Hoshi Imo (Dried Japanese Sweet Potatoes)

Hoshi Imo is a classic fall snack in Japan, offering the natural sweetness inherent in Japanese sweet potatoes. You can enjoy the rich, concentrated flavor with every bite, leaving you craving more.

Hoshi Imo is a Japanese snack made by steaming or boiling Japanese sweet potatoes and then sun-drying them. "Hoshi" stands for drying, and "Imo" means potatoes, specifically referring to Japanese sweet potatoes used in this snack, also known as satsumaimo. The drying process gives the sweet potatoes a texture similar to that of dried fruits and a concentrated natural sweetness.

It is a staple snack in Japan, commonly found in grocery stores, especially during fall. While the sun-drying process takes time, you can easily make it at home as long as you have Japanese sweet potatoes. Packed with nutrients and having a good shelf life, it makes for an ideal snack to keep on hand.

When purchasing Japanese sweet potatoes, choose the best ones available. You can assess their quality based on the following appearance factors:

• They should have black, soil-like markings on the surface.

These dark spots are the result of the white liquid called 'yarapin' that oozes out of the sweet potato and oxidizes. Yarapin emerges from sweet potatoes with a high sugar content, indicating the potential for sweetness. They should have a glossy appearance, be slightly firm to the touch, and feel a little sticky. Be careful not to mistake them for mold or black spot disease.

• Avoid overly large ones.

Sweet potatoes that are too large have less sweetness and can become difficult to cook through. A weight of 9-12.5 ounces (250-350 g) is optimal for hoshi imo. To ensure even cooking, it is recommended to choose sweet potatoes with consistent thickness.

Even if they are the same size, their weight may differ. In such cases, it is recommended to choose the heavier one, as Lighter sweet potatoes may have less dense flesh.

In Japan, sweet potatoes are typically harvested from around September to November, but they become sweeter and more delicious after an aging period of approximately 2-3 months after harvest. Therefore, Japanese sweet potatoes available from December to February are the best for consumption.

Additionally, while you can make hoshi imo with any type of Japanese sweet potatoes, if you have the opportunity, I highly recommend trying Beni-Haruka (紅はるか) or Anno-Imo (安納芋). These varieties boast remarkably high sugar content, resulting in pronounced sweetness and a visually translucent appearance due to the high water content in the finished hoshi imo.

In Japan, hoshi imo is available in various sizes, ranging from large vertically sliced pieces to stick-shaped portions. In this recipe, I cut it into bite-sized pieces, but feel free to choose your preferred size.

The key point to note is the thickness rather than the size. When cutting sweet potatoes, make sure the slices are approximately ⅓-inch (7-10 mm) thick. This ensures quick drying of hoshi imo, resulting in a uniform texture.

If the slices are too thick, the interior may remain moist while the exterior becomes too hard. Additionally, uneven thickness can lead to variations in the texture of each piece of hoshi imo.

The texture of hoshi imo depends on how long it is dried in sunlight. My recommendation is 2 days, which results in a subtly soft texture. The most common duration in Japan is 3-5 days. The longer the sun-drying period, the harder the texture becomes, making it more suitable for longer storage.

However, keep in mind that the number of days for sun-drying is influenced by temperature and humidity, so treat it as a rough guide. It is recommended to make it during the cold, low-humidity seasons. If made under different conditions or without direct sunlight, you might need to increase the number of days for sun-drying. To achieve your preferred texture, consider periodically checking the state of your hoshi imo by sampling during the drying process.

Additionally, on nights without sunlight, store it in a well-ventilated, cool place. Avoid keeping it in a warm room with heating, as this can lead to mold growth.

When sun-drying hoshi imo, you may notice a white powder on the surface. This is crystallized sugar content from the sweet potatoes, and it is safe to consume.

However, if it rains during the sun-drying process or if they are stored in a warm room overnight, white mold may develop. While white powder only on the surface indicates sugar crystallization, if it has penetrated the interior of the sweet potato, it is likely white mold. Additionally, be cautious if you observe black spots, as they could also be mold; it is advisable not to eat those hoshi imo.

Ingredients

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Instructions

🕒 Total: 2 days days 1 hr hr 10 mins mins

Step 1
Wash sweet potatoes thoroughly and remove any dirt. Fill the steamer with water and heat it until it boils. Once boiling, add the sweet potato and steam for an hour. Alternatively, you can choose to boil it for an hour.

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Step 2
Remove the sweet potato from the steamer. Trim both ends, and peel off the skins and any inner brown parts. Cut it into your preferred size*, making slices approximately ⅓-inch (7-10 mm) thick.

* I cut the sweet potato into bite-sized pieces, but you can also slice it diagonally or lengthwise into larger pieces, as long as each piece maintains a thickness of ⅓-inch (7-10 mm).

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Step 3
Arrange the sliced sweet potatoes on a wire rack or bamboo colander, ensuring they don't overlap as much as possible. Let them dry in the sunlight for 2 or more consecutive sunny days. Once they have reached your desired level of firmness, they are ready to be enjoyed.

Note: If you want to prevent insects from reaching the sweet potatoes, cover them with a net or something similar. Store them at night in a cool, well-ventilated place to prevent mold growth. Drying for 2 days results in a softer texture (recommended), while drying for 3-5 days yields a slightly firmer texture.

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To store

If you dry your sweet potatoes in the sun for 2 days, you can store them in the refrigerator for up to 4 days. Sun-drying them for 5 days allows them to be preserved for up to a week. However, be cautious, as hoshi imo tends to harden and lose moisture when exposed to air for an extended period.