Thermoses are a great way to keep food hot during the day so you can have a warm lunch or dinner that you brought from home. Rice is a popular leftover as often we make too much and it would be great to take that rice and curry or stir fry to work or school for eating at lunch time.
But can you put rice in a thermos? Will it hold it's heat and more importantly is it safe to put rice in a thermos or could it potentially grow harmful bacteria and make you sick?
As the weather is getting colder and I'm looking to send my kids to school with warm lunches (as well as hard warm lunches myself) I wanted to know the answer to this question so I did some digging into whether or not you can keep rice in a thermos.
The opinions were mixed and varied but I think I worked it out:
Keeping rice warm in a thermos can be done but it is risky. Between the temperatures of 40°F-140°F (4.4°C-60°C) a bacteria called Bacillus cereus can grow quickly which can lead to food poisoning. To keep rice hot in a thermos heat up to boiling point and ensure it stay above 140ºF the entire time in order to ensure it's safe to eat.
Below I have written up more details about the health risks of keeping rice warm in a thermos flask as well as a couple of ways to safely keep rice hot in a thermos so you can eat it without getting sick.
Health Risks Of Putting Rice in a Thermos
I didn't know this but rice is actually one of the most the most dangerous foods to keep warm as it can contain and easy grow a bacteria called Bacillus cereus which can actually survive some cooking processes.
Uncooked rice can often contain spores of this bacteria that can survive when the rice is cooked. This is a strange of bacteria that can cause food poisoning and even in some rare cases caused death so we need to take this seriously.
According to the USDA there is a “danger zone” for food to be kept at which can lead to rapid bacteria growth.
This temperature is between 40°F-140°F (4.4°C-60°C). This is a pretty wide range of temperatures.
Given that rice is prone to bacteria growth from the outset it can actually be quite dangerous to keep it in a thermos if it's going to be in this danger zone of warmth.
If these bacteria cells multiply it can lead to food poisoning, vomiting or diarrhea. The longer you keep the rice in this danger zone the great the chances the rice will become unsafe to eat.
In summary: Keep rice “warm” in a thermos (in that range from 40°F – 140°F) is a no-go. Bacteria might grow making the rice unsafe to eat. It could give you food poisoning and that isn't a risk worth taking.
Ok, so we know about the danger zones and keeping rice “warm” but not hot in a thermos is not going to be good for us.
But people sometimes keep rice on rice cookers on the “warm” setting for DAYS AT A TIME and this is considered absolutely fine?
Why is this the case and how can you keep rice safely in a thermos?
Rice warmers keep rice above that 140ºF (60ºC) temperature which is out of the “danger zone” and actually kills most bacteria because it's so hot. This keeps the rice safe to eat for longer periods of time.
How To Safely Keep Rice in a Thermos
There actually is a way to keep rice hot in a thermos whilst keeping it safe to eat. It's not completely risk free, but with the right precautions it could work.
In order to keep your rice hot in a thermos for a long period of time you would need to ensure it stays at 140°F (60°C) or higher the entire time.
Medical news today has this great article on reheating rice safely with the main idea being:
- When reheating rice you want to reheat it to ABOVE 165ºF (74ºC) to kill any bacteria
- You then want to eat the rice as quickly as possible (within an hour)
I'm going to personally take this a step further.
If you want to keep rice in a thermos safely you'll want to:
- Preheat the inside of the thermos by filling it with boiling water and leaving it for a couple of minutes before tipping out
- Heat your rice up to around boiling temperature throughout to kill of bacteria and make it hot enough to store
- Quickly put the rice/leftovers in the thermos and close the lid
- Check temperature when going to eat it to ensure it's above 140ºF
By preheating the inside of your thermos the stainless steel is not going to suck any heat out of your rice.
But heating your rice up to boiling point (around 212ºF or 100ºC) it's going to stay above and out of the danger zone for a longer period of time.
Ideally when it comes time to eat it the rice is still at 140ºF or higher, meaning it never entered the danger zone of bacteria growth and should be safe to eat.
However, this still contains some risk as rice can cool down unevenly and can enter the danger zone and grow bacteria.
It may be worth investing in a cheap little pocket thermometer in order to check the temperature before eating, especially if you've kept it warm for a long time.
These only cost $3-$5 and I recommend checking out this little pocket thermometer at Amazon as it easily fits into your lunch box and doesn't need any batteries in order to work.
The Safest Way To Keep Rice in a Thermos: Cook The Rice In The Thermos
There are loads of videos out there from people living in vans or off the grid who actually use a thermos to cook rice.
To me this seems like a much safer method if you want to have hot, safe rice to eat at lunchtime.
To do this:
- Preheat the inside of your thermos with boiling water and leave for 2-5 minutes before discarding water
- Bring 3/4 cup of water to boil in a pot
- Put in 1/2 cup of rice in pot and leave for 1-2 minutes until boiling again
- Quickly pour all contents into your thermos
- Close the lid quickly
- Leave thermos lying on its side for 2-3 hours
- Check temperature before eating
Doing this means you aren't reheating previously cooked rice which may have not been cooled down quickly enough.
The boiling water is dense and super hot and therefore less likely to cool down into that danger zone compared to pre-cooked rice with less water content.
They recommend you leave it 2-3 hours to cook, any longer than this and it may drop into the danger zone and become unsafe to eat.
There's a video below of a guy doing this in his van:
Will Rice Stay Hot In a Thermos?
The general rule of thumb is the denser the food and the more water content it contains the longer that food will stay hot.
Dense rice like brown rice will stay hotter longer than fluffy white rice which doesn't have a huge amount of water left in it.
Rice as a whole isn't super dense and neither are things like fried eggs/omelettes or bread.
So rice by itself won't stay extremely hot in a thermos for long unless it is densely packed and has a decent amount of water content.
You'll want to keep it about 140ºF if you want to keep it safe to eat. If it falls below this then bacteria can grow that will lead to food poisoning.
If the rice is mixed with a curry or stir fry which contains a lot of yummy sauce, that sauce will have a lot of water content and be denser and thus the rice will stay hotter for longer.
But always be careful when keeping rice hot in a thermos and follow your local safety guidelines.
Will I Personally Keep Rice Hot In a Thermos?
While the idea of tasty vege and tofu stir fry or curry for lunch sounds amazing on the surface and would be a nutritional meal for me and my kids I personally wouldn't take the risk.
I personally wouldn't try to keep rice warm or hot in a thermos.
The risk of food poisoning is just too high and the idea of having to take a thermometer and then throwing out the food if it becomes to cold (thus having no lunch at all) just all sounds like a bit too much for me.
I'll stick to sending my kids to school with sandwiches or fill up their thermoses with other hot leftovers instead.