Adjusting Lids and Bands on Canning Jars
After each jar is filled and the jar rim cleaned, use a magnetic lid wand, or kitchen tongs to remove a lid from the hot water and place the lid on the jar rim. Hold it in place and remove the wand or release the kitchen tongs. Center the sealing compound on the glass being careful not to touch the sealing compound. Only the sealing compound should be touching the glass. Place a screw band over the lid and screw it onto the jar just until a point of resistance is met -- fingertip tight. The adjustment of the band should be firm and snug, but not as tight as you can make it. Once the screw band is in place, the sealing compound will mold to the rim of the jar. Use a jar lifter and place the jar onto the canner rack in the canner.
A lid wand is a long, plastic rod that has a magnet attached to one end. The magnet grabs on to the lid and lifts it out of the hot water keeping your hands safe and dry. This inexpensive gadget is better than trying to get the uncooperative lids (they tend to slide and stick to one another) out of the pan using a pair of kitchen tongs.
During processing in a hot water bath (boiling water) or pressure (steam pressure) canner, air is forced out under the lid as the contents inside the jars heat and expand. After the jars are processed and removed from the canner, the contents start to cool, the remaining air inside the jar contracts, forming a vacuum, and pulls the lid down firmly against the jar forming a tight seal. As the jars cool, the sealing compound will set up firmer and the vacuum inside the jars will keep the lids in place.
Screw bands showing any signs of rust should be discarded and not used. The rust may prevent the screw band from being screwed down firmly on the jar. Without a firm pressure on the lid during processing, some of the preserved food or liquid inside the jar may escape with the air. Food or liquid trapped between the jar and the lid may not allow a vacuum to form in the jar, preventing a tight seal.
Screw the bands, sometimes called rings, on firmly by hand but do not twist too tight. The band must be snug enough to keep the preserved food from seeping out from under the lid during processing, while still allowing air to escape and form a vacuum in the jar. If the screw bands are tightened down too much, the jars may not vent properly and the lids may buckle or the jars may break from the pressure inside the jars. Screwing the bands on with excessive force will also cause the sealing compound to squeeze out from between the lid and the jar, resulting in a poor seal. On jars where the lids and screw bands are applied too tightly, the seals may fail a day or two after processing.
During the processing, the screw band may loosen. Never retighten any loose screw bands after processing. This can force the still soft sealing compound to squeeze out from between the lid and the jar, allowing air back into the jar and causing the seal to fail. After processing, wait until the jar and contents cool completely before finger tightening the band. The screw band doesn't need to be tight since the lid is firmly attached and the band has no effect on the jar being kept sealed. Also, sometimes if you tighten the band before the contents have completely cooled and the band and jar have dried, the band will stick to the side of the jar (especially if there is a little rust on the band). You may never be able to remove the band and enjoy the contents of the jar, you will not only loose the contents but the glass jar as well.
The purpose of the screw band is to tightly hold the lids in place on the jars during processing. It is not necessary to keep them on the jars during storage. The bands may be removed from the jars 24 hours after processing, when the jars have completely cooled and sealed.