The mistake of storing leftover rice in the refrigerator causes poisoning

Many people have the habit of putting leftover rice directly into the refrigerator, but experts warn that this action can pose potential food safety risks. Doctor Yen Tong Hai, Director of the Clinical Toxicology Center at Truong Canh Hospital (Taiwan), said that Bacillus cereus bacteria has caused many large-scale food poisoning cases at schools. Most of these cases are related to improper storage of starchy foods such as rice and boxed lunches. The key point is not in choosing the refrigerator or freezer, but the time to put the rice in the refrigerator.

In response to opinions saying that white rice should not be kept in the refrigerator, many experts in the rice industry believe that the optimal way to handle leftover rice is to put it in a sealed container and store it in the freezer. They explain that the refrigerator temperature is often not cold enough to preserve rice perfectly, making the rice grains susceptible to food odors and losing surface moisture, leading to a dry, hard and less delicious texture. The ideal way is to divide the rice into specialized boxes and put it in the freezer as soon as the rice is still fresh.

The microwave is the best way to help frozen rice regain its delicious elasticity like when it was first cooked. When using this method, the rice does not need to be defrosted first; Just spray a little water on the surface and then spin at 500W for about 3 minutes and 30 seconds. In addition, using a rice cooker to steam rice for about 15 to 20 minutes is also a suitable option.

According to Dr. Yen, simply putting food in the freezer does not make food absolutely safer. The key lies in how to store it, meaning that after cooking food needs to be put in the refrigerator as soon as possible. If white rice is left at room temperature for many hours before being stored, Bacillus cereus bacteria may have had time to multiply and secrete toxins. At that time, even if you steam the rice again the next day, reheat it or roast it, high temperatures cannot destroy these harmful toxins.

Food poisoning caused by Bacillus cereus bacteria is divided into two main types. Based on health education materials from the Taiwan Food and Drug Administration, this type of poisoning includes vomiting and diarrhea. In particular, the type that causes vomiting is mainly related to foods containing starch and dishes made from rice.

Patients often have symptoms of nausea, vomiting, abdominal pain and other unpleasant feelings. The incubation period is quite short, symptoms usually appear after only about 30 minutes to 6 hours. In Taiwan, most previous large-scale food poisoning cases related to school meals originated from improper storage of rice, leading to the invasion of Bacillus cereus bacteria.

The form of poisoning that causes diarrhea often originates from more diverse food sources. The doctor said that unlike the form that causes vomiting, the type of poisoning caused by Bacillus cereus bacteria that leads to diarrhea has a relatively long incubation period. Foods that easily trigger diarrhea symptoms are very diverse, from sausages, sauces, broths to jams, salads and puddings.

Doctor Yen emphasized that some toxins secreted by Bacillus cereus bacteria have extremely good heat resistance, and this is also the origin of “fried rice syndrome”. The toxin that causes vomiting is so persistent that once the rice is contaminated, whether reheated or roasted at high temperature, the toxin still exists without being destroyed.

He further explained that the temperature in the refrigerator compartment is usually maintained at 4 degrees Celsius. This temperature level only inhibits the growth of microorganisms and cannot kill bacteria. If the rice has been contaminated with the emetic toxin of Bacillus cereus bacteria, this toxin will become extremely “stubborn” and cannot be removed by normal reheating methods.

According to Dr. Yen, in medicine there is a concept called “dangerous temperature zone”, specifically from 7 degrees Celsius to 60 degrees Celsius. Most microorganisms, including Staphylococcus aureus, E. coli bacteria, Bacillus cereus and Salmonella, can easily multiply and multiply quickly in this temperature frame.

The average indoor temperature usually falls around 20 degrees Celsius, completely within the above dangerous temperature zone. Therefore, it is ideal to refrigerate rice within one hour in summer and two hours in winter. Maintaining the refrigerator temperature at about 4 degrees Celsius will help food avoid the danger zone, thereby significantly reducing the risk of Bacillus cereus infection.