John Miller
Sterilizing mushroom jars is an important step in the process of growing mushrooms at home. It involves eliminating any bacteria or fungi that could compete with the intended mushroom culture. The most common method for sterilizing mushroom jars is using a pressure cooker, which combines steam, time, temperature, and pressure to kill living organisms and spores. Other methods include boiling, using an oven, or a microwave, though these may not guarantee complete sterilization. The type of jar, its size, and the specific mushroom species being grown also play a role in determining the sterilization method and parameters.
Characteristics and Values of Sterilizing Mushroom Jars
| Characteristics | Values |
|---|---|
| Type of equipment | Pressure cooker, rice cooker, oven, microwave, stove/hob, autoclave |
| Temperature | Above 250°F (121°C) |
| Time | Minimum 2 hours, up to 90 minutes at 15 PSI |
| Water level | Enough to last the duration without running dry |
| Jar preparation | Cover lids with tinfoil or foil to prevent dripping |
| Jar filling | 2/3–3/4 full, with grains rinsed and soaked |
| Post-sterilization | Allow to cool before handling and inspecting |
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What You'll Learn
Using a pressure cooker
To sterilize mushroom jars using a pressure cooker, you will need a pressure cooker, jars or bags of prepared substrate, and a metal cooking rack. Before using your pressure cooker, check carefully to ensure that all parts are in good working order and there are no dents, bulges, or cracks. Check that the safety valve is clear and working correctly, and that the air vent is unblocked.
Next, measure and add the appropriate amount of water to the pressure cooker according to the manufacturer's instructions. Generally, you will need enough water to last the duration of the sterilization without running dry. Most growers recommend starting with around 3 quarts (2.8 liters) of water, or enough to go 1 to 2 inches (2.5 to 5 cm) up the side of the bags or jars. Place empty jars or jar lid rings at the base of the pot to prevent jars from floating and breaking. Then, set the cooking rack over these. When using jars, tilt them to release any trapped air bubbles beneath.
Afterward, carefully place the bags or jars on the rack, ensuring they are properly spaced and not touching each other or the sides of the pot. You can line the lower sides with a kitchen towel or cloth if necessary. Close and lock the pressure cooker lid securely, ensuring the pressure release valve is in the closed position to create a pressurized environment. Place the pressure cooker on a heat source and turn it on, following the manufacturer's instructions to achieve the desired pressure level of 15 PSI, which will raise the temperature to approximately 250°F (121°C). Once the desired pressure is reached, start the timer and maintain the pressure for the recommended sterilization time, typically around 90 minutes.
After sterilizing, allow the pressure cooker to cool down naturally for a few hours. Do not attempt to release the pressure manually, as this can cause the glass jars to break. Once the cooker is fully cooled down and safe to open, carefully open the lid, taking caution as hot steam may still be present. Then, remove your sterilized jars in a clean, sanitized area, ready for inoculation with mushroom spores or mycelium.
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Alternative methods: boiling, oven, microwave
Boiling is a common method for sterilizing small batches of grain spawn jars. To do this, fill a large pot with enough water to reach 1 to 2 inches or halfway up the side of the jars. Place the jars inside and bring the water to a boil. Once boiling, reduce the heat and let the jars simmer for 60 to 90 minutes at sea level, adding an extra minute of boiling time for every additional 1,000 ft of elevation. Keep an eye on the water level to prevent it from boiling dry. After sterilization, let the jars cool before handling them.
An oven can also be used for sterilization. Preheat your oven to 150°C (300°F) and place the jars on a baking sheet. Bake for 2 to 3 hours, or until the grain inside the jars is sterilized. The exact time and temperature may require some trial and error to suit your specific oven.
Microwaving is not a reliable method for sterilizing mushroom substrates as it doesn't kill all fungal spores. However, you can use a microwave steamer to pasteurize small quantities of the substrate and reduce potential competitors. The effectiveness of microwaving depends on the water content of the substance being heated, as microwaves work by causing water molecules to vibrate and generate heat. As fungal spores don't contain much water, they are challenging to heat effectively. While a microwave can exceed the boiling point of water (100°C or 212°F), this temperature may not be sufficient to kill all life forms, and higher temperatures are required for sterilization.
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Avoiding common mistakes
To successfully sterilize mushroom jars, it is important to avoid common pitfalls. Here are some key points to consider:
Equipment
Firstly, ensure you have the correct equipment. A pressure cooker is the standard tool for sterilizing mushroom substrates, and it needs to be able to maintain a pressure of at least 15 PSI. Check your cooker carefully for any damage, such as dents or cracks, before using it. Make sure your cooker is large enough to hold your jars without the jars touching the sides or base, as direct contact with the cooker's base can cause jars to crack. You can line the sides with a kitchen towel if necessary.
Water
Use enough water to last the duration of the sterilization. Most growers recommend starting with around 3 quarts (2.8 liters) of water, or enough to go 1 to 2 inches (2.5 to 5 cm) up the side of the jars. Keep an eye on the cooker and take notes to learn how much water is needed for future attempts.
Temperature and Timing
To sterilize a substrate, you need temperatures higher than 250°F (121°C) for at least 2 hours. At sea level, water boils at 212°F (100°C), so boiling water is not hot enough to sterilize. When using a pressure cooker, wait for the pressure to reach 15 PSI and then adjust the heat to maintain this pressure. Sterilize for at least 90 minutes.
Work Environment
Keep your work environment clean and sterile to maximize the chances of success. Incomplete preparations or deviating from the chosen technique can lead to a higher risk of contamination. Always allow your substrate to cool completely before inoculation.
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Sterilizing the needle
To sterilize a needle, you must use a flame to sterilize the needle of a spore syringe between inoculations of each jar. A butane lighter, gas stove, or alcohol lamp will all work perfectly.
The substrate is made of vermiculite, brown rice flour, and purified water. It is important to mix the vermiculite and water first. Make sure that the vermiculite has soaked up all of the water before adding the brown rice flour.
The needle must be sterile so that it can inject directly into the jar without having to open the lid. When you pull out the needle, the hole seals back up, without introducing outside air or other contaminants.
It is important to note that the sterilization process requires temperatures higher than 250°F (121°C) for at least 2 hours. Boiling water or steam alone is not hot enough to sterilize a substrate as the boiling temperature of water at sea level is 212°F (100°C).
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Using steam sterilization
Sterilization is an important process in mushroom cultivation, as it kills unwanted microorganisms like fungi, bacteria, and archaea. While pressure cookers are the go-to equipment for sterilization, you can also use steam sterilization. Here is a step-by-step guide on how to sterilize mushroom jars using steam:
Prepare the Jars and Cooking Equipment:
- Use wide-mouthed mason jars or specific mushroom grow jars/bottles that can withstand high sterilization temperatures.
- Place a steaming rack or a cloth (such as a washcloth or thin dishcloth) at the bottom of a large pot or pressure cooker. This will prevent the jars from directly touching the hot metal and cracking.
- Fill the jars with your chosen substrate, such as brown rice flour (BRF). Make sure to follow the correct procedure for preparing the substrate.
- Place the jars in the pot, ensuring they are stable and secure.
- Add water to the pot. The amount of water will depend on the size of your jars and pot. Generally, you want the water to go about an inch or halfway up the jars.
Sterilization Process:
- Bring the water to a slow and calm boil. Avoid a vigorous or violent boil, as it can cause overflow or splashing, and water cannot exceed 100ºC (212ºF) no matter the pressure.
- Maintain the boil and cover the pot with a tight-fitting lid. Ensure the lid is secure and does not allow steam to escape.
- Let the jars boil for at least 60 to 90 minutes. The longer sterilization time ensures that the temperature reaches at least 121ºC (250ºF), which is the minimum temperature required for sterilization.
- After boiling, turn off the heat and carefully remove the jars from the pot. Be cautious, as the jars will be hot.
- Allow the jars to cool down. It is recommended to let them cool for longer than it takes for the outside of the jar to reach room temperature, as the middle will still be warmer.
- Once completely cooled, you can proceed with the next steps of mushroom cultivation, such as knocking them up with spores or liquid myc.
It is important to note that while steam sterilization is effective, it may not achieve the same level of sterilization as a pressure cooker, which combines steam, time, temperature, and pressure. Additionally, the sterilization process may vary slightly depending on your specific equipment and substrate, so adjustments may be necessary.
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Frequently asked questions
The best way to sterilize mushroom jars is to use a pressure cooker. This is because boiling water or steam alone is not hot enough to sterilize a substrate as the boiling temperature of water at sea level is 212°F (100°C). To sterilize a substrate, you need temperatures higher than 250°F (121°C) for at least 2 hours.
Alternative ways to sterilize mushroom jars include using a rice cooker, oven, microwave, or stove. However, none of these methods guarantee complete sterilization and there is always a risk of contamination.
It is important to ensure that your jars are not touching the sides of the pot or the cooker's base to prevent melting or cracking. Additionally, you need enough water to last the duration of sterilization without running dry.
