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Anne Marie's Chemistry Blog

By Anne Marie Helmenstine, Ph.D., About.com Guide to Chemistry since 2001

Are Century Eggs Soaked in Horse Urine?

Thursday October 16, 2008
Century Egg (irrational_cat, Flickr

I love Japanese cookies and candies. I have come to the conclusion the Kasugai fruit gummy candies are dusted with crack rather than sugar because nothing should be that addictive (joking! it's sugar... at least I think so... let me taste another to check). When I stock up on candy at my favorite Asian market, I go down every aisle and sometimes try a new food. That is how I discovered Century Eggs.

A century egg, also known as hundred-year egg, thousand-year egg is a Chinese delicacy. A century egg is made by preserving an egg, usually from a duck, such that the shell becomes speckled, the white becomes a dark brown gelatinous material, and the yolk becomes deep green and creamy. The surface of the egg white may be covered with beautiful crystalline frost or pine-tree patterns. The white supposedly doesn't have much flavor, but the yolk smells strongly of ammonia and sulfur and is said to have a complex earthy flavor. I say 'is said' because I haven't tried a century egg yet. Oh, I would, but only if it was made right.

Ideally, century eggs are made by storing raw eggs for a few months in a mixture of wood ash, salt, lime, and maybe tea with rice straw or clay. The alkaline chemicals raise the pH of the egg to 9-12 or even higher and break down some of the proteins and fats in the egg into flavorful molecules. The ingredients I named are not the ingredients listed on the eggs that I have seen in stores. Those eggs are made from duck eggs, lye or sodium hydroxide, and salt. That sounds scary, but it's probably ok to eat. The problem is, the curing process can be accelerated by adding another ingredient to the eggs... lead oxide. Lead oxide, like any other lead compound, is poisonous. This hidden ingredient is most likely going to be found in eggs from China, where the faster method of preserving the eggs is more common. Sometimes zinc oxide is used instead of lead oxide. Though zinc oxide is an essential nutrient, too much of it can lead to a copper deficiency, so it's not really something you want to eat either. How do you avoid poisonous century eggs? Look for packages that explicitly state the eggs were made without lead oxide. Don't assume the eggs are lead-free just because lead isn't listed as an ingredient. Personally, I'd avoid the eggs from China no matter how they are packaged because there is still a big problem with inaccurate labeling.

Many people avoid eating century eggs because of the rumor that they have been soaked in horse urine. I don't believe there is any horse urine involved, since urine is slightly acidic, not basic. If anyone knows otherwise, by all means post a comment. If you know of a good place to buy non-Chinese century eggs in the Myrtle Beach area, let me know. I'd love to try an egg, but I don't have any urge to incur heavy metal poisoning from the experience.

Comments

October 18, 2008 at 9:17 pm
(1) Heather says:

how ever it is made, it sounds really gross!

November 2, 2008 at 6:24 pm
(2) rebecca says:

horse urine is basic because of thier diet

March 7, 2009 at 1:50 pm
(3) Jeanne Lee says:

According to Wikipedia, significant quantities of ammonia are produced through the bacterial action on urea which changes the pH of urine from acidic to basic. Uh…

March 20, 2009 at 10:55 am
(4) gloria says:

These eggs are delicious. They’re very often used in rice porridge.

April 9, 2009 at 12:44 am
(5) T$ says:

They aren’t soaked in horse piss. Even though the Chinese may be a little different from us when it comes to foods, but they’re not SkankNasty!

May 30, 2009 at 3:32 am
(6) Dan W says:

as gross as it may be these are very delicious! i had them in the philipines.

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