The gardening explosion across the nation due to the recession and the desire for home-grown food means that many people will soon have fruits and vegetables to can or freeze, but a food-safety specialist in Penn State's College of Agricultural Sciences says "putting up" your harvest is not as simple as going back to Grandma's favorite canning recipes.
While the home-canning process has been around for hundreds of years, said Luke LaBorde, associate professor of food science, scientific research into safe food preservation techniques is revealing that the old ways aren't always the best.
"It was only recently -- in the last 10 to 20 years -- that scientific studies on home food preservation were conducted and accurate processes were determined," he said. "In the old days, your great aunt might have used a recipe for canned green beans that used a boiling water bath, and nothing bad happened -- perhaps, that she knows of. But there's always the chance that that process will allow clostridium botulinum contamination. So, we have to gently recommend to such people that they really shouldn't be using old recipes, that we should be using the tested recipes."
LaBorde said it's wise for both new and seasoned canners to invest a little time learning the proper way to preserve the fruits of their labor.
"The first thing people should do is learn a little about the different techniques of pressure cooking and boiling-water bath processing used in canning," he said. "They have to know the difference between certain kinds of low-acid vegetables and more acidic fruits. Each fruit or vegetable requires its own specific canning variation, and we recommend that people only use those recipes and methods that have been developed to be safe for each type of food."
Low-acid foods such as green beans, corn and mushrooms require processing in a high-pressure canner, he said, while more acidic foods such as strawberries, cherries, grapes, apples and other fruits require processing in a boiling-water bath. LaBorde also warns against revising recipes, since safe preservation is a combination of food selection, heating/cooling technique, equipment and other factors.
"For instance, heat is what kills the bacterial spores in low-acid products, and there are many things that influence the amount of heat that penetrates into that product," he said. "The size of the particles, the ratio of food to brine, and the type and size of the package all play a role in the time and pressure requirements for the process -- it's not one-size-fits-all."
For the rookie canner, LaBorde said, boiling-water bath canning is the method to start with -- it's easier to use and requires less expensive equipment than pressure canning.
"The equipment is inexpensive, the techniques are easy and if you make a mistake, it will only affect the food quality -- the jam will be a bit runny or the pickles not the right texture," he said. "But there's no critical food-safety hazard in that area. Then, if you decide that you're committed to home food preservation and you're going to be doing it in the future, go out and get a pressure canner. They're more expensive and you should take a course to learn to use it."
Canners also have to separate traditional canning recipes from the unsafe practices such recipes call for. LaBorde said he's found it hard to quell familiar-but-risky practices including turning jars of homemade relish upside-down for several minutes in hopes that jars will seal themselves, pouring hot food into a canning jar and waiting for the lid to "pop" (also known as "open kettle canning"), and canning soup made from homemade recipes (since soup is a low-acid product with greater risk of unstable recipes).
"Food is a very emotional issue," he said. "There are the brand-new canners who've found Grandma's old recipe for green beans, and often it's associated with family get-togethers and good times. Others have been canning for 40 years and are sure that their methods are safe. We want to lead these people to the newer, tested recipes, so we gently recommend to these people that the newer recipes are just as tasty."
Detailed canning information is available on the Home Food Preservation Web site at http://foodsafety.psu.edu/preserve.html. "Let’s Preserve" is a free series of 13 fliers on canning and freezing a variety of fruits and vegetables available from your county Penn State Cooperative Extension office or from the Penn State Home Preservation Web site.