As soon as frost threatens here in Illinois, my brother Henry drops everything and calls all hands to help dig the sweet potatoes.
As I walk the rolling hills to his rich bottomland fields, my footsteps prompt the plaintive call of the Japanese yaki-imo man whose refrain — yaki-imo, ishi yaki-imo (roasted sweet potatoes, stone-roasted sweet potatoes) — resonates in my head.
This East meets Midwest moment is not so strange since both Henry and I spent the better part of the 1980s in Japan, and since sweet potatoes were grown all over the warm zones of the Americas for some 5,000 years before they were “discovered” by Europeans and disseminated throughout the rest of the world. China now produces most of the world’s sweet potatoes.
In temperate zones like Illinois, we need to balance keeping the tubers in the ground as long as possible, with getting them out as quickly as possible when the temperatures fall. It’s during those last weeks that the sweet potatoes enter an exponential growth phase, but as soon as the soil temperature falls below 55 degrees, the tubers will begin to rot. This is why Henry has called for everyone to come and help get the sweet potatoes dug. The sooner they are out of the ground and cured, the better their flavor will be, and the longer they will keep.
Curing sweet potatoes
After a long hard day of digging, Henry takes over a room in the apprentices’ quarters, spreads tarps over the floor, and puts the sweet potatoes out in a single layer. He then creates tropical conditions in the room: 90 degrees and 90 percent humidity. He creates this sweet potato sauna by bringing in a small electric space heater and draping soaked towels and sheets from a clothesline suspended from the ceiling and walls.
It looks like a sauna, but it isn’t. It’s a cure, a means of preservation.
Meats are often cured with smoke or a mixture of salt, sugar and nitrate. Some vegetables, such as garlic and onions, are cured by dry air, and others by high temperature and humidity. Sweet potatoes need this latter cure, which causes the periderm, the skin and layer underneath it, to thicken and reform, healing any bruises or cuts, and triggering the development of enzymes that convert some of the starch in the roots to sugar.
After curing, sweet potatoes can last up to six months if they are stored between 55 and 60 degrees. Any temperature lower than that, like in your refrigerator, will lead to the same problems caused by the cool autumn soil, namely, rot.
Storage at the proper temperature improves sweet potatoes, as the maltose sugar-creating enzymes continue to work. Some years, our family has had perfect sweet potatoes clear into May, bringing us full circle to when the new slips are in the hoophouse getting ready to be transplanted for the next season’s sweet potatoes.
The joy of Japanese sweet potatoes
Henry grows many varieties of sweet potatoes, including the classic orange, moist varieties such as Beauregard, Georgia Jet and Jewell, often incorrectly identified as yams. Henry also grows Japanese and Korean varieties, which generally have a purplish skin and a yellow or cream-colored flesh that is much drier, sweeter and more flavorful than the “yam” varieties.
My favorite way to cook sweet potatoes is in the ash pan of a wood stove, where the wood coals char the skin, making the potato even sweeter and slightly smoky. Every time I eat one of the Japanese sweet potatoes this way, I hear the song of the old Japanese yaki-imo man who walked his cart through the west-Tokyo neighborhood where I once lived. In monotone he would sing”Yaaaaa-kiiiii-moe, iiiiiiishii yaaaa-kiii-mooooe.”
His song, and the sweet smoky smell emanating from his cart, often made me turn in my tracks and dig around for a few hundred-yen coins. The yaki-imo man would carefully choose the perfectly roasted sweet potatoes at the edge of the fire, and put them in a thick paper bag — making an edible hand-warmer as winter approached.
Sweet potatoes from the ashes
It turns out that George Washington Carver, during his years as director of agriculture at the Tuskegee Institute in the first half of the 20th century, also was a fan of sweet potatoes roasted on wood coals, although I doubt he ever heard the song or tasted the wares of the yaki-imo man. In November 1936, he published a bulletin entitled “How the Farmer Can Save His Sweet Potatoes, and Ways of Preparing Them for the Table.”
Here is his method, which is very similar to that used by me and the yaki-imo man. If you don’t have a fire handy, simply roast the potatoes in a heavy roasting pan at 375 F until they can be easily pierced with a fork.
Sweet potatoes, baked in ashes
In this method, the sweetness and piquancy of the potato is brought out in a manner hardly obtainable in any other way.
Cover them with warm ashes to a depth of 4 inches. On top of the ashes, place live coals and hot cinders. Let the sweet potatoes bake slowly for at least two hours.
Terra Brockman is an author, a speaker and a fourth-generation farmer from central Illinois. Her latest book, “The Seasons on Henry’s Farm,” now out in paperback, was a finalist for a 2010 James Beard Award.
Photos, from top:
Timing is critical when it comes to taking sweet potatoes from the ground.
Sweet potatoes being picked at Henry’s Farm in central Illinois.
Sweet potatoes in the curing room.
Credits: Terra Brockman