Century eggs

Picture of century eggs
Whether you call them century eggs, hundred-year eggs, millennium eggs or whatever, these outlandish ova are a Chinese delicacy dating back centuries to the Ming Dynasty. The boastful name suggests these eggs take forever to make, this is a misnomer. Century eggs take about 4-5 weeks to make, a few minutes to work up the courage to open, and a few seconds to eat.

Traditionally century eggs were made by preserving chicken or duck eggs in a mixture of salt, lime and ash, then wrapping in rice husks for several weeks. During this time the pH of the egg raises transforming the egg, the chemical process breaks down some of the proteins and fats into smaller, more complex flavours. After curing the yolk of the egg turns a dark green and has a creamy consistency, while the white turns amber and is gelatinous. 

I chose a more modern method to achieve the same results: a salt and lye pickling solution, and encasing in modelling clay. After about a month my eggs were ready, and I'm happy to say they turned out perfectly!

Want to make your own? Of course you do! 
Enough talk, let's make some eggs!
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Step 1: Supplies + materials

Picture of supplies + materials
  • 100% lye/caustic soda (NaOH - sodium hydroxide)*
  • salt (NaCl - sodium cloride)
  • chicken egg (duck or quail egg)
  • scale
  • plastic wrap
  • clay (I used modeling clay)
  • glass jar with lid
* Technically lye is a corrosive, not poison. Though, it' can be labelled as either. It's incredibly dangerous to handle and can cause severe burns with contact to skin, there's also an inhalation risk. Use gloves and a respirator.
There's plenty of other foods that are made/prepared with lye, but use caution and common sense.
Always use pure, 100% lye (sodium hydroxide).

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RayL425 days ago

Alright! I'm gonna start the process tonight! Thanks so much for this write-up! How in the world did you even get the asian century egg sensei's to give up their secrets??

jacobevolved10 months ago

I wonder if sodium silicate could be used instead of the clay....

byesuah11 months ago
i had this in China a few years ago. everyone was freaked out by this and didn't try , but I didn't think it was bad. I'm interested to try it on my own. :-)
rtiamson1 year ago
if i will use lye many cups i need?
mikeasaurus (author)  rtiamson1 year ago

See Step 2

phettsack3 years ago
As those eggs aren't cooked, I am courious about germs.
Whats about bacteria like salmonella? Are they gone?
the curing process kills the microbes that would otherwise spoil the egg, that's why the egg can last as the name suggests a hundred years and still be edible. as long as you don't mind something that smells of rotten eggs, it takes a lot to attempt to eat one and is an aquired taste (not to mention texture) so they are safe to eat, but if they'll stay down, that depends on the person eating them. they were invented as a way to preserve eggs through the winter months back when there were no green houses pumping out fresh fruit all year round or imports from africa and south america in the corner shop less than a week after being picked. so it was an emergency solution that evolved into a delacacy
abbyr phettsack3 years ago
who cares about poison
Gone, the Lye killed them all off, and the modelling clay prevents any air(along with germs) from coming back in. I find it easier to compare to prosciutto, which is also served raw and is only salted. The salting kills all germs in it.
I am not sure about the the germs issues, but I ate it from child till now, not cooked. But will cook with pork Congee most.
GnomeToys1 year ago
"Drain opener" style sodium hydroxide may contain heavy metals. You should really, really, find food grade lye online instead.
They taste like urine- andrew zimmerman - think thats how you spell it
In china there are eggs like this that are made really quickly but were kinda dangerous to eat (due to chemicals). but how does NaOH and NaCl pickle the egg?
BioT3 years ago
I'm very concerned about the number of people I've seen referring to these as being made with "drain cleaner" (or some variation of that statement).

Lye itself is corrosive but if it's used in the right amounts and carefully it is perfectly safe for preparing food (it is such a high pH base that it kills bacteria, similar to pickling with vinegar -- a low pH acid)

But most dry "Drain Cleaner" usually contains bits of aluminum. The lye (NaOH), when it becomes liquid in water, reacts with the aluminum and creates:
- (A) bubbles,
- (B) heat... and lots of it. Enough to cause heat burns (I've seen it melt plastic bottles!). and then
- (C) the bubbles are likely pure Hydrogen -- thus, flammable or explosive!!

As a Biology teacher (hence the "BioT" name) I made these in class but I also had to teach some Chemistry. I used to use this Lye + Water + Aluminum to show that it would make hydrogen.  I collected the gas in a balloon in class. Then to prove it was Hydrogen I'd have someone ignite the balloon with a match at the end of a yard/meter stick. BOOM!   

SO, I'M JUST SAYIN' -- #1. Don't use Draino, drain cleaner, etc... use plain old Lye (NaOH), and #2. Don't use the Lye if it might come in contact with Aluminum... the catalyst that causes it to release Hydrogen gas!

Other than that, have fun and enjoy your eggs. They're good. As I said, we made these in my Biology class, too. But only a couple students were "gutsy" enough to try them. ;-)
chiao3 years ago
Yes! I love these! Unfortunately, my wife just bought some, so she won't let me make them right now. I like to eat them sliced with soft tofu and thick soy sauce. Mmm! Now I just need to learn to make my own rice wine and tofu...
Often served in Chinese restaurants in Thailand - in Thai language referred to as "horse urine eggs" - go figure!

(It's the ammonia.)
Thanks - always wondered how they made them!
Here in thailand, these "kai yeow maa" (horse piss eggs) are used in a few dishes.
I would say the best is "kai yeow maa gaprow grop" which translates to horse piss eggs with crispy basil.
Simple recipe:
1. Heat oil in wok and flash fry basil leaves until crispy. Here we use holy basil which is slightly spicy. The fried basil loses most of its flavour though so any basil will probably do - it's for colour and texture anyway!

2. Quarter horse piss eggs and deep fry until outsides are a medium brown. Drain or put on paper to soak up excess oil.

3. Make a sauce using soy sauce, vinegar, sugar, chilis (optional but gooooood!), then corn or tapioca starch in water to thicken the sauce. Heat and simmer to thicken the sauce. Add basil leaves (lots) in the last 30 seconds of cooking.

Put the eggs on a plate, pour sauce over them, then sprinkle the fried leaves over top.
ksexton13 years ago
Everyone thinking lye is artificial, lye is traditionally made by slowly leaching water through wood ash. The eggs might even be able to be considered an organic food. Powdered drain cleaner is lye+aluminum shavings+possibly color crystals, anti-clumping agents, fillers, etc.

try eating them steamed. it takes the "edge" off the taste. Also, great steam with egg and salted egg!

ChrisSWK3 years ago
I am Chinese from Malaysia and in my country, we eat this with pickled sliced ginger and its taste is awesomely great. However, do take caution as this egg is high in cholesterol. Won't want to have heartattack after taking it...

To have this in Fear Factor, eating it will be a piece of cake...

Great stuff in sharing the "Recipe"....
branhamr3 years ago

See comment by submark on Step 1 page.
PCBrewing3 years ago
Correct me if I am wrong, but I think you could use; Pickling Lime (Calcium Hydroxide) to increase the Ph and remain food safe.
hammer98763 years ago
There is got to be a good way to keep the eggs submerged since that seems to be important.

You don't mention your gloves. Is that to protect you from the brine or the eggs from contamination?

As for "Step 5 Encase" - plastic wrap, modeling clay, and a resealable bag? Gosh, what happens if you don't do this well? Do the eggs go bad? Please define "bad." :-)

Congrats on being Featured!
vasarian3 years ago
It is delicious, you can siliced and eat it cold paired with rehydrated Skitaki mushrooms , or my favorite with hot Pork Congee. Very good ible!
damionflynn3 years ago
Very interesting instructable. I will pass on actually attempting to eat what looks like a rotten egg though - we throw those out around our house :-)
tonyellard3 years ago
There's food grade lye available on the market. I'm not sure the difference, but it might be worth trying that over the lye marked "drain cleaner"...
The difference would be the purity with which it's manufactured. The food grade stuff they take precautions to make sure nobody sneezes in it and that there aren't any other chemicals in it. For this application it's not likely to make much of a difference since the shell of the egg makes a pretty good filter and the drain cleaner version is going to be at least as pure as the original salt-water and wood-ash recipe. Wash them before you crack them open.
submark3 years ago
Sorry about the screaming, but this IS IMPORTANT.
A relative boiled a lye solution in an aluminum pot to make soap and the pot dissolved and caused severe chemical and heat burns to her.
Stainless steel or porcelain clad steel or iron are best and wooden spoons work really well with lye. A teflon coated aluminum pot with no scratches might be OK, but why chance it?
It would be best to heat the solution just enough to ensure that the lye/salt mixture dissolves completely. You are not sterilizing anything and boiling lye can spatter.
Could you bypass the plastic wrap and clay and just put the eggs in a plastic bag and vaccuum seal it?

I thought it was the minerals from the mud that infused the egg thru osmosis that caused the color and flavor/smell.... ?
cblair13 years ago
I am speechless which is not me, I come from a catering back ground and have been asked to make many food oddities over the years, where were you 10 years ago?, when I was asked if I could make these for a Multi-cultural event. I could not have made these because of the lye but I am sure there has to be a health Department acceptable alternative out there for the lye! Great Post! CJB
RWWestbrook3 years ago
I agree with Tony. I've always been told NOT to drink the stuff under the kitchen sink. I'm glad this worked out for you but I'll make sure to have poison control on speed dial if I ever muster up the courage to try this.
KeLaiFu3 years ago
I live in China and there's a lady selling these just outside my apartment. She also has a larger varient where the white turns a black colour. I never knew they were called Century eggs.
I have also eaten them back home in the UK, where they were described as the blue cheese of the east!
The worst thing about them is the texture, especially the yolk with can stick to your mouth, they taste pretty good.
pcgirl3 years ago
This is a fantastic ible... but I'm sorry - I just feel sick looking at the zombiefied eggs. You are a bigger man that me. Your dangly bits must be gigantic! I shall pass on this one.
hlagas pcgirl3 years ago
What she said.
superbird3 years ago
This is a Chinese traditional snack food but not for rice, I like it . Of course, I am Chinese. It better to match with "gari" or "sugar" together, Or match with congee. It's rich taste and very nice. But the smell is a little special. If you try it, you will never stop. But we don't suggest to eat it always.
FoolishSage3 years ago
I didn't know that only the yolk of the egg became the blackish colour, I always thought it was the whole egg. I've only ever eaten them cut into bits but I do not recall seeing any amber part.. Is the amber part also safe/tasty to eat or is it discarded and only the yolk eaten?

Either way I'm gonna make these. My colleagues already think I always eat weird stuff and this will be a great way to keep them freaked :D
Being Chinese, I have had the before. They are very tasty in my opinion. My sister has different thoughts.

(Also just to get this straight it is 1000 year eggs if you use abit of translation but most Chinese people won't penalize you for it.
Im so excited to do this, its like bizarre foods i would love to try all the stuff on that show. Well Im going to make a youtube video. We will see how my ulcerative colitis likes this !
susanrm3 years ago
Wow... just wow.

I don't know what the natural foodies would say about eating eggs pickled in drain cleaner.
Wow I'm impressed, this is totally hard core! I bought a package of 6 because I like them in Jook (rice porridge) however I didn't realize that eating them alone would be...well pungent. They don't call them horse urine eggs for's not the taste, it's the smell. But seriously these things are like blue cheese, small bits make a great impact.

Now I just get them when I get more trying to tough my way through 6 of those babies at a time :)

My hat is off to you sir!
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