By KARLY HARRISON

University of Wisconsin-Madison Division of Extension FoodWIse

coordinator for Florence/Forest/Oneida/Vilas counties

Instructions for two unsafe methods of “dry canning” have been circulating through Facebook and other social media platforms. University of Wisconsin-Madison Division of Extension Food Safety Specialist Barb Ingham has provided the following information on “dry canning.”

One unsafe method of dry canning is “oven canning” of dry goods such as dry beans, nuts or flour. This method of preserving dry foods is not really canning and it is not considered safe. What makes this method unsafe? Even dry foods contain moisture. Common foods like dry flour, dry beans and dried fruits contain 11 to 30% of water or moisture.

By placing food in a heating oven moisture will move from the food and condense on the inside of the container or it could create pockets of moisture to form within the food. Once the container is sealed, these pockets of moisture could support the growth of mold, bacterial spores, and some pathogens.

The second unsafe method of “dry canning” involves placing raw vegetables such as, corn, green beans, carrots, and beets in canning jars with no added liquid, sealing jars, and pressure canning for the same amount of time as if you had added the required liquid. What does research tell us about “dry canning” of vegetables and other low acid foods?

— Pressure canning low-acid vegetables without liquid in jars is extremely hazardous. The liquid that we add to jars before pressure canning is required for safety.

— Liquid added to canning jars circulates heat inside the jars. As steam builds pressure inside the canner, the temperature inside the canner rises. Hot, circulating steam transfers heat to the glass walls of the jars. Liquid circulating inside the jars then picks up the heat from the glass and transfers the heat to ALL points inside the container to ensure safe product. This type of heating is also known as convection heating.

— Without added liquid food is heated by conduction. The food heats from the outside to the inside, similar to when cooking a roast. The time that it takes to heat the middle of the jar depends on the rate of heat transfer to the food and can take much longer than convection heating.

— Besides being an efficient way of transferring heat within the jars the liquid increases the “killing power” of heat on bacteria and bacterial spores.

Dry canning of vegetables presents the risk of botulism poisoning. To find out more about this deadly illness, go to the CDC website at www.cdc.gov/features/homecanning/index.html. Fortunately, there are research-tested recipes for home canning and preserving and following these recipes will yield safe, high-quality foods for you and your family. UW-Madison Division of Extension does provide safe preserving recipes on the Safe and Healthy Food for Your Family website at https://fyi.extension.wisc.edu/safefood/recipes/.

For more information on “dry canning” and food safety, contact Barb Ingham at bhingham@wisc.edu or the local Extension Office.

Learn more about the programs and services of UW-Madison Division of Extension Florence County at http://florence.extension.wisc.edu or call Jeanne Richard, Florence County FoodWIse educator at 715.528-4480, ext. 4.