How to sterilize a mushroom substrate without a pressure cooker?

Posted by Lisa on December 22, 2022
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    Mushrooms grow from a substrate, which is basically a mix of organic matter and nutrients. The most common type of substrate used for mushrooms is horse manure mixed with straw or hay, but you can also make your own using cardboard, coffee grounds or even spent coffee grounds. Sterilizing the substrate before adding it to your growing chamber ensures that it won't contain any harmful organisms or diseases that could infect your mushroom garden later on.

    Don't use a pressure cooker.

    A pressure cooker is designed for high heat and pressure, which can kill the mycelium. You don't want to use a pressure cooker because you will kill the mycelium on your substrate. Instead, you should use an oven or large pot with water at low temperatures (around 70 degrees Celsius).

    Use tin foil to wrap your substrate and put it in the oven on low for 1 hour, 2 hours at most.

    You can also use tin foil to wrap your mushroom substrate and put it in the oven on low for 1 hour, 2 hours at most.

    You will need:

    • Tin foil
    • A baking tray (or something similar)

    You can also use a stockpot and boil water, then add the substrate with no lid (covered with tinfoil) and place in an oven preheated to 200°F.

    You can also use a large pot with water and bring it to almost boiling and then add the substrate, without lid, cover with tinfoil (for safety reasons). Place in oven with light on (so you can see when it is done).

    Don't forget to preheat oven before putting tin foil in there.

    Don't forget to preheat oven before putting tin foil in there.

    How long should you preheat your oven? It depends on what kind of mushroom substrate you're using and how many substrates you have, but we recommend at least 30 minutes. If you're using a small amount of substrate, then 20 minutes should be enough time for the temperature inside the tin foil package to reach around 120 degrees Celsius (250 degrees Fahrenheit).

    How do I know if my oven is hot enough? Just check it with a thermometer!

    This can be done using a large pot or the oven.

    The following steps will be similar to the ones you would follow if you were using a pressure cooker, except there will be no pressure involved.

    To sterilize your substrate using this method:

    • Preheat your oven to 250 degrees Fahrenheit (121 Celsius).
    • Place tin foil over a baking sheet and spread out your substrate evenly across it. Make sure that there is enough space around each piece of material so that they can breathe while they bake. It's also important not to pack them too tightly together or else they may stick together during sterilization!

    Sterilize your jars and lids

    • Sterilize your jars and lids

    While you can use plastic bags to contain your substrate, I recommend using jars. They are easier to work with and they look professional when you're ready to fruit your mushrooms. To sterilize them, put some water in a pot and bring it to a boil on the stovetop. Then place your empty jars (with lids removed) into the boiling water for about 10 minutes; be sure no part of the glass touches another part of itself or anything else during this time! After 10 minutes have passed, remove from heat immediately so as not to crack/break any part of your jar or lid while still hot from being boiled!

    Prepare the substrate mix

    A substrate is a material that contains nutrients for growing mushrooms. The most common substrates are composted manure, straw, or peat moss; but you can also use coffee grounds and other materials.

    The substrate mix is simply the combination of these ingredients in proper proportions. There are many recipes available online for making your own mushroom substrates from scratch (see Resources), but if you don't have time to do this or just want something quick and easy, there are many ready-made products available at garden centers and hardware stores that will work just fine for growing mushrooms indoors on small scales such as this one!

    Fill the jars with substrate mix

    Once you've got your sterilized jars and substrate mix, it's time to fill them. First, make sure that the jars are clean and dry before you begin. Then, use a spoon to carefully fill each jar with substrate mix until it's about three-quarters full--you don't want to overfill them or leave air pockets in the bottom of each one!

    Spore syringe to each jar, then shake for 30 seconds to disperse spores evenly throughout the substrate

    • Spore syringe to each jar, then shake for 30 seconds to disperse spores evenly throughout the substrate.
    • Place lids on jars and tighten with your hands (don't use a wrench or other tool).

    Put on lids and rings

    • Fill your canning funnel with substrate.
    • Put on lids and rings and tighten.
    • Place jars in pressure cooker for 90 minutes at 15 PSI (1.03 bar).

    Sterilize for 90 minutes at 15 PSI (1.03 bar)

    The next step is to sterilize your substrate in a pressure cooker. This will kill off any fungus or bacteria that may be present, leaving only the mushroom mycelium to grow on top of it.

    Step 1: Place your substrate in the pressure cooker, fill it with water up to about 10% higher than the level of your substrate (so if you have a half pint jar of grain, use 5 ounces/150 mL), then place on high heat until boiling (this usually takes about 5 minutes).

    Step 2: Once boiling begins and steam starts coming out of both valves at top and bottom sides of cooker lid respectively--turn off heat! Do not open lid during sterilization process! Leave this alone for 60 minutes at 15 PSI (1 bar)

    It's tricky, but this method can work if you take it slow.

    It's tricky, but this method can work if you take it slow.

    First, start with a substrate that is already sterilized and ready to go. If you're using grain jars, make sure they have cooled down completely before inoculating them. Next, fill the pressure cooker with water and put the lid on tight--you want as little air in there as possible so that no mold spores can get in while they're being cooked at high temperatures (this also helps prevent explosions).

    Then set your stovetop to medium heat and bring that pot of hot water up to 150 degrees Fahrenheit (66 Celsius). Once it reaches this temperature turn off the heat source but leave everything else exactly where it was--it won't hurt anything if there's still steam coming out from under that lid! Make sure all four corners are securely fastened so nothing moves around when pressure builds up inside later on; any movement could cause cracks which would allow air into places where we don't want any air getting through just yet...


    I hope this article has helped you to understand how to sterilize a mushroom substrate without a pressure cooker. As always, please feel free to leave any comments or questions below.

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