Published November 1, 2008.
Too often, roasted sweet potatoes turn out starchy and wan. To hit their sweet spot, was it time to throw out a cardinal rule of roasting?
Sweet potatoes don’t always behave like their white and yellow-fleshed brethren. Handled the same way, they can come out of the oven tasting overly starchy. Returning them to the oven for crisping doesn’t usually solve the problem—and can even worsen it by burning their edges.
We wanted sweet potatoes that emerged from the oven with a nicely caramelized exterior, smooth creamy interior, and an earthy sweetness.
We started with cutting the sweet potatoes into rounds for roasting—while the diameter varied, each round was the same height on the pan; 3/4 inch thick turned out to be just right for even cooking. Next, we experimented with the oven temperature and noticed that the lower the temperature, the less browning that occurred, but the sweeter the potatoes became. After a little digging, we found an explanation: The starches in sweet potatoes are converted into sugars between 135 and 175 degrees. Thus the lower the oven temperature, the longer the potatoes would stay within this range and the sweeter the spuds. But dropping the temperature also meant more time in the oven, and we didn’t want a simple side dish to take all day. That’s when we remembered a technique that turned the standard approach to roasting on its head. By starting the sweet potatoes in a cold, versus preheated, oven, we kept their internal temperature lower longer. After some testing, we covered the potatoes with foil before starting them in the cold oven, then removed the foil after 30 minutes and continued to roast. These potatoes were perfect—super-sweet and tender, with a slightly crisp, caramelized exterior.
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