RICE is such a mainstay of the Malaysian table, from nasi lemak to nasi goreng, that it is hard to imagine a meal without it.
But that innocent mound of leftover rice sitting in your rice cooker overnight may be harbouring something far less appetising than tomorrow's fried rice.
Can reheating old rice really give you food poisoning?
Verdict:
TRUE
Reheating rice can cause food poisoning, but the real culprit is not the reheating itself. It is what happens to the rice before it goes back on the heat.
When rice is cooked, the heat kills most bacteria, but the spores of a bacterium called Bacillus cereus can survive.
Unlike common food-borne bacteria such as Salmonella and E. coli, cooking or reheating food will not protect against a Bacillus cereus infection because the toxins it produces are heat-resistant, and the spores can also survive cooking.
If cooked rice is subsequently left at room temperature, the bacteria multiply and produce a heat-stable toxin that can survive brief heating, such as stir-frying.
This is particularly relevant in Malaysia, where rice is commonly left sitting in rice cookers for hours or stored at room temperature between meals.
A review of studies published between 1974 and October 2023 found that the primary cause of Bacillus cereus contamination in rice was improper food handling and storage temperature during the cooking, cooling and reheating stages.
Signs of Bacillus cereus food poisoning include nausea, vomiting, headaches, abdominal cramps and diarrhoea, with symptoms typically appearing one to five hours after consuming contaminated food.
In severe cases, vomiting or diarrhoea can lead to dehydration, which can be life-threatening, and rarely the infection can spread to other parts of the body, damaging organs.
Research published in a peer-reviewed study found that rapid bacterial growth was observed after a minimum of six hours at 30°C, a temperature well within the range of a typical Malaysian kitchen.
Bacillus cereus grows best between 4°C and 48°C, with optimal growth occurring between 28°C and 35°C, conditions that describe the Malaysian climate year-round.
The good news is that food poisoning from reheated rice is entirely preventable with the right habits.
After cooking, rice should either be kept hot at above 63°C or cooled quickly and refrigerated within two hours.
Cooked rice can be safely reheated by adding a little water or broth, covering it so the rice can steam, and heating until the internal temperature reaches 74°C.
Rice should not be reheated more than once, and leftovers should be discarded after reheating.
Getting sick from Bacillus cereus is not particularly likely compared to other sources of food poisoning, and many cases go unreported because symptoms are usually mild and short-lasting.
But for young children, the elderly and those with weakened immune systems, the consequences can be more serious.
The bottom line: yesterday's rice is fine as long as it went into the fridge promptly and comes out piping hot.
Sources:
1. https://pmc.ncbi.nlm.nih.gov/
2. https://pmc.ncbi.nlm.nih.gov/
3. https://pubmed.ncbi.nlm.nih.
4. https://pmc.ncbi.nlm.nih.gov/
5. https://my.clevelandclinic.
7. https://fcs-hes.ca.uky.edu/
