What can and can't you use when canning? Just because something looks usable, doesn't mean it is. Credit: Sarah Walker Caron | BDN

This story was originally published in July 2020.

Whether you want to preserve your gardening harvest or take advantage of bumper crops in local produce, canning is a great way to preserve delicious fruits and vegetables from the summer months to eat throughout the year. Canning may seem like a big upfront investment for beginners who are purchasing the required materials, but many parts of the canning equipment can be reused year after year.

“First-time canners will make an investment in a case of jars and say, ‘Oh, this is an expensive hobby,’” said Kathleen Savoie, extension educator at the University of Maine Cooperative Extension. “It becomes more economical each year.”

The primary elements of the canning process that cannot be reused are the circular metal lids, also known as dome lids. Once the lids have been used in either a pressure canner or a boiling water bath and that vacuum seal has been formed, a deep groove is formed in the orange sealing compound, which leads to a higher risk of seal failure if you attempt to use the lid again.

“Nobody wants to go through all of the work of canning something and have the seal fail,” Savoie said.

Kate McCarty, food systems professional at the University of Maine Cooperative Extension, also noted that this sealing compound will not be compromised with heat, like in a dishwasher, or from using it for storage purposes prior to canning.

“Once you have used it, you can reuse [the lids] to store things, but not reuse them for canning,” she added.

Staff writer Sam Schipani joins Kate McCarty, food systems professional at the University of Maine Cooperative Extension, to learn how to make and can onion jam. Credit: Linda Coan O'Kresik

Savoie said that lids can be sold in individual packs for pint or wide mouth jars, which many years will be the only cost home canners incur once they have the other basic materials.

However, Savoie said that canning jars themselves are “made to use over and over and over.” The metal screw bands can also be used again and again for canning projects.

“As long as you keep the jars crack-and-nick-free and clean, you can reuse those,” she explained. “Same with the screw bands. You need to keep those dent-free and rust-free and then they can be reused.”

Used jars can even be purchased from the thrift store if they are carefully inspected.

“Take the time to look at the jars,” Savoie said. “Are they cracked, do they have nicks, do they look like they are relatively clean? Then you can buy those.”

However, commercial jars, like those used for store bought spaghetti sauce or jam, are not recommended for reuse in canning.

“They weren’t meant for repeated heating [so] you run the risk of them breaking in the canner,” McCarty explained. “It’s best to use a jar that was made for canning. It’s about reducing the risk of bad things happening.”

Savoie also said to resist the temptation of the jars that have hinged glass lids, which prevents you from being able to see if a vacuum seal has formed to lock out the air that carries mold, yeast and bacteria.

“Those style jars are no longer recommended,” Savoie said. “The dome lids allow you to see and test for a vacuum seal.”

Over time, Savoie said that proper storage will help preserve the longevity of the jars and screw bands — and help you to find them when you need them.

“Come up with a plan for where you’re going to store those things in your house,” Savoie said. “I recommend that people keep the case boxes that those come in because they have the dividers. It’s a really easy way to store them. I’ve had to come up with creative approaches so that my kitchen isn’t constantly cluttered with empty canning jars.”