Hokkaido and Aomori prefectures are always competing with each other for the largest shipment volume of nagaimo, a variety of mountain yam, in Japan. Combined, these two regions account for about a 90% share of nagaimo production. Nagaimo is said to have originated in Southeast Asia and records indicate it was first used as a medicine in China around the year 2000 BCE. It was first cultivated in Japan during the Jomon period. Nagaimo can be prepared in a number of ways, from freshly grated to simmered, deep fried, stir fried or pickled.
The fact that nagaimo contain large amounts of digestive enzymes makes it fundamentally different than other varieties of yams and potatoes. It contains a larger amount of amylase, an enzyme that breaks down starches, than daikon radish, which is why it is easily digested even when eaten raw. Since ancient times nagaimo has been considered as good for nutritional fortification and recovering from fatigue because it contains enzymes that breakdown protein. Nagaimo’s unique sticky and gooey consistency is attributed to mucin, which protects the stomach lining and prevents the body from absorbing cholesterol.
Nagaimo is mainly grown in the Tokachi and Abashiri regions because of the ideal soil conditions.
■Map / Main producing municipalities
Obihiro City, Makubetsu Town, Memuro Town, Otofuke Town, Ozora Town, Shihoro, Nakasatsunai Village, Abashiri City, Ikeda Town
The ideal growing environment for nagaimo has large temperature differences and well drained soil, which makes the Tokachi region ideal. Nagaimo grown in the best conditions have delicate white flesh that produces a sticky and gooey consistency when grated. They also are highly nutritious and taste particularly delicious. Today, Tokachi-grown nagaimo can be found widely throughout Japan under the brand Tokachigawa Nishi Nagaimo, which is distributed well beyond the local JA and towns where it is grown. Nagaimo is also exported to Taiwan, which is witnessing a boom in medicinal cooking. The thick high quality nature of Hokkaido-grown nagaimo has received strong acclaim overseas.
Nagaimo is cultivated between April and November, with most grown outdoors. In November and December after the harvest it is housed in cold storage so it can be shipped throughout the year.