Green plums are popular in Korea for their supposed medicine-like benefits that help ease stomachaches and prevent food poisoning, but they should be consumed with caution. The fruit can in fact be toxic if prepared improperly.
As the plums are quite sour, they are often prepared as a chutney, pickled or mixed with alcohol -- each of which can unlock the fruit's toxic effect. When the pit comes into contact with alcohol, a harsh carcinogen called ethyl carbamate can be produced. This compound can be found naturally in wine and fermented food but is not frequently associated with plums.
Luckily there are steps prudent consumers can take to make them safer. Removing the pit, preserving them for up to 100 days before consuming and storing them in cool places below 25 degrees Celsius all minimize the amount of ethyl carbamate produced.
Whole plums can also be preserved in alcohol or sugar for about a year before eating as ethyl carbamate reaches the highest level four to five months after preservation and decreases from then on.