Published October 3, 2024.

Rice cooked and placed in the fridge within an hour of cooking is safe to consume for days. Rice cooked and not quickly placed in the fridge may be unsafe to eat if it was contaminated with bacillus cereus spores.

Rice can be contaminated with bacillus cereus during farming, harvesting, processing, or bagging from contact with soil, water, dust, animals, and insects. Bacillus cereus is a gram-positive rod-shaped bacterium that can cause food-borne illness. It is unknown exactly what percent of raw rice contains bacillus cereus spores. Different studies have estimated that the number is between 9-52.8%. The USDA’s food safety inspection service (FSIS) considers bacillus cereus growth over 3 log CFU/g (colony-forming units per gram) to be a public health concern.

To test the growth of bacillus cereus in cooked food, a group of researchers inoculated samples of rice, beans, and pasta with strains of b cereus spores and cooked them. The researchers cooled the samples to 7.2°C or 44.96°F at different speeds to see how b cereus grew since the bacterium can survive cooking.

The researchers found that rice, beans, and pasta cooled down to 7.2 degrees within 6 hours of being cooked were the only samples with bacillus cereus growth below the public health concern threshold. These were the same findings with rice mixed with chicken and vegetables and rice mixed with beef. For cooling times greater than 6 hours, all samples had bacillus cereus growth levels above the concern threshold. It’s important to note that the research purposefully inoculated all of the samples with bacillus cereus at levels just below the threshold of 3 colony-forming units per gram. These concentrations don't represent the actual amounts of bacillus cereus that would be in raw rice before cooking as not all samples will be contaminated and the amount would likely be much lower. Additionally, most fridges cool down to 4°C or 39.2°F, which is a lower temperature than the 7.2°C used in the study. At a temperature 7.2°C, bacillus cereus can still grow.

The main takeaway is that rice should be consumed after cooking or refrigerated within one hour. Quickly placing the rice in the fridge ensures the rice rapidly cools to 4°C within 6 hours of cooking to prevent the potential growth of bacillus cereus. I couldn’t find any research proving that all rice becomes moldy and toxic 24 hours after cooking, a viral claim circulating social media. If rice is contaminated with bacillus cereus and not refrigerated quickly after cooking, it can harbor bacillus cereus growth within a day. These conditions could potentially lad to food-borne illness. If the rice is cooked and quickly placed in the fridge, it should keep for several days without concerning levels of bacteria. Study three showed that levels of bacillus cereus remained non-detectable for seven days in quickly cooled rice.

Study One Link

Study Two Link

Study Three Link