Tracing the roots of Shikohin through Geo-Gastronomy with Magmatologist Yoshiyuki Tatsumi 

If you hear the theme “Drink the river and mountain”, what kind of flavor drink would you imagine? 

DIG THE TEA’s series on the theme “Drink the river and mountain” explores the use of local botanicals to create beverages that are unique to Japan and the next generation of luxury experiences.

If one were to contemplate the very fundamentals of rivers and mountains, we would arrive at the study of geology.

At its core, rivers and mountains are shaped by geology. Whether an ocean or a river—its depths ultimately rest upon soil and rock. Mountains, too, are vast formations of earth and stone.

Everything we consume is intrinsically linked to geology.

In this sense, food, beverages, and even shikohin are deeply rooted in the geological world.

Understanding geology means understanding the origins of taste itself.

This idea forms the basis of Geo-Gastronomy, a field that explores the relationship between geology and food. One of its pioneers, Yoshiyuki Tatsumi, is a leading magmatologist who studies the formation of the Earth and the Japanese archipelago.

Tatsumi believes that the key to exceptional flavor lies in geology. 

From sake and dashi (Japanese soup stock) to tea, the finest shikohin experiences can be discovered by understanding the geological foundations of our favorite flavors.

The essence of good flavor is found in geology

—— To start off, please tell us more about the study of Geo-Gastronomy. 

To put it simply, Geo-Gastronomy is the study of the art of enhancing the flavors of food and beverages.

Many factors determine whether something tastes delicious—where and with whom it is eaten, the method of preparation, and the skill of the chef all play a role. Scientifically, it is well known that compounds such as inosinic acid and glutamic acid directly contribute to the perception of umami and good flavor.

However, I wanted to research what makes good flavor on a deeper level. 

I wanted to research how the cultivation of ingredients used in cooking, such as fish, meat, vegetables and grains, influence the flavors. I hypothesized that elements like geological strata, topography, and climate all influence the taste of ingredients at a fundamental level.

I embarked on the study of Geo-Gastronomy because I believed there was a profound connection between the deliciousness of food and my field of expertise—geology.

—— So you think that understanding the geology and topography of the land where our food and drink resources are cultivated will lead to a better understanding of the essence of good flavor?

To give an example, one of the most defining characteristics of Japanese cuisine is respecting the various flavors of each ingredient. Dashi (Japanese soup stock) is at the base of bringing out all these flavors. It can be said that dashi exists because Japan is surrounded by the ocean, or more specifically because of the geographical features of the Japanese archipelago. 

Dashi is the essence of Japanese cuisine, and at its core is the geology of the Japanese islands.

It is well known that Japan’s water is classified as “soft water”—a term often used ambiguously—meaning it has a low mineral content. This soft water directly influences the characteristics of dashi, making it an essential element of Japanese cooking. To understand this, let’s first explore how the properties of water are formed.

The water we use in daily life comes from a variety of sources, including dams, lakes, rivers, and underground reservoirs, but ultimately, most of it originates as rainfall. As rain falls onto mountains, it dissolves minerals from the soil, shaping its composition as it flows through rivers or seeps into underground water systems.

—— Do the types of minerals dissolved in water determine whether it is soft or hard?

Yes. For example, much of the water in Europe is hard water. This is because the European plains are largely composed of limestone, and the distance between the mountains and the sea is vast. With such a gentle gradient, rainwater that falls on European mountains moves slowly through rivers and underground channels. 

As the water travels, it dissolves various minerals from the soil. Limestone, which dominates much of Europe’s geological strata, is rich in calcium and magnesium—both of which easily dissolve in water. As a result, European rivers and underground water sources become mineral-rich hard water, which is then used in daily life.

On the other hand, Japan is an island nation surrounded by the sea, with 75% of the land covered by mountains. The distance between the mountains and sea is extremely short, with very little plains in between. This unique topography causes Japanese rivers to flow much faster compared to those in Europe.

There is an anecdote about a Dutch engineer invited by the Meiji government to Japan. Upon witnessing the rapid flow of the Joganji River in Toyama Prefecture, he is said to have exclaimed, “This is not a river, it’s a waterfall!”

That is just how steep the gradients of Japanese rivers are. When it rains, the water rushes toward the sea with little time to dissolve minerals from the soil.

This is why Japan has soft water.

Why did kombu dashi soup stock become popular in Japan?

—— How does the soft water in Japan influence dashi, and by extension, Japanese cuisine?

Dashi, the foundational broth in Japanese cuisine, is typically made from kombu (kelp), bonito, or shiitake mushrooms. Bonito is rich in inosinic acid, and shiitake mushrooms contain guanylic acid—both key sources of umami. However, it is the glutamic acid found in kombu that has a particularly deep connection to water.

While theories vary, it is believed that as early as the Jomon Period (14,000–300 BC), the Japanese people consumed seaweed that washed ashore, likely in the form of soup. Although the concept of dashi may not have existed at the time, they would have learned through experience that boiling seaweed enhanced its flavor.

During the same period, people also hunted wild boars and bears for food. Given this, one might expect that a soup stock made from animal bones and meat—similar to fond de veau in French cuisine, where veal bones are simmered with aromatic vegetables and spices—would have become a staple in Japanese cooking. However, meat-based broths never took root in traditional Japanese cuisine. In fact, while roasted meat was consumed during the Jomon Period, there is no historical evidence suggesting it was ever prepared as soup.

I believe the reason for this lies in the properties of soft water, which is ineffective at neutralizing the strong odor of animal meat.

The primary umami component in meat is inosinic acid, but the smell of blood tends to overpower it. When animal meat is boiled in soft water, it often results in an unpleasant taste. In contrast, hard water—which contains calcium—helps coagulate blood, turning it into soup scum that can be easily removed. This process results in a clear, rich fond de veau, where the umami flavor from inosinic acid is more pronounced.

However, kombu broth does not work well in hard water. The calcium in hard water reacts with alginic acid, forming a slimy film on the kombu’s surface. This reaction prevents the extraction of glutamic acid, the key umami component of kombu, diminishing its flavor.

—— So the soup stock culture around the world has been largely shaped by the hardness of the water in the region?

In France, where natural water sources are hard, soup stocks developed with animal meat as their base. In contrast, in Japan, where soft water is prevalent, kombu-based dashi became the foundation of its cuisine.

As I mentioned earlier, the hardness of water is shaped by the region’s topography, meaning that the essence of a region’s unique food culture is deeply rooted in its mountains, rivers, and surrounding geology.

The biggest difference between Japanese sake and wine

—— I would like to ask more about shikohin products. Are the shikohin products made in different regions also influenced by geology, topography and climate of the land?

Of course. Take Japanese sake for example. Sake is undoubtedly a product cultivated by Japan’s climate. 

To explain how sake is made in very simple terms, the process of making sake involves converting the starch in the rice into sugar (glucose) using enzymes from koji (mold), and then fermenting the sugar into alcohol with the help of yeast. This fermentation technique using Aspergillus oryzae, the koji (mold) used for saccharification, was unique to Japan.

The reason being that the fungus Aspergillus oryzae was only found in Japan. While fermented foods have long been made across East Asia using various fungi, including Rhizopus, the use of Aspergillus oryzae was distinct to Japan.

Making fermented foods is also common in Europe, but malt is typically used instead of koji or the fungi found in East Asia. This is because koji mold requires a specific level of humidity to thrive.

In humid climates like those of East Asia and Japan, koji can fully develop its potential, leading to a deep-rooted culture of fermentation centered around it. 

This is why koji based fermented food culture took root in East Asia and ultimately gave rise to key staples of Japanese cuisine, such as soy sauce, miso, and sake, all of which rely on Aspergillus oryzae.

Water also plays a crucial role in the production of Japanese sake.

While wine is the most renowned alcoholic beverage in Europe, a key distinction between wine and sake lies in the use of water during production. Although some modern wines are made with added water, traditional winemaking typically relies solely on the natural juice of grapes. In contrast, nearly all sake is brewed with additional water, making it an essential component of the final product.

For wine, the primary factor influencing flavor is the grapes themselves because no water is added. 

However, in sake brewing, both the rice and the water used in the process significantly shape the final taste. No matter how flavorful the rice or how distinct the character of the koji mold, if the water is not suitable for brewing, the result will not produce a delicious sake. 

—— Does that mean that the water in Japan was suitable for making Japanese sake?

More specifically, water in Japan has an exceptionally low iron content.

While not a strictly scientific expression, it is often said that both the koji mold and yeast used in sake brewing “dislike iron.” When water with high iron content is used, the brewing process does not go well. The presence of iron can cause the sake to take on a reddish-brown hue, significantly reducing its quality. For this reason, low-iron water is essential for producing high-quality sake.

So why is it that Japanese water contains so little iron?

As previously mentioned, Japan’s topography plays a role, but geology is also a key factor. Nearly one-third of Japan’s land mass—including underground areas not exposed to the surface—is composed of granite, a type of rock that contains almost no iron.

When rain falls onto Japan’s mountainous regions, it flows rapidly through this iron-poor granite, without enough time to dissolve significant amounts of minerals from the soil. These factors contribute to Japan’s characteristically low-iron water, making it ideal for sake brewing.

Additionally, the abundance of granite in Japan can be traced back to large-scale magmatic activity that occurred across the Japanese archipelago approximately 100 million years ago. During this period, massive volcanic eruptions took place, with some magma remaining trapped underground, where it eventually cooled and hardened into granite.

This geological history also explains why granite has been widely used in some of Japan’s most prominent structures, such as the National Diet Building and Osaka Castle— as it was readily available and easy to source.

Why is sake from the Nada District so good? The answer lies in a rare and precious type of hard water in the region

—— So we are enjoying delicious sake today thanks to magmatic activity 100 million years ago. 

Yes, in the sense that it contributed to creating water with low iron content, you are absolutely right.

Although I previously mentioned that Japan has soft water, some argue that hard water, which contains higher levels of calcium and magnesium, is actually more suitable for sake brewing.

As we discussed, the sake-making process involves converting rice starch into sugar (glucose). This conversion is driven by enzymes secreted by koji, and calcium is known to enhance the koji’s ability to produce these enzymes.

Additionally, alcoholic fermentation relies on enzymes produced by yeast, and magnesium plays a crucial role in stimulating the secretion of these enzymes. In other words, hard water, rich in calcium and magnesium, can accelerate fermentation, making sake brewing more efficient.

A slower fermentation process increases the risk of rice spoilage during brewing, so a faster fermentation is generally preferable. Moreover, quicker fermentation can also contribute to a higher alcohol concentration, which is another advantage.

Taking these factors into account, soft water is actually less ideal for sake brewing compared to hard water.

—— Even so, the Toji (sake brewing masters) have been using soft water to make sake. Is there some kind of special technique behind this?

Before the Meiji Period (1868–1912), sake brewing with soft water was feasible in colder regions with minimal risk of spoilage. However, in warmer areas, it was not uncommon for sake to go bad due to the slower fermentation process associated with soft water.

A breakthrough method developed in Saijo City, Hiroshima Prefecture, between 1887 and 1930 revolutionized soft water sake brewing. This technique minimized spoilage by controlling fermentation speed through low-temperature brewing. By slowing down fermentation under carefully maintained cool conditions, brewers were able to overcome the challenges of soft water production. Once this method became widely adopted, it transformed Japanese sake production.

That said, certain regions in Japan have historically used hard water for sake brewing. One notable example is the Nada region, located between Kobe and Nishinomiya in Hyogo Prefecture.

—— So some Japanese sake is made with hard water?

Sake production is believed to have flourished in the mid-Edo period, around the 18th century, and even then, Nada sake was highly regarded for its exceptional quality.

The key to its superiority lay in a rare source of hard spring water known as miyamizu.

At the time, most sake was consumed in the bustling city of Edo (present-day Tokyo). Nada sake gained immense popularity not only for its rich flavor but also for its high alcohol content and remarkable ability to withstand long-distance transport in barrels without spoiling. By the late Edo period, it is said that Nada sake dominated the market, accounting for an estimated 80% of the sake consumed in Edo.

——From a Geo-Gastronomy perspective, I’m curious about what caused the presence of hard water in the springs of Nada.

The answer lies in the region’s geology.

Nada is situated at the foot of Mt. Rokko, a mountain composed primarily of granite. As water flows through this granite, it remains low in iron. However, the geology of the land between Mt. Rokko and Nada consist of clayey strata rich in seashells—an environment that naturally produces hard water, as we have mentioned before. 

So how did the geology of this region end up with so many seashells? The reason is that the land was once an inland bay of the sea.

A geological formation called the Osaka Group, which dates back approximately three million years, provides evidence that this area alternated between being a lake and part of the sea. During ice ages, sea levels dropped as seawater froze into ice sheets, transforming the region into a lake. Conversely, during interglacial periods, the sea advanced inland.

When the area was submerged as part of the sea, it formed a closed, low-oxygen body of water similar to present-day Osaka Bay. This created an environment where marine clay, rich in sulfur, accumulated—an ideal habitat for shellfish.

Over time, crustal movement lifted these marine clay layers toward the surface, exposing them to an oxygen-rich environment. The sulfur within the clay reacted with oxygen, forming sulfuric acid, which dissolved the embedded seashells.

Today, the miyamizu waterway is believed to flow through a marine clay layer formed around 100,000 years ago. The calcium and phosphorus that leached into the clay from these dissolved seashells are what give miyamizu its characteristic hardness—creating the perfect water for brewing the mellow yet dry Nada Otoko sake.

—— Japanese shochu is another popular alcoholic beverage in Japan, but is it also affected by geology in the way Japanese sake is?

Very much so. Take potato shochu for example. Kagoshima is well known for its production, but the region itself does not have particularly fertile land. Evidence of a massive volcanic eruption from around 30,000 years ago has been discovered near Kagoshima, and the resulting volcanic ash formed the Shirasu Plateau— an area unsuitable for rice cultivation.

To adapt to these challenging conditions, people turned to sweet potato farming instead. It is believed that sweet potatoes were first cultivated in Kagoshima in the early 18th century, and by the mid-18th century, shochu production using sweet potatoes had begun.

This is a perfect example of how the agricultural choices of our ancestors—shaped by their geological and environmental conditions— eventually gave rise to regional specialties like shochu.

The geological reason why green tea became popular in Japan

—— Besides alcoholic beverages, what other shikohin products are influenced by geology?

Tea serves as an excellent example of the relationship between shikohin products, geology, and human cultivation.

It is said that good drainage and a warm climate is more important than soil fertility when it comes to cultivating tea trees, or the raw material for tea. 

While Shizuoka Prefecture is often regarded as Japan’s leading tea-producing region, Kagoshima Prefecture produces just as much tea. In fact, some predict that Kagoshima will soon surpass Shizuoka to become the top tea-producing region in the country. Although Kagoshima has a shorter history of tea cultivation, its mild climate and volcanic soil with excellent drainage provide ideal conditions for large-scale tea production.

Tea production in Shizuoka began in the Meiji Era (1868-1912).  It is said that tea cultivation started in the Makinohara region, located in the lower reaches of the Ōi River.

The beginning of tea production in the Makinohara region during the Meiji period is closely related to the aftermath of the Boshin War (1868–1869). After the war ended, the last shogun, Tokugawa Yoshinobu, retired to Sunpu (present-day central Shizuoka Prefecture), which had a significant influence on the development of tea cultivation in the region.

Yoshinobu came to Sunpu with a group of his samurai who served as his personal guards. However, due to the return of lands and registers to the emperor (known as hanseki hōkan), these samurai were relieved of their duties. They needed to find a new livelihood so they began cultivating the Makinohara Plateau. 

The Makinohara Plateau has a fan-shaped topography that is shaped by the Oigawa River. Originally, it was barren land covered in stones and rocks, unsuitable for traditional farming. However, the samurai, having traded their swords for hoes, worked relentlessly to cultivate it. As they searched for crops that could thrive in such poor soil, they discovered that tea trees could take root.

Yet, while tea trees don’t require highly fertile soil, they don’t grow just anywhere. The pioneering cultivators enriched the land by composting Japanese pampas grass, gradually improving the soil. This effort laid the foundation for tea production on the Makinohara Plateau, a tradition that continues in Shizuoka to this day.

—— So it was not until the Meiji Period (1868-1912) that large-scale tea cultivation began in Shizuoka?

Green tea is one of Japan’s most beloved beverages, and it is said that the country’s soft water has played a significant role in shaping the Japanese palate and preferences for shikohin products.

The color of green tea is often described as suishoku (water color). Scientific studies suggest that green tea brewed in soft water has a more vibrant hue and allows for better extraction of catechins from the tea leaves.

Japan’s naturally soft water enhances the delicate balance of sweetness and bitterness in green tea, making it particularly enjoyable. This may be one reason why Japanese people traditionally favor green tea over black or oolong tea.

Interestingly, black tea—a fully fermented tea—develops a richer, more vivid color when brewed in hard water. This could be one of the reasons black tea flourished in England, where hard water is more common.

Shikohin experiences as an “art”

—— Would you say that local shikohin products are directly connected to the local water sources and food?

Each region of Japan has its own distinctive local cuisine, shaped by its water sources, climate, and the lifestyle of the people who live there.  Local sake has been crafted to complement these unique local cuisines.

This is why I believe the best pairing is between regional cuisine and sake, and enjoying both together offers one of the most enriching shikohin experiences.

My hope is that food culture, rooted in the mountains, rivers, climate, and the layers of strata beneath them— along with the water that flows through them— continues to thrive in the future.

For example, wouldn’t it be wonderful to enjoy a glass of Nada sake while savoring sea bream from Akashi, all while overlooking the Seto Inland Sea from the top of Mount Rokko?  I believe that the scenery and the moments created in such a setting can truly be called an art. 

Translation: Sophia Swanson

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