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Sushi stock photo

"Crunch" on top of a sushi roll. The tasty topping is being blamed for two Madison restaurant fires.

How can a tasty sushi topping cause a fire? Two Madison restaurants learned the hard way.

The Madison Fire Department issued a fire hazard warning Thursday about "crunch", or "crunchy," a deep-fried batter sprinkled on top of sushi rolls, that can spontaneously catch fire when not stored properly.

Two Japanese restaurants, Sumo Steakhouse and Sushi Bar on April 5, and Takara Japanese Restaurant on May 10, had such fires, with damages from the two fires estimated to total at least $575,000.

"The fires were caused by a food preparation technique where oil used to make a tempura-like crunch self-heats and spontaneously combusts," said MFD spokeswoman Cynthia Schuster.

What happens is the batter is fried in vegetable oil, then the crunch is put into a bowl or colander to drain and cool. If unattended while cooling, the crunch can retain heat and get to the flash point.

"Cooking oils, especially soybean oil and canola oil, are known to have a propensity to self-heat under certain circumstances," Schuster said.

"For example, rags saturated with cooking oil residue can self-heat and undergo spontaneous combustion after being laundered."

The fire department recommends anyone making crunch, either in a restaurant or at home, spread it on a baking sheet to cool and not in a container where heat can build. Don't leave it unattended, and possibly put it under a wet-chemical fire suppression hood as it cools.

During the course of the investigation into the two restaurant fires, five other restaurants, three in Wisconsin and two nationally, were identified as having similar fires.

"Our objective in sharing this bulletin is to raise awareness of this trend, in hopes of preventing additional similar fires," Schuster said.

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