Kimchi should be discarded immediately if green, blue or black spots appear on the surface when a storage container is opened, according to the World Institute of Kimchi. Mold of those colors signals that the kimchi has spoiled and is producing toxins harmful to humans. Cutting away the moldy portion or heating the kimchi does not make it safe.
The white film commonly found on kimchi at home is not mold but golmaji, a harmless surface layer, the institute said on the 21st. Golmaji is produced by five species of aerobic yeast, including Hanseniaspora uvarum, and genome analysis found no toxin-producing genes. Thread-like green, blue or black mold, by contrast, is distinct from golmaji and is a product of spoilage that should not be eaten. Kim Tae-woon, head of the institute's Green Process Research Division, said kimchi with a light golmaji film can be skimmed, rinsed and cooked, but that kimchi showing mold should never be eaten.
Mold toxins are heat-resistant and are not fully removed during cooking. Even if the visible moldy section is cut out, spores or toxins may have spread throughout the kimchi. An internal medicine specialist said in a recent media interview that toxins remain in long-aged kimchi that has developed mold even after the mold is removed. Among mold toxins, aflatoxin is classified by the World Health Organization as a Group 1 carcinogen, and even small amounts consumed over a long period can cause liver cell damage, cirrhosis and liver cancer.
Spoiled kimchi also compounds a sodium problem. Average daily sodium intake in South Korea was 3,136 milligrams as of 2023, above the World Health Organization's recommended 2,000 milligrams, according to the Korea Disease Control and Prevention Agency's national health information portal and the Korea National Health and Nutrition Examination Survey. More than half of that sodium comes from everyday foods such as kimchi, soups and stews, so eating spoiled kimchi on top of that adds to the health burden, according to the data.
Preventing mold comes down to storage. The World Institute of Kimchi recommends keeping kimchi fully submerged in its brine to block contact with air and covering the surface with food-grade plastic wrap. Storage temperature should be kept at or below 4 degrees Celsius, and the seal on container lids should be checked periodically.
