Can reheating rice cause food poisoning?
Yes, you can get food poisoning from eating reheated rice. It's not the reheating that causes the problem, but the way the rice has been stored before it's reheated.
How does reheated rice cause food poisoning?
Uncooked rice can contain spores of Bacillus cereus, bacteria that can cause food poisoning. The spores can survive when rice is cooked. If rice is left standing at room temperature, the spores can grow into bacteria. These bacteria will multiply and may produce toxins (poisons) that cause vomiting and diarrhea. The longer cooked rice is left at room temperature, the more likely it is that the bacteria or toxins could make the rice unsafe to eat.
Symptoms of food poisoning
If you eat rice that contains Bacillus cereus bacteria, you may be sick and experience vomiting or diarrhoea about 1 to 5 hours afterwards. Symptoms are relatively mild and usually last about 24 hours.
Tips on serving rice safely
Ideally, serve rice as soon as it has been cooked.
If that is not possible, cool the rice as quickly as possible (ideally within 1 hour).
Keep rice in the fridge for no more than 1 day until reheating.
When you reheat rice, always check that it's steaming hot all the way through.
Do not reheat rice more than once.
Sushi and food safety
Sushi is ready-to-eat cooked rice that has been acidified with a vinegar solution and formed with a variety of ingredients including raw or cooked seafood, fresh chopped vegetables, cooked egg, etc. Ready-to-eat sushi is considered a potentially hazardous food and must therefore be handled with care to prevent foodborne illness. The health risks associated with sushi arise from the raw seafood products used in preparation and the acidified sushi rice. Raw seafood may contain the infective form of parasites such as Anisakinae and Diphyllobothrium. Sushi rice is traditionally held at room temperature which may support the growth of pathogenic bacteria if not uniformly and adequately acidified. Food operators must ensure that sushi is kept at 5°C (41°F) or below during transport, storage, and display.
Definitions Acidified Rice - Cooked rice with vinegar added to achieve a pH of 4.6 or less
Approved Source - A source that has been determined to conform to principles, practices, and standards that protect public health.
Cross-contamination - Means the transfer of harmful substances or disease-causing microorganisms to food by hands, food-contact surfaces, sponges, cloth towels and utensils that touch raw food, are not cleaned, and then touch ready-to-eat foods. Cross-contamination can also occur when raw food touches or drips onto cooked or ready-to-eat foods.
Hangiri - A round, flat-bottom wooden tub or barrel used in the final steps of preparing rice for sushi.
Potentially hazardous food - Any food that consists in whole or in part of milk or milk products, eggs, meat, poultry, fish, shellfish, edible crustacea, or other ingredients, including synthetic ingredients, in a form capable of supporting rapid and progressive growth of infectious or toxigenic microorganisms, but does not include foods which have a pH level of 4.6 or below or a water activity value of 0.85 or less.
Shamoji - Japanese term for the spatula or spoon used to turn and spread the sushi rice.
Sashimi - Thin slices or slabs of raw fish that are presented ready-to-eat.
Sushi - Ready-to-eat cooked rice that has been acidified with a vinegar solution and formed with a variety of ingredients including raw or cooked seafood, fresh chopped vegetables, cooked egg, etc. Product forms can include:
• nigiri – small balls of rice with ingredients on top,
• maki rolls – layers of rice and nori sheets rolled with a bamboo mat to form cylinders that contain various fillings, and hand rolls – cone shaped rolls formed by a sheet of nori filled with various ingredients.
Sushi-grade - Freezing and storing seafood at-20°C (-4°F) or below for 7 days (total time), or freezing at-35°C (-31°F) or below until solid and storing at -35°C (-31°F) or below for 15 hours, or freezing at -35°C (-31°F) or below until solid and storing at -20°C (-4°F) or below for 24 hours.
Sushi Rice - Cooked short grain rice mixed with vinegar and other ingredients such as sugar and/or salt.
Surimi - A type of gelled fish paste that can be used to make simulated seafood products such as fabricated crab meat that can be used in sushi.
Tamago - Is the Japanese omelet commonly used in maki, nigiri and Temaki sushi. Unlike a regular omelet, the tamago is made with sugar, soy sauce, and mirin.
Purchasing and storing foods A. Supplier and food information
It is imperative to obtain seafood products only from approved, reputable sources. Upon purchasing frozen seafood products, request written documentation from the supplier to ensure the product meets parasite reduction freezing requirements.
Only buy foods that are within their use by date or best before date.
B. Ready-made sushi
Only buy sushi that has been transported in refrigerated vehicles.
Sushi must be kept refrigerated at 5°C (41°F) or less.
Sushi must be covered during purchase and storage to protect against contamination.
C. Potentially hazardous raw ingredients
Potentially hazardous foods and raw materials will need to be stored refrigerated. This would include meat, chicken, seafood, non-acidified cooked rice and dairy products.
Only buy potentially hazardous foods that have been transported under temperature control.
All potentially hazardous foods must immediately be placed under refrigerated storage at 5°C (41°F) or less.
Only sushi-grade tuna or fish should be used in raw fish sushi.
Refrigerated raw ingredients must be stored separately from finished sushi and ready-to-eat foods and ingredients such as tuna or salmon.
Raw foods such as uncooked chicken and meat must not be placed above ready-to-eat foods in the refrigerator, to prevent the raw juices from dripping onto them.
Refrigerated ingredients must be covered during receipt and storage to protect against contamination.
D. Shelf-stable foods
Shelf-stable foods include uncooked rice, seaweed (nori) sheets, wasabi powder and pickles.
When buying shelf-stable foods make sure that the packaging is intact.
Shelf-stable foods must be covered during storage to protect against contamination.
E. Frozen foods
All frozen foods must be received in a frozen state.
If foods are to be kept frozen, they must be placed in a freezer immediately.
When buying and storing frozen foods, ensure they are adequately covered and the package is intact.
Parasite Destruction for Raw Fish
Seafood products to be served raw must have been frozen at a temperature of –20°C (-4°F) for 7 days or below –35°C (-31°F) for 15 hours, to destroy parasites that might be present.
Preparing Sushi
Preparing sushi involves a great deal of handling of both raw and cooked foods. Because sushi is eaten without any further cooking it is important that it is prepared correctly and safely.
A. Equipment and utensils
With the exception of bamboo mats, wooden utensils must not be used for food preparation. All utensils must be able to be easily cleaned.
Only clean and sanitized equipment must be used when preparing sushi.
It is recommended that prior to preparation all benches and utensils which come in contact with the sushi and ingredients are sanitized.
Sushi rolling machines must be periodically cleaned and sanitized during the day to remove the build-up of rice and destroy pathogenic bacteria. Other utensils and equipment will also need to be periodically cleaned to remove build-up of rice and other ingredients.
Boards and utensils must be cleaned and sanitized between uses, especially when preparing foods that will not be further cooked (eg. raw fish and cooked teriyaki chicken).
Bamboo and plastic mats must be cleaned and sanitized daily. If bamboo mats are used then it is recommended that they be covered with clean cling wrap and the cling wrap changed at least every 2 hours.
B. Preparation of acidified rice
Rice must be cooked before acidification. The rice must be cooled rapidly to 5°C (41°F) from the time it has been taken out of the rice cooker.
Proper preparation of acidified rice is important to ensure the rice is safe to use. Rice acidified to a pH of less than 4.6 will inhibit the growth of pathogenic bacteria. Acidification of rice should occur as soon as possible after cooking.
The pH of the rice is to be checked to ensure proper acidification has occurred. Once acidified, the rice must be stored covered when not being used.
Acidified rice can be stored up to 8 hours and at the end of the day, the remaining rice must be discarded. Note: If cooked rice is not acidified, it must be stored under refrigeration at or below 5°C (41°F) at all times.
C. Preparation of fillings and sushi
All potentially hazardous raw materials should be kept under refrigeration until used, especially for raw fish.
Frozen foods are to be thawed under refrigeration, in a microwave oven, or under cold running water.
Vegetables must be washed under running potable water before use.
Meat and chicken must be thoroughly cooked.
Prepared potentially hazardous ingredients (e.g. cooked chicken, tamago) must be placed under refrigeration after cooked and when not being used.
Once prepared, sushi should be placed under refrigeration (at 5°C/41°F or less).
Businesses with limited storage and display space should only make an amount of sushi that can be properly placed within the storage or display section. Sushi must not be left unrefrigerated.
References
AlbertaHealthServices.(2004) GuidelinesforthePreparationofSushiProducts. www.albertahealthservices.ca
NSW Food Authority. (2007) Food Safety Guidelines for the Preparation and Display of Sushi.www.foodauthority.nsw.gov.au
United States Food and Drug Administration. Food Code. (2009) http://www.fda.gov/
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