Mushrooms are a low-acid food, which means pressure canning is the only safe method for preserving them at home. A water bath canner cannot reach high enough temperatures to destroy the spores that cause botulism. With a pressure canner, you can safely put up half-pint and pint jars of mushrooms that will hold their quality on the shelf for about a year.
Why Pressure Canning Is Non-Negotiable
The bacterium that causes botulism cannot grow in acidic environments (below a pH of 4.6), which is why fruits and pickles can be water-bath canned. Mushrooms sit well above that pH threshold, making them a perfect environment for botulism spores to survive and produce toxin if the food isn’t heated enough during processing. Only a pressure canner pushes water temperature to 240 to 250°F, hot enough to kill those spores. A boiling water bath tops out at 212°F, no matter how long you process.
Choosing and Preparing Your Mushrooms
Stick with cultivated mushrooms: button, cremini, or baby bella varieties. The National Center for Home Food Preservation has tested and approved processing times for these common types. Wild mushrooms introduce variables in density and composition that don’t have validated canning guidelines, so they’re best preserved by freezing or dehydrating instead.
Start by trimming the stems and cutting away any discolored parts. Soak the mushrooms in cold water for 10 minutes to loosen dirt, then wash them again in clean water. Leave small mushrooms whole and cut larger ones into halves or quarters so they’re roughly uniform in size. This matters because even-sized pieces heat through at the same rate inside the jar.
Parboiling
Place the cleaned mushrooms in a saucepan, cover them with water, and bring to a boil. Boil for 5 minutes. This step partially cooks the mushrooms, shrinks them so you can fit more in each jar, and helps drive out air trapped in the tissue. Keep the hot cooking liquid nearby; you’ll use it or fresh boiling water to fill your jars.
Packing the Jars
Use only half-pint or pint jars for mushrooms. Quart jars are too large for mushrooms to heat evenly all the way to the center during processing, so no tested times exist for that size.
This is a hot pack method. Spoon the hot, parboiled mushrooms into your clean, warm jars. If you’d like, add half a teaspoon of salt per pint (or a quarter teaspoon per half-pint) for flavor. A small splash of ascorbic acid solution or lemon juice in each jar helps prevent darkening, though it’s optional.
Ladle hot cooking liquid or fresh boiling water over the mushrooms, leaving 1 inch of headspace at the top of each jar. That inch of space is important: too little headspace and liquid can boil out during processing, interfering with the seal. Run a thin utensil (a chopstick or bubble remover tool) around the inside edge to release trapped air bubbles. Wipe each jar rim clean with a damp cloth, then place a lid and screw on the band until it’s fingertip-tight.
Processing Times and Pressure
Place the filled jars on the rack inside your pressure canner, which should already have 2 to 3 inches of hot water in the bottom. Lock the lid and heat the canner until steam vents steadily from the vent pipe. Let it vent for 10 minutes to exhaust all the air inside, then close the vent or place the weighted gauge.
Process both half-pints and pints for 45 minutes at the correct pressure for your canner type and altitude:
- Dial-gauge canner: 11 PSI at 0 to 2,000 feet elevation. Increase to 12 PSI between 2,001 and 4,000 feet, 13 PSI between 4,001 and 6,000 feet, and 14 PSI between 6,001 and 8,000 feet.
- Weighted-gauge canner: 10 PSI at 0 to 1,000 feet elevation. Use 15 PSI for any altitude above 1,000 feet.
Watch the gauge throughout the entire 45 minutes. If the pressure drops below the target at any point, you need to bring it back up and restart the timer from the beginning. Fluctuating the heat too much can also pull liquid out of your jars, so aim for a steady, consistent pressure.
Cooling and Checking the Seal
When the processing time is up, turn off the heat and let the canner depressurize naturally. Don’t try to speed this up by opening the vent or running cold water over the canner. Rapid pressure changes can cause jars to crack or lose liquid. Once the pressure gauge reads zero, wait another 10 minutes, then remove the lid (tilting it away from you to avoid a steam burn).
Lift the jars out with a jar lifter and set them on a towel or wooden cutting board, leaving at least an inch of space between each jar. Don’t tighten the bands. Let the jars sit undisturbed for 12 to 24 hours.
After they’ve cooled completely, press the center of each lid. A properly sealed lid won’t flex up and down. It will be concave and firm. Any jar that didn’t seal should go straight into the refrigerator and be used within a few days. Remove the screw bands from sealed jars before storing, since a band can mask a broken seal by holding a lid in place even after it has loosened.
Storage and Spotting Spoilage
Store your sealed jars in a cool, dark place. Properly canned mushrooms maintain their best quality for about 12 months, though they remain safe longer if the seal stays intact. Label each jar with the date so you can rotate through your stock.
Before opening any jar, inspect it carefully. Hold it at eye level and look for streaks of dried food running down from the top, rising air bubbles inside, or any unnatural color changes. When you open the jar, smell for anything off. Spurting liquid, a foul or fermented odor, or cotton-like mold growth (white, blue, black, or green) on the surface of the food or underside of the lid are all signs of spoilage. If anything looks or smells wrong, don’t taste it. Discard the entire contents where neither people nor animals can reach them.
Equipment Tips That Affect Safety
If you use a dial-gauge canner, have the gauge tested for accuracy once a year. Many county extension offices offer this service for free. A gauge that reads even 1 or 2 PSI too low means your food isn’t reaching a safe temperature, even though the dial looks right. Weighted-gauge canners don’t need calibration since the weight itself is the measurement, which is one reason many home canners prefer them.
Inspect your canner’s rubber gasket before each use. A cracked or hardened gasket won’t hold pressure reliably. Replacement gaskets are inexpensive and widely available for most canner brands. Also check that the vent pipe is clear by holding the lid up to a light and looking through it. Any blockage can cause dangerous pressure buildup or inaccurate readings.