Can I leave my rice cooker on warm overnight?

By | March 16, 2022

Sometimes after the rice was done cooking in the rice cooker, there was still some leftover rice after the meal was served.

Most of the time the rice is left in the rice cooker in a warm mode.

There is a question left in our mind, can I leave my rice cooker on warm overnight?

Would it be safe to eat the rice which was left warm overnight?

Here I am going to discuss this matter of whether we should leave the rice cooker warm overnight.


Can I leave my rice cooker on warm overnight?

You may leave the rice in the rice cooker in a warm mode (more than 65ºC) for about 11 to 12 hours. As bacteria (Bacillus cereus) grows rapidly on rice in temperatures between 5ºC to 60ºC, and produce toxins that are able to cause health risks like vomiting and diarrhea.


Bacteria grow and produce toxins on rice.

Once the rice is cooked, the thing that does matter is how to prevent bacteria called Bacillus cereus from growing on the rice.

The bacteria grows and will produce toxins on the rice which will cause vomiting and diarrhea after consuming.


What is Bacillus cereus?

Bacillus cereus is a rod-shaped bacteria widespread in the environment and often found in soil, and also found in plant and animal types of food.

It grows best in a temperature range of 39ºF (4ºC) to 118ºF (48ºC) and grows optimum in the range of 82ºF (28ºC) to 95ºF (35ºC) and a pH range of 4.9 to 9.3.

This type of bacteria is able to produce toxins that cause nausea, vomiting, abdominal cramps, and diarrhea.

Bacillus cereus bacteria are existing everywhere and easily spread to fresh food like rice, meat, vegetable, and milk.

When the food is not properly cooked and stored in temperature between 41ºF to 135ºF, it will cause illness to people who consume it.

Bacillus cereus bacteria will be destroyed when the food is heated (by frying, steaming, boiling, or grilling) to temperature ≥ 145ºF (63ºC).

Reheating of cooked food to 165ºF (74ºC) for 15 seconds to kill growing B. cereus bacteria effectively.

But the spores of B. cereus are able to survive at 100 °C for hours.

Food that is already contaminated with toxins is not safe to eat as toxins are heat stable to 249ºF (121ºC) for more than 80 minutes.

Therefore toxins contaminated food should be immediately dumped away.

Some B. cereus spores will still be able to survive in freezing and boiling, so it is encouraged to eat the cooked food immediately once prepared.


What happens if you leave the rice at room temperature for 2 hours?

After the rice is done cooking in the rice cooker, if the rice cooker is not set with a warm mode, you are advised to eat the rice within 2 hours.

When the rice is still in raw condition, it contains Bacillus cereus bacteria.

Bacillus cereus is able to survive in boiling (high temperature) by forming itself into a spore.

When the rice is left at room temperature after cooking, after 2 hours the spores will activate, grow rapidly and start to release toxic into the rice.

The toxins from bacillus cereus will cause nausea, vomiting, and diarrhea, so called food poisoning.


What happens if you leave the rice cooker on warm overnight?

After the rice has been cooked, avoid storing the rice in a temperature between 5°C and 60°C.

Between 5°C and 60°C, Bacillus cereus bacteria are in optimum environment range and able to grow rapidly.

Once the rice stays at room temperature (5°C to 60°C) for more than 2 hours, bacteria will grow fast and start to create toxins.

When you set the rice cooker in warm mode, it will maintain the temperature at more than 60°C.

Under the rice cooker’s warm condition, the rice is able to stay inside the pot for 11 to 12 hours.

But after the rice is left in the rice cooker for a long time, the rice will dry up and get crunchy.


How to handle leftover rice?

So to effectively handle the leftover rice that we can’t finish, put the rice into a container and keep inside the refrigerator with less than 5°C.

Temperature of less than 5°C can prevent spores from undergoing activation.

The cooling process from 60°C to 5°C should be less than 6 hours to avoid bacteria growing and producing toxins on rice in that period of time.

Rice can be kept inside the refrigerator for 1 to 2 days.

Make sure the leftover rice containers are not stacked to each other for better airflow around the container and rapid cooling of the rice.

Once the cooled rice has been taken out from the refrigerator, the rice shall immediately be sent to reheat like steam heating or making fried rice.

If you are feeling something wrong with the rice and doubt its safety, just dump the rice.


Final thought

Rice that is just cooked has a risk of bacteria (Bacillus cereus) toxins contamination.

Therefore it is encouraged to eat the rice within two hours after it is cooked.

For leftover rice inside the rice cooker with warm mode, it can be left for 11 to 12 hours, but the quality of the rice will be changed.

Leftover rice could be put inside the container and stored inside the refrigerator with a temperature less than 5°C.

Reheat of rice that has just been taken out from the refrigerator should be made immediately, and heating temperature should 74ºC for 15 seconds to kill growing B. cereus bacteria.

Rice that is contaminated with toxins will cause nausea, vomiting, abdominal cramps, and diarrhea.

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