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Duck Boys, Duck Eggs, and Egg-chemists

by Irving Beilin Chang


Spring Volume: 2002 Issue: 9(1) page(s): 9 and 10

The city of Nanjing borders the Yangtze River and on two lakes called the Xuan Wu and the Mo Chou. Besides those bodies of water, there are many scattered small ponds and canals that criss-cross this city. For the above reasons, it became a good area to raise ducks. That is why Nanjing Duck is nearly as famous as Beijing Duck; and both have histories that go back many centuries.

Duck farmers generally own both ponds and fields. Since raising ducks is their main business and their main source of income, they house their ducks in a barn. In the morning, using bamboo poles, they gently drive them through the streets and into their fields to feed them. Then, after they are fed, the farmers allow the ducks to wallow in the ponds while their food is digesting. Some hours later they drive the ducks back into the barn, usually in the evening, for safe keeping. Those whose task it is to drive ducks back and forth became known as the ‘Duck-boys of Nanjing.’

The city and environs of Nanjing is known as one of the ‘ovens’ of China. This city is one hundred and fifty-five miles inland from the China Sea. During the summer months, the temperature stays at or manages to get even higher than ninety-five degrees Fahrenheit. To make matters worse, the humidity hovers around one hundred percent. When evening comes, there is no sea breeze to cool things off, so this city is like an oven day and night.

In the old days in Nanjing, when the ducks the farmers raised were dressed for market, there were neither freezers nor refrigerators. How could they store and keep duck carcasses from spoiling? The duck merchants salted the ducks and used bamboo frames to stretch the carcasses so that they would dry fast. They also pressed the salted ducks flat during this process so that they could be smoked and then stored. This way they took up less space. This is how Nanjing Pressed Duck came into being.

There is another hurdle to surmount in order to make this venture a financial success. What are they going to do with all the fresh duck eggs their flock laid and that they collect every day? Fresh duck eggs are quite nutritious, but they certainly do not taste as good as fresh chicken eggs. And, in cooking, duck whites do not hold a foam as do the whites of chicken eggs. These farmers found, probably because of these reasons and others, that not very many folk would purchase their fresh duck eggs.

Then, someone had a bright idea to add salt to some mud, and coat the duck eggs with this mixture. Then, when cured, the duck egg is salted and firm--almost hard-cooked. The white of these duck eggs are very salty and the yolks become golden in color. This change in color and texture make for another change, the duck egg becomes quite tasty. This is because the salt migrates through the egg shell and into the egg white, but not into the egg yolk. Such eggs are best eaten with something bland because then the salt migrates away from the egg white. With them, a very tasty dish can be prepared. The salt serves several important functions. It preserves the eggs and prevents bad bacteria and other unhealthy microorganisms from growing in them. Made this way, salted duck eggs still have a limited market.

Then, an ingenious fellow took slaked lime, mixed it with mud and coated some duck eggs with that. After that coating dried, approximately one hundred days later, the coating was removed. Then, the white of the egg becomes bouncy, nearly clear, and a translucent gel. Some of the yolks turn a dark green color, others become dark green on the outside but keep their golden color in the center. This is called the 'honey center' and the Chinese call these lime-cured eggs: pi dan.

Some of the eggs made this way have a distinct ammonia smell. Worry not, peel one or more eggs and set them aside for an hour and most, if not all of the odor, will disappear before you need to use them. Obviously, the egg protein has been changed making an egg with a very distinct flavor all its own. Like many western cheeses, this flavor may need to be cultivated. Do so, and you will be delighted that you did.

As to the chemistry, the egg shell and the membrane inside of it act as ‘ion exchangers.’ The membrane under the shell allows the alkalinity of the lime-mud coating to affect the egg protein so that the white gels and the yolk gets firm. Selectively, only the good micro-organisms react with the egg protein in this process.

We eat pi dan and while some think it is raw, more correctly it is aged somewhat akin to preserving seafood in lime juice. The preserved duck eggs are excellent dipped in soy sauce to enhance their flavor. Chinese people from Shanghai prefer soy sauce as the dipping sauce for their preserved eggs while Cantonese folk eat these eggs with pickled ginger, vinegar, and sesame oil. Either way, these are interesting combinations; try them both. Shanghai people also add pi dan to their rice congee, which they prefer cooked with pieces of chicken. This is a nutritious combination, is easy to digest, and is often recommended when the digestive system is upset. It is also recommended for the elderly.

To make pi dan sounds mysterious and inscrutable. Is that why someone once named these eggs ’One hundred Year Old Egg?’ We don’t know, but do know that the name stuck; probably because they looked and tasted so different from any other egg seen.

Lots of folks have seen them since they were first made and they have grown to adore them. You can find both the salted duck eggs and the mud covered pi dan at any large Asian market. eat them and you learn to love them.

They are generally packed in a cardboard or foam container made especially for them, six to a package, often without mud on the exterior. Some are wrapped in plastic pouches, also without the mud coating. Nowadays, most are cured in a chemical solution, eliminating the need for mud altogether.

By finding a solution to the by-products of these duck farmers, food chemists changed duck eggs into a very interesting gourmet food. They increased demand for them and a brand new industry was born! Today, pi dan is produced in China and Taiwan wherever ducks are raised.

Here are a few favorite recipes from my wife Wonona. She says you can use either the salted egg or the pi dan in any of them. She also hopes that you try every one of them. I say, that after you have, go on and be a kitchen chemist by inventing your own recipes. We both say thanks to the editor who recently made and tested these recipes. She advises they are terrific.
Steamed Pork with Salted Egg
1/2 pound ground or hand-chopped pork
1/2 teaspoon minced fresh ginger
1 teaspoon dry sherry
2 teaspoons light soy sauce
1/2 teaspoon sugar
1 teaspoon cornstarch
1 salted egg, peeled, then beaten as thoroughly as possible
1/2 teaspoon corn oil
1. Combine pork, ginger, sherry, soy sauce, sugar, and cornstarch. Mix thoroughly and form into a ball.
2. Oil an eight-inch pie pan. Roll the ball of meat in the beaten egg and place in the oiled pan and flatten the ball. Pour any extra egg mixture over the meat and steam this thirty minutes over boiling water. Cut into pieces and serve hot.
Chicken Congee with Pi Dan
4 large dried Chinese black mushrooms
1 boneless and skinless chicken breast, cut in cubes
dash of salt or to taste
2 teaspoons dry sherry
1/4 cup minced Virginia ham
1/2 cup glutinous rice
1 thirteen and three-quarter ounce can of chicken broth
4 slices fresh ginger, minced
1 pi dan, shelled and cut into six pieces
2 scallion tops, minced
1. Soak mushrooms for fifteen minutes in warm water. Drain and set the water aside. Discard the stem and cut each mushroom in six to eight pieces.
2. Mix chicken cubes with salt and sherry and steam this over boiling water for twenty minutes. Drain and reserve the liquid.
3. Combine mushrooms, ham, rice, chicken broth, ginger, and the reserved mushroom and chicken waters and bring this to the boil. Add a half-cup of water and the pi dan and reduce the heat. Simmer for one hour, them mix in the chicken pieces, sprinkle with the scallions, and serve.
Jelly Fish with Cucumbers and Pi Dan
1/2 pound package shredded jelly fish
1 or 2 cucumbers
4 Tablespoons cider vinegar
2 Tablespoons sugar
1 teaspoon salt
1 teaspoon sesame oil
4 pi dan, shelled and cut one each into six pieces
1. Soak jelly fish for one-half hour(
2. Peel cucumbers, discard seeded part and shred the same size as the jelly fish pieces.
3. Mix vinegar, sugar, salt, and sesame oil and mix with jelly fish. Add the cucumbers and the pi dan and fold gently. Serve cold.
Note: If shredded jelly fish is not available, cut whole ones into one-quarter- to one-half-inch by two inch slices and blanch for them for thirty seconds; yes, just thirty seconds. Then drain and let rest a few minutes until they are again at room or refrigerated temperature.

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