Each year we receive questions about whether a canning practice is safe. Here are some of the unsafe practices still being used and why they are unsafe, based on information from the National Center for Home Food Preservation (NCHFP). For more information about canning visit NHFP at http://nchfp.uga.edu.
Canning a recipe you made up your self can be unsafe
NCHFP: Under-processed low-acid foods run the risk of allowing survival of Clostridium botulinum and its spores, and consumption of these foods can lead to botulism, an often fatal disease, and one that involves expensive health-care costs and health complications for those that do survive. Again, there is no formula for converting a process time for one low-acid food to another food or jar size. Too many characteristics of the particular food and processing procedures can influence the rate of heating. If you are experimenting with untested recipes for pickled products or other acidified foods such as salsas and there is not enough acid to treat them as a boiling-water canned food, you may also9 end up with the same risk of botulism by under-processing. Even if you have an acid food and do not process it long enough, food spoilage can result.
Using a small pressure saucepan/cooker to can foods is not recommended
NCHFP: Pressure cookers have less metal, are smaller in diameter and will use less water than pressure canners. The result is the time it takes a canner to come up to processing pressure (that is, the come-up time) and the time it takes the canner to cool naturally down to 0 pounds pressure at the end of the process (known as the cool down time), will be less than for the standard pressure canner. The come-up and cool-down times are part of the total processing heat used to establish USDA process times for low-acid foods. If the heat from the come-up and cool-down periods is reduced because these times are shortened, then the heat from the process time at pressure alone may not be enough to destroy targeted microorganisms for safety. That is, the food may end up under-processed. Under-processed, low-acid canned foods are unsafe and can result in foodborne illness, including botulism poisoning, if consumed.
Open-kettle canning and the processing of freshly filled jars in conventional ovens, microwave ovens and dishwashers are not recommended.
NCHFP: These practices do not prevent all risks of spoilage. Steam canners are not recommended because processing times for use with current models have not been adequately researched. Because steam canners do not heat foods in the same manner as boiling-water canners, their use with boiling water process times may result in spoilage. It is not recommended to pressure process in excess of 15 PSI be applied when using new pressure canning equipment. So-called canning powders are useless as preservatives and do not replace the need for proper heat processing. Jars with wire bails and glass caps make attractive antiques or storage containers for dry food ingredients, but are not recommended for use in canning. One-piece zinc porcelain-lined caps are also no longer recommended. Both glass and zinc caps use flat rubber rings for sealing jars, but too often fail to seal properly.
Green beans must be canned in a pressure canner.
NCHFP: Canning low-acid vegetables, meats, fish and poultry requires the use of a pressure canner. Spores of Clostridium botulinum bacteria, as found naturally in soils, are very, very heat resistant. Even hours in the boiling water canner will not kill them if they are inside your jars of beans. Left alive after canning they will eventually germinate into actively-growing bacterial cells that will produce a deadly human toxin when consumed. The bacteria like the conditions inside close jars of low-acid foods (such as vegetables and meats) sitting at room temperature, so they must be killed during the canning process for safe storage.
Jars of improperly canned vegetables and meats can contain the deadly botulism toxin without showing signs of spoilage. People who see their beans spoiling after under-processing them (not using enough heat when canning them) may also have jars that contain botulism toxin because they are showing signs of under-processing by other spoilage that might include cloudy, bubbling liquid and jars that pop open after initially sealing.