When Wilmington’s buzzy Italian restaurant Bardea closed temporarily at the beginning of the COVID-19 pandemic, one might say the kitchen got moldy. But don’t call in the health inspectors yet — Chef Antimo DiMeo likes it that way.

DiMeo took the forced downtime to delve deep into the world of fermentation, particularly, koji — Japan’s national mold, most often used to make miso and soy sauce.

With Bardea on a two-month hiatus, DiMeo finally found time to read all of the cookbooks he’d been collecting. Three stood out: The Noma Guide to Fermentation, Art of Fermentation, and Koji Alchemy. “Koji caught my attention,” DiMeo says.

He built a fermentation chamber — essentially an enclosed speed rack with a heater and humidifier to control the temperature and moisture — and started growing umami-rich koji on farro and barley. From there, he ferments it into salty shio koji for sauces, creates a variety of flavor-bomb miso pastes, pulses it into flour to make puff pastry dishes, and ages steaks with it.

“Growing koji reinvigorated my passion for cooking,” DiMeo says. “It makes each ingredient the best version of itself.”

Put simply, fermentation “makes food more delicious or preserves it,” according to Amanda Feifer, the Philadelphia-based author of Ferment Your Vegetables. She describes it as “the digestive activity of certain microbes.” In chopped cabbage, for example, microbes eat the vegetable’s natural sugar, which in turn preserves it and helps it become products like sauerkraut or kimchi. Other fermented foods include miso, soy sauce, kombucha, certain pickles, leavened bread, aged cheeses, tempeh, yogurt, beer, and wine.

According to Nordic Food Lab, koji (called qu in Chinese and nurukgyun in Korean) “is a culture made by growing different fungi on cooked grains or legumes in a warm, humid place.” That culture, or mold, is then used to ferment other foods. Just like in the cabbage example, koji enzymes enrich flavor by breaking down starches, proteins, and fats in food.

At Bardea, koji is sprinkled throughout the whole menu, sometimes literally. DiMeo coats steaks with koji flour before sticking them in a dry-aging chamber. Within days, “porterhouses and bone-in strips smell like they’ve been aged for a month,” he says. The savory koji magic adds “funk, umami, and a beefiness” that normally takes months to develop.

The chef’s favorite use of koji involves fermenting it with water and salt to create shio koji — a sweet and salty fermented paste that enhances umami and tenderizes food. He marinated an avocado in it and “without even seasoning it, it was like an avocado on steroids.” He’s also using it in marinated tiger prawns, whole roast chicken, and glazes. For a spin on a traditional Italian dish like vitello tonnato, DiMeo adds shio koji to tomato sauce as it cooks down to add “sweet, floral, and nutty tones,” he says. “It’s five times more flavorful.”

DiMeo, who grew up working in his family’s pizzeria and honed his skills in Gennaro Esposito’s Michelin-starred Sorrento restaurant, Torre del Saracino, has always loved fermentation. “Naturally leavened bread and dough is a living thing.” Though dough is his “first love,” embracing centuries-old Asian techniques and ingredients isn’t a leap.

As his fermentation skills grew over the past 18 months, he added to Bardea’s in-house repertoire. DiMeo is now culturing butter, growing yeast, fermenting kombucha, brewing the sweet fermented rice drink amazake, and using koji to make several other culinary products, including one with Italian roots.

Ancient Romans fermented fish into garum, a counterpart to the Asian and Southeast Asian staple, fish sauce. “Just three drops of fish sauce can change a dish,” fermentation expert Feifer says. “Garum can massively up umami and change food’s complexity.”

Swapping meat for fish and employing koji for a speedy, umami-rich fermentation, DiMeo has created beef, pork, lamb, and bison garums. That rich, meaty flavor lends itself to vegetable-centric dishes that even staunch carnivores can get behind. Bardea served a peppers and onions dish with beef garum broth that DiMeo says tasted like steak fajita, despite having no meat on the plate.

With sustainability in mind, it’s part of his “personal challenge” to create a vegetable-forward menu. Plants become the star of the dish with meat making a cameo in the sauce or glaze.

Koji fermentation can even give veggie scraps a place on the table — DiMeo used to toss a case of leek tops each week, but now turns them into a miso-based glaze for his stuffed leeks. Miso paste and its cousin, amino paste, come from koji-fermented soy beans, lentils, or other legumes and starches. DiMeo uses them to amp up his “interpretive Italian” dishes, like a traditional herb pesto.

Mold and fermentation have been “a silver lining from the pandemic,” says Bardea co-owner Scott Stein. In a small (but growing) market like Wilmington, Bardea has been busy since opening three years ago. A 2019 James Beard award nod kept Stein and DiMeo in the weeds, but the shutdown gave the duo time to catch their breath and try something new.

When they reopened, Stein says Bardea’s staff became fermentation enthusiasts, and customers loved the new direction. “People were losing their minds,” he recalls. Now, guests ask for kitchen tours after dinner to see where the fermentation magic happens.

In 2022, Stein and DiMeo plan to open their modern take on a classic steak house next door to Bardea. They’ll be dry-aging steaks in-house with — what else? — koji.

DiMeo, just 28 years old, says that the future of professional cooking involves understanding and harnessing the science of food. When it comes to mold and fermentation, “the possibilities are truly limitless.”

Bardea, 620 N. Market St., Wilmington, 302-426-2069, bardeawilmington.com/, Tue.-Thurs. 5-9 p.m., Fri.-Sat. 5-10 p.m.