In almost all supermarkets in Japan, you can find a starchy vegetable with a purple (or pale brown) skin and sweet taste that is available throughout the year. This food is normally called sweet potato, or “satsumaimo” in Japanese, which is regarded as a standard seasonal food in winter and is consumed in various ways. Since Japanese sweet potato is known for its delicious taste and healthiness, its consumption has been expanding globally among health-conscious consumers and also those who interested in Japanese food. In this article, we will dig down into the details of satsumaimo sweet potato including:
- Basic information on satsumaimo
- Health advantages of satsumaimo
- Satsumaimo recipes
- Variations of satsumaimo
- Tips for selecting/storing satsumaimo
What is Satsumaimo?
Satsumaimo sweet potato is a root vegetable that originates from Central America. Although there are different stories about the origin of satsumaimo in Japan, it was first introduced to Okinawa from China at the beginning of the 17th century, following which it was disseminated to Kagoshima-han (Kagoshima domain of the Tokugawa Shogunate) in the early 1700s. Since then, it has been Kagoshima Prefecture’s local specialty.
Naturally, satsumaimo is primarily used for food, but it also has other usages. For instance, its starch is a natural sweetener that can be widely used in snacks and processed foods. Moreover, high in viscosity, its starch can also be a natural material for adhesives, dentifrices, and even medicines.
It is said that there are roughly 50 satsumaimo cultivars in Japan. Although it varies slightly, satsumaimo usually features a starchy texture and pleasant sweetness. The satsumaimo with flaky, light dry texture is regarded as an original variation, but ones with rather a moist bite feel are currently trendy in Japan.
Health Benefits of Satsumaimo
Satsumaimo is a wonderful food because it is not only delicious but also nutritious. Specifically, jalapin, a white liquid that leaks from a cutting surface of raw sweet potato, is said to exist exclusively in satsumaimo and can improve bowel condition and skin turnover. If possible, eat its skin too: satsumaimo’s purple color derives from a polyphenol called anthocyanin and this promises to improve asthenopia and visual function.
Satsumaimo is a natural fiber supplement that can help prevent obesity, digestive system diseases, and strokes. Rich in vitamin C and E, it also helps enhance antioxidant effects. For minerals, satsumaimo has an abundance of potassium and copper, which supports the release of excess salt and helps prevent cardiovascular diseases, respectively.
Even though satsumaimo is a low GI food, you should note that its calorie is relatively higher than most vegetables (120~130kcal per 100g). Further, it has a high sugar content, and the sweeter variations tend to have more, so it is not a good choice for low carb diets. However, this will not be a serious issue if you eat no more than one satsumaimo a day.
Cooking Guidance of Satsumaimo
You can eat satsumaimo in various meals, from appetizers to dessert. Here are some major examples of how it is cooked in Japan:
- Yakiimo (baked sweet potato) – this is the simplest yet the best way to enjoy this potato. When it gets slowly heated, its starch eventually changes to sugar so it gets sweeter. If you wish to experience a moist texture, boil the potato. You can also enjoy satsumaimo by steaming or microwaving it. For better results, soak satsumaimo in the water for about 10 minutes in advance to remove harshness.
- Satsumaimo tempura – dip round slices of sweet potato into batter and deep-fry them to create sweet and crunchy tempura. Although you can enjoy this dish without any seasoning, you can add a pinch of salt if you wish to enjoy the contrast between sweetness and saltiness. It also goes well with mayonnaise or tempura sauce (you can create your own by mixing soy sauce, sugar, mirin, and dashi stock).
- Stir-fried satsumaimo – pan-fry some pieces of satsumaimo to enjoy its pleasant taste and texture. Cook with foods rich in umami such as bacon, mushrooms, and chicken to enrich its taste. Here are some examples of seasonings you should try: butter, garlic, sesame oil, Japanese mayo, sesame dressing, and Japanese curry.
- Satsumaimo niku-jyaga – this simmered dish normally consists of meat, carrot, onion, and potato, but it is totally okay to replace the potato with satsumaimo. You will not be able to resist the sweet flavor that is enhanced with a sweetened soy sauce. This dish is a great companion to white rice as well as alcoholic drinks. Instead of soy sauce, you can make Western-style niku-jyaga by adding tomato sauce.
- Daigaku-imo – daigaku-imo literally means “college potato” in English, and is one of the most popular and famous satsumaimo dishes in Japan, though the origin of its name has not been identified so far. Daigaku-imo is a plain-fried sweet potato that is seasoned with a sugar syrup and black sesame seeds. Enjoy its crispy outer side and flaky inner side.
- Sweet potato – did you know that there is a traditional Japanese confectionery called “sweet potato”? To try this sweet, cook a peeled satsumaimo; mash then strain it; blend it with sugar, butter, egg yolk, and milk; shape the mixture into 1/2 cup-sized pieces (roughly 1~2 ounces); glaze the top of it with egg yolk with a basting brush; and bake it until the top turns golden brown.
Satsumaimo Sweet Potato Cultivars - Texture, Taste, and Color
Most satsumaimo cultivars commonly have a spindle-shaped appearance, purple skin, and sweet flavor. However, there are some variations that have different characteristics. In this section, you can learn about some popular satsumaimo varieties consumed in Japan.
Beni Azuma – the most classic Japanese sweet potato
If your first impressions of satsumaimo are a flaky texture and mild, earthy sweet taste, Beni Azuma may be the one you ate. It has been the most popular variety in Japan for more than three decades, and is mainly cultivated in the Kanto region including Ibaraki and Chiba Prefectures. Beni Azuma is neither too sweet nor too fibrous, so you can enjoy its flaky yet smooth texture regardless of cooking methods from stir-frying to simmering.
Anno Imo – juicy flesh with a creamy feel in the mouth
Traditionally, flaky satsumaimo was extremely popular in the Japanese market, but it is said that the Anno Imo changed this trend. Unlike Beni Azuma, it features a watery, viscous biting feel and lovely round appearance. The true value of Anno Imo is its strong sweetness; if this satsumaimo is baked, you can find its flesh hydrated with a sweet syrup that trickles from its golden flesh. Its sweet and creamy flavor is a must-try.
Beni Haruka – super sweet as if glazed with sugar syrup
Beni Haruka is another emerging type of satsumaimo that has both intense sweetness and a pleasant stickiness. The word “haruka” means “far better” or “much greater” and it was used in its name because it is literally much sweeter than any other types of satsumaimo. Its beautiful fusiform shape and pleasant aftertaste also account for the popularity of this satsumaimo. If you are a great lover of sweets, you should not miss out on Beni Haruka.
Naruto-kintoki – all-round sweet potato gaining popularity
Beni Azuma is mainly cultivated in Eastern Japan while Naruto-kintoki is normally marketed in Western Japan. The locals often express this satsumaimo as “a variation that is similar to kuri (sweet chestnut)”; indeed, its sweet taste and flaky yet moist texture is quite close to that of sweet chestnut. Naruto-kintoki has a beautiful yellow flesh and red purple skin, so it is highly appreciated as an ingredient of confectionery providing a vibrant hue. It can also pair well with any non-sweet dish.
Silk Sweet – unprecedentedly silky smooth satsumaimo
Are you looking for a type of satsumaimo that has a smooth texture like a silk? The feel when you bite Silk Sweet has fascinated many fans of sweet potato; now it is your turn to enjoy its melty feel. Silk Sweet has a comparatively beautiful spindle shape and creamy yellow flesh, but when it is cooked the flesh turns a more vivid yellow and it becomes moister. For this reason, the best way to enjoy Silk Sweet is by eating it as yaki-imo (baked satsumaimo).
Purple Sweet Lord – both skin and flesh are fully purple
Although in some countries, murasaki sweet potato is recognized as one of the synonyms of satsumaimo, in Japan it refers to potatoes with purple flesh and these are often called “murasaki imo (purple sweet potato)”. Purple Sweet Lord is one of the sweetest types of murasaki sweet potato and you will be amazed at its purple skin and flesh. It becomes more brilliant when baked, so you can make your dishes look even more colorful.
Ayamurasaki – deep colored satsumaimo perfect for decoration
Another type of purple sweet potato is called Ayamurasaki. This variation has a deeper purple color than the Purple Sweet Lord, but it is mainly used for processing purposes such as for a colorant of beverage, paste, and powder. It has a flaky texture and is less sweet than most Japanese types of satsumaimo, so it goes perfectly as a natural colorant of sweet potato, Mont Blanc, and potage soup without making them too sweet.
Ayakomachi – wholesome and beautiful orange flesh
Orange fleshed types of satsumaimo are often consumed in the United States but are not so common in Japan; however, there is a Japanese variation that is interbred with this American sweet potato. It is called Ayakomachi, which is developed in Okinawa in 2004, and features a pleasant sweetness, sticky texture, and brilliant orange flesh due to its rich carotene content. It is very healthy, easy to eat because its flesh is not so stringy, and you can enjoy its sweet taste even if it cools off.
Kogane Sengan – starch-rich variation ideal for alcohol production
Although Kogane Sengan is unsuitable for eating, when it comes to the production of imo-jyochu (sweet potato spirit), this satsumaimo plays a critical role. This cultivar has high brewing aptitude: it is rich in starch, which is essential for alcohol fermentation, so it can efficiently produce imo-jyochu spirits. The alcohol made from Kogane Sengan has a sharp sweetness and elegant aroma with a less pungent potato-like odor. In terms of appearance, it has a pale brown skin and white flesh.
Tips for Selecting and Storing Satsumaimo
In this section, you can learn how to find high quality satsumaimo and get some tips on how to store them properly. When you find satsumaimo at grocery stores or gourmet supermarkets and are planning to add them to your cart, check whether it meets the following criteria:
- It has a vivid color and shiny skin with less darkened areas.
- The skin has fewer scratches and less unevenness on its surface.
- It does not have thick and hard fibrous roots.
- The weight is heavier than you imagine when holding it.
- It is thick and plump in appearance; keep in mind that thickness is the most important aspect.
Regarding storage, although satsumaimo is a convenient food that can last a long time even when stored at room temperature, it may sprout or generate black dots. To prevent this, wash it lightly, cut it into convenient sizes according to your preference, pack it in a preservation bag, and freeze. Using this method allows the sweet potato to last for a month without its color decreasing or losing its shape when simmered.