“My jars of homemade raspberry jam exploded in my cupboard!” my exasperated caller told me.
At the time of our conversation, she was taking a break from scrubbing sticky jam from her pantry walls.
As we visited, another jar of jam flipped its lid and spewed its ruby red contents.
Although I had heard about canned goods building up gas inside the jars and popping their tops, I hadn’t talked to someone in the middle of the experience.
Did I mention that she was not happy? Her language was as colorful as her walls.
Her pantry must have looked like a scene from a horror movie. I probably would have run out the door. This brave woman was tackling the mess.
We talked about safe cleanup procedures. She was wearing rubber gloves and using an appropriate disinfectant, so that was good.
She wanted to know what had happened and how to prevent it in the future. We talked through all the steps she had taken.
She had used a recipe formulation that was still valid. She was using two-piece lids, not paraffin wax, to seal the jars. This was consistent with what we recommend.
As we visited, we figured out the likely reason for the colorful mess. Turns out, the recipe she was using did not recommend boiling the filled jars of jam in a water-bath canner for a specified time (usually five minutes, sometimes longer depending on the altitude where you live).
Sometimes old recipes or online recipes do not include this information.
The U.S. Department of Agriculture has recommended a boiling-water bath process for jams and jellies for many years. Because her lids had sealed, she thought she would be enjoying homemade jam in the winter.
Why did this happen? If microorganisms are not deactivated by sufficient heat for the right length of time, some can produce gas in an airtight container.
I visited with a microbiologist later that day. The raspberry jam jars likely had a “prolific gas-producing type of bacteria.” It was not as dangerous as the type that causes the potentially deadly botulism foodborne illness.
Of course, you would not want to taste food from a foaming jar.
When you preserve food, you are a scientist using principles of chemistry and physics in your home kitchen. Follow the directions on research-tested recipes closely.
Fruit-based jellies and jams are acidic, so the type of organism that can produce a deadly toxin would not grow in this environment.
However, don’t get creative and add extra ingredients to your canning recipes.
The boiling-water bath processing of jams and jellies prevents mold growth (until the jar is opened) and ensures a tight seal.
Lately, I am hearing comments from people whose jar lids pop open even though they sealed at first. This is a different issue and more likely linked to the preparation or application of the lids.
Be sure to follow the directions on the lid box. Most manufacturers do not recommend boiling the lids, even if your grandma or mom always did that. Most of the time, you do not have to warm the lids at all.
According to canning experts at the corporation that produces Ball canning jars, the practice of pre-warming lids dates back before 1969. In earlier canning, people used red rings made of latex, which required heating to soften the plastic.
According to Ball, “Wash lids and bands in hot, soapy water. Do not use abrasive materials or cleansers that might scratch or damage the coatings applied to the lids and bands. Rinse them under hot water. Dry lids and bands and set aside until they are needed.”
If you experience sealing failures, did someone with a powerful grip apply the screw bands too tightly? The screw band should be applied fingertip tight using your thumb and ring finger.
Perhaps the jar rim is chipped, or maybe the rim of the jar has food particles. Inspect your jars and wipe clean the jar lids.
By the way, you can remove the screw bands before storing your canned goods.
If you are the recipient of home-canned foods, don’t be shy about asking questions about the canning method used. In some cases, it could save your life. If someone has “oven canned” or “dishwasher canned” a food, politely decline. Those are not safe methods.
We at NDSU Extension have many resources to help you preserve food safely and be proud of the quality of the product. For free, research-tested recipes from the U.S. Department of Agriculture and universities throughout the U.S., see https://www.ag.ndsu.edu/food and click on “Food Preservation” whether you want to can, dry, freeze, cure, ferment or pickle.
Strawberries and rhubarb are “in season,” so consider this tasty recipe as an introduction to food preservation. For best quality, use home-canned foods within a year of canning them. They will be safe longer, though.
Rhubarb-Strawberry Jam With Pectin
1 cup cooked red-stalked rhubarb (about 1 pound rhubarb and 1/4 cup water)
2 1//2 cups crushed strawberries (about 1 1/2 quart boxes)
6 1/2 cups sugar
1 pouch liquid pectin
Wash rhubarb and slice thin or chop; do not peel. Add water, cover and simmer until rhubarb is tender (about one minute). Sort and wash fully ripe strawberries: remove stems and caps. Crush berries. Measure prepared rhubarb and strawberries into a kettle. Add sugar and stir well. Place on high heat and, stirring constantly, quickly bring to a full boil with bubbles over the entire surface. Boil hard for one minute, stirring constantly. Remove from heat and stir in pectin. Skim. Fill hot jam immediately into hot, sterile jars, leaving 1/4 inch head space. Wipe rims of jars with a dampened clean paper towel; adjust the lids and process the jars
This makes about seven or eight half-pint jars. One serving (1 tablespoon) has about 40 calories, 0 grams fat, zero grams protein, 11 grams carbohydrate, less than 1 gram fiber and zero milligrams sodium.
(Julie Garden-Robinson is a North Dakota State University Extension food and nutrition specialist and professor in the Department of Health, Nutrition and Exercise Sciences. Follow her on Twitter @jgardenrobinson.)