How to Seal Lids for Canning

Using the jar lifter helps you avoid touching the jar lid after processing.

If you look at a sealed, home-canned jar, you'll see a thin lid sitting atop the mouth of the jar with nothing apparently holding the lid of the jar in place. In fact, what affixes the lid to the jar is something you can't see, namely air pressure. The pressure on the inside of the jar is lower than outside, causing the outside air pressure to seal the lid's rubber gasket firmly to the mouth of the jar. To get a canning lid to perform this bit of "magic," all you need is correct canning technique.

Things You'll Need

• Canning jars filled with a high-acid food
• Canning lids and rings
• Thin, flexible spatula
• Hot water bath canner with lid
• Canning rack
• Jar lifter
• Water
• Cooling rack

Instructions

1. Inspect your jars. Look for nicks or scratches along the rim of the jar. If your jars are damaged, the lid can't create a tight seal to them.

2. Fill the jars properly. Jars require an appropriate amount of headspace. The typical headspace for jars of high-acid food going into a hot water bath canner is 1/2 inch. Too little headspace can cause foods to expand and run out while they are being processed, thereby breaking the seal. After filling the jar, run a flexible spatula around the inside of the jar to release air bubbles. Then add more liquid to adjust the headspace.

3. Wipe the rim carefully. Even small bits of food between the rim and the lid can cause jars to fail to seal.

4. Inspect and boil your lids. Look for any scratches or gaps in the gasket. Defects can cause the lid to fail to seal. Boil the lids according to the manufacturer's instructions. Don't let them cool down before using them.

5. Tighten the bands properly. You want the lid to be tight enough not to let liquid out but not so tight that heated air can't escape. If the band is too loose, food can boil out and create a seal break. If the band is too tight, heated air won't escape, and the jars will have too much pressure inside to create a proper seal.

6. Lift the jars into and out of the canner with a jar lifter. Doing so allows you to keep the jars level, preventing food from getting between the jar rim and the lid. Set them upright on the canning rack. Don't tilt them or lay them on their side.

7. Cool the jars after processing without touching them. Don't tighten the bands. Don't push on the lids. Don't touch the jars at all for 12 to 24 hours. As the jar cools, the pressure inside it will fall, and the lids will seal. Touching them as they are cooling can jostle the connection between the jar and the lid, breaking the seal before its set.

Tips & Warnings

• If you want more detailed instruction on how to home-can food, check out the USDA's "Principles of Home Canning," available online. It can give you detailed instruction and safety tips.

• Never can food without a thorough knowledge of canning safety. Improperly canned food can become contaminated with botulism and can kill you.

• If your lids are old, they won't seal properly. When you get a box of lids, date the box. Try to use them all within a year or two. If they get more than five years old, throw out the box. Also, never use used lids.

References

• University of Minnesota; Use Good Ingredients, Methods when Preserving Foods; Carol Ann Burtness; July 2005
• Univeristy of Minnesota Extension; Home Canning Equipment; Carol Ann Burtness
• University of California Cooperative Extension; How to Ensure a Good Seal

Resources

• USDA: Complete Guide to Home Canning
• University of Missouri Infonet: Canning - Why Lids Don't Seal