Leftovers that look and smell fine can effectively be petri dishes for bacteria. An experiment by a microbiologist has exposed how easily food poisoning arises in everyday kitchens.
Food poisoning cases in South Korea totaled 319 in 2025, with 9,780 people affected, up 20% and 28% respectively from a year earlier, according to the Ministry of Food and Drug Safety on the 18th. Sample surveillance data from the Korea Disease Control and Prevention Agency also showed that the number of patients with intestinal infections, or food poisoning, more than doubled over five years, rising to 30,143 in 2025 from 14,087 in 2020.
September saw the highest number of outbreaks by month, while winter cases jumped by about 900 from a year earlier, making food poisoning a year-round threat rather than a seasonal one.
Experts say leaving leftovers at room temperature for long periods is one of the most common causes of food poisoning. Microbiologist Primrose Freestone stressed that improper storage of leftovers, not just the cooking process itself, is a major factor.
The key is refrigerating food within two hours of cooking. Because refrigeration only slows bacterial growth rather than stopping it entirely, food left out at room temperature should be avoided even if it shows no change in appearance or smell.
Risk levels and recommended storage periods vary by food type. Pizza left at room temperature becomes a favorable environment for bacteria to multiply again, even though the heat of a freshly baked pie kills off microbes. Refrigerated pizza should be eaten within two days.
Chicken dishes are more vulnerable to bacterial growth because they are high in moisture and nutrients and low in acidity. They should be cooled thoroughly, refrigerated as soon as possible and eaten within three days. Rice is especially risky because Bacillus cereus spores present in uncooked grains are heat-resistant and can survive cooking. Rice left at room temperature for more than two hours can cause vomiting and diarrhea, and should be eaten within 24 hours.
Food poisoning can occur even when food looks and smells normal, because pathogenic bacteria cannot be detected by the senses. The drug safety ministry recommends heating leftovers thoroughly all the way through when reheating, and advises against reheating food more than once because of the risk of indigestion and gas.
