Trippy Tek
At Trippy Tek, we’re passionate about making mycology accessible and enjoyable for everyone. We combine extensive research, community insights, and hands-on experience to offer proven techniques and tips for mushroom cultivation.
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A pressure cooker is one of the most important tools in a mushroom lab. It helps sterilize materials, making sure no unwanted bacteria or mold can grow.
It is one of the most expensive items and, suprisingly, many people rush to use it without fully understanding how it works.
Home mushroom growers use pressure cookers instead of commercial autoclaves because they are more affordable and still effective.
In this guide, we will focus on the Presto 23Qt pressure cooker, one of the best options available. Other alternatives are either too expensive or not worth the cost, as we saw in this article.
Learning how to properly use and care for your pressure cooker will make your mushroom-growing journey safe, fun, and sustainable . By understanding your equipment and using it correctly, you can avoid mistakes and get the best results.
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Pressure Cooker Basics
What is a Pressure cooker ?
A pressure cooker is primarily designed to cook food quickly by using high pressure to raise the boiling point of water, allowing it to cook food faster than standard methods.
By trapping steam inside a sealed container, the pressure cooker builds heat and pressure, cooking food efficiently It’s commonly used for canning and cooking beans, meats, and vegetables.
Why Use a Pressure Cooker for Mushroom Growing?
When growing mushrooms, keeping things sterile is super important to stop bacteria, mold, and germs from ruining your setup.
A pressure cooker heats up to 121°C (250°F) at 15 psi, which kills most harmful spores and germs.
This makes it perfect for sterilizing materials like grains or agar used to grow mushrooms.
Sterilizing the growing medium ensures mushrooms can grow without being taken over by unwanted contamination. It gives your spores or mycelium the best chance to thrive.
Big mushroom farms use fancy machines called autoclaves to sterilize, but these are very expensive. For home growers, a pressure cooker is an affordable alternative to commercial sterilizers, making it accessible and effective for small-scale mushroom cultivation.
How the pressure cooker is used in mushroom cultivation
Sterilizing Spawn and Mushroom Substrates in Jars or Bags
Pressure cookers are used to sterilize spawn and substrates in jars or bags typically at 15 psi for 60-90 minutes . This high pressure and high temperature create a clean, contaminant-free medium for mushrooms to grow.
Preparing Agar
Agar, a nutrient medium for growing mushroom cultures, can also be sterilized in a pressure cooker. It’s usually sterilized at 15 psi for 20-40 minutes to ensure no contaminants spoil the growth process.
Presto Pressure Cooker 23 Qt 101
Why Presto 23 Qt is the best?
The Presto 23-Quart Pressure Cooker is one of the most popular models for mushroom cultivation due to its size, capacity, and affordability
Large Capacity : The 23-quart size is ideal because it can hold multiple jars (7 and up to 10 quart jars if 3 laying down), allowing you to sterilize several jars or bags at once, making it efficient for small to medium grows.
Reliable 15 psi Pressure : The Presto 23q easily reaches 15 psi, which is the standard pressure needed to properly sterilize substrates for mushrooms. Careful to check when buying a PC that it can reach 15 PSI (if you don't buy the Presto)
Affordable and Widely Available : Compared to high-end sterilizers (like All American Model 921 at 380$+), the Presto 23q is affordable (125$), making it accessible for home growers and beginners who don’t want to invest in more expensive equipment right away.
Versatile : It can be used on standard stovetops and doesn’t require additional equipment, making it easy to use at home right out of the box.
The main difference, apart their price, between the Presto 23 qt pressure cooker and the All American Pressure Cooker Model 921 is their sealing method.
The Presto uses a gasket for sealing, which usually lasts about three (3) years before needing replacement.
The All American, on the other hand, uses a durable steel-to-steel sealing system that doesn’t rely on gaskets and requires less maintenance over time.
You can save some money with a 16Qt version where you will be able to hold less jars. Presto 01745 16-Quart pressure Canner and Cooker worth about US$80 and can hold 7 jars.
Presto 23qt Parts
Let's go over all the Presto Part one by one so you have a good understanding of your pressure cooker.
Pressure Dial Gauge
This part is very important and fragile, so handle it with care. Even if the pressure gauge shows "0," it doesn’t always mean there’s no pressure inside. You should also check the air vent or cover lock to confirm that it is ready to be opened.
If the gauge shows "0" but the pressure regulator is still jiggling, the gauge isn’t working. In this case, replace the pressure dial gauge as soon as possible to ensure safe use.
You can verify your gauge this way:
Make sure the Dial Gauge is properly calibrated. When the pressure regulator start releasing steam, the gauge should be at 15 PSI.
Pressure Regulator / jiggle weight
Only rate for 15PSI.
Some people add weights to remove the noise and keep the pressure regulator down even at 15PSI, but it is at your own risks. I don't recommend. If you don't want too much noise during the operations, just keep your heat low. Find the sweet spot. If it is too hot, the PC will loose a lot of steam and make a lot of noise. You don't want to risk over pressurize.
In an ideal world, like in autoclave, it is better to not have any steam leave the pressure cooker for our mushroom cultivation (here's an other reason people would put additionnal weight on the Pressure Regulator). Other reason also is to not have the agar to boil. So do your best to avoid excessive steam lost.
Vent pipe / Main relief valve
This is where the steam will evacuate and where you put the pressure regulator. This is super important that it is clear and not obstruct. Make sure it is clear before you start your operation.
Air vent / cover lock
Act as visual indication of pressure in the canner. This is the only viable indication of pressure in your PC if it is equalize to outside (or 0).
As soon as there is pressure, the mechanism (locking Bracket) will make the lid lock and you won't be able to open it. So it is stupid proof for you.
There is also a white gasket to verify once you receive a new PC to check.
It is important to be sure it’s there.
Locking Bracket
The locking bracket is a safety feature that prevents the pressure cooker lid from opening when there’s pressure inside the canner. It automatically locks as soon as pressure builds up, which you can confirm by checking the air vent / cover lock (Part 4).
This "safety, foolproof" feature ensures that you can’t accidentally open the lid while the canner is pressurized. The locking bracket is located underneath the lid and works as an important part of the overall safety system.
Sealing Ring (gasket rubber seal)
The sealing ring (gasket rubber seal) is the main part that keeps pressure from escaping the pressure cooker. It’s the key difference between regular pressure cookers and the All American Sterilizer, as the latter doesn’t use a gasket. Gaskets need regular maintenance to keep them working properly.
The gasket is a rubber ring that seals the pressure cooker lid to the base of the cooker, allowing pressure to build. After each use, remove the gasket and check it for cracks or damage. They should be replaced every 3 years.
Extra Tip (Not in User Manual): To keep the gasket flexible, gently stretch it and apply a small amount of mineral oil or silicone oil. Avoid petroleum jelly, as it can wear down the rubber over time, although some people still use it. After lubricating, place the gasket back into the lid and close the cooker as usual. This simple step helps the gasket last longer and perform better.
Overpressure Plug
The overpressure plug is a safety feature that releases pressure if the main vent pipe gets blocked. If pressure cannot escape through the normal venting system, the plug will pop automatically to prevent the cooker from becoming dangerous.
Always check the plug for wear or damage before use and replace it every three (3) years along with the sealing ring. This ensures your pressure cooker stays safe and functions properly.
Canning-Cooking Rack (Trivet)
The trivet is a small metal rack placed at the bottom of your pressure cooker. Its purpose is to keep jars off the bottom so steam, not direct heat, sterilizes or cooks them. It also prevents jars or items from sitting in water during the process.
In the Presto 23-quart pressure cooker, place the trivet at the bottom and add 3 quarts of water. If you are sterilizing only a few jars and they start to float or tip over, you can lift the trivet higher. To do this, place foil balls or extra jar lids under the trivet.
This setup makes sure the water level reaches just below halfway up the jars, helping steam spread evenly.
Good steam flow is important because it sterilizes the jars properly and keeps your mushroom grow safe.
For a long-term solution , you can upgrade the trivet by attaching bolts and nuts to raise it higher. Another option is to buy an elevated rounded rack , which creates a stable and adjustable setup. This helps keep the jars steady, preventing them from tipping over and ensuring safe and even sterilization .
Operating your Pressure cooker
Pressure Cooker Pre Check
Pre-Check Before Using Your New Pressure Cooker for the First Time
Before using your pressure cooker for the first time, make sure to wash all the parts thoroughly. Wash the gasket separately to ensure it’s clean and free of debris. Check the air vent and cover as they may be loose; if needed, tighten them securely using the white gasket.
Attach the pressure dial gauge to the canner cover, as this part won’t be pre-attached. Only tighten the gauge by hand—do not over-tighten. These steps ensure your pressure cooker is clean, assembled correctly, and ready for safe use.
Pre-Check Before Using Your Pressure Cooker Every Time
Before each use, perform these safety checks:
Vent Pipe : Ensure the vent pipe is clear and not blocked by any debris or residue.
Air Vent / Cover Lock : Check that the air vent and cover lock are functioning properly and move freely.
Gasket : Inspect the gasket for cracks, wear, or damage, and make sure it’s seated correctly in the lid.
These steps help ensure your pressure cooker operates safely and effectively every time.
Add the Correct Water Level
To use the Presto 23-quart pressure cooker, start by adding 3 quarts of water. This amount may seem like a lot, but it’s the correct minimum for this size of cooker. The water level is crucial because it ensures proper steam generation for sterilizing or cooking.
The absolute minimum is 3 quarts—running out of water can be catastrophic because your jars or bags can overheat, crack, or burn. The maximum amount is 2/3 of the cooker’s capacity when pressure cooking. To make things easier, there are small marks inside the pressure cooker to guide you.
Using distilled water is recommended by the manufacturer, but tap water works fine and you can optionaly add 1–2 tablespoons of white vinegar. The vinegar prevents white, chalky stains on jars caused by hard water. If you don’t have distilled water, use hot tap water with vinegar (optional) for the same effect. These steps will protect your jars and keep your pressure cooker clean.
Next, add your spacers (like jar rings) and the trivet to the bottom of the pressure cooker. These spacers prevent small mason jars (like 4 or 8 oz) from floating on the trivet. Floating jars can tip over during sterilization, which is why spacers are so important.
Similarly, if you’re sterilizing agar media in bottles, spacers keep the bottles at the right level to avoid submerging the media and causing it to boil over.
Vinegar helps prevent white, chalky stains caused by hard water—keeping your jars and pressure cooker clean
Another important tip is to make sure no air bubbles are trapped under the trivet. To do this, gently tilt each grain jar after placing it on the trivet, ensuring they’re steady and evenly positioned.
Don’t forget to cover the tops of the jars with foil. This prevents water from splashing inside the jars during sterilization and keeps your contents safe and uncontaminated. Always double-check that the jars are secure and foil is tightly fitted before starting the process.
Now your jars are safe, properly spaced, and positioned at or just above the waterline, ready to be pressurized.
Venting and heating
Venting is a crucial step when starting up your pressure cooker for sterilization. Here’s how to do it right:
Fill with Hot Water : Use very hot or near-boiling water to fill the pressure cooker. This helps it reach sterilizing temperature faster.
Lid On, Weight Off : Once you secure the lid, make sure the weight is OFF the vent.
Turn Up the Heat : Set the heat to high. As the water boils, you’ll start to see steam coming out of the top vent.
Wait for the Safety Plug : After a minute or two, the safety plug and locking mechanism will pop up. This locks the lid in place, so you can’t open it while it’s pressurized.
Vent for 10 Minutes : Once you see steam steadily coming out, set a timer for 10 minutes. Venting this long is important to make sure that all air is pushed out of the cooker and replaced with steam.
Why Venting Matters : If air remains inside, the gauge may show 15 psi, but this pressure will be a mix of steam and air pressure, which lowers the temperature inside.
For full sterilization, we need 100% steam at 15 psi, which is 121°C (250°F) .
Without venting, trapped air can reduce the temperature, leaving you at less than 121°C and risking incomplete sterilization.
By venting properly for 10 minutes, you ensure that only steam fills the pressure cooker and jars, which is essential for reaching the full sterilization steam temperature.
Sterilize at 15 PSI
After venting your pressure cooker for 10 minutes, you might see the pressure gauge show a few PSI—this is normal.
- Add the Weight: Place the weight on the vent to let the pressure inside the cooker rise steadily.
-
Adjust the Heat: Start with high or medium-high heat to quickly build pressure. As it approaches 15 PSI, lower the heat to maintain that pressure without overheating. If the heat is too high, the weight will jiggle constantly, releasing more steam and causing water to evaporate faster.
Once the cooker reaches the desired pressure of 15 PSI, reduce the heat—low is often enough to maintain pressure. Monitor Pressure and avoid vigorous jiggling, as it leads to water and steam loss.
Sterilization Time Guidelines (at 15 PSI):
Agar plates: Sterilize for 20–30 minutes.
Grain spawn: Sterilize for 90–120 minutes, depending on the size of the jars or bags.
Substrates (e.g., sawdust, straw): Sterilize for 120–180 minutes, as larger volumes require more time to ensure all contaminants are destroyed.
Temperature Facts with 0% Air (Sterilization Levels):
5 PSI = 228°F (109°C) – Not hot enough for complete sterilization.
10 PSI = 240°F (116°C) – Effective for some sterilization but may not kill all contaminants.
15 PSI = 250°F (121°C) – The standard sterilization temperature, capable of killing bacterial spores and other contaminants.
This comparison shows that 15 PSI is the ideal pressure for mushroom cultivation because it reaches 121°C, ensuring thorough sterilization of agar, grains, and substrates. Lower pressures don’t achieve the required temperature for complete sterilization.
Optional Quieting Technique:
Some users add extra weight (like taping 2–3 quarters to the jiggle weight) to reduce noise, making the jiggle weight move only at 18–19 PSI. This lets the cooker run quietly between 15–18 PSI, reducing water loss. However, this method is risky and not recommended due to the chance of over-pressurization.
Instead, adjust the heat to find the "sweet spot" where the weight jiggles occasionally but doesn’t constantly release steam. Keeping the pressure at 15 PSI without constant noise ensures effective sterilization while minimizing steam and water loss.
Always prioritize safety over convenience during operations.
Instead, adjust the heat to find the "sweet spot" where the weight jiggles occasionally but doesn’t constantly release steam. Keeping the pressure at 15 PSI without constant noise ensures effective sterilization while minimizing steam and water loss.
Cool and Sit Overnight
After the pressure cooker cycle is complete, turn off the burner and allow it to cool naturally. For most uses, let it cool for 8 hours or overnight (except for agar POUR TEK) .
You can move the pressure cooker off the heat source to another spot on the stovetop if needed.
Do not remove the pressure regulator (jiggle weight) while the cooker is still pressurized.
This could cause rapid depressurization, which may lead to issues like boiling over agar or spilling liquids. Allow the pressure to drop naturally.
If you are sterilizing agar, you don’t need to wait until the pressure cooker is fully cool, as agar will start to solidify if left too long and temperature drop.
Once the pressure gauge reads zero and the air vent/cover lock confirms there’s no remaining internal pressure, you can safely open the lid.
When opening, tilt the lid so the steam escapes away from you to avoid burns. This allows you to access the sterilized agar before it cools too much and solidifies, making it easier to pour into plates or containers. Always handle the pressure cooker and its contents with care to avoid accidents.
Care and Maintenance
To remove discoloration from your pressure cooker, use 1 tablespoon of cream of tartar for every 1 quart of water . Add the mixture to the cooker, heat it briefly, and then rinse thoroughly to restore the shine.
At least once a year, clean the inside of the cooker with an aluminum and stainless steel cleaner to maintain its condition and prevent buildup. This keeps the cooker in good shape for long-term use.
When storing your pressure cooker, place the lid upside down on the base to allow air circulation. Ensure the cooker is completely dry and free of any water to prevent rust or mold. A dry, well-stored pressure cooker will last longer and remain safe to use.
Conclusion
Great job! You now understand how to use and maintain your pressure cooker for mushroom cultivation. With proper care, it will last longer and keep your agar sterile. Keep practicing, and you'll get even better results!
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