There’s a little something that makes Seafood Shack Executive Chef Gerard Jesse’s grouper sandwiches stand apart. You probably wouldn’t guess it was Japanese fungus. Koji: full-time fungus mold and foundational element of Japanese cuisine. Central to the creation of rice vinegar, soy sauce, sake, mirin and miso, koji lays claim to much of the island country’s distinct flavor but remained guarded for centuries. Fermentation recipes have been passed down among the trusted, first as family secrets and, until 2005, as protected intellectual property. Today, koji makes a resurgence in its root form, with chefs like Jesse growing their own and putting it to their own uses. “It heightens the flavor of just about anything,” says Jesse, who puts house-made koji on nearly every fish that passes through his kitchen, giving the meat an “umami blast” similar to soy sauce or shiitake mushrooms. Not a condiment or sauce, koji tastes a bit off on its own, but as a rub or marinade applied before cooking, it expands the flavor profile and adds a touch of tantalizing sweetness to the whole affair. For fish especially, koji fills out any thin or biting flavors typically balanced with a heavy sauce but without the extra dietary weight. A natural tenderizer as well, prepping a fish with koji is akin to soaking chicken in buttermilk, says Jesse, hailing the saprophytic champion as “the most versatile and useful” ingredient in his arsenal.

Available store-bought, Jesse prefers to make his own. A friend brings koji spores from Japan and Jesse ferments the raw mold in a mash of semi-cooked sushi rice. The process takes around three weeks but the resulting rub—technically shio-koji—is more than worth it when done the old-fashioned way. “It goes back thousands of years and these people knew what they were doing,” he says. “And if you’re going to serve something that’s from Japan, then it should have those ingredients.” Like kombucha or sourdough cultures, each chef’s blend will have its own singular flavor defined by process and environment, so Jesse’s koji won’t taste quite like anyone else’s—that doesn’t mean it isn’t authentic. Coating the grouper for another sandwich, Jesse bronzes the fish on a slightly lower heat than normal but otherwise prepares the fish in a simple fashion—blackened and served with fresh lettuce, tomatoes and house-made tartar sauce on a King’s Hawaiian roll. The koji will do its job. 

The Seafood Shack Marina, Bar & Grill, 4110 127th St. W, Cortez, 941-794-1235.