How long does it take for rice to become toxic? A food safety guide

January 2, 2026 •

4 min read

According to the Centers for Disease Control and Prevention (CDC), an estimated 63,000 people in the U.S. get sick from Bacillus cereus annually, the bacteria responsible for making rice toxic. The risk of food poisoning from rice depends on how long it is left at room temperature, not on the reheating process itself.

Quick Summary

Cooked rice can harbor Bacillus cereus spores that germinate and produce toxins if left in the temperature danger zone. Rapid cooling and proper refrigeration within two hours are crucial for safety, as reheating does not destroy the heat-resistant toxins.

Key Points

Two-Hour Rule: Cooked rice should be refrigerated within two hours of cooking to prevent the growth of Bacillus cereus bacteria.
Spores Survive Cooking: The bacteria responsible for rice poisoning form spores that can withstand the cooking process, making safe storage essential.
Toxins Resist Reheating: The toxins produced by Bacillus cereus are heat-stable and will not be destroyed by reheating, so proper cooling is the main preventative measure.
Cool Rapidly: Use shallow containers to cool hot rice quickly before refrigerating to prevent it from lingering in the temperature danger zone.
Refrigerate for 3-4 Days: Once refrigerated, leftover rice should be eaten within three to four days to ensure safety.
Watch for Spoilage Signs: An unpleasant smell, slimy texture, or discoloration are signs that rice has spoiled and must be discarded.

Understanding the Bacteria Behind Rice Toxicity

The primary culprit behind food poisoning from improperly handled rice is a spore-forming bacterium called Bacillus cereus. While other foodborne illnesses often come from undercooked food, the danger with rice is different. The spores of Bacillus cereus can survive the high heat of the cooking process. If the cooked rice is then left at room temperature, these resilient spores can germinate and begin to multiply rapidly. As they multiply, they produce a heat-stable toxin, meaning it is not destroyed by simply reheating the rice later on.

The Critical Danger Zone

The most important factor determining how long it takes for rice to become toxic is how much time it spends in the 'danger zone'—the temperature range where bacteria can thrive. This zone is between 40°F and 140°F (4.4°C and 60°C). The USDA advises that perishable foods, including cooked rice, should not remain in this temperature range for more than two hours. On a hot day, with ambient temperatures above 90°F (32.2°C), that timeframe drops to just one hour. If rice is left out longer than these limits, it is safest to discard it to prevent illness.

Safe Cooling and Storage Practices

To prevent Bacillus cereus from multiplying to dangerous levels, quick and proper cooling is essential. Simply leaving a large pot of rice on the counter to cool is not enough, as the heat can be trapped and create an ideal environment for bacterial growth.

Best Practices for Storing Leftover Rice:

Cool rapidly: Spread cooked rice into a shallow container or multiple small containers to help it cool quickly and evenly.
Refrigerate promptly: Transfer the rice to an airtight container and place it in the refrigerator within one to two hours of cooking.
Use within days: Properly refrigerated cooked rice is generally safe to eat for three to four days. Be aware that some sources recommend a more conservative two to three days.
Portion before freezing: If you want to store rice for longer, portion it into freezer-safe containers immediately after cooling. Frozen rice can last for one to two months.

Reheating and Recognizing Spoilage

Reheating rice is a common source of confusion, but the process is perfectly safe as long as the initial cooling and storage were handled correctly. When reheating, the goal is to kill any vegetative bacteria that may have grown, though the toxin itself will remain.

Safe Reheating Guidelines:

Heat thoroughly: Ensure the rice is heated until it is steaming hot all the way through. The internal temperature should reach at least 165°F (73.8°C).
Stir during reheating: Stirring the rice, especially when using a microwave, ensures it heats evenly and eliminates cold spots where bacteria could survive.
Do not re-reheat: For both quality and safety, never reheat rice more than once. The flavor and texture will decline, and repeated reheating increases the risk of bacterial growth.

How to tell if rice has gone bad

While Bacillus cereus toxins are odorless and tasteless, the rice itself will often show signs of spoilage if left too long. Trust your senses and always throw out any rice that seems questionable. Key signs to watch for include:

Off odor: A strange or unpleasant smell is a primary indicator of spoilage.
Slimy texture: If the rice grains become mushy or sticky and slimy, discard it immediately.
Discoloration: Any visible changes in color, such as a grayish or yellow tint, means the rice is no longer safe to consume.

Comparison of Safe vs. Unsafe Rice Practices


Aspect	Safe Practice	Unsafe Practice
Cooling	Spread rice in a shallow container and refrigerate within 2 hours.	Leave hot rice in a deep pot on the counter overnight.
Storage Time	Refrigerate for 3-4 days in an airtight container.	Leave rice in the fridge for over a week.
Freezing	Portion cooked rice into bags and freeze for 1-2 months.	Leave rice out before freezing, allowing bacteria to multiply.
Reheating	Heat to an internal temperature of 165°F (73.8°C) only once.	Reheat rice multiple times or only warm it slightly.
Reheating Method	Use a microwave or stovetop, adding a splash of water for moisture.	Rely on reheating to destroy pre-existing toxins (it won't).
Sniff Test	Use your sense of smell alongside visual cues for quality, but do not rely on it alone for safety.	Trust the smell test alone to determine safety, which is unreliable for tasteless, odorless toxins.
Leftovers	Discard if left out longer than 2 hours (or 1 hour if above 90°F).	Consume rice that has sat at room temperature for an extended period.

Conclusion

In short, it takes surprisingly little time for cooked rice to become toxic if handled improperly, with the critical window being the first two hours after cooking. The primary risk comes from the bacteria Bacillus cereus, which produces a heat-resistant toxin when left in the temperature danger zone. Proper food handling is the most effective defense, not reheating. By rapidly cooling your leftovers, refrigerating them promptly, and consuming them within a few days, you can dramatically reduce the risk of food poisoning. When in doubt, it's always safest to throw it out.

For more information on food safety, you can visit the FoodSafety.gov website.

Frequently Asked Questions

Yes, you can get food poisoning from leftover rice if it is not cooled and stored correctly. The bacteria Bacillus cereus can grow in cooked rice left at room temperature and produce toxins that cause illness.

Reheating rice until it is steaming hot will kill the bacterial cells, but it will not destroy the heat-resistant toxins that may have already been produced if the rice was left out too long.

Cooked rice should be refrigerated as soon as possible, and definitely within two hours of cooking. If the ambient temperature is above 90°F (32.2°C), refrigerate within one hour.

Using the 'keep warm' setting on a rice cooker is safe only if it maintains the temperature above 140°F (60°C). If the temperature drops below this, the rice enters the danger zone where bacteria can multiply.

With proper storage, cooked rice is generally safe to eat for three to four days in the refrigerator. After that, it should be discarded.

No, the 'sniff test' is not a reliable indicator for rice safety because the dangerous Bacillus cereus toxins are odorless and tasteless. Always follow proper cooling and storage times to ensure safety.

To cool rice quickly, transfer it from the cooking pot to a shallow, wide container. This increases the surface area and allows the heat to dissipate faster before refrigeration.