Way back in the Ming Dynasty a farmer found duck eggs buried in a pool of caustic mud in his backyard.

He tasted them, because that's what you do, and he enjoyed them so much that he decided to make some for himself.

That story almost definitely isn't true, but pidan, which is alkaline fermented duck eggs, are a beloved comfort food in China.

Fermentation extends the shelf life of food and improves its flavor.

Usually, friendly microorganisms do the heavy lifting in fermenting, but Pidan is different.

In this case it's pure chemistry.

And that chemistry really works, because you can eat pidan over six months after it's made.

Not actually a century--they just look like they could be a hundred years old.

There are a handful of traditional methods for making pidan, but they all lead to more or less the same result.

The raw eggs are coated in a paste made from salt, quicklime, sodium carbonate, tea, and ash.

Then they're rolled in rice husks and left to ferment for at least 20 days.

What's happening over that time is that the sodium carbonate and calcium oxide, from the quicklime, are getting to know each other and reacting to produce what we actually need here, which is sodium hydroxide.

That sodium hydroxide diffuses through the egg shell and gets to work, basically chopping up egg white proteins into smaller pieces.

Those pieces are sticky, and they grab the water in the egg white to turn it into a gel., It's kind of a balancing act, because too much sodium hydroxide will rip apart the proteins completely and cause the whole thing to liquefy, and nobody wants to eat it that way.

There iiiisss an ingredient that keeps the sodium hydroxide from going too far: lead oxide.

The lead helps keep the egg yolk soft and prevents over-fermentation of the egg white.

Fortunately, other elements like magnesium, calcium, and zinc can help fill in--though not quite as well.

The color of the egg white comes partly from the tea, and partly from Maillard reactions happening between the degrading proteins and sugars in the egg white.

Yes, the exact same chemistry that makes your toast brown also creates the somewhat less tempting color of these eggs.

And the greenish yolk?

That's from iron sulfide (iron(II) sulfide), which forms from iron and sulfur already present in the yolk.

The degradation of the proteins also gives off ammonia and hydrogen sulfide, which smell like Windex and flatulence respectively.

Pidan may smell and look funny, but it's also surprisingly nutritious and even used as a home remedy for toothache, thanks to the cooling sensation they leave in your mouth.

This stuff might seem weird to me, but one person's funky black egg is another's favorite comfort food, so I tried some and... Ok, you know, the texture was pretty nice, but overall I think it's an acquired taste.

Thanks for watching.