When introducing wines in Japan, it seems that reference to the type of soil in which the grapes were cultivated is frequently made as one of the elements expressing a wine's character. While this tendency is not limited to Japan alone, it appears particularly pronounced here.
Even in tasting notes, one often encounters descriptions like "granite" or "sedimentary rock," followed by observations about how this influences the wine's taste or aroma.
Given this strong emphasis placed on soil as an important factor in understanding wine in Japan, how much influence does soil actually have?
Today, we focus our attention on examining the concept of "soil."
Can Grape Roots Penetrate Rock?
Not only grapes, but all plants extend something into the earth: their "roots."
While roots serve various functions, the most important is acquiring the water and nutrients necessary for the plant's growth. In the case of grapes, the devastation known as the "Phylloxera crisis" was precisely an example of massive damage caused by the impairment of this root function.
Roots extend into the soil in search of water. If water is readily available nearby, they remain shallow; if water exists only at depth, they extend deep.
Consider this question: Can grape roots penetrate granite? Even if they could penetrate granite, would the desired water be found within that rock?
Generally speaking, the answer is "no." Grape roots do not penetrate rock, nor do they absorb anything from rock along with water. In this sense, whether granite or sedimentary rock exists in the vineyard soil makes no difference. Grapes extend their roots around these rocks, and grapes cannot grow on bedrock consisting only of stone.
This is where the process of rock weathering becomes important.
What Is Soil?
What comes to mind when you hear the word "soil"?
This is frequently misunderstood, but soil does not mean the ground itself, nor does it mean bedrock.
Expressed in the simplest terms, soil refers to the earth that exists at the surface layer of the ground—that is, "topsoil." Being earth, it fundamentally does not contain "rock." The rocky materials existing beneath the topsoil are called "geology."
However, conversely, the soil discussed in wine contexts consistently involves "rock"—that is, "geology"—which comprises the majority of such discussions. What does this mean?
The Three Components of Soil
To understand the prominence of rock, we must first know what constitutes soil.
Originally, soil is understood as a mixture of inorganic matter, organic matter, gases, liquids, and living organisms. However, when examining soil academically, it is understood as a mixture of three elements: sand, silt, and clay. The properties of the resulting soil change according to the mixing ratio of each of these elements, resulting in different soils and different soil types.
What distinguishes these three elements is particle size—the size of each individual grain. The smallest particles are sand, the largest are clay, and those in between are called silt.
The Cycle of Soil Formation
Soil on Earth exists within a grand cycle, and within this cycle lies the relationship between rock and soil.
The starting point of soil is rock. Rocks existing on Earth reduce in size through various influences such as rain, wind, tectonic movement, and geothermal activity. Through long-term weathering processes, fragmented rocks become progressively smaller, passing through sizes called clay and rock powder before reaching sand.
While there is a flow of gradually decreasing size, during this long weathering process, fragmented particles are also subjected to geothermal and pressure effects at various times, solidifying and gradually increasing in size to become rock again. These newly formed rocks then weather over long periods, with some becoming soil and others becoming rock again.
Here, the characteristic of "rock" emerges. Vineyard soil contains accumulated earth formed by rock weathering, but rock weathering does not proceed at such a rapid pace. Therefore, the original rock often still exists within that soil. This is essentially a state where geology that should be covered by topsoil appears at the surface. This explains why rock names frequently appear when discussing soil, despite rocks not being directly related to soil.
What Are the Characteristics of Rock?
When discussing the characteristics of the rock from which soil originates (that is, "geology"), minerals are very frequently mentioned.
The minerals—inorganic substances—contained in soil are numerous in variety, and each has different concentration ratios depending on the rock that became the soil's origin. Therefore, there is no dispute that the ratio of minerals existing in soil differs according to rock type and degree of weathering.
The claim that this appears as the individual character of each vineyard also seems "at first glance" to be correct.
However, the current prevailing academic view is that while minerals in soil affect grape growth, they do not influence wine taste or aroma. More specifically, all minerals absorbed through roots are used for the growth of the vine and do not accumulate in the fruit.
Based on this view, there is no correlation between the presence of minerals in soil and the mineral sensations felt in wine.
Furthermore, this expression "mineral" actually lacks unified definition in its content, representing an extremely ambiguous expression where different users point to different meanings. Some specialists have explicitly stated they intentionally avoid using this term.
Therefore, at least at present, introducing the word "mineral" when discussing soil or geology is not appropriate from multiple perspectives.
Is There Commonality in Soil?
We have now surveyed what soil and geology are and whether they influence wine.
Here is one question: Is there commonality in wines made from grapes cultivated in vineyards with soils originating from the same geological system?
This is an extremely interesting question. If the answer is "yes," then the commonly heard expression "because it's soil from ~ rock, it has ~ characteristics" would be valid. Conversely, if the answer is "no," these expressions would be completely meaningless. Which is it?
As mentioned earlier, current research results indicate that minerals in soil, which are primarily derived from geology, do not affect wine taste. Focusing only on this point, there is no correlation between soil similarity and wine similarity.
However, soil properties are not limited only to the minerals they contain. They extend across a very broad range including water content, acidity, air volume, and more. Even if minerals have no direct influence on wine taste, they significantly affect grape growth.
If conditions across this broad range align "on the same soil," this can be considered to appear as commonality in wine taste.
Therefore, the answer to the earlier question is "correct, provided several caveats are attached." These "several caveats" will be published as a separate article at a later date, so those interested should look for that.
Summary | Soil and Geology Are Similar Yet Different
We have examined the complex topic of soil and geology and their relationship to wine influence. Through this content, you should now understand that what is called "soil" in wine tasting often refers to geology.
While soil and geology might seem similar, there is a significant gap between them in grape cultivation and winemaking. This is because grape roots, in most cases, do not reach the geological layer.
As long as grape roots remain within the soil domain, what we should focus on is soil—not the direct influence of rock.
Rock certainly influences soil, but it is not soil itself. Soil is not influenced only by rock either. The influence of geology is merely one component of soil composition, and it is impossible to discuss soil based on geology alone.
How much influence can an element that represents only a small portion of the composition have on wine taste?
Following the flow of our discussion thus far, one might conclude that such influence is absent or minimal, but this cannot be stated categorically. However, the way this influence works is probably beyond your imagination.
This represents the "several caveats" mentioned above.
Soil influences wine. This point cannot be expressed in such simple terms—it is an extremely profound topic.
For those willing to engage with this discussion, please look for the article "Soil, Grapes, and Wine".
