Understanding Terroir Through Volcanic Soil

We love terroir. We love the way it melds the mystical with the scientific, empirical analysis with intuition.

Perhaps nothing more singularly exemplifies terrior more than volcanic soils. Precious little is known about exactly why volcanic soils affect the grapes that grow in them. There is no doubt, however, that they do. All over the wine world, from the slopes of Mount Etna in Sicily, to the Columbia River Valley in Washington State, to the Bio Bio valley in southern Chile, examples of fine wines made from grapes grown in volcanic soils abound. All of them exude a degree of character and a sense of place rarely rivaled.

Before we begin, we should note what terroir is not. It is not just the soil, though it is often misunderstood as such. Instead, terroir is the combination of everything happening in the environment where grapevines grow that have an impact on the characteristics of the resulting wines. By this definition, even the people that own, manage, and work in the vineyards should be considered as part of the overall terroir. It excludes, therefore, winemaking practices and everything that happens after nature hands the grapes over to humans. 

We might as well begin our dive into (attempting) to understand volcanic soils with the most controversial piece: do vines actually absorb minerals from not just volcanic soil, but any soil? The answer, for most minerals, is likely “no.” With the exception of iron, there’s a distinct lack of evidence that minerals are absorbed through grape vines. In chemistry terms, the molecules are simply too big to pass through the root stocks, through the vine, and into the grapes themselves.

However, grapes grown in volcanic soils do, with few exceptions, display dazzling mineral flavors. Many come across as even salty. Why?

Part of the answer may lie in the fact that volcanic soil is porous, which allows water to pass over the roots with relative speed. This also allows the roots to travel further in search nutrients. This combination leading to high mineral wines has been shown to be true in other regions that do not possess volcanic soil, but do have porous, or loose, soil. Burgundy is perhaps the most famous region where this is the case.

Along the same lines, volcanic soil does not retain water the way clay does. This in turn heavily stresses the vine, which prompts it to produce grapes that are more concentrated across the board. Grapes grown in volcanic soil tend to have more tannin, more minerals, and more intense flavors, because of this.

There are many other ways that volcanic soil may affect the vines and the grapes they produce. Unlike other soil types, the color of volcanic soil depends on the eruption event that caused them. This means the vineyards will absorb heat differently depending on the color of the soil, in turn leading to differences in ripeness. Believe it or not, average temperature is more closely associated with ripeness than even direct sunlight.

And though it may seem obvious, don’t forget that you’re likely to find volcanic soil near actual volcanoes. Being mountains, they play a huge role in the climate within their vicinity. They can change the behavior of the wind, for instance. Wind can keep a vineyard dry and pest free, but it can also cool the vineyard down. Where you find mountains, you find valleys, which have their own micro climates. Mountain also have slopes, each with different orientations to the sun and quickly changing altitude. Mount Etna, a huge active volcano in Sicily, impacts the terroir around it so much that each quadrant of it produces completely different varietals of grapes.

We could go on and on about the thousands of ways any given terroir may differ from another. It’s not an understatement to say that even regions with over a hundred years of data and research, we’ve only scratched the surface of truly understanding terroir. Which is why winemaking and grape growing remain a combination of artistry and reason. Perhaps no element of terroir better exemplifies this than volcanic soils. Yet, despite its many mysteries, one thing remains true and easily identifiable: wines from regions with volcanic soils are downright delicious!