According to experts, this situation can be divided into four cases as follows:

Case 1: The majority of bacteria will have been eliminated if the rice is left in the rice cooker after it has boiled without the lid being opened. It won’t hurt if the lid isn’t opened because bacteria can’t get inside. When the power is turned off and the temperature decreases, germs will not grow even though the rice’s moisture and nutrients are perfect for their growth. In this instance, leaving the rice overnight or longer won’t cause it to spoil.

Case 2: After the rice is cooked, if you open the lid, take some rice out while it’s still hot, and then close the lid again, the temperature inside the rice cooker remains relatively high. While there might be some bacteria entering when the lid is opened, the high temperature inside the cooker can help kill off any bacteria that might have come in. As the temperature drops, there won’t be many surviving bacteria, and they won’t multiply much overnight. Therefore, in this situation, consuming the rice left overnight is typically safe.

Case 3: If you’ve taken out some rice and it has cooled down, but you used a clean utensil and the air in your home is clean and well-ventilated, only a small number of bacteria will enter. By the next morning, the bacteria won’t have multiplied significantly, so eating it won’t cause major issues, though it isn’t entirely risk-free.

Case 4: If you took some rice out using chopsticks, spoons, or forks that were used to eat with, or if the air is not clean and contains more bacteria, and then the rice was returned to the cooker, a large number of bacteria will have entered and become trapped inside. The moist environment inside the rice cooker is ideal for bacteria to thrive, so the rice has a high chance of spoiling, particularly in warmer weather.