5 Methods Of Sterilizing Mushroom Substrate Without A Pressure Cooker

During the cultivation of mushrooms, sterilization is one of the most important steps. Many people make use of pressure cookers to sterilize mushroom substrates. However, there are some who do not have pressure cookers or just wish to find an alternative way for purifying these substances. If you are one of those people who want to gain knowledge on how to sterilize mushroom substrate without using a pressure cooker, then you are at the right place.

In this article, we are going to discuss 5 different techniques for sterilizing mushroom substrates. You will be bewildered by seeing the various easy methods that can be applied to kill the pathogens present in mushroom substrates.

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How to Sterilize Mushroom Substrate Without a Pressure Cooker?

Sterilization is the process by which the contaminants present in a mushroom substrate are killed. Killing off the pathogens will help the mushrooms to grow speedily and healthily. Moreover, a higher yield of mushrooms will be received after the cultivation process, if sterilization is done.

Sterilizing is extremely necessary if you want to gain a rich amount of freshly brewed mushrooms. The five effective techniques for sterilization that we plan to discuss in this article are as follows:

  1. Chemical: A) Hydrated Lime  B) Peroxide
  2. Hot water immersion (Scalding)
  3. Composting
  4. Tyndallization
  5. Pasteurization

1. Chemical Sterilization

Many people are fond of sterilizing mushroom substrates through the chemical process. This is because chemical sterilization is relatively cheaper than the other options available as it does not require heating.

However, chemical sterilization can turn out to be hazardous. Henceforth, it is necessary to be equipped with necessary safety protocols while dealing with this process. In this section, we will describe the process of using two different chemicals for sterilizing substrates. The two chemicals are:

  • Hydrated Lime
  • Peroxide solution

a) Hydrated Lime

Hydrated lime is a useful chemical for sterilization purposes. Calcium hydroxide raises the pH. Such an increase of most contaminants. If you are planning to cultivate oyster mushrooms, then you must go for this process of sterilization.

Ensure that the lime you use has a magnesium content of less than 2% and a higher calcium concentration. This is because lime with more than 2% magnesium presence can cause a hindrance to the growth of the mushroom.

However, we would like to advise you to refrain from using dolomitic lime, which can be found in the gardens, for this process. Moreover, you have to keep your gloves and masks ready while conducting this process. These are the basic safety methods you can apply to keep the lime from contact with your skin.

Now, it’s time to follow a few steps:

Step 1: Prepare the substrate

Cut your substrate into long pieces of 1-6 cm in length. You have to do so to ensure a higher level of biological efficiency throughout the process.

Step 2: Mix the water and the lime

You have to use 0.2 grams of lime for every gallon of water. It would be ideal for you to mix 300g of lime within 55 gallons of water.

Step 3: Soak the Substrate in the water

Afterward, you have to place the substrate on the water and let it be soaked up for 24 hours.

Step 4: Drain the water

Now it’s time to inoculate the mushroom spore by draining the water. You have to remove the substrate from the water and place it on a metal plate. Let the water dry itself for 2 hours straight. However, you may not need to rinse it.

Make sure that you do not leave the substrate for too long to be dried, as the more you let it rest on the plate, the more it will be likely for contaminants to get attached to the substrate.

Step 5: Inoculate the dried substrate

It is time for you to grab the sterilized and dried substrate. Make sure that there is a spawn rate of 15 to 17 percent.

Step 6: Bagging

Collect the sterilized substrate in your bag and place them on the grow chamber afterward.

b) Peroxide

To sterilize mushroom substrates using hydrogen peroxide, you do not have to follow any arduous steps. You can follow these steps to execute this process:

  • Firstly you have to gather 3% Hydrogen Peroxide.
  • Then you have to place the mushroom substrates on a water surface of one gallon. After 20 minutes let the water to be dried.
  • Now you have to spill one liter of 3% hydrogen peroxide on the liquid solution.
  • Let the substrate submerge into the hydrogen peroxide and water mixture. You have to let the substrate rest on the mixture for one complete day.
  • After 24 hours are over, displace the substrate from the mixture. Then rinse it with old water twice.
  • After cleaning it twice, inoculate the substrates.

2.  Hot Water Immersion Scalding Process

If described, through the scalding process, we keep the substrate immersed within hot water for more than 1 to 5 hours and let the overexposure of heat kill the pathogens present with the substrate. The scalding process is one of the simplest and easiest ways to sterilize.  Just follow a few steps:

Step 1: Prepare the substrates

Gently chop the substrates into long, slender pieces with each length of 1 to 6 cm. This is done to ensure higher biological efficiency and easy breakdown of contaminants.

Step 2: Heat the water

You have to provide maximized heat exposure to the water you plan to use for sterilization. Provide heat and raise the temperature of the water to approximately 80°C.

Step 3: Add the Substrate to the water

Now it is time to place the substrate on the heated water. After doing the placement, you have to mix the mushroom substrates within the liquid thoroughly. You have to continue mixing the constituents for 1 hour to get satisfying results.

Step 4: Drain the water

Pick the substrate from the water and place it on a dry metal surface. Let the water evaporate from the substrate and be dried. You can leave the sample on the metal surface for as long as 2 hours.

Step 5: Inoculate the sterilized substrate

Now, you can inoculate the dried substrate. However, it would be wise of you to ensure that the spawn rate is below 5%.

Step 6: Bagging

Collect the sterilized mushroom substrates and place them in the growing chamber

3.  Composting Process of Sterilizing Mushroom Substrate

Haven’t you seen those cute little button mushrooms? Well, they are commonly known as Agaricus mushrooms. Did you know you can grow them using the Composting process? Moreover, you can breed some sterilized oyster mushrooms using this process.

Follow a few steps for sterilizing mushroom substrate using the composting process:

Step 1: Prepare the substrates

Gather all the mushroom substrates that you have planned to sterilize. Create a pile of your mushroom substrate in a suitable area.

Step 2: Moisturize the mushroom substrate

Pour the optimum amount of water onto your substrate. Mix the constituents properly. On average, the whole mixture should have 70 to 75% moisture. You have to continue mixing and moisturizing the substrate sample for 7 days. You have to do so to keep the pile from getting overheated. If the substrate is not moisturized, hot spots might grow. Henceforth, moisturizing is very necessary. During this process, the pile of substrates will heat up to 60 to 70 degrees.

Step 3: Store the moisturized substrate into tunnels

Now it is time for you to get your hands on the shovel. You have to form a tunnel and store the moisturized and heated substrate over there. Afterward, seal the tunnel with a frim barricade.

Step 4: Stabilize the temperature within the tunnel to 65 degrees for the next 18 hours

Furthermore, you have to ensure that the temperature for the next 18 hours within the tunnel is kept at 65 degrees. You can do so by managing a supply of aerated steam within the tunnel. This process is known as pasteurization.

Step 5: Lower down the temperature to 48 degrees

After 18 hours are done, you have to decrease the temperature level to 48°C. It should be noted that the temperature has to be kept constant and keep the temperature for 48 hours.

Step 6: Reduce the heat exposure to 25 degrees

After 48 hours are done, reduce the heat exposure. Cool down the substrate and bring it to room temperature at 25°C.

Step 7: Inoculate the Substrate

Now, you have to inoculate the substrate. However, you have to ensure the byproducts or spawn rate is less than 6% during the injection.

Step 8: Collect the sterilized mushroom substrate

Now it is time to collect your sterilized and composted mushrooms. Fill them inside a bag and place them on your grow chamber.

4.  Tyndallization Process of Sterilization

Tyndallization is the sterilization process that involves killing pathogens by the manipulation of varying temperatures. Along with being a very accurate process, it is a method that is executed through various cycles. Henceforth, you will have to be very vigilant if you plan to carry it out:

Follow a few steps for sterilizing your mushroom substrates through tyndallization:

Step 1: Prepare the substrates.

Firstly you have to gather the substrate in bags. You can chop them into long, slender pieces if you want to.

Step 2: Raise the temperature to 100 degrees for 30 minutes

Place the bag of the substrate in a container. Raise the temperature to 100°C for 30 minutes by providing heat.

Step 3: Keep the temperature 37 degrees for the next 12 hours

After 30 minutes are done, you have to reduce the temperature to 37 degrees. Keep the temperature at that point for the next 12 hours.

Step 4: Increase the temperature to 100 degrees for the next 20 minutes

After the 12 hours are done, increase the temperature to 100 degrees. Stabilize this temperature for the next 20 minutes.

Step 5: Repeat 2 to 3 for the next 3 days

You have to repeat steps 2 and step 3 for the next three days.

Alternative process:

The alternative process of sterilizing mushroom substrates with tyndallization takes lesser time. You can follow these steps to conduct it:

  • Prepare the chopped substrates in bags. Then, place the bags in a container
  • Provide heat exposure and raise the temperature to 100°C. You have to keep It at 100 degrees for one hour.
  • Afterward, for the next day, you have to keep the temperature to 25 degrees.
  • Then repeat step 2 and step 3 thrice.

5.  Pasteurization Process of Sterilization

Pasteurization is a very commonly used sterilization process. In the pasteurization process, substrates are kept at 60-80°C, for at least 5 days. At the same time, Super-Pasteurization involves placing substrates at 80-100°C for approximately 10 to15 hours.

Follow a few steps for carrying out the pasteurization process:

Step 1: Prepare the Substrate

Split and chop your substrates into slender, long pieces, with each measuring 1-6 cm. It will enhance the disintegration of the pathogens.

Step 2: Collect the chopped substrate

Fill the chopped substrate into a sealed bag.

Step 3: Heat the water

Provide maximized heat to the water you are going to use for the process. Heat it until it reaches a temperature above 100°C. The more temperature you provide, the lesser time it will require for the process to be completed.

Step 4: Place the bags with substrates on a barrel with heat exposure

Now, you have to arrange a barrel with a stable pressure relief valve. You have to provide hot steam into the barrel and let the temperature rise. Then, place the bags with substrates on the steamy barrel. Let the process be continued for 15 to 18 hours.

Step 5: Cool down the substrate bags

Take the bags away from the barrel. Then keep it in a cool place to decrease its temperature. You have to let the substrate cool down.  You have to let them rest for 24 hours to have the temperature decrease to 28 degrees.

Step 6: Inoculate

Now you can collect the sterilized mushroom substrates and keep them in your growing chamber.

Frequently Asked Questions

Do you have to pressure cook mushroom substrate?

Pressure cookers are very helpful tools for mushroom cultivation. They are widely used for the sterilization process of mushroom substrates. For example, substances such as agar, grain spawn, and others are sterilized using pressure cookers. On that note, if you are willing to learn how to use pressure cookers for sterilizing mushroom substrates, have a look at this article.

Does mycelium grow faster in the dark?

There is a common hypothesis or superstition that goes among mushroom cultivators that, mushrooms can grow speedily amid the darkness. However, it is just a superstition. There is no scientific proof behind this statement. However, it is true that direct exposure to excess light can hamper the growth of mushrooms. It is wise to keep these substrates under substantial and natural light

How long does it take to sterilize at 15 psi?

You have to perform the sterilization in autoclave cycles to make the process effective. During the autoclave, you have to make sure that you have kept the temperature at 121° C for approximately half an hour. You can do so, by exposing saturated steam under the pressure of 15 psi, within the system. How long you plan to heat and run the cycles, depends on the volume of substrates being sterilized.

What can I do with an old mushroom substrate?

While some growers choose to dispose of them, some spread them over a big pile or stack them up in containers or plastics. They even make these leftover substrates go through composting.


As we have seen, there are many promising alternative methods for sterilizing mushroom substrates other than using pressure cookers. So, it is time to sterilize your mind and get rid of all those toxic thoughts that say that you cannot sterilize substrates without using pressure cookers.

We hope you have liked this article. Do not forget to share it with your fellow mushroom cultivating amigos! Do comment down below, if you are aware of any other mushroom sterilization technique. Happy sterilizing!

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