Instructions have been circulating for ‘dry canning’ of products such as dry beans, flour, and pasta. Just because this process uses traditional canning jars, it isn’t ‘canning’ and, according to the National Center for Home Food Preservation, this method of food preservation may not be safe. What is canning? Canning as a method of food preservation or processing refers to a procedure of heat-treating closed containers of moist food for long enough, and at a high enough temperature, (using an approved recipe!) so that, after processing, the food can be safely stored in an air-tight container at room temperature. Food that is canned using an up-to-date, research-tested recipe can be safely stored on the shelf for an indefinite period of time.
Why dry canning isn’t canning. “Dry canning” techniques generally call for putting dried food like grains, beans, or nuts into canning jars, placing lids on the containers, and then heating sealed jars in an oven, usually at around 200°F . In other directions, the food in jars is heated without the lids, which are then placed on the jars when they come out of the oven.
What may make dry canning unsafe. Even dry foods contain moisture. Common foods like dry flour, dry beans and even dried fruits contain 11-30% moisture (water). Placing any food in a heating oven causes moisture to ‘move’ or migrate towards the surface of the food where the moisture may evaporate. Moisture migration in dry foods can actually cause pockets of moisture to develop within a food or moisture to condense on the inside of the container. Once the container is sealed, these pockets of moisture could support the growth of mold, bacterial spores (think Clostridium botulinum), or even some pathogens such as Salmonella that are resistant to drying. This could be especially true of home-dried foods that are ‘canned.’
Dry canning may also cause product quality to deteriorate. Lipid (fat)-containing nuts and grains show increased oxidation on heating; so nuts and whole grains may go rancid more quickly if subjected to dry ‘canning.’
Oven canning is never a recommended or approved method. Dry canning may have developed from the unsafe process of ‘oven canning.’ In oven canning, food is placed in a sealed canning jar and heated for a period of time in the oven until the process is ‘done.’ The ‘oven canned’ product is stored on the shelf. Oven canning has incorrectly been touted for preserving of meat and poultry, and presents a real risk of botulism poisoning. The only way to safely can meat or poultry is to use a pressure canner. See B3345 in the Wisconsin Safe Food Preservation Series.
What are safe ways to store dried foods like nuts, beans and flour? Thoroughly dried foods may be stored in airtight containers at moderate room temperatures or in the freezer. If you want to vacuum seal containers of dry foods, methods that may preserve them safely and may retain quality include*:
- Using a vacuum-sealing machine that has adapters for jars (FoodSaver is one manufacturer). No heating is involved so the food retains quality.
- Using oxygen absorbers inside jars of food (sold at retailers such as WalMart). Oxygen absorbers may help preserve the quality of foods and may aid in insect control.
*Provided for purposes of illustration. Neither of these methods is recommended nor endorsed. Utah State University has created a comprehensive guide on storing food, A Guide to Food Storage for Emergencies.