Most have a pronounced neck / bump on the top, though on some, the bump is quite minimal. The skin is a bit warty or bumpy, because the fruit is aged before it is sold. Despite the thick skin, the fruit is actually susceptible to bruising, particularly the bump at the top. It is often shipped in padded boxes for this reason.
Dekopons are larger than most oranges, but smaller than a grapefruit.
Inside, the orange is divided into segments by very thin, tender membranes that melt in your mouth. The flesh is firm and very juicy, with a complex taste that some compare to tangarine. They are sweeter than navel oranges. Some Dekopons that you encounter will be sweeter than others; some will have more aroma than others.
Dekopon trees need to be pruned, to let in light through the leaves, which makes the fruit sweeter. The trees need about 20 years of growth to reach peak production, at which point they may produce up to 320 pounds (145 kg) of fruit a year each.
In Japan, the trees are often grown in large greenhouses. From June to November the roofs are open on the greenhouses. When it turns cold, the roofs are closed, both to keep in heat, and keep the birds away from the developing fruit. The fruit from these greenhouse trees is harvested December to February. Fruit from fully outdoor trees is harvested March to April.
After harvesting, the fruit is let rest for 20 to 40 days in a special storage process which “cures” it. During this period, the acid level diminishes, making them less sour, and the sugar level increases.
To be sold under the name Dekopon, the sugar in the fruit must reach a minimum of 13 brix, and the citric acid level has to be below 1.0 %. It is not unusual, though, for the sweetness to reach 16 and 18 brix (compare this to navel oranges and clementines at 11 to 13 brix.)
In Japan, the name “Dekopon” is a trademarked name owned by a grower’s association in Kumamoto region. Anyone in Japan, though, can use the name — provided they pay a fee, and meet the quality standards.
Dekopons are being grown now in several places outside Japan. In Brazil, they are grown in São Paulo state, and sold under the name of “kinsei” (meaning “venus” in Japanese.) They were introduced into Brazil by a Japanese farmer named Unkichi Taniwaki. In Brazil, the harvest is from May through September.
They have been grown on Jeju Island, South Korea since 1998. In South Korea, they are sold as “hallabong.”
In America, they are currently (2011) sold under the trademarked name of “Sumo.”
Dekopons were originally called shiranuhi or shiranui (不知火), after a town near Kumamoto. That in fact is still their generic name.
The fruit was developed in 1972 from a cross between ponkan mandarin oranges and kiyoumi tangors at a Japanese government fruit research station in Nagasaki Prefecture, Japan.
At the time, Japan was under pressure from the US to open up for imports of fresh oranges (ironic, given that America itself bans imports of citrus fruit.) Japanese farmers felt they wouldn’t be able to compete with the large, sweet oranges from California, so, the Agriculture Department wanted to develop a large, sweet orange for them. After initial trials by farmers, though, the verdict wasn’t great: they said the yield was low, the shape inconsistent, and that the harvested fruit was quick to rot. Plus, it was ugly and sour. Consequently, the agricultural scientists gave up on it.
However, an (unidentified) fruit grower in Kumamoto saw promise in the fruit, and stole a cutting from a tree at the government research station. He began to grow it, and did some improvements of his own. In 1979, he was ready to start selling the fruit, but marketers wanted a better name than the government name for it of “shiranuhi”, which they felt wasn’t catchy enough.
They came up with Dekopon, from “deko” meaning “bump” (in Japanese, referring to the bump on top) and “pon” referring to one of the parent fruits, “ponkan.” Sales took off slowly but grew steadily. People liked the fruit, and its funny name.
Because the growers cooperative in Kumamoto had registered the Dekopon name, farmers elsewhere who wanted to grow it had to come up with other names. Dekopons grown in Ehime prefecture in Japan were marketed as “himepon”; ones from Hiroshima prefecture were marketed as “hiropon” (until they discovered “hiropon” was becoming the name for an illegal stimulant in popular culture.) Finally, licencing arrangements were reached with the Kumamoto grower’s cooperative for growers anywhere in Japan to use the name Dekopon.
The fruit first arrived in America in 1998 as tree cuttings. The import into America of any citrus fruit, including Dekopons, is banned, in order ostensibly to protect American crops. Consequently, in 1998, a citrus grower in Strathmore, California named Brad Stark, had cuttings legally imported, and paid for them to be grown at a plant quarantine station in Riverside, California, grafted onto trees.
There, professionals from the Citrus Clonal Protection Program grew the stock for several years in quarantine to ensure it was free of any diseases such as tristeza virus that could affect American citrus crops. In the ensuing years, Stark’s business went bankrupt, but the trees remained growing in the quarantine station. During that time, the Stark family sold the rights to the budwood to the Griffith family, a wealthy family in southern California who owned the Suntreat and TreeSource companies.
Finally, in 2008, the Suntreat company engaged 13 growers southeast of Fresno, California, in the San Joaquin citrus belt, to plant 430 acres of the trees. The growers had to sign confidentiality, exclusivity and secrecy agreements.
The first harvest started in January 2011, and began arriving at stores in February 2011. The first crop was mostly sold in California.
Through a series of marketing focus groups, the company decided to call the fruit “Sumo.”
By 2011, rights to the budwood from the quarantine station were re-acquired by government authorities, and the tree was released as a publicly available variety. But by then, the Suntreat company had got its big head start on any competitors — at least seven years, the company reckoned.
Atkinson, Greg. Nishida Dekopon Orchard. On “Westcoast Cooking” blog. 22 July 2010. Retrieved February 2011 from http://www.westcoastcooking.com/content/view/187
Gordenker, Alice. Dekopon. Tokyo: Japan Times. 22 January 2009.
Karp, David. The Dekopon arrives in California. Los Angeles Times. 17 February 2011.