyards of Petrus in Pomerol are credited as the reason these vines produce such spectacular wines. It’s a balancing act: Replenished over winter the water table drops gradually from spring to autumn, the perfect terroir will leave a vines roots just out of reach come August and veraison. Shoots and green growth halt sending energy and concentration into the berries.
The dark slates of the Mosel valley, the white albariza soils of Jerez. These visual differences mark valuable properties for the vine. Dark slates hold heat and warm the vines into the evening on the steep east facing slopes that may otherwise struggle to ripen grapes in a cooler year. Sweltering heat and drought are buffered by the white albariza soils capacity to reflect the heat and harden over any moisture, reducing evaporation rates and preserving any valuable water that lands on the vineyards.
Large rocks, round stones, gravel; unwelcoming to most plants, a responsible host for vines. Look at Bordeaux, a region of two halves, designated by the gravel / clay differences found on either side of the Gironde. Traditionally a marginal maritime climate with late springs, the Bordelais found the left bank gravels gave the later ripening Cabernet Sauvignon a head start come spring as their free draining rocky soils warmed up quicker than the stodgy clay based right bank vineyards. The pudding stones of Chateauneuf du Pape, retaining warmth to boost the sun greedy Grenache. Essential elements in successful viticulture.
Soil composition. The subject of much study, a black spot in the understanding behind the relationship between soil and wine quality.
- Nitrogen is essential for healthy vines, a lack of Nitrogen limits the build up of aroma precursors in whites, further down the line stuck fermentations and malodorous aromas such as hydrogen sulphide emerge at fermentation. Too much and your vines shoots become a jungle.
- Potassium sits on a see-saw of complexity. Too much and you risk a high pH and the associated bacterial problems in your must, too little and the photosynthetic properties of the vine are challenged.
- Trace elements are necessary but comprehension of specifics is blurry. Manganese, Boron, Iron, Zinc, Magnesium, Phosphorus and Molybdenum all play a part.
Increasingly evident is the inaccessibility of nutrients without the help of microbes in the soil. Humus and organic matter is important to create life and build organisms under the ground. The word Terroir has no scientific basis. Traditionalists base its meaning on the soil and the corresponding characteristics. Scientists are looking closely at the symbiotic relationship between soil and the microbes within. Research is on-going, personally I don’t think that we’ll find an answer soon. The network of alliances that convene to create each wine style lead to such a broad filigree of options that forks in the road are numerous making study of similarities and trends an exceptionally complex task.
“Microbes are the secret as to why we can make wine in Argentina… we have very very poor soil”. Dr Laura Catena (IMW Symposium, Spain 2018)