Why Does Kale Sometimes Spark in the Microwave?

By Cook's Illustrated Published May 2014

Sometimes, when making kale chips chips in the microwave, the kale will spark during the cooking process. What’s causes this?

Sparking never happened when we developed our recipe for Quick Microwave Kale Chips (see related content), but we've received letters from readers indicating that this has happened to them on occasion. We revisited our microwave method for kale chips, making batches in 10 different microwaves. But try as we might, we couldn’t get sparks to fly. That said, research informed us it can in fact happen, and the phenomenon even has a name: arcing. There are a few theories about what causes it. It could be that the mineral or moisture content of certain vegetables makes them more prone to spark. Others say it’s more likely to happen when pieces of food with sharp (rather than rounded) edges are arranged too closely together in the microwave.

Using a reduced power level won’t solve the issue. Waves can be emitted by a microwave at only one energy level, so the appliance just cycles on and off when set on a lower power setting—one burst of waves can still cause arcing. We suggest making sure that the kale is dried thoroughly and that the pieces are spread out on the plate. If this doesn’t help, the best bet is to stop using the microwave to make kale chips (according to the U.S. Department of Agriculture, prolonged arcing can damage your microwave).