From a health perspective, eggs have been given a significant reprieve in recent years. Although the yolk contains cholesterol, it is now known that cholesterol already in food contributes very little to the levels inside your body, and it is the cholesterol made inside your body from saturated fat (found in fatty meat, full dairy products and processed food) that you really need to worry about.
Thankfully, no matter the production method, Century eggs (pi dan) have not been hanging around for the last 100 years. Traditionally, the eggs were encased in a mixture of clay, ash, lime, salt and rice straw and left for weeks to months. The alkaline nature of this concoction causes the pH of the egg to rise resulting in a type of alkaline fermentation. Consequently the white turns brown and transparent whilst the yolk develops a green color with a strong sulfur odor. Typically these eggs are served sliced on their own, or added with pork into rice congee to make pidan shourou zhou.
In fact the cholesterol (and fat) within an egg is confined to the yolk, and so you can use egg whites more freely. Eggs contain a wealth of nutrition; they are an excellent source of high quality protein, and are high in energy processing B vitamins riboflavin and B12 (an important source if you avoid meat). They also provide minerals such as zinc, iron and phosphorous, and are a valuable source of the fat-soluble vitamins D and A.
The British Heart Foundation recommends that those with high cholesterol limit their intake to four hen's eggs per week while the American Heart Association recommends limiting cholesterol intake to 200 mg per day for those with heart disease, and 300 mg for the rest of the population - an average hen's egg contains around 200 mg.
Just when I thought all methods of egg-cooking had been exhausted (boiling, poaching, frying, coddling etc) I came to China and discovered many, admittedly far more involved, egg preparation methods.
Tea eggs (cha ye dan) can be seen bobbing in caddies down many a street throughout China, the cracked shells disclose their delicious whites, marbled brown with tannin and soy sauce. In fact, many other ingredients besides tea are used in the infusion. The eggs are initially boiled in water for a few minutes, removed and their shells lightly tapped to crack them. Soy sauce, star anise, cassia bark, pepper corns and dried mandarin peel may then be added to the water and the eggs returned to simmer in the brown concoction for 2-5 hours.
Steamed egg - zheng ji dan geng - is a savory dish with an almost custard-like consistency. It is made by whisking two eggs with half a cup of water and a dash of soy sauce, the mixture is then placed in a ramekin, sat in a pan with boiling water and steamed for 10 minutes until the egg is set. This is then served with a few drops of sesame oil and chopped spring onions on top.
Of course hens are not the only fowls producing eggs. Quail eggs, a delicacy where I'm from, are inexpensive and widely available here. They are often added whole to stews or served hard boiled. Their cholesterol concentration is higher but their overall size is smaller - two and a half quail's eggs contain the cholesterol equivalent of one hen's egg.
Duck eggs are also abundant here and are typically salted in brine or packed into salted charcoal to produce xian ya dan (salted duck eggs). This results in a concentrated vivid yellow yolk and liquid white, the eggs are then cooked before being eaten. Be cautious, duck and goose eggs are obviously larger, but also have a higher cholesterol concentration - a duck egg contains around 620 mg cholesterol, whilst one goose egg contains 1,225 mg - equivalent to around six hen's eggs.