Is Cooking Congee with Cooked Rice Harmful?

Reheating cooked rice to prepare congee—or rice porridge—is a common practice in many cultures and poses no inherent health risks when done properly. From a nutritional and food safety perspective, the primary concern is not the reheating itself, but rather how the rice was stored prior to reheating.

Cooked rice, like other starchy foods, can support the growth of Bacillus cereus—a spore-forming bacterium that survives cooking temperatures. If rice is left at room temperature for more than two hours after cooking, these spores may germinate and produce heat-stable toxins. Subsequent reheating, even to boiling, will not neutralize these preformed toxins and could lead to foodborne illness characterized by nausea, vomiting, or diarrhea.

However, when cooked rice is promptly cooled and refrigerated (at ≤4°C) within two hours of preparation—and reheated thoroughly to an internal temperature of at least 74°C—the process is safe and nutritionally sound. The nutritional profile of rice—primarily carbohydrates with modest amounts of B vitamins and trace minerals—remains largely unchanged during reheating. While minor losses of heat-sensitive nutrients such as thiamine (vitamin B1) may occur with repeated heating, these are clinically insignificant in the context of a balanced diet.

In summary, preparing congee from previously cooked, properly stored rice is both safe and practical. The key preventive measures are rapid cooling, appropriate refrigeration, and thorough reheating—not avoiding reheating altogether.