Cuisine
Purple sweet potatoes — Beni Imo
From food crops to Okinawan gift symbols
Okinawa purple sweet potatoes
Vibrant purple isn't just for beauty — Beni imo is a famine staple, an antioxidant superfood and a mainstay of the Okinawan longevity diet.
The article travels from its Central American roots, its journey to Ryukyu, the magical anthocyanin pigment, its nutritional power, its Blue Zone connection, to its homeland of Yomitan and its famous tart.
The island's purple gem
Beni imo (紅苋) is a purple-fleshed sweet potato typical of Okinawa — a type of plant they are convolvulus (Ipomoea batatas), famous for its vibrant purple color and nutritional value.
That magical purple color comes from anthocyanins — the same antioxidant pigment that gives blueberries, purple cabbage and red grapes their color. Considered by Okinawans as symbol of health and longevity, it has been a staple food for centuries.
Pale skin, purple flesh — first surprise
When alive, beni imo has a light brown skin that is almost white, and the inside is only slightly lavender purple - from the outside it is almost impossible to guess what is inside. Only when cooked, the skin darkens and the intestines turn Dark purple, almost black.
It's not a potato, it's not "ube" either.
Very often mistaken. These three types of “purple” tubers come from completely different plants:
| Criteria | Purple sweet potato (beni imo) | Purple yam (ube) | Potatoes |
|---|---|---|---|
| Species/family | Ipomoea batatas — convolvulus family | Dioscorea alata — brown bulb family | nightshade |
| Origin | Central/South America | Native Asian | Andes, South America |
| Texture | Drier, slightly fibrous, honey sweet | Moist, chewy, with a hint of vanilla/hazelnut | bitter, not sweet |
| GI (blood sugar) | Low (~46) | Higher (~79) | Usually high |
Same purple color, different nature
Both beni imo and ube are purple thanks to anthocyanins, but ube is real yam (true yam) of Asia. In Okinawa, the two are sometimes referred to together Beni imo, but Okinawan purple sweet potatoes have a lower GI — better for blood sugar.
From the Aztec empire to the Ryukyu kingdom
Beni imo's journey is an early globalization story:
15th century · Left Central America
Sweet potatoes originate from Central/South America (Aztec land). Spanish explorers brought it to the Philippines and China in the 1400s.
1594 · “Fan-shu” in Fujian
Grown in Fujian (China), called fan-shu — “foreign potatoes”.
1605 · Noguni Sokan brought back
Noguni Sokan — a minor official on a Shuri imperial merchant ship — was at the Ryukyu trading station in Fuzhou, learning how to grow and bring potato seeds to Okinawa.
Early 17th century Gima Shinjo popular
Quan Gima Shinjo learned farming techniques and spread them throughout the island (he also brought sugar cane and cotton to Ryukyu).
1615 · Spread to Japan
Potatoes became so important that they were brought from Okinawa to mainland Japan — with records associated with British trader William Adams.
Why potatoes — not rice?
Okinawa is often hit by strong storms, making rice difficult to grow. Sweet potatoes grow well in hot, humid climates and withstand storms — so they quickly became a staple food instead of rice.
Why is it so special?
Anthocyanin pigments, high nutritional density and a central place in the longevity diet — three reasons why beni imo goes beyond the average potato.
Magical purple pigment
Anthocyanins don't just provide color — they're a group of powerful antioxidants, studied for their anti-inflammatory, anti-cancer, anti-diabetic, and antibacterial properties.
More than blueberries
Same pigment as blueberries but higher concentration — many sources estimate ~150% Antioxidant activity compared to blueberries.
Durable when cooking
Mostly acylated anthocyanins — more heat resistant than pigments in berries, retains color well when processed.
Natural light color
Used as a natural food coloring instead of synthetic foods; The outer shell contains a particularly high concentration.
With the "purple family"
Anthocyanins in beni imo (such as cyanidin, peonidin) are similar to the coloring substances for blueberries, purple cabbage, and red grapes. One cup of cooked potatoes provides approx 500 mg — not much worse than a cup of blueberries (~600 mg).
Power in a potato
In addition to anthocyanins, beni imo is also a storehouse of vitamins, minerals and fiber with a low calorie density:
Vitamin A
One cup can provide up to ~500% of daily vitamin A (beta-carotene) needs.
Fiber
~5 g fiber/cup — full for a long time, good for digestion and intestines.
Low calories
Only ~1.5 calories/gram (~220 calories/cup) — low energy density, helping to control weight.
Low GI
Blood sugar index ~46 — rarely causes sudden increases in blood sugar.
Plus: vitamins C, E, group B, potassium, manganese; The same antibacterial, antifungal and blood sugar regulation properties have been recorded in many studies.
"Discovered" by the world
Beni imo appeared on the Oprah Winfrey show (2009) and was recognized by Dr. Oz included in the top 5 superfoods in 2010 — contributing to bringing Okinawan purple sweet potatoes to the world.
Pillars of the longevity diet
Imo — Okinawa meal platform
Okinawa is one of those Blue Zone World-famous longevity, where many people live over 100 years old. Purple sweet potatoes used to be daily staple food.
Traditional diets are more than 90% plant-based; There was a time when ~70% of the energy came from purple sweet potatoes and orange potatoes — along with the habit of eating “hara hachi bu” (eating only until 80% full).
Why longevity?
Low calorie density + rich in fiber → full for long with little energy; Low GI → stable blood sugar; anthocyanin + antioxidant vitamins → reduce inflammation. That trio fits into a long-term healthy diet.
Scientific caution
Lifespan is influenced by many factors (genes, exercise, society...), and the Blue Zone theory itself is still controversial. Beni imo is part painting, is not the only "miracle drug".
Potatoes preserve life
Before becoming a “superfood”, beni imo was a literal lifesaver. During the famines of the 18th–19th centuries, when crops failed, sweet potatoes were the main famine food crop of Ryukyu farmers.
Withstands storms and bad soil
Unlike rice, potatoes can survive in poor soil, storm-prone areas — they can still be eaten.
Planted all year round
The humid subtropical climate allows for continuous cultivation, providing a stable food source.
Full for a long time, enough energy
Rich in starch and fiber, providing energy for heavy agricultural labor.
Spread to all of Japan
The role of potatoes in famine relief in Okinawa and Satsuma inspired the expansion of cultivation to the mainland to fight famine.
Sugar cane for export, potatoes for eating
The Ryukyu people developed sugar cane as a profitable export crop, also sweet potato is a key domestic food. The government even controlled sugarcane growing areas so as not to threaten food sources.
Culture & enjoyment
From the fields of Yomitan to the famous tart and the hero worshiped like a god.
Hometown of beni imo
Talking about beni imo is talking about Yomitan village on the west bank of the main island — called beni imo no sato (“homeland beni imo”). The purple potato plant is closely associated with the culture and pride of the people here.
Like Ayamurasaki
Purple potato variety rich in anthocyanin, high yield, bred by the Kyushu–Okinawa Agricultural Research Center (NARO) in 1995.
Potato weevil law
Due to the potato weevil epidemic, it is forbidden to bring beni imo fresh out of Okinawa; must be treated with heat at 47–48°C (potatoes remain raw).
Soil & climate
Yomitan is famous for its blue sky, clear water, and good soil — producing soft beni imo with its characteristic vibrant purple color.
One reason potatoes are difficult to buy outside of Okinawa
The potato weevil quarantine regulations make fresh beni imo very difficult to find outside the island. Other Okinawan restaurants often use hot-treated potatoes.
The famous tart
If there is a gift (omiyage) attached to beni imo, that is purple potato tart — crispy crust covered with sweet purple potato filling, completely natural purple color.
Okashi Goten & “Ganso” tart
Okashi Goten bakery (headquartered in Yomitan) is famous for Ganso Beni-imo Tart — one of Okinawa's most purchased omiyage dishes. Customers can also make their own tarts at the store.
Not just tarts
Beni imo ice cream is sold at almost every convenience store, along with cakes, tea, and purple all over Naha. There are even towels and fabric bags printed with tart images.
Real purple color, no artificial products
Quality tart products used 100% Okinawa purple potatoes, no preservatives or coloring — the purple color comes entirely from natural anthocyanins.
Noguni Sokan & festival of remembrance
The man who brought the potato seed to Okinawa — Noguni Sokan — is remembered as the benefactor who saved countless lives from starvation. “Sokan” is actually a position (manager on a merchant ship), so his real name is no longer clear.
Noguni Sokan Festival
Held every year in the town of Kadena — his hometown — with a potato harvesting contest for children, art performances and fireworks.
Be grateful for food crops
The festival pays tribute to the potato that has fed generations — from famine food to cultural icon.
The bottom line
Beni imo is special because it converges three roles: historical famine plant, anthocyanin-rich superfood, and Okinawan cultural symbol – longevity.
One potato, an entire island
Point to remember
- What is it?: purple-fleshed sweet potatoes of the morning glory family, different from ube and potatoes.
- Purple: due to anthocyanin — strong antioxidant, stable when cooked.
- Nutrition: rich in vitamin A, fiber; low in calories; Low GI.
- History: landing at 1605 (Noguni Sokan), famine relief tree.
- Culture: Yomitan hometown, tart, Blue Zone mainstay.
One line summary
Beni imo is special not because of the color purple, but because it both starved an entire kingdom and nurtured the world's longest-lived people — purple is just a visible sign of inner strength.