The Culture of Japanese Chesnuts

Chestnuts: used in various sweets such as the Mont Blanc dessert and in Japan, chestnut yokan (jellied dessert) and kurikinton, the mashed sweet potato and sweetened chestnut delight that is an indispensable part of traditional New Year's cuisine. The Japanese chestnut, or kuri, with its refined sweetness and chewy texture, has many fans. However, raw chestnuts are exclusively seen in the stores during a short period around September-October. With most produce available in the shops year-round these days, chestnuts are a special treat that can only be bought when they are in season.

Ibaraki Prefecture is Japan’s leading chestnut-producing region in terms of area under cultivation and production volume. The large diurnal temperature difference found in the basin area that comprises a large part of the prefecture and the rich volcanic ash soil with excellent water retention and air permeability properties combine to make for a highly suitable chestnut growing environment. The largest growing area can be found in the Iwama district of Kasama City, located in the heart of Ibaraki; chestnut groves can be found everywhere here. To find out more about chestnuts, a visit to Yasuhiko Odaki — also known as ‘Professor Kuri’ — the president of manufacturer and seller of processed chestnut products, Odaki Shoten.

The rich history and variety of Japanese chestnuts

Chestnut cultivation began in Japan during the Jomon Period more than 5,500 years ago. With the 1992 discovery of the Sannai Maruyama Site in northern Aomori Prefecture, it became clear that people at the time had planted chestnut trees around their villages and used the nuts as a stable food source. It seems that the nutritious and tasty chestnuts were an important staple of the Jomon diet. Furthermore, recent archaeological studies of the site revealed that the chestnut grove there had been cultivated and maintained for around 1,500 years. In other words: long before rice became the staple food, chestnuts were integral to supporting the people of prehistoric Japan.

There are four main species groups of chestnut around the world: the American, European, Chinese, and Japanese chestnuts. Compared to the Western or Chinese chestnuts, the Japanese species is larger, has a stronger aroma, and is known for its inner skin (pellicle) being harder to peel. There are over 100 varieties in all with varying characteristics, from the very sweet to the richly flavorsome.

In 2006, the National Institute of Fruit Tree Science (NIFTS) developed the new cultivar, Porotan, a groundbreaking chestnut that has a pellicle that becomes very easy to peel after roasting. It is known as the ‘Miracle Chestnut’, one that changed the course of the 10,000-year old Japanese chestnut and has rapidly gained popularity around the country. Ripening and harvesting times differ depending on the variety. The earliest of the early varieties is the Tanzawa, while the Rihei is a medium maturing chestnut, coming into season at the end of September/start of October. The Ganne is a late-season chestnut, available from mid-October. In general, the earlier varieties are said to have a richer color while the medium and late ones are sweeter.

Another specialty of Ibaraki is the premium grade Iinuma chestnut.

While ordinary chestnuts contain three nuts per shell, a unique method of cultivation ensures that just one large nut grows in the shell in the case of the Iinuma. These nuts that develop to the equivalent of a 3 to 4L sized regular chestnut are characterized by their exceptional sweetness. In 2017, the Iinuma was the first chestnut to receive Geographical Indication (GI) protection in Japan.

A myriad of processed chestnut products from Iwama

From May to June, Iwama’s chestnut groves are filled with white, fluffy flowers. At the base of each flower, the nut begins to form as it is bathed in the sun over summer. This is also the time the green chestnut bur starts to take shape. The end of summer sees the bur begin to turn brown; in time, it splits open, allowing the shell containing the chestnuts to fall to the ground. Harvest season starts in late August at the earliest, peaks in September, and can last until late October, depending on the variety.

“With chestnuts, freshness is everything,” Odaki explains. “According to research, around 30% of chestnuts will go to rot if left overnight at a temperature of 25℃. That is why harvested chestnuts are either immediately chilled or cooked for processing."

According to Odaki, there are two patterns when it comes to eating chestnuts: some are best fresh and some become delicious with age.

“It is actually a mistake to say, ‘Freshly picked, sweet chestnuts’. The main component of chestnuts is actually starch and freshly picked chestnuts are not sweet; they are in fact quite dry and bland. In contrast, the fresh chestnuts have a strong aroma. This gradually fades with time.”

Odaki recommends that freshly harvested chestnuts are best used for kanroni (boiled and sweetened chestnut), kurikinton, or kurimushi-yokan (chestnut steamed sweetened bean-jelly). Conversely, the starch in chestnuts that have aged gradually changes to sugars and the sweetness becomes stronger; he therefore recommends they be eaten roasted, boiled, or in kuri-okawa (chestnut rice).

“If you keep the chestnuts in a refrigerator at 0 degrees, they will have their sweetness doubled after two weeks, and even tripled or quadrupled after one month.”

Odaki Shoten tries to maximize the taste of the chestnuts they use in their processed goods according to the particular chestnut characteristics and variety. “Up to now, most of the processing of chestnuts ignored variety and type. For instance, the Rihei contains a lot of starch, meaning it splits easily when making kanroni. However, it makes for a fantastic steamed chestnut. After trying each kind of chestnut and a lot of trial and error, we were able to determine the suitability of each for processing. We now have more than 20 different products that cover a wide range, from the classics to the new and original, from chestnut kanroni and chestnut paste to chestnut ice cream and chestnut dumplings.”

Roasted chestnuts, which Odaki Shoten only sells at its store for a limited time each year, are cooked only until medium rare inside so that they do not lose any flavor. The company prides itself on its kuri-okowa, a simple dish made only with Porotan chestnuts mixed with sticky rice and salt.

“Even the salt we use is simple — no strong-tasting rock salt. As the chestnuts and rice are cooked together, the flavor is fully absorbed by the rice. The chestnuts replace the dashi (stock).”

One of the best-selling products Odaki Shoten makes is one they have dubbed Gyu, a sweet treat made from only chestnut and sugar. It was apparently created so that visitors to Iwama could enjoy local chestnuts in a tasty way when it was not harvest season.

“Chestnuts in their original state score 10 out of 10 on the deliciousness scale!” proclaims Odaki. “Every time you do something to chestnuts, that score goes down. If you go doing too much to them, the aroma and taste are ruined. Getting the flavor balance right can be quite difficult.”

Passing on Japan’s ‘Chestnut Culture’ to future generations

While Iwama chestnuts are becoming more well-known, chestnut growers are getting older and the area under cultivation and production volume are decreasing every year. On top of this, Odaki says that selective breeding of the trees to produce more nuts has in fact reduced their average lifespan.

“I realize transformation is a sought-after thing in agriculture. Until now, farmers had wondered how they could obtain the biggest yield from the smallest area, but I think we have now entered a time where people are looking for ways to continue chestnut cultivation while coexisting with the natural environment and without degrading farmland. If this can be achieved, it may be possible to get closer to having chestnuts reflect their true flavor.”

To make Odaki Shoten’s processed foods, mukiko-san (“peelers”) work on removing the husks and pellicles. The chestnut-peeling skills they display are unique to region. However, after peaking in the 70s and 80s, the number of mukiko-san has declined in tandem with the aging of society.

“Chestnuts have been supporting Japanese life since the Jomon Period and have a special place in our history. There has to be land dedicated to chestnut cultivation in order for this ‘chestnut culture’ to survive. The Sannai Maruyama Site showed that the people there had maintained chestnut cultivation for over 1,500 years. We need to look at the techniques by which this was achieved in order for us to ensure that Iwama chestnuts are around for tens of thousands of years to come! It would be good if Ibaraki Prefecture can assess how it can recreate this ‘chestnut culture’ to achieve this.”