How to sterilize Mushroom Substrate without a Pressure Cooker?

Pressure cookers are the go-to equipment for mushroom cultivation. They are pretty much required for the sterilization of substrates and equipment. They create the conditions needed for the removal of unwanted microorganisms. If you do not have access to a pressure cooker, it is highly recommended.

If you decide to try sterilizing without a pressure cooker, there are some methods you can try. They may not be the best or conduct true sterilization, but they may work for your needs.

Why do you sterilize Substrate?

Sterilization is an important process in the world of mushroom cultivation. It’s required for the sterilization of equipment, substrates, and other growth mediums. It is a process that requires long periods of heat and pressure. This kills unwanted microorganisms like fungi, bacteria, and archaea.

Can I pasteurize? What’s the Difference?

Pasteurization is a similar process to sterilization but conducted with less intensity. When using heat it requires lower temperatures, less time, and no elevated pressures. It doesn’t kill ALL the microorganisms just the majority. Pasteurization works well for unsupplemented substrates, like straw, used for growing oyster mushrooms.

  • Pasteurization occurs with temperatures of 160 degrees F for 1-2 hours.
  • Sterilization requires temperatures >250 degrees F at 15 PSI for 2 hours.

Sterilization is important for:

  • Spawn Production
  • Liquid Culture
  • Cleaning of laboratory tools/equipment
  • Agar work
  • Preparing supplemented substrates
  • Substrates for particularly picky mushroom varieties

Can you sterilize without a Pressure Cooker?

Not really. It’s unlikely you will ever achieve the same results without a pressure cooker.  Without elevated pressure, you cannot reach the temperatures needed to remove harmful microorganisms. Without elevated pressures, it’s unlikely you can reach above the temperature of boiling water (212F). Many microorganisms need temperatures above 250F to be eliminated.

This said it is possible to get close to sterilization without a pressure cooker. This requires keeping high temperatures for LONG periods of time.

Best Alternatives to sterilizing with a Pressure Cooker

For sterilization first prepare your substrate. Make sure it is at the right humidity level. Afterward,  place it in a heat-proof container like a glass jar or mushroom grow bag. This allows you to sterilize it and bring it into your lab space without exposing it to the air.

  • Steaming
    Place your substrate above a steaming pot of water for 3-4 hours. Like this, you can get pretty close to sterilization. Temperatures will only reach about 212F compared to 250F in a pressure cooker.
  • Oven
    Place your substrate in the oven at 350 for 3-4 hours. Wait for your materials to completely cool down within the oven. Don’t put plastic grow bags in the oven!
  • Electric Pressure Pot
    Many people have these nowadays. They’re like a mixture between a crockpot and a pressure cooker. They usually only reach 12 PSI so use 3-4 hours in the pressure cook setting for greatest results.
  • Hot Water Bath
    Try boiling your substrate for 3+ hours. Won’t be as effective as a pressure cooker, but worth a shot if you got the motivation. You can do this in a large barrel over a burner if your working with large quantities.
  • Lime Bath
    Submerge your substrate in 0.2% activated lime water for 12 hours. This isn’t a sterilization technique but a way to conduct pasteurization. This works well if you want to prepare straw for oyster cultivation.

Serious Mushroom Growers use Pressure Cookers

If you’re serious about growing mushrooms get a pressure cooker. They’re cheap, readily available, and will make your efforts worthwhile. Look for cheap ones at thrift stores, online, or garage sales. You don’t need fancy laboratory equipment, but at least invest in this small piece of equipment. Believe me, it will save you time and energy!

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