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Choose Autoclave, Pressure Cooker or Instant Pot for grain substrate sterilization

To prepare grain substrate (also liquid culture media, agar media) for further inoculation, you need to sterilize your jars/bags to be sure your substrate is free of contaminants such as mold spores and bacteria.

To get rid of mold spores is easy. It is enough to use heat treatment at 140-160F° (60-70°C) for 1 hour.

But bacteria is more resistant. You have to prolong high heat treatment over 212°F (100°C) to kill them. This process called "heat sterilization". For grain substrates it takes 1.5-2.5 hours. For liquids (LC media or Agar media) - around 40 minutes.

Typically, the recommended temperature is 250°F (121°C). It's impossible to gain that high temperature without high pressure - 15 PSI (103 KPA).

The most common devices for this purpose are autoclave, pressure cooker and... instant pot. Which one to choose?

Autoclave is a professional device for sterilization tools (dental, surgical, cutting etc.) and it is used for mycological purposes as well. Good quality laboratory autoclave makes perfect job, but it's pretty expensive. It is worth to buy if mushroom cultivation became a great part of your life. However, it is worth pointing out that some Lab Autoclave models can't gain required pressure fast or can't be used for more than 1 hour due to fast water release.

Instant Pot is a household device for cooking. Most of them have PC mode or Steam mode with high pressure. The disadvantages are: small size; relatively low pressure (up to 10-12 psi) so you need to sterilize jars/bags for longer. Using instant pot, a good approach would be a double sterilization (kind of tyndalization) for 1.5 hours with 24-48 hours break between sterilizations.

Instant pot is a good start for DIY grain jars. No problem with LC/Agar media sterilization as well. Actually, it was my sterilization tool for a few grows, before I got a Pressure Cooker. There was zero contamination. I wouldn't recommend to buy it for long-term mushroom cultivation hobby, but for occasional mushroom growing it works great + you can use it for healthy food cooking.

Pressure Cooker/Canner (PC) is a household device for cooking/canning that is suits well for grain jars/bags, LC/Agar media, tools sterilization. Most of them have pressure gauge. Average PC is 3-5 times cheaper ($90-180) than autoclave. The pressure cooker brings excellent results for fair price. PC is the best investment in your mushroom cultivation hobby + using it for canning, cooking healthy food is a great bonus. That's why PC is the best choice!

A few notes to consider:

  1. Prefer Pressure Cooker with pressure gauge.

  2. Choose a PC with large capacity over 20 quarts/ liters. It allows you to sterilize 19 pint or 7 quart jars at a time.

  3. Some cheap models of Pressure Cookers gain pressure up to 10-13 psi, thus have lower temperature for sterilization process. Adjust the sterilization time according to pressure/temperature of your device. Check the table below for grain substrate sterilization

For more details, visit complete guide on Substrate sterilization

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Here I've prepared a list of devices for your choice and, of course, for your budget and your purposes.

Some models on Amazon also have "used" devices with good discounts.