Century egg

Century egg

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Century egg or pidan also known as preserved egg, hundred-year egg, thousand-year egg, thousand-year-old egg, and millennium egg, is a Chinese cuisine
Chinese cuisine
Chinese cuisine is any of several styles originating in the regions of China, some of which have become highly popular in other parts of the world – from Asia to the Americas, Australia, Western Europe and Southern Africa...

 ingredient made by preserving duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

, chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

 or quail
Quail
Quail is a collective name for several genera of mid-sized birds generally considered in the order Galliformes. Old World quail are found in the family Phasianidae, while New World quail are found in the family Odontophoridae...

 eggs
Egg (food)
Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have probably been eaten by mankind for millennia. Bird and reptile eggs consist of a protective eggshell, albumen , and vitellus , contained within various thin membranes...

 in a mixture of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

, ash, salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

, lime
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

, and rice hulls
Rice hulls
Rice hulls are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material, or fuel.-Production:...

 for several weeks to several months, depending on the method of processing.

Through the process, the yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 becomes a dark green to grey colour, with a creamy consistency and an odor of sulphur
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, while the white
Egg white
Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...

 becomes a dark brown, translucent jelly with little flavor. The transforming agent in the century egg is its alkaline material, which gradually raises the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 of the egg to around 9, 12, or more during the curing process. This chemical process breaks down some of the complex, flavorless proteins and fats, which produces a variety of smaller flavorful compounds.

Some eggs have patterns near the surface of the egg white that are likened to pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...

 branches, and that gives rise to one of its Chinese names, the pine-patterned egg.

History


The origin of the method for creating century eggs likely came about through the need to preserve eggs in times of plenty by coating them in alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

ne clay, which is similar to methods of egg preservation in some Western cultures. The clay hardens around the egg and resulted in the curing and creation of century eggs instead of spoiled eggs.

According to some, the century egg has over five centuries of history behind its production. Its discovery, though not verifiable, was said to have occurred during the Ming Dynasty
Ming Dynasty
The Ming Dynasty, also Empire of the Great Ming, was the ruling dynasty of China from 1368 to 1644, following the collapse of the Mongol-led Yuan Dynasty. The Ming, "one of the greatest eras of orderly government and social stability in human history", was the last dynasty in China ruled by ethnic...

 600 years ago in Hunan
Hunan
' is a province of South-Central China, located to the south of the middle reaches of the Yangtze River and south of Lake Dongting...

, when a homeowner discovered duck eggs in a shallow pool of slaked lime
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

 that was used for mortar during construction of his home two months before. Upon tasting the eggs, he set out to produce more, this time with the addition of salt to improve the taste, thus resulting in the present recipe of the century egg.

Traditional



The traditional method for producing century eggs is a development and improvement from the aforementioned primitive process. Instead of using just clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

, a mixture of wood ash
Wood ash
Wood ash is the residue powder left after the combustion of wood. Main producers of wood ash are wood industries and power plants.-Composition:...

, quicklime
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

, and salt
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

 is included in the plastering mixture, thereby increasing its pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 and sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 content. This addition of natural alkaline compounds improved the odds of creating century eggs instead of spoilage and also increased the speed of the process. A recipe for creating century eggs through this process starts with the infusion of three pounds of tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...

 in boiling water. To the tea, three pounds of quicklime (or seven pounds when the operation is performed in winter), nine pounds of sea salt
Sea salt
Sea salt, salt obtained by the evaporation of seawater, is used in cooking and cosmetics. It is historically called bay salt or solar salt...

, and seven pounds of wood ash from burned oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...

 is mixed into a smooth paste. While wearing gloves to prevent the lime corroding the skin, each egg is individually covered by hand, then rolled in a mass of rice chaff
Chaff
Chaff is the dry, scaly protective casings of the seeds of cereal grain, or similar fine, dry, scaly plant material such as scaly parts of flowers, or finely chopped straw...

 to keep the eggs from adhering to one another before they are placed in cloth-covered jar
Jar
A jar is a rigid, approximately cylindrical container with a wide mouth or opening. Jars are typically made of glass, ceramic, or plastic. They are used for foods, cosmetics, medications, and chemicals that are relatively thick or viscous...

s or tightly woven basket
Basket
A basket is a container which is traditionally constructed from stiff fibres, which can be made from a range of materials, including wood splints, runners, and cane. While most baskets are made from plant materials, other materials such as horsehair, baleen, or metal wire can be used. Baskets are...

s. The mud slowly dries and hardens into a crust over several months, and then the eggs are ready for consumption.

Modern



Even though the traditional method is still widely practiced, modern understanding of the chemistry behind the formation of century eggs has led to many simplifications in the recipe. For instance, soaking the eggs in a brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

 of salt
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

, and sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 for 10 days followed by several weeks of aging while wrapped in plastic is said to achieve the same effect as the traditional method. This is because egg-curing in both the new and traditional methods is accomplished by introducing hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 ions and sodium into the egg.

Although poisonous, lead(II) oxide
Lead(II) oxide
Lead oxide is the inorganic compound with the formula PbO. Lead oxide occurs in two polymorphs, red, having a tetragonal crystal structure and yellow, having an orthorhombic crystal structure...

 is also known to increase the curing speed of century eggs, leading some less-scrupulous century egg producers in the past to add it to their curing mixtures. However, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 oxide is now used as a safer alternative. Although zinc is an essential micronutrient, excessive zinc consumption can lead to copper deficiency
Copper deficiency
Copper deficiency is a very rare hematological and neurological disorder. The neurodegenerative syndrome of copper deficiency has been recognized for some time in ruminant animals, in which it is commonly known as "swayback" The disease involves a nutritional deficiency in the trace element copper...

, so the zinc content needs to be checked for safety.

Uses



Century eggs can be eaten without further preparation, on their own or as a side dish. As an hors d'œuvre, the Cantonese wrap chunks of this egg with slices of pickled ginger root
Ginger
Ginger is the rhizome of the plant Zingiber officinale, consumed as a delicacy, medicine, or spice. It lends its name to its genus and family . Other notable members of this plant family are turmeric, cardamom, and galangal....

 (sometimes sold on a stick as street food
Street food
Street food is ready-to-eat food or drink sold in a street or other public place, such as a market or fair, by a hawker or vendor, often from a portable stall. While some street foods are regional, many are not, having spread beyond their region of origin. Most street food are both finger and fast...

). A Shanghainese recipe mixes chopped century eggs with chilled tofu
Tofu
is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is part of East Asian and Southeast Asian cuisine such as Chinese, Japanese, Korean, Indonesian, Vietnamese, and others. There are many different varieties of tofu, including fresh tofu and tofu...

. In Taiwan, it is popular to eat century eggs on top of cold tofu
Tofu
is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is part of East Asian and Southeast Asian cuisine such as Chinese, Japanese, Korean, Indonesian, Vietnamese, and others. There are many different varieties of tofu, including fresh tofu and tofu...

 with katsuobushi
Katsuobushi
is the Japanese name for dried, fermented, and smoked skipjack tuna .Shaved Katsuobushi and dried kelp - kombu - are the main ingredients of dashi, a broth that forms the basis of many soups and sauces in Japanese cuisine.Katsuobushi's distinct umami flavor comes from its high...

, soy sauce
Soy sauce
Soy sauce is a condiment produced by fermenting soybeans with Aspergillus oryzae or Aspergillus sojae molds, along with water and salt...

, and sesame oil
Sesame oil
Sesame oil is an edible vegetable oil derived from sesame seeds. Besides being used as a cooking oil in South India, it is often used as a flavor enhancer in Chinese, Japanese, Korean, and to a lesser extent Southeast Asian cuisine.The oil from the nutrient rich seed is popular in alternative...

 in a style similar to Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

ese hiyayakko
Hiyayakko
is a popular Japanese dish made with chilled tofu and toppings. It is usually served during the summer season. There are two kinds of tofu used in hiyayakko: kinugoshi , which is more frequently used, and the less common momen ....

. A variation of this recipe common in northern China is to slice century eggs over chilled silken (soft) tofu
Tofu
is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is part of East Asian and Southeast Asian cuisine such as Chinese, Japanese, Korean, Indonesian, Vietnamese, and others. There are many different varieties of tofu, including fresh tofu and tofu...

, adding liberal quantities of shredded young ginger and chopped spring onions as a topping, and then drizzling light soy sauce and sesame oil over the dish, to taste. They are also used in a dish called old-and-fresh eggs, where chopped century eggs are combined with (or used to top) an omelet made with fresh eggs.

Some Chinese households cut them up into small chunks and cook them with rice porridge to create "century egg and lean pork congee
Congee
Congee is a type of rice porridge popular in many Asian countries. It can be eaten alone or served with a side dish. Names for congee are as varied as the style of its preparation...

" . This is sometimes served in dim sum
Dim sum
Dim sum refers to a style of Chinese food prepared as small bite-sized or individual portions of food traditionally served in small steamer baskets or on small plates...

 restaurants. Rice congee, lean pork, and century egg are the main ingredients. Peeled century eggs are cut into quarters or eighths and simmered with the seasoned marinated lean slivers of pork until both ingredients are cooked into the rice congee. Fried dough sticks known as youtiao are commonly eaten with century egg congee. Another common variation of this dish is the addition of salted duck egg
Salted duck egg
A salted duck egg is a Chinese preserved food product made by soaking duck eggs in brine, or packing each egg in damp, salted charcoal. In Asian supermarkets, these eggs are sometimes sold covered in a thick layer of salted charcoal paste. The eggs may also be sold with the salted paste removed,...

s into the congee mixture.

On special events like wedding banquets
Wedding reception
A wedding reception is a party held after the completion of a marriage ceremony. It is held usually as hospitality for those who have attended the wedding, hence the name reception: the couple receives society, in the form of family and friends, for the first time as a married couple. Hosts...

 or birthday parties, a first course platter of sliced barbecued pork
Char siu
Char siu , otherwise known as barbecued meat in China or Chinese-flavored barbecued meat outside China, is a popular way to flavor and prepare pork in Cantonese cuisine. It is classified as a type of siu mei, Cantonese roasted meat...

, pickled
Pickling
Pickling, also known as brining or corning is the process of preserving food by anaerobic fermentation in brine to produce lactic acid, or marinating and storing it in an acid solution, usually vinegar . The resulting food is called a pickle. This procedure gives the food a salty or sour taste...

 baby leeks
Leek
The leek, Allium ampeloprasum var. porrum , also sometimes known as Allium porrum, is a vegetable which belongs, along with the onion and garlic, to family Amaryllidaceae, subfamily Allioideae...

, sliced abalone
Abalone
Abalone , from aulón, are small to very large-sized edible sea snails, marine gastropod molluscs in the family Haliotidae and the genus Haliotis...

, pickled
Pickling
Pickling, also known as brining or corning is the process of preserving food by anaerobic fermentation in brine to produce lactic acid, or marinating and storing it in an acid solution, usually vinegar . The resulting food is called a pickle. This procedure gives the food a salty or sour taste...

 julienned
Julienning
Julienne is a culinary knife cut in which the food item is cut into long thin strips, not unlike matchsticks. Sometimes called 'shoe string', e.g. 'shoestring fries'...

 carrot
Carrot
The carrot is a root vegetable, usually orange in colour, though purple, red, white, and yellow varieties exist. It has a crisp texture when fresh...

s, pickled julienned daikon radish
Daikon
Daikon , Raphanus sativus var. longipinnatus, also called White Radish, Japanese radish, Oriental radish, Chinese radish, lo bok and Mooli , is a mild flavoured, very large, white East Asian radish...

, seasoned julienned jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

, sliced pork
Pork
Pork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....

, brawn
Head cheese
Head cheese , or brawn , is a cold cut that originated in Europe. A version pickled with vinegar is known as souse. Head cheese is not a cheese but a terrine or meat jelly made with flesh from the head of a calf or pig , and often set in aspic. Which parts of the head are used can vary, but the...

 and the quartered century eggs is served. This is called a lahng-poon in Cantonese, which simply means "cold dish".

Misconception and etymology


According to a persistent misconception, century eggs are, or were once, prepared by soaking eggs in horse urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

. The myth may arise from the pungent odor of ammonia given off by century eggs, which is reminiscent of urine. Horse urine itself, however, is only slightly basic, ranging in pH from 7.5 to 7.9. Though human urine left standing can reach a maximum pH of around 9.4—the same as a 1-molar solution of ammonia—it is still less than that produced by mixing quicklime (calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

) or wood ash in water.

In Thai and Lao
Lao language
Lao or Laotian is a tonal language of the Tai–Kadai language family. It is the official language of Laos, and also spoken in the northeast of Thailand, where it is usually referred to as the Isan language. Being the primary language of the Lao people, Lao is also an important second language for...

, the common word for this type of preserved egg literally means "horse urine eggs", either due to this myth or the distinctive ammonia odor of century eggs: kʰàj jîaw máː (RTGS
Royal Thai General System of Transcription
The Royal Thai General System of Transcription is the official system for rendering Thai language words in the Latin alphabet, published by the Royal Institute of Thailand...

: khai yiao ma) kʰāj jāw mâː

See also


  • Balut (egg)
  • Iron egg
    Iron egg
    Iron eggs are a speciality egg-based dish from Taiwan. They are considered a delicacy and originated in the Tamsui District of New Taipei City....

  • Lutefisk
    Lutefisk
    Lutefisk or Lutfisk is a traditional dish of the Nordic countries and parts of the Midwest United States. It is made from aged stockfish or dried/salted whitefish and lye . It is gelatinous in texture, and has an extremely strong, pungent odor...

  • Pickled egg
    Pickled egg
    Pickled eggs are hard boiled eggs preserved by pickling.After the eggs are hard boiled the shell is removed and they are submerged in a solution of vinegar, salt, spices, and other seasonings. Recipes vary from the traditional brine solution used for pickles to other solutions which can impart a...

  • Soy egg
    Soy egg
    Soy egg is a type of Chinese egg cooked in soy sauce, sugar, water, as well as optionally other herbs and spices.-Usage:Soy eggs may be eaten individually as a snack. They are sometimes used as a condiment in congee...

  • Tea egg
    Tea egg
    Tea egg is a typical Chinese savory snack commonly sold by street vendors or in night markets in most Chinese communities throughout the world.-Regular/traditional method:...


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