Century Egg - Misconception and Etymology

Misconception and Etymology

According to a persistent misconception, century eggs are, or were once, prepared by soaking eggs in horse urine. The myth may arise from the pungent odor of ammonia (a side-product of protein breakdown) given off by century eggs, which is reminiscent of urine. Horse urine itself, however, is only slightly basic, ranging in pH from 7.5 to 7.9. Though human urine left standing can reach a maximum pH of around 9.4—the same as a 1-molar solution of ammonia—it is still less than that produced by mixing quicklime (calcium oxide) or wood ash in water.

In Thai and Lao, the common word for this type of preserved egg literally means "horse urine eggs", due to this myth and the distinctive ammonia odor of century eggs:

• Thai: ไข่เยี่ยวม้า (RTGS: khai yiao ma)
• Lao: ໄຂ່ຢ່ຽວມ້າ