Deep-fried tempura flakes, a key ingredient sprinkled on sushi rolls for crunch and known as agedama or tenkasu, Japanese for “heavenly waste,” have been linked to a series of restaurant fires in multiple states.
Five of them occurred in Wisconsin, said Kara Nelson, a fire investigator in the capital, Madison, where two restaurants sustained more than $500,000 combined in fire damage. She has also learned of similar fires in Minnesota, Virginia and Canada.
Nelson said she worked with the Bureau of Alcohol, Tobacco, Firearms and Explosives to pinpoint the unusual cause of the blazes, which she said were an example of spontaneous combustion.
The crunchy flakes are made by ladling drops of batter into a deep fryer — canola and soybean oils are commonly used. Nelson said that both vegetable oils have a propensity to self-heat and that keeping the mix densely piled in a pot or bowl does not allow the heat to dissipate.
It is no different than the chemical reaction that causes more well-known substances to spontaneously combust, she said.
“It can happen in hay bales,” Nelson said. “It can happen in mulch piles.”
And now in tempura flakes.
The first fire in Madison happened on April 5 at Sumo Japanese Steakhouse & Sushi Bar, where security camera footage showed smoke billowing in the kitchen six hours after the crunch mix had been left in a metal colander to cool. Four hours later, flames engulfed the kitchen. The second fire broke out at Takara Japanese Restaurant on May 9.
“Don’t leave it unattended,” she said of tempura flakes. “It can take anywhere from three to 10 hours for the heat process to start before it goes into ignition. We want to get the word out there.”
K Dong, the owner of MIKU, a sushi restaurant in Greenwich, Connecticut, where former President Bill Clinton recently dined, and its sister location, KUMO in Scarsdale, New York, said he had heard about the fire hazard.
“We’re very careful about how to cool it down,” Dong said. “It’s a very high temperature, especially during summertime. That’s the point we need to avoid.”
He said leaving the deep-fried flakes in a pot is a recipe for trouble.
“You need to spread it out,” he said. “You don’t want it to be contained.”
The owners of both Madison restaurants damaged by fire did not respond to requests for comment.
Michael Barry, head of media and public affairs for the Insurance Information Institute, an industry-funded consumer education organization in New York City, said it was too early to draw conclusions from the fires.
“Insurers look very closely at their claims data,” Barry said. “If a trend starts to develop, it will start to show up in the price these types of restaurants pay for insurance.”
Barry said a Maryland insurance agency listed flour as a combustible food in a blog post in 2018. He also cited a 2018 blaze at a Mexican food factory in Georgia that was caused by cornflakes that caught fire in a pipe.
In the case of the two fires in Madison, he said their business owners’ policies should cover the damage.
“If it’s a fire, it’s covered,” he said.