My first encounter with the delicacy known in Chinese as pi dan (“skin-eggs”), and in English as “thousand-year-old eggs”, was dreadful. Friends had invited me for dinner at a famous Hong Kong restaurant, and we were offered them, sliced in half with a dressing of ginger and vinegar, as a so-called appetiser. They leered up at me from the plate like the eyeballs of some nightmarish monster. Their albumens were a filthy, translucent brown, their yolks an oozy black, ringed with a layer of greenish, mouldy grey. About them hung a faint haze of sulphur and ammonia. I tried one, just to be polite, but was so aghast at its appearance that I found it hard to swallow, and I felt nauseous afterwards. To make matters worse, a slick of black slime from the yolk clung to my chopsticks, threatening to contaminate everything else I ate. I tried surreptitiously to wipe them on the tablecloth.
Since then, I have come to love pi dan, and I regularly inflict them on guests at my London dinner parties. A little psychological preparation generally helps. Think of them as the Chinese equivalent of blue cheese, I suggest to sceptical friends. Mouldy old milk is a pretty disgusting idea, but isn’t it delicious? I find that a blindfold can also be useful because it’s the appearance of the pi dan that is so off-putting, rather than their taste. And if you allow the ammoniac aromas to disperse before you serve them, your guests won’t suspect anything. “It tastes kind of...eggy,” says Stephen, when I feed him, blind, with a good slice of pi dan. “Nice, reminds me of mayonnaise,” says Sarah. It is only when they are allowed to open their eyes that they are revolted, and amazed.
Pi dan is made by coating raw eggs, usually duck eggs, but sometimes quail, in a thick paste made from a combination of mud, tea, rice husks and salt, with strongly alkaline ingredients such as wood-ash, soda, lye and lime (this paste is the “skin” in their Chinese name). The alkalis in the paste penetrate the eggshell and “cook” the eggs chemically, raising their pH value from around 9 to 12 or more, denaturing their proteins and causing spectacular changes in colour and texture. The proteins break down into simpler, more flavourful components, the albumen gels, and the yolk becomes thick and creamy. Small amounts of hydrogen sulphide and ammonia are released as by-products of these chemical reactions. The process takes two or three months – the names “thousand-year-old egg” and “century egg” are foreign inventions. Pi dan can also be made by immersing the raw eggs in a strongly alkaline liquid: more convenient, but some say this produces a coarser taste.
Straight out of their shells, pi dan, although raw, seem like cooked eggs in their slightly rubbery solidity, and they can be eaten immediately, although it’s best to cut them open and leave them to rest for a while to disperse the harsher accents of their fragrance. The black-and-brown pi dan that I first tasted in Hong Kong are the most frightening for the uninitiated. In Sichuan, they favour a more friendly kind of pi dan, in which the albumen is typically a pale amber colour, and the yolk a rainbow of layers, grey, green and yellow. Chinese sources often describe their colours poetically, using terms like black-green, grass-green, tea-coloured, ash-green and earth-yellow.
If pi dan aren’t as disgusting as they look, what do they taste like? One feisty American missionary lady of the 19th century, Constance F. Gordon Cumming, in a remarkably broad-minded account of a Fujianese dinner party (“I may safely say that I tasted everything uncommon, and indeed I thought all the special dishes very good”) compared their flavour to that of “plover’s egg hard boiled”. A Swedish food-writer friend of mine says they remind her of brown crab meat, intense and savoury. In fact, the products of the disintegrating egg proteins are modified amino acids that include glutamates – the same sort of fabulously tasty compounds that are responsible for the flavours of mature cheeses, cured hams and Asian fish pastes. Pi dan taste like eggs, but more so. The pi dan most prized by Chinese gourmets have pretty, flower-like patterns that seem to be etched beneath the glassy surface of their albumens. According to kitchen science authority Harold McGee, these are formed by crystals of modified amino acids, and are therefore an index of the extent of protein breakdown, and, accordingly, of the deliciousness of the eggs.
A generation ago, many Chinese people made their own pi dan at home. One friend of mine remembers mixing the ash left after burning rice straw with mud, lime, soda, salt and tea leaves, and using this paste to coat the raw duck eggs. In those days, for farming families, making pi dan was a way of ensuring that a glut of eggs in the high laying season wasn’t wasted. Now, it’s more about taste, and the eggs are produced on an industrial scale.
Supermarkets sell branded pi dan attractively packaged. But in the street markets you can still find those made in small, fly-by-night workshops. My own attempts to visit one were beset by difficulties. In the end, one manufacturer agreed to admit me, on condition that I didn’t reveal the name or location of his factory (it was a filthy yard without an official licence). His staff claimed that their eggs took a mere seven to 10 days to mature, a sure sign, said the friend who accompanied me, that they were kuai supi dan (”fast pi dan”), speeded-up by additives such as ammonia. But even some respectable pi dan should perhaps carry a health warning because lead oxide is a traditional additive to the paste: it improves the texture of the yolk, says one written source. Chinese state regulations do restrict the permitted level of lead for health reasons, but those who are still concerned can seek out low-lead or lead-free pi dan.
No-one is quite sure who invented this method of egg preservation. The first written mention of it is in an early 16th-century Ming Dynasty text but the practice may date back much earlier. There are some colourful legends about its origins. Some say an elderly tea-house owner found some eggs that his ducks had laid in a pile of wood ash and tea leaves, and discovered their shiny dark flesh to be marvellously tasty. Others tell the tale of a farmer who stumbled across some eggs his ducks had laid in a lime pit behind his house. Whoever it was who first decided to taste a black and smelly old egg, one has to admire their courage.
So what do you do with pi dan? The Cantonese like to eat them with slivered ginger and a slosh of vinegar, which neutralises their alkaline taste, or to simmer them in congee for breakfast, with slices of pork. The Hunanese blacken red or green peppers over a charcoal grill, peel them, and then toss them with slices of pi dan in a dressing of garlic, soy sauce and vinegar, or use the eggs to flavour a soupy dish of purple amaranth. The Taiwanese chop pi dan and scatter them over a cool slab of silken bean curd, with drizzles of soy sauce and sesame oil, while the Sichuanese serve them with chopped green peppers, soy sauce and chilli oil. Banquet chefs will set pi dan in aspic, and then cut this terrine into slices patterned like 1960s wallpaper. All of these I have grown to love. But there’s one pi dan concoction that still makes me shudder, I must confess, and that’s the Cantonese tea-time pastries made by baking them in a rich, sweet pastry – ugh. If you are brave enough to tackle this final pi dan frontier, you can probably find them in your local Chinatown bakery.
Fuchsia Dunlop is the author, most recently, of ‘Revolutionary Chinese Cookbook’ (Ebury Press, London and W.W.Norton, New York)
Good eggs
Salted duck eggs (xian dan)
In the shell, these look no different from untreated duck eggs but crack them open and you’ll find that the yolk is a hard, waxy sphere, writes Per-Anders Jorgensen. They are made by coating raw duck eggs in a salty paste or steeping them in brine for a couple of weeks. Simply hard-boil them and serve them, cut into sections, on the shell, for a snack or appetiser, or cut up the yolks and use them in stir-fries.
Tea eggs (cha dan)
Eggs (usually chicken eggs, but sometimes those of quail) are hard-boiled and then gently rolled around in cold water to crack the shell all over without breaking the inner membrane. They are then simmered in a spiced broth stained dark brown by tea, until the tea-colour has penetrated the cracks in the shell and created a lovely pattern all over the egg-white. These eggs are a common street snack in China and are sold on railway station platforms.
‘Iron eggs’ (tie dan)
The Taiwanese like to snack on chicken or quail eggs that have been simmered for many hours in a richly spiced broth until they have shrunk considerably in size, darkened in colour and become firm and chewy. They are sold in vacuum packs and are delicious.
