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Sterilization involves applying heat to kill germs and the like.

• See also Cleaning and deodorizing mason jars

It might be possible to wash but not sterilize, since vinegar's acidity natural inhibits microbial growth. In that case, expect markedly lower shelf life, or a shelf life that necessitates refrigeration. If not sterilizing, you'd have to be very careful about what things touch what. Even "clean" hands and washed surfaces have bacteria, and you must reduce or eliminate contact with them.

Sterilizing mason jars ∞

• Inspect all jars for chips and cracks
• Hand-wash them carefully with dish detergent and water

• Rinse them thoroughly

Do one of:

• Stovetop sterilization:

  • Heat jars under hot tap water to avoid thermal shock.
  • Elevate the jars from the bottom of the pot. This avoids extreme heat at that contact point which would cause a thermal shock (see below). Use a canning rack, a screw band, or perhaps a dish towel so long as it doesn't wrap around the jars.
  • Do not have the jars touch the sides of the pot.
  • If you're at higher altitudes, add 1 minute for every 1,000 feet above sea level.
  • If you cannot submerge them upright because your pot is not tall enough, then a slight slope with the entry upwards is acceptable. Perhaps try propping up one side with a ball of aluminum foil or an extra screw band.
  • If you boil multiple jars at a time, ensure they do not touch, since they may rattle around and bump into one another.
  • Raise the water to a boil. Leave for 10 minutes at sea level, add 1 minute for every 1,000 feet above sea level.
  • After removing the jars, ensure they are fully dry before canning by inverting them on a cooling rack.
  • If you boil many jars in batches, ensure the water returns to a boil each time.

• Oven sterilization:

  • Place them on the middle rack so they are not near heating elements. Make sure they are not near the sides.
  • 300 °F (150 °C) Leave for 10 minutes at sea level.
  • 10 minutes at sea level, add 1 minute for every 1,000 feet above sea level.

• Toaster oven sterilization:

  • Make sure they do not touch heating elements or the sides.
  • 300 °F (150 °C)
  • If you can, have the door be slightly ajar for a little air circulation and more even heating. Consider wedging something heatproof in the door.
  • 20 minutes at sea level. If you're at higher altitudes, add 1 1/2 minutes for every 1,000 feet above sea level.

Handle hot jars carefully with a jar lifter (preferred) or tongs. When removed from their sterilization environment, make sure they are covered or at least placed upside-down to reduce airborne contamination. Aluminum foil loosely placed (no need to wrap) is okay.

Warning: Avoid cracking or shattering glass from thermal shock, such as pouring cooler liquids into hotter jars. Beware of using your counters! Use a wire rack instead of placing jars directly on a counter. A wet counter is a dangerous surface!

This advice holds true for all glassware or ceramics, be they glass or borosilicate glass.

Sterilizing lids ∞

Heat (But Don’t Boil)

• Inspect all lids for imperfections, such as degraded seals or a warp

  • Degradation is common. Many lids will not be reusable often if at all. Use your judgement as to whether you want to use use a different lid.
• Hand-wash them carefully with dish detergent and water
• Rinse them thoroughly
• Place the lids in a small saucepan filled with water.

• Heat the water to simmering (82°C or 180°F), but do not allow it to reach a boil.

  • Boiling can damage the rubberized sealing compound.

• Leave the lids in the simmering water until ready to use.

  • This softens the sealing compound, improving the seal.

Handle hot lids carefully a magnetic lid lifter (preferred) or with tongs. Avoid touching the bottom-side of the lids with unsterilized tools. Leave their tips in boiling water while you sterilize your jars to sterilize them too. You may need oven mitts to touch the handle of your tools.

A note on lids: It is smart to test the lid seal at the end of the canning process, when the contents are cooled, by removing the screw band and gently pushing at the lid and pressing down on it. If it shifts or pops off, then the seal is bad and you should use your judgement as to whether you should re-can from scratch with another lid, refrigerate instead of shelving the item, or consume the contents quickly.