Jul 8, 2024

Real Wasabi Wonders: Unveiling the Secrets Behind the Sushi and Soba Essential

Written by Ito Ryo

With its refreshing sharpness that tingles the nose, wasabi is a uniquely Japanese spice that enhances the flavor of iconic dishes like sushi, sashimi, and soba.

So, what is wasabi? Typically served as a pale green paste in restaurants, real wasabi is made from the rhizome, or underground stem, of the native Japanese plant known as wasabi. It is finely grated and made into a paste-like texture. But despite its widespread use, not many people have actually seen wasabi in its natural form before being processed or how it is grown.

Curious to learn more, Team Musubi recently joined a wasabi cultivation tour in the lush, natural surroundings of Okutama, located at the western edge of Tokyo. In this article, we'll introduce you to how wasabi is cultivated and reveal the secrets behind its unique flavor.

The Tradition of Wasabi Cultivation in Okutama Since the Edo Period Young Farmers Carrying on the Tradition of Wasabi Cultivation Cultivating Wasabi Amidst the Natural Beauty of the Okutama Tasting Freshly Harvested Wasabi

The Tradition of Wasabi Cultivation in Okutama Since the Edo Period

For over 400 years, since the Edo period (1603 CE–1868 CE), vegetables have been grown throughout the Tokyo area and are collectively known as Edo Tokyo vegetables. Among them is the Okutama Wasabi from the Okutama region. As of 2022, Okutama produces about thirty two tons annually, making it the third-largest production area in Japan after Shizuoka Prefecture and Nagano Prefecture.

Records from 1823 in the late Edo period indicate that wasabi from Okutama was delivered to the city of Edo and even presented as an offering to the Edo Shogunate.

Additionally, wasabi (not limited to that from Okutama) was widely used by the common people of Edo. It was used to mask the fishy smell of sushi and served as a condiment to mellow the flavor of bonito flakes in the dashi for soba dipping sauce.

Interestingly, the practice of grating wasabi (oroshi wasabi) became common a bit earlier, during the mid-Edo period. By that time, wasabi was already recognized as an ingredient that could neutralize toxins in fish and soba, likely referring to wasabi’s antibacterial properties that help prevent food poisoning.

Young Farmers Carrying on the Tradition of Wasabi Cultivation

Wasabi cultivation in the Okutama region has a long history, but in recent years has faced significant challenges. The aging farmer population, lack of successors, and natural disasters like typhoons have led to a reduction in cultivation areas and a steady decline in production.

Amid these challenges, brothers Tsunoi Hitoshi and Tatsuya, wasabi farmers who also operate tours of their wasabi farm, work hard to preserve and pass on the tradition of Okutama's wasabi to the next generation. They aim to showcase this exceptional product, unique to Tokyo, and share its greatness with the world.

Taking over fields abandoned by other farmers, the Tsunoi brothers restored them by hand from scratch, researching old documents and learning from experienced farmers. They are now in their fifth year of wasabi cultivation.

After a brief explanation, we changed into rubber boots and, guided by younger brother Tatsuya, set off to explore the wasabi farm.

Cultivating Wasabi Amidst the Natural Beauty of the Okutama

Reaching the wasabi fields nestled in the mountains takes a short fifteen-minute hike.

As we stepped onto the forest trail, we found ourselves on a different side of Tokyo, far removed from the bustling skyscrapers and old-town charm of the city.

Ninety percent of the Okutama region is covered by forest. Historically, this area thrived on forestry, particularly cultivating cedar and cypress for construction. However, this industry has declined in recent times.

The path we walked, with its dark brown soil and protruding rocks, was damp. Descending the mountain trail, lush green vegetation thrived on both sides, and eventually, the path led to a refreshing babbling brook.

Walking a bit upstream, we arrived at the Tsunoi brothers’ wasabi fields.

Before us appeared terraced fields built with stone walls along a mountain slope. Here, hydroponic cultivation is practiced by channeling spring water from nearby, cascading it down from the topmost field to the lower ones. Each terrace holds approximately 200 lush wasabi plants, creating an captivating sight.

Similar to rice cultivation, wasabi fields are known as “wasabi paddies” because the plants are grown in water. Seedlings are planted between small stones that cover the surface and are carefully nurtured for about a year and a half to two years, aiming to produce firm and flavorful wasabi.

“With an optimal water temperature of 12-13°C, wasabi grows best in the spring when the seedlings are planted and in the fall. Spring water, with its relatively stable temperature throughout the year, is ideal for wasabi cultivation. Even during heavy rains, unlike river water, spring water doesn't become muddy and hinder the growth of wasabi,” explained Tatsuya.

“The free-flowing water serves multiple purposes for wasabi plants beyond supplying moisture and oxygen. Unlike many plants, wasabi lacks VA mycorrhizae in its roots, which typically help gather nutrients from the soil. This makes wasabi vulnerable to nutrient deprivation if other plants grow nearby. To counter this, wasabi releases allyl isothiocyanate from its roots to keep other plants away. However, this compound also inhibits wasabi's own growth, so it needs to be constantly washed away with freshwater."

“Actually, the spray from the spring water flowing down the stone walls can also hinder growth. Normally, we would cover the walls with nets to keep the spray off the plants. However, we want to show the natural state of wasabi cultivation as much as possible, so we deliberately do not set nets on the stone walls in our fields.”

Wasabi plants also dislike prolonged exposure to direct sunlight. The tall trees surrounding the fields likely provide natural shade.

“This farm can only be accessed by walking along a narrow mountain path. As each field is small and agricultural machinery cannot be used, all the stone walls were built by hand. While this method was certainly labor-intensive, it preserves the natural environment and landscape. Moreover, this approach is the traditional style of wasabi cultivation passed down through generations in the Okutama region, and maintaining this tradition is highly meaningful,” according to Tatsuya.

Tasting Freshly Harvested Wasabi

After touring the fields, it was time to taste the wasabi.

On the day of our interview, we got lucky with the timing and had the chance to join in on the actual harvest.
“Thick stems and large, sturdy leaves are signs of a well-grown wasabi plant,” Tatsuya advised. Following his guidance, we finally managed to find a good wasabi plant and cautiously pulled it out after carefully clearing the surrounding stones and mud.

“That’s a good one!” Tatsuya remarked, confirming that we had found a top-quality wasabi. The rhizome was about 12 cm long and 2.5 cm in diameter, with distinctive horizontal ridges where stems had fallen off as it grew. The finer and denser these ridges are, the more carefully the wasabi has been cultivated, indicating superior texture, spiciness, and flavor.

“As wasabi grows upwards, the cells in the lower part, deeper in the soil, are older and have a stronger spiciness, while the newly grown part near the leaves is fresher, softer and more vibrant in color,” Tatsuya explained. “The finer you grate it, the more refined and delicate the spiciness becomes. On the other hand, if you grate it coarsely, you can enjoy a fresh, vegetable-like texture.”

The spicy component of wasabi, allyl isothiocyanate, is a volatile substance produced when the compound "sinigrin" inside the wasabi cells is broken down by enzymes during grating. This means the spiciness peaks about five minutes after grating and then fades along with the flavor over time.

Today, wasabi is also sold in tubes and small packets as a paste (neri wasabi). The reason the spiciness lasts in these products is due to a special technique that preserves the spiciness by encapsulating allyl isothiocyanate with oil and sugars. Additionally, the wasabi powder found in tubes, packets, and dry forms often uses horseradish, which originates in Europe and is spicier than Japanese wasabi.

Tatsuya served us a dish for tasting: warm white rice generously topped with bonito flakes, drizzled with soy sauce, and finished with a dollop of wasabi, freshly grated to a creamy texture using his special metal grater.

The simplicity of the dish highlighted the excellent compatibility of the ingredients, making it incredibly delicious. The freshly grated wasabi had a refreshing, vegetable-like aroma and taste, with a hint of sweetness. Naturally, it was completely different from the wasabi found in plastic tubes. Combined with the stunning location overlooking the wasabi fields, it became a truly memorable meal.

It is worth mentioning that while wasabi can be harvested throughout the year, its peak season, when the spiciness is at its strongest, is in spring and fall. Indeed, it would be interesting to taste wasabi harvested in the colder months from Okutama.

With the global spread of Japanese cuisine, wasabi has become well-known overseas.

In recent years, wasabi has started to be cultivated in places such as the United States, Canada, the United Kingdom, and Australia. However, through this visit, we learned that without pristine water and an excellent natural environment, quality wasabi cannot be grown.

Wasabi pairs well not only with Japanese dishes and seafood but also with meat and Western cuisine. It's perfect for adding a refreshing touch to fatty meats like steak, roast beef, and yakitori. Plus, it works wonderfully with raw avocado or as a secret ingredient in salad dressings, making vegetables taste even better. Truly, it’s a versatile spice.

Wasabi, known for its various health benefits, is a key ingredient that represents the healthy aspect of Japanese cuisine. If you have the chance, try grating fresh wasabi yourself and experience its vibrant flavor firsthand.