Remove the screw band because a tightened band can hold the lid in place even when no vacuum formed, making the jar appear sealed. The correct sequence is to let the jars cool undisturbed after processing, remove the bands after 12–24 hours, and check each lid in three separate ways. A lid that stays in place without its band is, by itself, evidence of a vacuum seal.
Two separate pieces close a canning jar. The flat lid with its sealing compound creates the seal, while the screw band holds that lid in place during processing. After processing, the band’s job is done; the vacuum formed inside the jar now keeps it closed. If the band is left tight, it continues pressing the lid down mechanically, so a jar that never formed a vacuum can still look sealed. The defect in a jar that sits on the shelf for months may only be discovered when it is opened, though it could have been detected on the first day. Tightening the band too soon makes the check itself misleading.
After removing the jars from the pot, arrange them on one towel with space between each jar and leave them undisturbed to cool. Pressing the lid, shaking a jar, or tightening the band at this stage can interfere with the vacuum forming. A metallic click during cooling means the lid has been drawn inward and is a good sign. Check the jars after 12–24 hours; checking earlier means judging a process that may not be complete. Do not cool the jars in a draft or on a cold surface; a sudden temperature difference can crack the glass.
When the time is up, remove the screw band and check the lid in three separate ways. First, look at it: the center of the lid should be slightly concave. Second, press it; the lid should not move or make a sound as it is pressed and released. Third, and most definitively, lift the jar by the lid alone a few centimeters off the counter. If a vacuum formed, the lid will hold the jar. If even one of the three checks fails, do not put the jar on the shelf. Perform the lifting check low over the counter.
An unsealed jar does not have to be thrown away, but the options are limited. If the problem is found within 24 hours, refrigerate the jar and use its contents within a few days, or transfer the contents to a new jar, use a new lid, and reprocess it for the full time. Do not reuse the old lid. If the jar has been at room temperature for a long time, reprocessing is no longer a solution; the jar is not considered safe and should not be stored. Do not put off the reprocessing decision until the next day; decide the same day.
After removing the band, wipe the jar rim, label the contents and date, and store the jar without the band. Storing it without the band has another benefit: if the vacuum fails at some point on the shelf, the lid loosens and the change is visible, while a tight band can hide the same defect. Inspect each jar again before opening it. If the lid is bulging, you hear an unexpected hiss when opening it, or the smell has changed, do not open or taste the contents. Adding the processing method to the label also makes next season’s work easier.