Why Don't We Reheat Rice? Understanding the Food Poisoning Risk

According to the Centers for Disease Control and Prevention, the bacterium Bacillus cereus causes an estimated 63,000 cases of foodborne illness annually in the United States. It's the primary reason why we don't reheat rice without first understanding the critical steps for proper cooling and storage to prevent dangerous toxins from forming.

Quick Summary

This guide explains the food safety science behind reheating rice, focusing on the bacterium Bacillus cereus. Learn why improper storage, not reheating, is the real risk factor for food poisoning, and how to prevent it.

Key Points

• Food Poisoning Risk: Improperly cooled cooked rice can grow a bacterium (Bacillus cereus) that produces heat-resistant toxins.

• Toxins Survive Reheating: Reheating the rice won't destroy the toxins that have already formed, so proper storage is key.

• Rapid Cooling is Crucial: Cooked rice must be cooled quickly, ideally within an hour, to prevent spores from multiplying.

• Store in Shallow Containers: Using shallow, airtight containers helps rice cool down faster and more evenly in the refrigerator.

• Never Reheat More Than Once: For both safety and quality, only reheat rice once and consume it immediately.

• Reheat to 165°F (74°C): When reheating, ensure the rice reaches an internal temperature of at least 165°F (74°C) throughout.

The Science Behind the 'Reheated Rice Syndrome'

The notion that you can't reheat rice is a common misconception, born from a valid concern about food poisoning. The danger isn't the reheating itself, but the improper storage of cooked rice that allows a specific type of bacteria to thrive. This pathogen, called Bacillus cereus, is a spore-forming bacterium found in soil and on raw rice. The spores are heat-resistant and can survive the initial cooking process.

How Bacillus Cereus Creates a Food Safety Hazard

When cooked rice is left to cool slowly at room temperature, the Bacillus cereus spores germinate and grow into harmful bacteria. These bacteria can then multiply and produce toxins that are resistant to heat. This means that even if you thoroughly reheat the rice, the toxins remain, and they are what can cause illness. The condition resulting from this is sometimes known as “fried rice syndrome,” because fried rice is often made from improperly handled leftover rice.

The Temperature 'Danger Zone'

Bacteria, including Bacillus cereus, multiply rapidly in what is known as the temperature “danger zone,” which is between 40°F and 140°F (4.4°C and 60°C). If cooked rice spends too much time in this zone—more than two hours—it can become unsafe to eat. The proper procedure is to cool the rice quickly after cooking and refrigerate it promptly to minimize the time spent in this hazardous temperature range.

Safe Handling Practices for Cooked Rice

To safely enjoy leftover rice, proper handling is paramount. It’s a multi-step process that minimizes the window for bacterial growth.

• Cool It Quickly: Never leave cooked rice to sit at room temperature for longer than two hours. To accelerate cooling, spread the rice in a thin layer on a tray or in shallow containers.
• Refrigerate Promptly: As soon as the rice has cooled, transfer it to an airtight container and place it in the refrigerator. This halts bacterial multiplication.
• Store for a Limited Time: Cooked rice can be safely stored in the refrigerator for up to three to four days. Any longer, and the risk of contamination increases. When in doubt, throw it out.
• Reheat Thoroughly: When you're ready to eat your leftover rice, make sure to reheat it until it is steaming hot all the way through, reaching an internal temperature of at least 165°F (74°C). Stirring during reheating can help ensure even heat distribution.
• Reheat Only Once: For both safety and quality, you should only reheat leftover rice one time. Multiple reheating cycles increase the risk of bacterial growth and degrade the rice's texture and flavor.

Proper Cooling and Reheating: A Comparison

Feature	Improper Handling	Safe Practices
Cooling Method	Leaving a large, hot pot of rice on the counter for hours.	Dividing rice into shallow containers to cool within one hour.
Storage Duration	Storing refrigerated rice for over four days.	Storing refrigerated rice for no more than 3–4 days.
Reheating Frequency	Reheating rice multiple times over several days.	Reheating rice only once and consuming immediately.
Reheating Temperature	Simply warming it up, potentially leaving cold spots.	Reheating until steaming hot, reaching 165°F (74°C) throughout.
Bacterial Growth	Creates the perfect warm, moist environment for Bacillus cereus spores to multiply and produce heat-resistant toxins.	Minimizes time in the danger zone, preventing spores from producing dangerous toxins.

Conclusion: Practice Safe Storage to Reheat Rice

So, why don't we reheat rice without caution? It's not the act of reheating itself that's the issue, but the bacterial contamination that can occur if cooked rice is left at room temperature for too long. The spores of Bacillus cereus can survive cooking and will multiply rapidly in the temperature danger zone, producing heat-resistant toxins. By implementing proper cooling techniques—spreading rice out quickly and refrigerating promptly—and ensuring thorough reheating only once, you can enjoy leftover rice safely and confidently. When in doubt about how long it's been stored, the safest option is always to throw it out.

How to Reduce Risk from Leftover Rice

1. Serve Immediately: For best results and safety, serve rice as soon as it's cooked.
2. Cool Rapidly: If you have leftovers, cool the rice as quickly as possible by spreading it on a tray.
3. Use Shallow Containers: Divide large portions into shallow, airtight containers to speed up cooling before refrigerating.
4. Refrigerate Within One Hour: Store the cooled rice in the fridge within 60 minutes of cooking.
5. Reheat Thoroughly: Ensure rice is steaming hot all the way through (165°F / 74°C) before eating.
6. Avoid Multiple Reheats: Only reheat the portion you plan to eat and never reheat rice more than once.

Safe Methods for Reheating Rice

• Microwave Method: Put rice in a microwave-safe dish with a tablespoon of water or broth per cup. Cover and heat on high, stirring occasionally, until it reaches 165°F.
• Stovetop Method: Add rice to a saucepan with a little water or oil. Cover and heat over low-medium heat, stirring until steaming.

Learn more about safe food handling practices from the USDA

How to Reheat Rice: What's the Best Way to Reheat Rice? and other questions answered

Question	Answer
Is it safe to eat cold rice the next day?	Yes, cold rice is safe to eat the next day as long as it was cooled and refrigerated correctly within one hour of cooking.

Frequently Asked Questions

Can reheating rice cause food poisoning?

Food poisoning from rice is not caused by the reheating itself but by how it was stored beforehand. If cooked rice is left at room temperature for too long, a bacterium called Bacillus cereus can grow and produce toxins that survive reheating.

What is 'reheated rice syndrome'?

'Reheated rice syndrome' is a term for food poisoning caused by the bacterium Bacillus cereus, which grows on starchy foods like rice when they are improperly cooled and stored at room temperature.

How quickly must I cool rice after cooking?

Cooked rice should be cooled as quickly as possible, ideally within one hour. Spreading the rice in shallow containers can help speed up the process before refrigeration.

How long can I store leftover rice in the fridge?

Leftover rice can be safely stored in an airtight container in the refrigerator for a maximum of 3 to 4 days.

Is it safe to eat cold leftover rice?

Yes, as long as it was cooled and refrigerated correctly, cold rice is safe to eat directly from the fridge the next day.

Can I reheat rice more than once?

No, it is not recommended to reheat rice more than once. Reheating it repeatedly increases the risk of bacterial growth and can negatively affect the texture.

What temperature should leftover rice be reheated to?

For maximum safety, leftover rice should be reheated until it is steaming hot throughout, reaching an internal temperature of at least 165°F (74°C).