If, like me, you aim to cook dinners that provide both your next day’s lunch as well as a freezer portion to be thawed at some future date, you may want to stop. At least with rice.
Uncooked rice can contain spores of Bacillus cereus, a bacterium that can cause two different types of food poisoning. The first type is characterized by vomiting (and thus is called the emetic form). It results from consuming a toxin produced by the bacteria while they’re growing in your food and has a short incubation time of 1-5 hours. The second is characterized by diarrhea (and is non-surprisingly called the diarrhoeal form). It results from a toxin that is produced in your small intestine as the bacteria grow there and has a longer incubation time of 6-15 hours.
The two forms are commonly associated with different types of foods. The diarrhoeal form has been linked with foodstuff like soups, meat, vegetables and milk products including formula. The emetic form comes from a more limited list of culprits, as it's mostly associated with starchy foods that have been improperly stored like rice, pasta, pastries or sauces.
But what does “improperly stored” actually mean?
If a raw food is contaminated with B. cereus (as much rice is) and then cooked, some spores will remain in the cooked product (unless you're in the habit of heating your rice to above 120 ˚C for extended periods of time). These spores, If left standing in temperatures between 10 ˚C and 50 ˚C, such as on your stove or countertop, find themselves in their ideal environment (wet and warm) to germinate, grow and produce the toxin that will make you sick.
It doesn’t take long for the spores to reproduce either. A colony of B. cereus can double in size within 20 minutes if kept at 30˚C. The routine reheating of your food will not help to deactivate the toxin or kill the bacteria. Since this bacteria and its toxin are so resistant to heat your only hope of dodging food poisoning is to avoid allowing the bacteria to germinate.
To sidestep a nasty bout of illness caused by B. cereus you should aim to eat your food as soon as possible after it is cooked. If you can’t do that, then hot foods should be kept above 60˚C and cold foods, below 5˚C. Meats and vegetables should be cooked to an internal temperature of 60˚C and kept there for at least 15 seconds. Frozen foods should ideally be thawed in the fridge or as a part of the cooking process.
If storing leftovers for later, they should be rapidly cooled in the fridge as fast as possible (according to the NHS, within 1 hour is best). You should avoid storing hot leftovers in deep dishes or stacking containers together, as it will cause the food to cool slower. When reheating leftovers make sure they reach an internal temperature of at least 74˚C and don’t keep them for more than seven days, even in the fridge.
When dealing with high-risk ingredients (like rice, grains and other starchy foods) it’s best to not keep leftovers at all. But if you do, try not to keep them for more than one day, and never reheat them more than once. Even freezing doesn’t kill bacteria but rather just stops them from multiplying, so, by all means, freeze your leftover curry, but make fresh rice when it’s time to eat it again.
Considering the amount of improperly stored rice I now know I’ve eaten it seems almost a miracle that I haven’t gotten sick yet. Then again, food poisoning with B. cereus is often confused with the 24-hour flu, so I may have already paid for my mistakes without even knowing it.
Let’s all learn from my mistakes and start storing our leftovers properly.
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