One of the problems some home food preservers face is having jars that do not seal. There can be a number of reasons why a jar may not seal. Sometimes it has to do with not following canning instructions as written. Faulty lids and rings can also prevent jars sealing. Failing to screw the bands or rings on tight enough and screwing the bands on too loosely can result in jars that do not seal. An important instruction provided in canning guides that home food preservers do not always follow is to leave adequate headspace in the jar.
What is headspace?
Headspace is the extra space at the top of the jar between the food and the lid. The goal of canning is to create a vacuum seal that does not allow air to enter the jar. Headspace plays an important in creating a successful vacuum seal.
Too little headspace
Sometimes home food preservers will try to pack as much food in a jar as possible. The result is too little headspace. When there is too little headspace, food can boil out of the jar as air is being expelled during processing. Some foods may expand when heated, increasing the likelihood of product boiling out of the jar. As a result food particles can become stuck between the rim of the jar and the lid, preventing the jar from sealing properly.
Too much headspace
If there is not enough food in the jar, there will be too much headspace. Too much headspace can result in food that is discolored and unappealing. When the jar is opened the food might look like it is unfit to eat. Failing to put enough food in a jar can also cause the jar to hold too much air. In this case if the jar is not processed long enough to drive out the extra air, an adequate vacuum seal will not be created.
How much headspace is required?
Even though the concept of headspace seems simple enough, home food preservers often forget to follow the headspace rules. The amount of headspace required depends on the type of product being preserved. Generally about one fourth inch of headspace needs to be allowed when canning jams, jellies and fruit juices. For fruits, leave about one half inch of headspace. Vegetables require one inch of headspace.
Always abide by headspace rules. Using the correct amount of headspace can reduce the risk of having jars that do not seal. When jars don’t seal properly food can spoil or bacteria thrive and cause food to become unsafe to eat.