× Expand Illustration by Britt Spencer

It’s one of the “bitter herbs” mentioned in the Old Testament. The Oracle at Delphi was a fan. So was famous forager and Grape Nuts spokesman Euell Gibbons. “Strangely,” he wrote, “the hot, biting taste and pungent aroma do not exist in the unbroken root, but are developed during the grating by a chemical reaction between constituents that are found in separate cells in the growing plant.”

Another fascinating fact about horseradish: Sixty to 80 percent of it is grown in Madison, St. Clair, and Monroe counties. Why? Well, it’s part nature, part culture, and part…pollution.

“If you’ve ever noticed the landscape in Metro East, you’ll see where the Mississippi once ran because of the bluffs,” says Wendi Valenti, executive director of the Collinsville Chamber of Commerce. “The low-lying area is where the river was eons ago. It left soil that’s rich in what’s called potash.” And the horseradish loves it.

In a 2012 article, the Illinois Farm Bureau mentioned potash and “horseradish families.” Lindsey Keller of Keller Farms belongs to one. “My grandpa’s grandfather started farming here in 1887,” she says. Southern Illinois’ sandy soil is a helpful factor, she adds. “You have to get pretty deep down into the ground to harvest it,” she says. Even so, harvest is a slow, careful, weather-dependent process. Automation is happening, slowly: “A lot of times, it’s modified potato-digging equipment,” Keller says. “You can’t call up the dealer and say, ‘Hey, I need a horseradish digger.’”

Elizabeth Wahle, extension educator for commercial agriculture at the University of Illinois Extension, agrees that multiple factors are at work. “The growers live here, because their immigrant ancestors moved here,” she says, “but because the river bottom ground is fairly light, it’s easier to dig—so it’s a combination.”

There’s another surprising reason: “beneficial pollutants.” “That would be sulfur compounds coming down from industry, before the enactment of emissions regulations,” Wahle says. Those sulfurous emissions helped the plants manufacture glucosinolates, the same “constituents” that Gibbons described, which give horseradish its heat when its cell walls are broken. Steel mills, which mostly shuttered in the 2000s, were the main source. “Our growers are starting to add sulfur to the soil to keep up the levels,” Wahle adds.

The number of horseradish farmers is declining, along with the Metro East’s “beneficial pollutant” levels, but Collinsville’s J.R. Kelly Company is still the largest horseradish distributor in the U.S. On June 1 and 2, the town will hold its 31st Annual International Horseradish Festival, which means that the Metro East is still No. 1 in horseradish.