Ishiyaki Imo (石焼き芋)
Ishiyaki imo (stone-roasted sweet potato) is a dish using sweet potatoes.
Place the sweet potatoes onto heated pebbles and cook them by indirect heating. By heating them slowly and indirectly, amylase (amylolytic enzyme) changes starch into glucose. Therefore they turn sweeter than ones cooked normally. Since they are sweet, they are popular among women and children. However, it is said that potatoes make you pass wind or make you fat, so women often hesitate before buying it.
The image of a special kettle on a stall and a lightweight truck is one of the winter traditions in Japan. When hawking it, it is typical to sing 'Ishiyaki imo, oimo' to a tune with a unique melody. A machine that makes a 'po' sound from the steam coming out of a stone roast kettle is sometimes used instead in cold climates. Recently, 'ishiyaki imo equipment' for household use is on the market, so everyone can easily enjoy ishiyaki imo at home. Currently, with a decreasing number of travelling stalls it is also sold on the street at the entrance to supermarkets and at convenience stores.
The varieties of sweet potato suitable for ishiyaki (baking in hot pebbles) are 'beni-azuma,' 'naruto-kintoki,' and 'beni-otome.'
Cooking sweet potato without an ishiyaki kettle is simply called yaki imo (baked sweet potato).
During the Showa period or before, pictures of people collecting falling leaves on the road or the garden during the winter season, and of putting sweet potatoes inside the leaves when burning them on the bonfire, were considered scenes which speak for winter, and ishiyaki imo is a season word to describe winter. Cooking in this way, the sweet potatoes should be wrapped in aluminum foil to avoid scorching them.
Since a naked flame is used, different from an ishiyaki kettle, it is difficult to control the flame. But you can enjoy a sweet fragrance from the steam when it is baked well.
However, due to the Revised Waste Disposal and Public Cleaning Law that came into force in December 2002, the regulation came into effect not to burn household trash in fields. Therefore, as it became more difficult to dispose of even falling leaves by burning them within a residential district, and as the rate of having a house with a garden declined, and the forests were cut down due to urban development, the sight can be seen only in a few areas in the 21st century. Many local governments instruct people to remove fallen leaves and branches and use them as burnable garbage or to dispose with in composting. For more details, you should contact the cleansing department of your local government.
In addition, since sweet potatoes are easy to cultivate and the yield amount can be predicted, potato dishes that use sweet potatoes including ishiyaki imo are eaten all year. In addition to baking, it can also be cooked by steaming or boiling.