Legendary Yuko Citrus from the Home of “Hidden” Christians

Yuko is a round, palm-sized fruit with bright yellow skin. “The fruit is similar to Yuzu. It’s said that it came about as a result of a mutation that happened while it was growing in the wild in the mountains,” says Mr. Nakao who runs a mandarin orange farm in the Nita community in Koba-machi, Nagasaki.

Only around 100 naturally growing yuko trees could be found standing in the Doinokubi and Sotome districts of the old Saga domain and some parts of the Goto Islands. While there’s a possibility that they were planted in the gardens of private houses located in these areas in the latter half of the Edo period (1603–1868), the true origins of this citrus remain a mystery.

Yuko was rediscovered as a new citrus species in 2001. A municipal employee was conducting a survey of the local area when, by chance, he was handed a fruit by the roadside. Surprised by its unique flavor, he asked an expert to look into this matter. The survey ultimately confirmed that Yuko was indeed a new species. After learning about Yuko, Mr. Nakao decided to research it by himself. In 2007, he established the Nagasaki Yuko Promotion Association in order to preserve and promote Yuko as a specialty of Nagasaki Prefecture. Serving as the association’s chairman, he seeks out farmers willing to grow Yuko and provides them with saplings. He is also involved in promotional activities and helps develop processed products using Yuko, such as food and beverages.

Nagasaki was the only port in Japan that was open to foreign trade during the period of Japan’s isolation in the Edo period. It was the gateway through which foreign novelties spread across the country. Why didn’t the same thing happen with Yuko? Many experts assume that it had to do with the population of “hidden” Christians.

“The areas of Doinokubi and Sotome, where Yuko trees were originally found growing, used to be home to many ‘hidden’ Christians who escaped there during the period of religious persecution when Christianity was prohibited in Japan. Since they needed to keep their whereabouts secret, they couldn’t start a fire. They committed themselves to eating berries and fruits as well as raw fish and shellfish in order to survive. It’s believed that Yuko that grew naturally in the mountains was part of their diet,” says Mr. Nakao. The fruit is rich in flavonoids that possess antibacterial and antimicrobial properties, so apparently, there’s a possibility that it was also used as a remedy for colds and lotion.

“Some people tear up when I tell them about Yuko and ‘hidden’ Christians,” says Mr. Nakao. Christians in Japan continued to practice their faith in secret under a ban on their religion that lasted for 250 years. In 2018, a group of “hidden” Christian sites located in Nagasaki and in the Amakusa region in Kumamoto was registered as a UNESCO World Heritage Site. The connection between Yuko and “hidden” Christians is nothing more but a theory. That said, the topic offers an opportunity to reflect on the history of Nagasaki.

The cultivation of Yuko has spread from the Doinokubi and Sotome districts to the Higashi Nagasaki and Mogi districts. Since this citrus species grows naturally in the mountains, it’s resistant to diseases and low winter temperatures. The trees growing in Mr. Nakao’s orchard are dotted with healthy-looking, yellow fruit. The harvest is usually over by the end of December, but Mr. Nakao leaves some of the fruit until January or even later for people who come to visit his orchard.

Mr. Nakao picks a piece of fruit from the tree and cuts it for us to try. Its flesh is juicy and, much like Yuzu, it has many seeds. The skin gives off a rich aroma of sweetness with a tangy hint and the juice is refreshingly sour. It seems sweeter and milder compared to lemon juice. We asked about its sugar content, and, as it turns out, it’s over 10%. Mr. Nakao tells us that adding a splash of freshly squeezed juice to meat or fish dishes gives them a beautiful aroma and cuts through the fattiness.

According to Mr. Nakao, drinks using Yuko can be enjoyed at local bars. Increasingly more shops offering dishes and sweets featuring this fruit are beginning to pop up in the area. A major domestic beverage company has developed a canned Yuko cocktail, and there’s a pair of people in Scotland who sell craft gin with Yuko. Moreover, at a welfare facility located near Mr. Nakao’s orchard, they squeeze juice from Yuko and sell it, creating more local employment opportunities.

“I’m sure Yuko will only become more popular from now on. I’ll continue looking for more experts who will spread the word on how delicious it is and gather enthusiastic farmers to promote it further,” says Mr. Nakao. The rare citrus that grows only in Nagasaki is a local treasure that speaks of the region’s charm. We hope that it’ll keep growing stronger.