The Environment Surrounding Winemaking | Is There Really Anything That Remains Unchanged?

The tasting method of comparing wines from different harvest years made from the same grape variety harvested from the same vineyard is called "vertical tasting." This vertical tasting serves two purposes.

The first purpose is to compare wines from new and old vintages to understand the aging characteristics and traits of wines made from grapes grown in that particular vineyard. The second purpose is to grasp how differences in climate from year to year have affected the grapes and what resulting differences have appeared in the wines.

Given my profession as a winemaker, I conduct these vertical tastings relatively frequently. Recently, however, I have begun to question what exactly I am comparing through these vertical tastings.

Of course, the individual objectives when conducting such tastings are clear. I seek to understand the degree of aging, compare with past years that had similar weather conditions, and identify important indicators for determining the style of wine to produce. Yet there are times when I become uncertain whether I am truly focusing on those differences.

In such comparisons, ideally there should be no differences in aspects other than the items being compared. If everything differs, it becomes unclear what is actually being compared.

Questioning the Immutability of Terroir

One word that is difficult to avoid in the wine industry is "Terroir." This term appears repeatedly in articles published on this website.

When looking up this word "terroir" in Wikipedia, it states: "Originally a French term referring to the characteristics of wine, coffee, tea, and other varieties based on the geography, topography, and climate of their growing regions. Since agricultural land in the same region shares common soil, climate, topography, and agricultural techniques, it imparts a character unique to that land to the crops."

Because "agricultural land in the same region shares common soil, climate, topography, and agricultural techniques, imparting a character unique to that land to the crops," we can compare differences in aging and climate through vertical tastings. This is based on the premise that two of the three elements comprising terroir—topography and soil—remain unchanged, excluding climate.

However, I have increasingly questioned whether these two elements of "topography" and "soil" are truly immutable. I sense that these elements are actually already changing and affecting the taste of wine.

Changes in Topography and Soil from a Viticulture Perspective

Among the three elements said to comprise terroir mentioned earlier, it is evident that climate is already undergoing significant change. This change has manifested as extreme weather events that we can visually observe. In contrast, topography and soil appear unchanged in their form.

Is this really the case?

Consider topography, for example. Indeed, it is rare for topography to significantly alter its form. In terms of vineyards, it would be difficult to perceive topographical change unless major improvement work were undertaken. However, as I wrote in a previous article "How Long Do Premium Vineyards Remain Premium? | Vineyard Location," the meaning that vineyard topography and location once held is changing.

While there has been no change in the structural components of vineyard topography and position, the landscape depicted within that framework has changed dramatically.

This also relates to soil, but topography is formed through the influence of weathering. Weather significantly affects the degree of this weathering. In other words, as climate is currently changing, the topography formed under its influence is also in a process of change from an ultra-long-term perspective.

"Soil" Experiencing Greater Impact

Soil is also an object often perceived as unchanging. Many people may have heard wine comments such as "the soil in this village is clay-based," "the soil in that region contains much slate," "therefore the wine tastes like this." However, I believe it is precisely this soil that is showing greater change.

When considering soil from the perspective of wine grape cultivation, the viewpoint can be broadly divided into two categories:

1. Composition
2. Effect

Composition refers literally to the structure of the soil. Effect refers to the role that soil plays—perhaps better described as the influence on grape growth.

The effects of soil are brought about by its composition. Therefore, when composition changes, the effects naturally change as well. A good example of this is precisely what we often discuss: the differences in soil characteristics due to different soil types and the resulting differences in wine taste.

On the other hand, even soils with the same composition can have different effects. Currently, the meaning of soil is changing from both perspectives simultaneously. Let us examine each in detail.

The Changing Composition of Soil

Soil consists of earth composed of three types of elements, and soil types are distinguished by differences in their compositional ratios. This is a frequently confused point, but soil and geology are different things. Descriptions like "clay-rich" or "high in sand" refer to soil, while expressions like "rich in granite" or "containing much limestone" describe geology.

As touched upon in the article "About Soil," soil refers to the earth existing in the surface layer of the ground—that is, "topsoil." In contrast, geology refers to the rock formations existing beneath the topsoil.

Soil is originally understood as a mixture of inorganic matter, organic matter, gases, liquids, and 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 element, leading to classification as different soils.

Each element composing this soil is, in most cases, obtained through the weathering of rock formations that constitute the geology.

As already mentioned, the degree and conditions of rock weathering may change in response to current climate condition changes. In other words, here too, as with topography, even if there is no major change in the geology that forms the source of soil, the soil produced from it is gradually changing its properties without our notice. When soil composition changes, the soil that exists as a mixture of these components also changes. If soil changes, the influence that plants receive from it will also change.

What Soil Changes Bring to Wine

I previously wrote in detail about the function and meaning of soil in wine grape cultivation in the article "Soil, Grapes, and Wine." To summarize that content very simply, the effect that soil brings is its influence on vine vigor.

Different types of soil have different degrees of influence on plants in each role that soil fulfills. As a result, the vigor of grapes grown in that soil changes.

Most of the influence that soil has on plants is caused by soil composition. Therefore, when comparing soils with different compositions, these differences become more apparent. However, there are cases where soil effects change even without such compositional differences. The cause of this is weather.

The influences that climate change has on soil, either directly or indirectly, can be roughly summarized as follows:

• Impact on water supply
• Impact on nutrient retention capacity
• Impact on microbial communities
• Impact on soil temperature

While some of these directly affect plants individually, they also influence plants indirectly by interacting with each other. The decomposition of organic matter in soil, nitrogen mineralization, and grape absorption efficiency are typical examples of such indirect influences.

This time, we will focus on the part related to water supply among these factors.

The Relationship Between Soil Composition and Water

As already mentioned, soil is a mixture of three elements: sand, silt, and clay. In actual soil, these three elements exist mixed in different ratios, and the water retention capacity of soil is largely determined by this ratio. The higher the proportion of clay with smaller particle size, the higher the water retention capacity of that soil. Conversely, the higher the proportion of sand with coarser particles, the lower the water retention capacity of that soil.

In simple terms, clay soils with more available water tend to produce stronger vine vigor and fruits that are higher in sugar content and more powerful. On the other hand, in sandy soils, grapes are constantly exposed to drought stress, resulting in weaker vine vigor and fruits that tend to have higher acidity and a harder character.

Comments when tasting wine are probably often written based on such tendencies.

However, changes are beginning to occur here. Would you be surprised if clay soils were becoming more acidic and harder, while sandy soils were producing grapes that give a softer impression?

However, this is not strictly a correct observation. It might be more appropriate to express it as: while sandy soil wines remain largely unchanged, clay soil wines have become relatively harder in taste.

The Reversal Phenomenon Caused by Extreme Drought

Soil water retention capacity is based on its composition. However, this difference in water retention capacity is maximized when the water retention ability can be used to its fullest. Conversely, under extremely dry conditions, there is no water in the soil that plants can extract in the first place, so regardless of soil composition, there is no difference in terms of "water supply."

What deserves attention are cases where there is some water present in the soil, though not reaching the maximum water retention capacity.

Plants cannot absorb unlimited amounts of water from soil. Soil has water retention capacity, but in other words, this is the force to hold water against gravity. In other words, in soil with greater water retention capacity, water is attracted to the soil with greater force. Plants, including grapevines, can only absorb water from the outermost part of this gravitational sphere of water retention—the part that is not attracted with very strong force. As mentioned earlier, the strength of the force with which soil attracts water is proportional to the soil's water retention capacity, so the more clay-rich the soil, the more water plants cannot absorb.

Moreover, this gravitational pull that soil has on water is based on the volumetric water content of the soil. It does not change with weather conditions. In other words, whether it rains sufficiently or remains dry, soil will strongly attract water up to a certain amount based on its water retention capacity and will not release it to plants until more water accumulates in the soil.

This amount of water that soil tries to retain is called PWP (Permanent Wilting Point). According to one study, there is nearly a five-fold difference in PWP between soil that is 100% sand and soil that is 100% clay (Brady and Weil, 2002). In other words, under water content conditions that exceed the PWP of sand soil but fall below the PWP of clay soil, plants in clay soil—which should normally be easier for water extraction—cannot obtain water at all, while sand soil allows normal water acquisition. This represents a complete reversal of conventional knowledge.

Furthermore, in environments below PWP, all organisms, not just plants, have difficulty obtaining water. This means that organic matter decomposition is also hindered. As a result, the growth state and physiological phenomena of grapes grown there are significantly affected. Consequently, the taste of wine changes.

Even if the amount of water present in soil does not fall below PWP but approaches that level, it means that the surplus water amount falls below the value expected from the soil's original water retention capacity, intensifying competition for water acquisition within the soil. In other words, in all aspects including grape growth and microbial activity, the original level achievable in that soil cannot be met. As a result, the wine taste inevitably changes from what is expected for "that soil" framework.

How Much Should We Consider Soil Changes Based on Climate Change?

Using soil water retention capacity as an example, we have seen that soil is also a changing subject due to climate variation. Topography and soil, long viewed as immutable objects, are changing in their internal aspects and meaning, even if their frameworks remain unchanged.

The changes are not sudden. They occur gradually, slowly, but certainly. The changes in wine taste resulting from such changes would likely be overlooked unless careful attention is paid, except in cases of extreme drought. Even in vertical tastings, I believe such changes would not be clearly perceived in comparisons between last year and this year, or the year before last and this year. However, when comparing over longer spans of 5, 10, or 20 years, they should be felt as "something different."

The problem is where to attribute the cause of such differences when they are perceived. In long-term comparisons, differences in aging degree, changes in winemaking methods, and simple differences in temperature and weather are simultaneously captured, making it unclear whether these are temporary differences or based on long-term changes. If they are temporary differences, some reproduction is possible when weather and temperature conditions match. However, if they are changes resulting from long-term soil and topographical changes, they can no longer be reproduced by any means.

If we consider soil and topography as immutable and base our comparisons on that assumption, the discussion becomes simple. But is that really acceptable? What do we see, feel, and compare in our glasses? Or are we merely under the impression that we are comparing? Perhaps it is time to reconsider from the perspective that soil and topography are also changing entities.

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