How was your backyard harvest this year? If you’re gardeners like us, you have more zucchini than you know what to do with, an abundance of tomatoes and peppers for days, and we’re just starting to pull up our carrots. To preserve the flavors of the season, we’re planning to can our extras and save them for another (snowy) day.

“Canning” involves placing fruits, vegetables and other foods in sealable jars, which you’ll heat up and then cool. Heating will kill the microorganisms that cause food to spoil, and the air pressure from the cooling process will seal the jars tight, preserving the food inside.

There are two basic methods of canning: boiling and pressure canning.

Pressure

Pressure canning is used to preserve low-acid foods, like vegetables, beans, meats, seafood and poultry. It involves a special pressure cooker heated to at least 240 °F, which will kill any possible Clostridium botulinum spores.

Boiling

Used to preserve high-acid foods like tomatoes, fruits, jams, jellies, relishes and pickles, this method involves placing your jars of food in a large pot, completely covered with boiling water (212 °F, at sea level) and cooked for a specified amount of time.

Botulism is the main foodborne pathogen in canning, but Clostridium botulinum doesn’t survive in acidic environments. The reason for using high heat in this canning method, then, is to kill other spoilage agents like mold.

When using the boiling method, make sure your jars are clean and unflawed (e.g. no cracks). Sterilize your jars, lids and the rings to the lids in boiling water first. The best way to do this is to place your jars on a rack or a rivet inside a pot so the jars don’t touch the bottom. Then, cover the jars with cold water, bring the water to a rolling boil, and then reduce it to a gentle boil for about 10 minutes.

When you add food to your jars, make sure to leave enough room from the top of the food to the top of the jar/bottom of the lid. Then, add spices, herbs and other flavors!

High Altitude

It’s important to keep in mind that, no matter which method you use, adjustments need to be made for canning at high altitude.

Edie McSherry, a Colorado State University Extension Educator and CSU-educated food scientist, says, “We have some unique circumstances even here at 5,000 feet along the Front Range. Our water boils at a lower temperature, we have lower atmospheric pressure, so we have to compensate for those things by adding time to our boiling water canning and adding pressure to our pressure canning to be able to achieve those higher temperatures that are a little easier to get to at sea level.”

Here are a couple of handy cheat sheets we adapted from Ball Canning:

You can also download CSU’s Preserve Smart App, which has a tool to determine elevation and cooking time adjustments.

Do you have a favorite canning recipe? Please share – we’d love to try it!