The sea slug is a boneless Chinese gastronomic prize that creeps along the ocean floor. It was referred to in a pre-fifth century fragment of a work scholars call The Canon of Gastronomy, which no longer exists.
At the time the sea slug was called hai-shu or "sea rat" and it was described simply as "looking like a leach, but larger."
Sometime between then and the Ming Period, about 1,000 years later, the creature's status had been upgraded considerably. It's name had become, as it's called today, hai-shen or roughly "ginseng of the sea." A Ming Period writer explaining the etymology said that it was named by the people who caught the sea slug in the North China Sea. They felt that this flabby sea animal had the same wondrous medicinal properties as ginseng, which was native to their region.
The Chinese have harvested the sea slug for centuries all along their own coast and beyond. A thousand years ago they ventured as far as East Africa in search of it. In 1415 a king of what is now Sri Lanka; annoyed at the hundreds of Chinese ships fishing for sea slugs right off his shore, ordered them away. The Chinese sent an army after him, captured him and continued to fish.
The Chinese have culled the waters for this creature east to Fiji and south to the tropical waters off Australia, which were nearly fished out by the beginning of this century. A modern shortage of sea slugs in China has led to soaring prices and black market sales.
When caught, they are dried as hard as a rock and shipped to market. After soaking sea slugs for several days, boiling them in changes of stock or water and cleaning them, one is left with a spongy, translucent seafood that, when finally cooked, has a tasteless crunch reminiscent of boiled pork fat. In spite of centuries of enjoyment, the Chinese have not managed to spread their love for this creature much beyond their borders.
According to a Ming Period description, the sea slug is "warming and restorative." Modern dietary experts might praise the fact that pound for pound, it has almost four times the protein of beef and zero cholesterol. But above all else was its supposed ability to enhance male virility.
Usually, but not necessarily featured in a dish, sea slugs are often cooked with other ingredients that give them a little flavor such as pork, chicken or mushrooms; they may be part of a seafood conglomeration in a dish called "Happy Family"; or they're added to soups. Sea slugs are most distinguished by the time involved in preparation, which literally takes days. There are practically as many soaking and cleaning methods as there are cooks who cook them, but the goal is always a certain gelatinous resilience. To soak and clean sea slugs:
Place the sea slugs in a large bowl with warm water to cover and soak them three days, changing the water every day. At the end of three days they should be softened; if not, continue another day or two. When softened, cut the sea slugs open lengthwise, and while rinsing them under cold tap water, clean the insides of debris and sand.
Using your hands, pull out and rub away as much as you can. Rinse and then simmer the sea slugs in light chicken or pork stock for 10 minutes.
Discard the stock, rinse the sea slugs in cold water and scrape away the inside membrane of the animals.
Simmer them again in fresh stock which again should be drained and discarded at the end of 10 minutes. Rinse the sea slugs, picking over them a final time if necessary.
Cut the softened sea slugs into one-inch sections and serve in a chicken broth with ingredients such as black mushrooms, chicken, shrimp and parboiled Chinese greens.