Using a Pressure Cooker

Part 1 : Unit 6 : Using a Pressure Cooker for Mushroom Cultivation

Learning how to use a pressure cooker safely is an important step in your mushroom growing journey. A pressure cooker stands at the center of the mushroom growing process. Cooking grain, sterilizing tools and grain spawn, pasteurizing bulk substrate…all these significant steps of mushroom cultivation happen inside a pressure cooker.

However, this tool is as dangerous as it is formidable. Misuse, lack of attention or focus, or poor maintenance and inspection can result in literally explosive situations. It is vital that you read your specific pressure cooker instruction manual to make sure you understand its specifics before first operating it. If you’ve never used a pressure cooker before, make sure to check out the writeup on “principles of pressure canning.” In the following module we demonstrate how to use a pressure cooker for a short 25 minute session of pressurized cooking of Liquid Culture at 15-17PSI.

How to use a pressure cooker
Pressure Cooker 15 Psi Pressure Regulator

How to Use a Pressure Cooker Safely

Items needed
Notes and Tips

Video Tutorial : Using a Pressure Cooker for Mushroom Cultivation

The video markers above 👆🏼correspond to the the various Steps in this Unit. Click on them to skip to a Step.

Step 1 : Inspect and Prepare the Pressure Cooker

Inspect the pressure cooker pot for dents, cracks, bulges or anything else out of the ordinary. Next, inspect the pressure cooker lid, its various gauges and seals. Make sure all screws are tight, and that the rubber seal is in good shape. When you are satisfied with the inspection, place the PC in the sink and fill as much water as needed. Here’s a rough guideline that can be used :

  • For 25 minute pressure cooking cycles (eg. agar, liquid culture) – 1.5″ inches of water in the pot.
  • For 90 minute pressure cooking cycles (eg. grain spawn) – 3.5″ inches of water in the pot. 

Step 2 : Place Items you want to Sterilize inside Pressure Cooker and Seal the Lid

Place the rack in the pot, and put the items you want to sterilize on top of the rack in such a way that they are not touching the sides of the pot. If necessary, use a towel to line the inside of the pot. Inspect the lid, verify that all the valves are securely screwed and in place, and that the seal is intact. Close the PC by aligning the marks on the lid with the corresponding marks on the top of the pot, and turn it to seal it. There should be a tight secure seal.

Step 3 : Turn Up the Heat and Pressure

Turn on the gas to high and allow the PC to heat up. As the water boils and heats up, the Interlock Assembly valve will eventually pop up. At this point, steam will be coming out of the vent pipe. Allow about 5 minutes for all the air to be expelled from the PC through the vent pipe, and then place the 15 psi pressure regulator on the vent.

Step 4 : Cook / Sterilize with Pressure

The pressure starts building up in the PC. If you have a gauge, you should see it slowly inching up towards the 15 PSI range. When the cooker reaches 15 psi, the pressure regulator weight will start bobbing around and hissing. At this point, turn down the gas to medium, to a point where the regulator weight continues to gently bob around. From this point, start measuring your pressure cooking time.

Step 5 : Cool off, Pressure Down and Open Lid

Once the high pressure sterilization has been completed, you can turn off the gas. The pressure cooker will slowly start to cool down. Do not open it yet. The pressure in the PC will slowly go down, and when the PC becomes pressure neutral, the Cover Lock valve will drop. From this point, wait at least 2 more hours before opening the PC. If in doubt, just wait until the PC is not too hot to touch, or leave the PC overnight before opening.

Next Unit: Understanding sterile workflow. Contamination is your enemy. Learn how to work in the cleanest way possible so that your mushroom cultivation journey is as successful as can be. 

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