Removing Air Bubbles in Canning Jars
Sometimes air is trapped between the food and the jar as the food is placed inside. After the food has been packed into the jar, any air bubbles (pockets of air) that are present must be removed. This can be done by placing a nonmetallic spatula or plastic knife inside the jar between the food and the side of the jar. Gently press the spatula against the food to create a path for trapped air to escape. Repeat several times around the inside of the jar. Even though air bubbles may not be visible, they can be trapped between pieces of food and must be removed. It is a good practice to use the spatula each time to remove any invisible air bubbles.
If additional space is created at the top of the jar after the air bubbles have been released, add more liquid to the jar to return it to the proper level before placing the lid on the jar. It is necessary to maintain the correct headspace to create a good vacuum seal.
Do not use metal knives or other metal or sharp utensils since they can scratch the glass and result in jar breakage. The high temperatures during heat processing stress the glass and may cause it to break along these weakened spots.
Trapped air bubbles in the jar produce too much air creating excessive pressure in the jar during processing. The pressure in the jar is greater than the pressure outside the jar during cooling. This imbalance interferes with the sealing process.
Air bubbles take up space. When there's trapped air between pieces of food before sealing the jar, the liquid level in the jar drops when the food is heated. These air bubble can prevent liquid from completely covering or surrounding the food, and may contribute to food spoiling. In addition, packing food without the proper amount of liquid in the jars results in floating and discolored food. Snuggly packed food eliminates air and allows enough liquid to completely cover the food with proper headspace. Air bubbles are more likely to happen with some types of foods than with others. Relishes and pickled vegetables and fruits are particular culprits.
If air bubbles still remain during processing, you may find that once the food cools and the liquid settles, certain foods, such as pickles, may end up protruding above the level of the liquid. This will produce unattractive food at the top of the jar once it discolors. It is best to refrigerate these jars and use them as soon as possible.