Japan’s Traditional Superfood: Why Field Caviars Shine Brighter with Purer Water

Have you heard of a food called Tonburi? These beautiful, shiny green balls are refreshingly aromatic with a fun texture similar to a mochi ball, and are referred to as “caviars of the field.” This soul food is processed with the pure waters of Odate City in Akita Prefectures and it is now even widely used in high-end Tokyo restaurants. It was introduced in the early Heian period and was used as an herbal medicine in the old days. Its highly nutritious contents are on par with that of Quinoa, a popular health food, which not only tastes good but also boasts great skin care effect. Yes, a superfood has existed in Japan for over 1000 years.

Tonburi (Field Caviar) Rice (2019)Original Source: Akita Tourism Guide

So, what is Tonburi?

The true identity of these green balls is summer cypress, which is an annual grass of the Rhipiceid Genus family. This plant is the raw material for making brooms. Tonburi is made by peeling the skin of this ripened fruit, and thoroughly washing and processing it. It’s a reliable health food for the modern people, as it's rich in  dietary fibers, vitamins, minerals and saponins that promote the metabolism of lipids just by eating it as-is.

Working at the Tonburi (Field Caviar) Processing Factory (2019)Original Source: Akita Tourism Guide

The people of Odate City

The tonburis being sold today are all from Odate City in Akita Prefecture. It used to be only consumed by the farmers in their own households, but became commercialized starting in 1975. Hitoshi Honma (right) from the tonburi factory that we visited said, “It’s difficult to process, and its production volume has been dropping from the peak period, but it's been recently garnering more attention from the media.”

Saigawa River Flowing Near the Tonburi (Field Caviar) Processing Factory (2019)Original Source: Akita Tourism Guide

The beautiful, clear stream

Clear water lively flows through the Sai River next to Mr. Honma’s factory. Tonburi-making requires a large amount of fresh water for rinsing, so it can only be done in places where the water is clean. Akita Prefecture is a perfect place to do so, as it still snows up until late March, and the fertile forests gather water. Tonburi accumulates pure water within its flesh to the point where it’s referred to as a “mineral water capsule.”

Rural scenery of Odate (2019)Original Source: Akita Tourism Guide

Odate’s natural landscape that brings blessings all year round

Agriculture is tough no matter the location, but it becomes even more severe in snowy Akita Prefecture. Tonburi is sown in late April, grows during the summer, and is harvested in September or early October before snow starts falling. Farmers process the tonburis indoors during winter when they can no longer do field work once the snow starts falling, which allows them to be productive year-round. This production cycle was established thanks to the wisdom of their predecessors.

Threshed Summer Cypress Seeds (2019)Original Source: Akita Tourism Guide

How to process a Tonburi

Let’s explore the processing method. The summer cypress fruits that have been dried using a dryer after being harvested are still far from the shining, final product. In its original state, it’s dry, and is bitter when licked.

Boiled Tonburi (Field Caviar) Seeds (2019)Original Source: Akita Tourism Guide

Step 1: boil

Boil the summer cypress fruit, which is called “jifushi” in China, in a kettle for 30 minutes. The continuous stirring process to prevent boiling over is quite a strenuous task.

The Pot in which Tonburi (Field Caviar) Seeds are boiled (2019)Original Source: Akita Tourism Guide

The tonburis start absorbing water and become heavy to the point where a novice would not be able to stir them effectively. They uses the whole body to stir it using a paddle in series of small motion.

Boiled Tonburi (Field Caviar) Seeds (2019)Original Source: Akita Tourism Guide

This is how it looks after draining the water. However, it still looks like there’s a long way to go to reach the beautiful green color that’s referred to as the “caviar of the fields.” From here, it becomes temperature-controlled and left for about 12 hours.

Transfer the Boiled Tonburi (Field Caviar) Seeds from the Strainer to the Bucket. (2019)Original Source: Akita Tourism Guide

The process of rinsing out impurities using fresh water is repeated many times to make the tonburis. Due to the cold winter air, you can see a lot of steam rising from the hot water after boiling. Since it requires using your hips a lot, it seems to require a lot of effort.

Peeling (Trade Secret) (2019)Original Source: Akita Tourism Guide

Step 2: machine peeling

This step involves peeling the thick skin that envelopes the surface. They started implementing a peeling machine in 1975, which Mr. Honma jokingly calls it their “trade secret.” We were only allowed to photograph the edge of this delicate machine that removed only the skin without crushing the flesh. You can sense history from the machine, which was thoroughly polished.

Honma-San, The Processing Factory Manager (2019)Original Source: Akita Tourism Guide

Mr. Honma joyfully explained the process to us. He says that the flavor of tonburi has been familiar to him from a young age. “The mountains in this region block wind from entering, which is tonburi’s kryptonite, thereby protecting the tonburis. Even within a particular region, there are specific spots that are suitable to grow particular crops.”

Repeat Washing and Sort Out Foreign Substances. (2019)Original Source: Akita Tourism Guide

Step 3: repeatedly rinse

To remove its thin skin, they gently and carefully rinse them. They use large amount of clear water from Sai River, which they extract from underground. When asked about the harshness of using water during winter, he replied, “It may be surprisingly, but the water is actually warmer during the peak winter season such as January. The water seems the coldest around March.”

Wash and Sort Out Foreign Substances from the Tonburi (Field Caviar) Seeds. (2019)Original Source: Akita Tourism Guide

Step 4: rinse repeatedly using a colander

To further remove any foreign debris, we move the tonburis so that the debris starts rising up. While visually inspecting the progress and re-positioning it, the colander is rhythmically moved. This is the moment when the black water gradually starts turning green.

Wash and Sort Out Foreign Substances from the Tonburi (Field Caviar) Seeds. (2019)Original Source: Akita Tourism Guide

As the tonburis are gracefully rinsed with the colander, it also depicts a beautiful pattern on the water’s surface. When properly and regularly sifted, the waves start showing a beautiful pattern. The sounds of the swaying water quietly echoed throughout the factory.

Draining (2019)Original Source: Akita Tourism Guide

Step 5: drainage

After being sufficiently cleaned, it’s placed under a stone weight for about 8 hours to thoroughly drain the water. There’s no need to worry that the small tonburis will be crushed. Gathering them in masses in a net will prevent damage.

Tonburi (Field Caviar) with Removed Husks (2019)Original Source: Akita Tourism Guide

You can begin to see its vivid luster! It smells refreshing like cured hay, which is counterintuitive to the common notion that “tonburis are odorless.” From here, there’s only one final step left to go.

Sift the Tonburi (Field Caviar) (2019)Original Source: Akita Tourism Guide

Step 6: redness removal

In this step, debris is further removed, which has already been mostly removed at this point. By using a sieving machine with different meshes, the red fleshes (unfinished product) drop to the bottom. They are then further visually inspected. A tweezer is used to remove fine branches, etc. that cannot be removed by a machine.

Tonburi (Field Caviar) Rice (2019)Original Source: Akita Tourism Guide

The final product: let's try one!

It pairs beautifully well with Akita's favorite rice, the “Akita Komachi.” Tonburi’s succulent texture and the mellow taste of rice spark an exquisite balance. Mr. Honma suggested me to put more servings on my plate in his Akita dialect. His favorite way of eating a tonburi is mixing it in natto (fermented soybeans).

Tonburi (Field Caviar) Cuisine (2019)Original Source: Akita Tourism Guide

Tonburi can be added, mixed or sprinkled on anything, as it doesn’t interfere with the taste of other ingredients. From top left in order: grilled egg, tuna mix, and crab salad. Every time I thanked him, he returned a smile and said “nanmo nanmo” (meaning, “there’s nothing to thank me for”) in a gentle Akita dialect.

Tonburi (Field Caviar), Packages (2019)Original Source: Akita Tourism Guide

Recreating the flavors of Akita at home

We recommend the “raw tonburi,” which can only be had during its peak season from October through March. It can only be stored for two weeks, but for the locals, the tonburi is something to be eaten raw. Other storage methods include vacuum packing and bottling, which last for 2 months and 6 months, respectively. Why not try incorporating tonburi, a healthy delicious superfood, into your lifestyle?

Credits: Story

Cooperation with
Hiuchi Tonburi Production Committee
JA Akita (North)
Akita Inu Tourism General Incorporated Association

Photos: Misa Nakagaki
Text: Makiko Oji
Edit: Saori Hayashida
Production: Skyrocket Corporation

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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