The AnswerLine Team receives many phone calls and emails regarding canning mistakes—incorrect processing time, canner wasn’t vented, wrong size jars used, forgot to add acid to tomatoes, incorrect headspace, hot water canner used for low-acid foods, elevation not considered–just to name a few. Mistakes happen but the biggest mistake of all is the assumption, “BUT, MY JARS SEALED!”
A SEALED JAR DOES NOT EQUAL A SAFE PRODUCT if a canning mistake has occurred, a recipe has been altered, or if an untested recipe was used. In the canning process, jars of food are heated to destroy pathogens, expel air, and create a vacuum seal. While this process provides shelf stability, it is also the perfect environment for food borne bacteria, especially Clostridum botulinum, to germinate and produce toxins when a tested canning procedure is not followed. In that ‘sealed jar,’ conditions favorable to producing the “perfect bacterial storm” exist:
MOISTURE,
‘DANGER ZONE’ TEMPERATURES that allow for bacterial growth (40⁰F – 120⁰F),
ABSENCE of OXYGEN (anaerobic) resulting from the air being driven out during processing, and possibly a LOW ACID food. (Foods high in acid, like most fruits, or foods to which acid was added, such as vinegar to pickles, are less susceptible to bacterial growth.)
IF YOU MAKE A MISTAKE, ACT QUICKLY.
Canning mistakes can only be rectified in the first 24 hours. Within that time, they can be reprocessed, frozen, or refrigerated for quick use. After 24 hours, the food needs to be disposed as it is no longer safe. This is also true for jars whose lids did not seal.
Reprocessing means following the same processing that would have been done if starting with fresh food—empting and washing jars, reheating, re-filling jars, using new flat lids, and processing with correct time and weight (pressure canning). Most foods do not tolerate reprocessing very well. Quality is diminished as they usually end up soft and mushy. Soft foods, such as applesauce, handle reprocessing better than foods with structure.
When reprocessing isn’t a good option, freezing is. Remove the contents from the jar and put into freezer containers or bags, label and freeze. Leaving food in the original canning jars is not recommended unless some of the contents are removed to allow for freezing expansion.
One may also put the jars into the refrigerator and use the contents within 3 days. This is a good option with small batch canning, but may not be so when 7 quart jars are in question.
Home canning is about following the science to make a SAFE product by preventing foodborne illness. One can never assume the contents of a sealed jar are safe if there has been any alteration to the recipe or procedure, whether intentional or by mistake.
Safe head safe for corn cob jelly. I seen where people can it below the quarter mark on jar, is this safe?
Hi Beja, the USDA recommendation for jams and jellies is 1/4 inch headspace. Headspace is an important consideration. The air in a food, its starch content and the processing temperature determine how much a food will expand. Air expands greatly when heated to high temperatures; the higher the temperature, the greater the expansion. If too little headspace is allowed, the food may expand and bubble out when air is being forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor and in some cases, actually mold. Also, the jar may not seal properly because there will not be enough processing time to drive all air out of the jar.