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Getting Fruitcake Off the Shelf with Basic Physics

Fruitcake cartoon

It's the perennial butt of jokes during the holiday season, but people keep giving it nonetheless. And now it seems that there may be hope for that holiday fruitcake after all. Peter Barham, a University of Bristol physicist and author of The Science of Cooking, says that by using a little chemistry and physics, even a stale fruitcake that's been sitting for years can be revived, and it may be better than ever.

"The reason fruitcake, or any cake for that matter, goes stale is because it appears to lose its moisture," says Barham. But the moisture isn't really lost; the starch in the cake has simply absorbed it. The problem, Barham explains, is that the molecules in the starch (flour) are trying to get back to the ordered form they had when they were wheat. But since the starch can't make that transformation, it does the next best thing by hijacking the water from the cake to form small crystals. With all the water caught up by these starch molecules, the cake tastes dry, and is tougher to digest.

But Barham says a little physics can solve the problem. "You just need to melt the starch crystals," he says, which can be done by heating the cake. He suggests wrapping the cake in aluminum foil to prevent any moisture from escaping, and slowly warming the cake in a 130 degree oven before serving. "This will melt the crystals, release the water, and refreshen the cake." Once the cake starts to cool, however, the drying process will begin again.

But what about the taste? Barham contends that fruitcakes actually get better the longer they sit. "The dried fruits in the cake can actually age," he says, "much like wine ages over time." The tannins present in the fruit seep into the cake, changing chemically to create intense and distinct flavor compounds. The longer the cake sits, he says, the more varied and intense the flavors become. In fact, if you're looking to bake a fruitcake this year, it's probably too late; it won't have time to age. But the one Aunt Maude gave you last year might do nicely.

—Inside Science News Service

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