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Sterilization and Pressure Cookers

Utilizing an at home pressure canner/cooker is an essential process for growing your own mushrooms at home. It is an investment that will pay itself off after 1 or 2 uses VS. buying presterilized substrates and grain. They are simple to use and the only effective way to properly sterilize your grow mediums. You can get a 22-Quart Presto Pressure Canner on-line for around $140.00. If you have a garage or basement, I would opt for an "induction computable" option and purchase an 1800W induction stove top. This makes your cooker portable and wont take up kitchen space come dinner time! There are more expensive brands for pressure cookers. Like most things you get what you pay for. Purchasing an All American canner is a good investment if you intend on doing some very serious canning. It will last a lifetime. However they are bulky and heavy. The average at home mycologist can get by just fine with a Presto for many many years.


Always be careful and read the owners manual to get familiar with the components before using a pressure cooker! No matter what type of cooker you get, it will get extremely hot during use. Keep away from children and always use caution while the cooker is in operation. NEVER OPEN OR ATTEMPT TO OPEN THE COOKER WHILE IT IS HOT OR UNDER PRESSURE! NEVER LEAVE YOUR COOKER UNATTENDED!


To operate your cooker, place it on a sturdy cooktop. I suggest laying 3 quart sized mason jars on their side. Then place the spacer plate (caning-cooker rack) provided with the cooker on top of the sideways jars. This will keep your jars or bags you want to cook out of the water. Then fill up the bottom of the cooker with warm tap water until is about 1 inch below the spacer plate. Add your bags or jars to the cooker. Be sure to leave some spacing between bags if you are using them. This will allow even temperature and pressure around the bags for even sterilization. Once the cooker is loaded up, securely put the lid on. Turn on the stove or hotplate to the highest setting. Keep the rocker or weight for the lid close by, but off of the vent pipe. You will hear the water begin to boil. When you hear steam hissing through the vent pipe, CAREFULLY set the "rocker" or weight provided on the vent pipe. Continue to let the pressure build in the cooker with the stove on high. Regularly check up on the cooker to see it is building pressure and there are no leaks. If it has stopped building pressure or you notice any leaks, immediately turn off the heat source and let the cooker cool naturally. Never pull the weight off of the vent pipe for faster cooling! Once you have built pressure up to 15 PSI on the pressure gauge, you will notice the weight will begin to rock or rattle. This is normal. Reduce the heat source (stove or cooktop) you will have to experiment with your individual stove, but if you turn the temperature dial on your stove down to around 7, you will typically maintain and PSI of 15. (The pressure cooker weight should rock or rattle during the entire duration on the cook.) Once your cooker is up to pressure set a timer for 90 minutes. Maintain pressure for the entire 90 min. If your cooker loses pressure without turning the heat down, it is likely out of water. Simply turn to stove off and let the cooker cool naturally. Once your timer is up, turn off the heat source and let the cooker cool. Do not pull the weight off of the cooker to decrease cooling time. This will cause a rapid decrease in pressure! This can cause bags to swell and break as well as pull in outside contaminates into the cooker and into your bags or jars. ALWAYS LET THE COOKER COOL ON ITS OWN! NEVER RUN COLD WATER OVER YOUR COOKER TO COOL IT! NEVER OPEN OR MOVE YOUR COOKER WHILE HOT OR UNDER PRESSURE! NEVER ALTAR OR MODIFY ANY PARTS OF THE COOKER!


Once your cooker has cooled and the pressure is at zero, remove the weight from the steam pipe to ensure there is no pressure in the pot. You can now remove the sterilized contents. Be sure to use clean gloves or a clean rag as the contents may still be hot. Allow your bags or jars to cool in the cleanest possible environment. Ideally in front of a laminar flow hood. This is not critical though. You can cool them inside of a clean trash bag or inside a clean box or tote. Once the jars or bags have cooled to room temperature, you can inoculate them with a spore solution or live culture. Always be sure the grain has cooled before inoculation!


Using a "steam bath" or boiling water in a pot to "sterilize" your jars or bags is not an effective way to achieve complete sterilization. A pressure cooker uses pressure (15 PSI) and heat for proper sterilization. When water is under pressure, it has to be a higher temperature to boil. This increases the temperature of the atmosphere inside of the cooker, resulting in sterilization of the contents inside. If you want to get into the hobby of mycology, a pressure cooker is an absolute necessity.


Always check your canner for defects before use. It is also a good idea to treat the sealing ring before the first use and every few cooks with cooking oil. I do this by applying some olive oil on a paper towel, removing the sealing ring, and rubbing the oil dampened towel on all surfaces of the ring. This will extend the life of the ring and make it easier to put the lid on and off of the cooker.


I hope this blog has helped inform you and possibly inspired you to get into canning!

Diagram of a Presto 22-Quart Pressure Cooker

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