Selected wasabi (Japanese horseradish) are assembled in Tokyo's Tsukiji market from throughout the country. In its vegetable and fruit sales floor, wasabi that line the storefront of long-established intermediate wholesaler Kushiya are especially conspicuous. They are priced at more than 20,000 yen (about $170) per kilogram, which is higher than tuna sold in the adjacent seafood sales floor.

This wasabi attracts customers not only in high-class sushi restaurants in central Tokyo but also overseas.

“If you know the flavors of ‘maguro’ (tuna) and ‘hirame’ (bastard halibut) served with this wasabi, you cannot eat them without it,” said Masahiro Sugimoto, president of Kushiya.

What wasabi elicits such high praise from the professional maven? We visited its producer, Keiichi Tashiro, 43, a farmer in Gotemba, Shizuoka Prefecture.

Tashiro's wasabi fields are dotted along a river that flows between the mountains. The area has an abundance of spring water, whose temperature ranges between 10 and 13 degrees throughout most of the year. His wasabi fields take in this spring water. The fields are slightly inclined so that the water spreads equally to the entire fields. However, each field differs in size and shape. He slightly changes the field depending on such factors as the amounts of sunlight and the tilt of the land.

There are various cultivation methods, and Tashiro is adopting a method called “ishiue” (stone on). It is called that because a stone is placed on a seedling when wasabi is grown.

“Another method is ‘chon-ue,’ whose word origin is said to be ‘chokon to ueru’ (planting it slightly). In addition, there is a cultivation method of protecting a seedling from outside elements by covering it with pipes,” he said.

In the ishiue method, wasabi is laid on its side, so it grows horizontally. As a result, almost all the parts of wasabi are exposed to spring water and become bright green.

Following in the footsteps of his father, Kaoru Tashiro, 78, Keiichi began to cultivate wasabi. His career has spanned about 20 years. However, he fails even now.

In 2016, wasabi grew to only about the size of the tip of a thumb in one field. He is raising a variety called “Mazuma,” which takes about a year and a half to one year and 10 months for the wasabi to grow from seedlings to a size large enough for shipping. The period from planting the seedling to harvesting is lengthy, unlike many other agricultural products.

Because of that, it is painful when wasabi have not grown large enough to be shipped at the time of harvesting.

“I don't know the clear reason for the failure. If my father cultivates it, he does not experience such a failure,” said Keiichi Tashiro.

What his father has that he does not have is intuition resulting from experience, which is important for growing wasabi.

According to Tashiro, three factors are indispensable for wasabi cultivation: abundant spring water, avoiding strong sunlight and soil with good permeability. Seeing the degrees in the growth of wasabi, he changes the amount of water when irrigating them, mixes soil to improve its permeability and covers the plant with black plastic sheets depending on the strength of the sunlight. These works have major influences on the growth of wasabi. And even if he continues to do the same work, wasabi does not necessarily grow as idealistically as hoped.

In September 2010, Tashiro's wasabi fields were completely destroyed by a flood caused by a typhoon. Reminders of those days remain around the area.

“It can't be helped because wasabi cultivation is influenced by nature,” said Kaoru Tashiro.

The Tashiros were forced to start to create wasabi fields from scratch. It took nearly six years to return the fields to their original state though Kaoru also made efforts to do so.

“As long as there are people who are waiting for my wasabi, I cannot stop cultivating it,” Tashiro said with a smile.

Takeo Sato, 45, manager of sushi restaurant Tsukiji Sushiko Jin, in Tokyo's Akasaka district, also fell in love with Tashiro's wasabi. He has continued to utilize it since the opening of the restaurant five years ago. He began to buy it under the recommendation of President Masahiro Sugimoto of intermediate wholesaler Kushiya. Recalling when he tasted it for the first time, Sato said, “The adhesiveness, aroma and taste that were produced when the wasabi was grated all harmonized with each other. They were completely different from ones I had tasted.”

Reactions from customers are also good. Some customers ask chefs to serve the wasabi on different plates so that they can adjust the size of the wasabi by themselves.

“When I serve wasabi in that manner, customers first taste the wasabi. At that time, some customers say, ‘Delicious,’ and others say, ‘This is the best among those I have ever eaten,’” Sato said.

To meet the expectations of such customers, Sato has adhered to a method of grating wasabi after receiving an order.

“Wasabi produces a hot flavor and an aroma for the first time only after it is exposed to air. From that moment, however, the hot flavor and aroma begin to be lost,” he said.

The aroma spreads quickly when Sato slowly grates it with a “samekawa-oroshi,” or a grater covered with sharkskin. Customers react immediately, saying, “It has a good aroma.”

Such a reaction is also a pleasure Sato feels when he makes sushi.

Sato entered the industry when he was 19, aiming to become a sushi chef.

“Until then, I was not good at tasting wasabi at all,” Sato said. While working as a trainee, he was gradually attracted by wasabi.

“If I eat sushi without wasabi, I cannot be satisfied with it. I am bored with it even if I eat it. But if I experience the wasabi's pungent fresh taste, the sushi becomes a completely different one,” Sato said.

According to Sato, what is important is adjusting the quantity of wasabi. If it is too much, it destroys the flavor of the ingredients. If it is too little, it cannot satisfy customers.

“When the portion of wasabi balances with the ingredients, sushi becomes extremely delicious,” Sato said.

It is a chef's skills to best grasp the quantity needed, depending on the ingredients. Wasabi becomes less effective with items with a lot of fat, such as “otoro” (extremely fatty tuna), and those with a strong flavor, including “anago” (whitespotted conger). Sato slightly increases the quantity of wasabi for those ingredients. On the other hand, he decreases the volume for ingredients with a plain taste, such as “hirame” (bastard halibut) and “ika” (squid), as wasabi becomes more effective.

“Wasabi also plays a role in preventing the ingredients from slipping from the rice,” said Sato.

Ingredients that contain a lot of water and are solid, such as “kazunoko” (herring roe) and “awabi” (abalone), do not easily slide off if wasabi is used. As a result, the ingredients fit better with rice. They do even more so if the wasabi has adhesiveness.

As the restaurant is located in Akasaka, it has many foreign customers.

“Regardless of whether they are from Asia, Europe or the United States, foreigners like wasabi very much. Most of them ask us to serve wasabi in different plates,” Sato said.

Like “gari” (pickled ginger), wasabi is offered to customers free of charge. In Sato's restaurant, however, it is one of the most expensive items when he buys it.

“In their early period, the prices of wasabi are the second highest following ‘shinko’ (young konoshiro gizzard shad). But I don't care because it is necessary,” Sato said.

Sato always puts wasabi in a case containing ice and displays it in a location that can be seen by customers. The wasabi is also a big appeal of the restaurant.