Crock pots and slow cookers are designed to cook food at a low temperature for several hours. Slow cookers heat the pot insert from underneath whereas a crock pot is heated by electrical elements that surround the pot insert. Tough cuts of meat can be tenderised using this cooking method and meals can be prepared ahead of time and left to cook so the meal is ready by the time you get home from a day out.
Pathogens (bacteria or viruses that cause illness in people) exist in the environment and on food but usually in harmless quantities. Pathogens can multiply to dangerous levels if food is stored or cooked at inadequate temperatures. Because food cooks at lower temperatures and for a longer period in a slow cooker or crock pot, the risks of this happening may be higher if care is not taken. However with careful food handling and preparation combined with the safe cooking temperatures and times, you can reduce the risk of getting sick from pathogens in slow cooked food.
Pathogens are in the soil, water and environment and are part of the normal gut flora of many animals and are usually harmless to them. Ingredients of plant or animal origin may carry small numbers of pathogens picked up during slaughter, harvest or processing, and can easily contaminate other foods via drips, or by dirty hands or equipment. These pathogens include Salmonella enterica, Campylobacter jejuni, Escherichia coli O157:H7, Staphylococcus aureus, Clostridium perfringens and Bacillus cereus.
Slow cooker temperatures are lower than most other cooking methods and cooking times are considerably longer, typically 5 - 9 hours. The core temperature of food in a slow cooker must reach at least 60oC for pathogens to be reliably reduced. The cooker itself heats to 77oC -138oC which ensures the eventual core temperature is typically 70oC - 80oC.
Remember that it is important that your slow cooker reaches safe cooking temperatures for a period of time that is long enough to destroy pathogens.
To make sure your slow cooker reaches a safe cooking temperature, follow these steps:
1. fill your cooker two-thirds full with luke-warm tap water and turn it on to ‘low’
2. after two hours check the water temperature with a food thermometer. It should record at least 70oC.
Temperatures below this may indicate that your slow cooker isn’t heating the food sufficiently to avoid potential food safety problems. You should check the manufacturers’ specifications to determine whether the appliance needs to be serviced.
• always defrost meat thoroughly before putting it in your slow cooker. This will ensure it reaches the required temperature rapidly and consistently
• store perishable foods like meat in your fridge until they’re needed
• cut meat into small pieces, or follow manufacturers’ instructions for large meat joints and whole poultry
• place vegetables that cook more slowly at the bottom and around the sides of the pot, then add the meat
• how full you have your cooker, and the amount of liquid in the recipe are important to how safely your food cooks. Follow the recipe.
• don’t leave raw ingredients sitting in the slow cooker at room temperature – start the cooking process straight away
• remove the lid only when you need to stir or to check that the food is cooked, and always cook with the lid on the pot. The longer the lid is off, the more heat is lost from your meal and it will take longer to cook through
• follow manufacturers instructions for safe cooking temperatures and times, specific to the recipes for your particular make and model.
• if you have leftovers, they must be cooled quickly so that the food passes through the temperature danger zone (especially 15oC – 45oC1) without giving pathogen spores a chance to germinate. Use a shallow container that allows the food to spread out.
• food should be left to cool at room temperature for two hours and then refrigerated
• if you want to reheat food and keep it hot, use a conventional oven or microwave to heat it thoroughly, then use the pre-heated slow cooker to keep it hot.
• if you are at home when the power goes out, finish cooking the food immediately by some other method.
• if the food has just finished cooking, and you can maintain that temperature, you may keep the food hot until you’re ready to eat it
• if your meal has cooked during the day and you get home to find the power has been off, throw away the food – even though it may seem cooked and hot. Toxins that are heat stable (not broken down at high temperatures) may have been produced by some bacteria during the power outage.
You cannot cook dried red kidney beans from their raw state in a slow cooker because it won’t reach a high enough temperature to destroy the natural toxin phytohaemagglutinin which is found in dried red kidney beans2. You must soak and boil dried red kidney beans before use:
• soak the red kidney beans in water for at least five hours
• pour away the water and, using fresh water, boil them rapidly for 10 minutes to destroy the toxin.
The beans are now safe to be used in your slow cooker. Alternatively, canned red kidney beans are safe for immediate use.
1 Note that in general, pathogens can multiply between 4oC and 60oC
2 USFDA (1992). Phytohaemagglutinin Fact Sheet: Bad Bug Book http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm071092.htm