Pasteurizing Techniques in Mushroom Farming

You must understand straw pasteurization if you want to grow some species of mushroom independently. While it may seem confusing from the onset, this article will guide you through the hows and scopes of pasteurizing straw.

Cereal straws (excluding hay) like wheat or oat are utilized as a substrate or a base for the mycelium to grow. Mycelium is a collection of cells having the shape of a thread that depicts the vegetative germination of fungus. Healthy mycelia are essential for the production of mushrooms.

What is Substrate Pasteurization?

This is the process whereby you reduce the number of microscopic elements in a growing substrate. This provides the mycelium leverage over harmful microorganisms, thus overriding the substrate and subsequently producing mushrooms.

The next question on your mind is how to prepare straw? Well, there are different techniques. However, hot water is the most common. There are other methods like steam, cold, or some chemicals.

Now, let’s dig deeper into how to pasteurize straw to grow mushrooms. Why pasteurize and not sterilize? What’s the theory behind pasteurization? What are the techniques, and are there alternatives to pasteurization? The answers are provided in detail below.

Should you Pasteurize or Sterilize?

You might have come across a term such as ‘sterilization’ while researching mushroom cultivation. However, for substrates like straw, the ideal method is pasteurization, not sterilization.

Pasteurization, just as I have defined earlier on the reduction of the number of harmful bacteria in a substrate. When you have completed this process, you may still have some active microorganisms in your substrate, such as beneficial bacteria.

To sterilize, on the other hand, means to eliminate every living organism in the substrate. At completion, you would have no micro-activity left. This procedure is most times carried out using chemicals or pressure and high heat.

Sterilization leaves your straw prone to contaminants, and the substrate is automatically conditioned for anything to germinate without the help of beneficial bacteria to prevent foreign microorganisms.

The presence of beneficial microorganisms affords you the opportunity of inoculating the straw without utilizing some sterile processes. Therefore, you can inoculate outside without a piece of fancy equipment or a flow hood.

Imagine possessing a house sitter when you go on vacation.

Sterilizing is leaving your doors open with no one around.

Pasteurizing is leaving a friend to watch over your house in your absence. While someone may break in, the chances are slim.

Straw Pasteurization Methods

Now let’s consider some techniques you can adopt to grow mushrooms.

You need to dissect your straw into one to three-inch sections before you utilize any of the techniques. You can make use of scissors, leaf-chopper, or any equipment that is effective for the job. You may not want to use manual labor if you have a lot of straw to cut.

This step is crucial. Mycelium tends to colonize small pieces of straw much easier and quicker, and it will also simplify the entire process.

Water bath

Pasteurization takes place between 160 to 180 degrees Fahrenheit. You risk having the good bacteria killed and permitting the bad ones to grow if it exceeds these temperatures.

You can pasteurize your straw in a water bath by soaking it for one hour in 160-degree water. You can adopt any means you like to achieve this, but here are some conventional approaches for a larger and smaller quantity of straw:


  1. Pour water into a large pot halfway. Boil and then reduce the heat by about one-third. You can verify the temperature using a thermometer.
  2. Continue to adjust the heat and check the temperature until it reaches stability at the 160-170 range. It may take some time, as well as fiddling.
  3. Put the straw in a nylon mesh bag. You can purchase some in a local store or online or close to a laundry supply. Ensure you utilize straws that can be easily submerged.
  4. Put your straw bag in the large pot and place a heavy object on it, so the straw is submerged. Allow it to stay there for an hour, monitor the water level, as well as the temperature.
  5. Remove the bag after an hour and place it in a strainer. Mind the hot water while doing this. You can wear rubber gloves.
  6. Let the bag drain, as well as cool to room temperature.
  7. Use it as soon as possible.

Large Scale:

The principle looks the same, but this time, with a bigger pot and a source of heat.

  1. Begin by pouring water halfway into a clean and food-grade container like a 55-gallon metal drum.
  2. Boil the water until it reaches stability at about 160 degrees Fahrenheit. Utilize a long thermometer for checking the temperature. You can use a gas burner as the heat source or any other safe source of heat.
  3. Place the straw in a wire mesh basket. Then, submerge in hot water for about an hour. Don’t forget to monitor the water, as well as the temperature level.
  4. Remove the straw after an hour and place it on a plastic tarp or clean table to drain and cool. Ensure the straw has cooled to below 100 degrees, then use it as soon as possible.

It is essential to note that this large-scale method deserves some level of caution. You will be working with a heat source and a lot of water. Ensure you maintain adequate safety, security, and sturdiness.

Don’t forget that wet straw can be heavy. Based on the quantity you use, you may require assistance to bring it out of the barrel. You can also tie the bag to a pulley to make it more comfortable while lifting it out of the water. You can also use more but smaller bags.

Cold Incubation

Paul Stamets, a mycologist, instituted this idea. While it may not be pasteurization in the actual sense, it is a means of manipulating straw to provide mycelium better leverage. This technique is based on the concept that the mycelium of some cold-adapting mushrooms will colonize given a lower temperature, and this temperature level incapacitates microscopic competitors.

You have to utilize mushroom strains that grow in colder temperatures to generate a result with this method.

So how do you go about this?

Soak your straw in a bucket filled with water for an hour.

Then, allow the straw to drain to the extent that it becomes moist and not soggy.

Mix the spawn and the straw in a plastic tub or bag thoroughly. Ensure you make use of sufficient spawn.

Close the bag or cover the top of it and allow it to colonize. As soon as the straw has fully colonized with the mycelium, bring it to fruiting temperature.

Hydrogen Peroxide Technique

Hydrogen peroxide is capable of killing foreign microbes and competitor spores without hurting mycelium.

How does it work?

Soak the straw in water for about an hour. Drain it, then rinse in water thoroughly, then drain again.

Let the straw soak for a day in a water bath of hydrogen peroxide. Utilize one quart (1 liter) of hydrogen peroxide per gallon of water.

Rinse, then drain your straw for some time after it is done. Incorporate spawn and incubate just as you would typically do. This technique does produce a useful result when compared to pasteurizing using hot water.

Other Techniques

Here are some other means of pasteurizing straw in mushroom farming.

Steam heat

Heat your straw to adequate temperatures via steam. You will need some steam-injection equipment.

Dry Heat

Place the straw in a container/closet/room that can be heated to an adequate temperature using dry heat.

Other chemicals

Some individuals are using chemicals or bleach.

Pasteurizing Substrate in Oven

Put the straw in an oven bag that you use for cooking a turkey. Pre-heat the oven to about 170 degrees F and position the bag inside on a baking sheet or tray. Allow it to cook for about an hour. Ensure the bag doesn’t touch the oven sides.

Alternatives to Straw Preparation

If you find the above methods daunting. Here are some other options to pasteurize your straw.

Utilize a different substrate

Straw is just a way to grow your mushrooms. The use of wood chips or logs may be effective.

Purchase it

You can purchase some bags of pasteurized straw online. They could be expensive, but you are saving yourself time and effort. This might be a good option if you want to experiment.


Regardless of the method you use, pasteurizing straw generates a good mushroom substrate, and it is an easy and exciting aspect of growing mushrooms.

So what’s stopping you now? Attempt to pasteurize your straw by using any of the techniques shared above.


1 thought on “Pasteurizing Techniques in Mushroom Farming”

  1. Sterilization, inherently, does not leave your substrate more prone to contamination, it might actually be the opposite. What does leave your substrate more prone to contamination is the use of suppliments ( e.g wheat bran). Mycelium are not the only organisms who benefit off of these suppliments as these suppliments also provide nutrients to other microbes. It should make sense now why applying pasteurization to supplemented substrate is not the best idea. It is because not all microbes are eliminated in pasteurization and hence suppliments would decrease the competitive advantage that mycelium have as other microbes have more of a chance to thrive because of these added nutrients. This is where sterilization comes in, this basically kills off all microbes present in the substrate. It should now make sense why this method is implemented over pasteurization for supplemented substrate. If proper care is taken to not introduce any other microbes into the sterilized supplemented substrate (such as use of laminar flow hood), then this only gives the mycelium a chance to thrive in the substrate as there are virtually no competitors present in the substrate. If other microbes such as mold do end up in your sterilized substrate, it would likely contaminate your substrate because of how nutritious the substrate is, bot because it was sterilized.


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