The unusual dish is typically made by taking dozens of fresh skate, a cartilage-rich fish that looks like a stingray, stacking them up in a walk-in refrigerator and waiting. Up to a month in some cases.
"You know when it's done by the smell," said Kang Han-joo, co-owner of a seafood store in the bustling fish market of Mokpo, a port city on the southwestern tip of the Korean Peninsula, a region that's considered the food's spiritual home. As Kang spoke, he sliced small, stinking, glistening dark-pink fish steaks with a large knife and laid them in plastic foam boxes for shipment to customers around South Korea.
The smell of the fish, called hongeo in Korean and usually eaten uncooked, is unmistakable, unavoidable and a deal-breaker for many. A profound, pungent stink of ammonia radiates from the animal after it's been ripening for weeks. First-timers often squeeze their eyes shut as they chew. Tears stream down the cheeks. The throat constricts with the effort of swallowing.
Kang notes, in a dramatic understatement: "When it's fermented a long time, the smell becomes deeper."
Americans are still getting used to gentler fermented Asian foods spicy Korean kimchi and Japanese miso, for example yet many South Koreans claim a love, an addiction even, for this extreme form of fermentation. Restaurants specializing in the fish can be found throughout the country. One online hongeo appreciation society boasts more than 1,300 members.
"Some people start to crave it as soon as they smell the ammonia," said Shin Jin-woo, a seafood store worker in Mokpo. "There's no need to advertise how intense the smell is. Everyone already knows."
Shin's store has two fermentation refrigerators. Walk into one and a blast of ammonia burns the eyes, the nose and sinuses, the tongue, throat and lungs. Skate are fermented up to 15 days in the first refrigerator, where the temperature is 2.5 degrees C (36.5 F), and up to another 15 days in the second at 1 C (34 F).
Shops in Mokpo custom-ferment the fish and ship the results to restaurants and hongeo fans around South Korea.
The vast majority of the more than 11,000 tons of hongeo consumed in the country comes not from South Korean-caught fish but from cheaper frozen imports. Shop owners thaw and clean the imported fish, which can cost up to five times less than the local version, and place the hongeo in refrigerators to ferment.
Hongeo's history is murky, but it emerged in the days before refrigeration, when food that could keep for a long time without rotting was prized. Someone maybe a fisherman on a long voyage or a clever, hungry or desperate farmer discovered that skate didn't spoil as easily as other fish and a dish was born.
Shop owners say the traditional method of making hongeo is to put the fish on a bed of hay in a clay pot, pile more hay on top and leave it.
Learning to love, or at least tolerate, what many consider the smelliest fish in Asia takes perseverance. Fans commonly say that if you try it four times, you'll be hooked. Nonfans may be mystified by how anyone could meet that threshold.
"It's a freaking punch in the face," said Joe McPherson, the founder of ZenKimchi, a Korean food blog, and an eventual devotee of the fish. "Like everyone else, I gagged the first time."
Natives of the southwest say hongeo should be eaten plain. They sometimes complain that the copious garnishes provided at restaurants disguise the taste and smell.
Most first-timers, however, tend to embrace all the extras they can, creating a hongeo "sandwhich" with garnishes that can include red pepper paste, salty mini shrimp, raw garlic, chili salt, slices of fatty boiled pork and some extraordinarily strong kimchi.
Even with "some of the most powerful flavors in the world to put up against it ... it does not cover up the flavor at all," McPherson said.
The extremely chewy texture spongy flesh and hard cartilage also makes for tough swallowing. And the smell of ammonia is so powerful it lingers for hours on clothes, skin and hair.
The second time, if there is one, is usually a little better.
One trick is to inhale through the mouth and exhale through the nose while eating. This helps fight the smell some and also intensifies a surprising tingling and cooling almost minty sensation in the mouth, throat and face.
There are various theories explaining the food's popularity. Some Koreans describe their craving as similar to the desire for a cigarette: You want it despite its obvious negatives. McPherson says the fish is also valued for its interesting texture and the sensation it produces in the mouth two things that can be as important to Koreans as flavor. There's also something convivial about hongeo restaurants, where large amounts of strong Korean booze are as ubiquitous as the fish.
Still, while some Korean restaurants in the United States serve hongeo, it's unlikely to catch on except "in hardcore foodie circles," McPherson said. "I can see maybe college fraternities hazing their freshmen with this, but it's very much a 'dare' food. Like live octopus."
AP writer Jung-yoon Choi contributed to this story.