Last year, as Todd Gray and his wife, Ellen Kassoff, prepared to open their restaurant at the Museum of the Bible, they faced a culinary conundrum.

The name they had settled on for the eatery was Manna, a reference to the food God sent down to the Israelites after their escape from Egypt in the Bible. But if the Washington, D.C., restaurant was to be called Manna, they wanted to be able to serve it to their guests.

“Oh, my gosh,” Gray recalled thinking. “Where are we going to get manna?”

Answering that question depends on how you define manna, which is a bit of a mystery substance. Even in the book of Exodus, the Israelites didn’t know what it was at first. The word derives from the ancient Hebrew phrase “man-hu,” which can be translated as a question: “What is it?”

As the story goes, the Israelites awoke one morning during their wanderings in the desert to find “thin flakes like frost on the ground.” It was “white like coriander seed” and tasted like “wafers made with honey.” Some biblical scholars believe that manna was a real food, though there’s disagreement on exactly which one.

“There’s a lot of theories out there,” said Susan Masten, the Museum of the Bible’s curator of antiquities, who has studied biblical plants extensively.

One of the oldest references Masten has found is from a monastery in Sinai region dating to the 3rd or 4th century. The monks used the term to describe a sweet resin that appears on certain shrubs in the Middle East, such as camel’s thorn and tamarisk.

Others believe manna refers to dried plant sap, or a type of mushroom with psychedelic properties. The Qur’an makes reference to the story of manna, and a hadith — a collection of sayings from the prophet Mohammed — refers to truffles as a type of manna.

“It’s very difficult to research things that fall from heaven,” said Lytton John Musselman, a botany professor at Old Dominion University in Norfolk, Va., who has written a book on biblical plants. He’s even heard some people claim manna is a type of lichen, though he doesn’t put much stock in that theory.

Restaurateur Gray was familiar with the resin version of manna, which he tasted for the first time not long before he named the restaurant. It comes in semi-translucent clumps that look almost exactly like Grape-Nuts and has a flavor comparable to molasses, caramel or honey. It crunches, like cereal, but dissolves quickly in your mouth.

A handful of other American chefs have cooked with manna, but now Gray envisions it becoming the next big foodie trend, like Himalayan sea salt or black truffles.

Just a couple of obstacles stand in his way: For one, many Americans think manna is a fictional crop. For another, the real thing is nearly impossible to get in the United States — thanks to political tensions.

Gray has experimented with his own version of manna, inspired by an Iranian formula. He dreams of one day refining his version into a marketable product that capitalizes on both its mystical name and the real-world health benefits of one of its ingredients, bee pollen, such as its antioxidant properties.

“Isn’t it amazing?” Gray asked. “If the pope comes, I want to be able to give him manna.”