Pasteurization is a process that mushroom growers use in a variety of ways.
The optimal technique for you will depend on your level of expertise, the species of mushrooms you intend to produce, and the type and quantity of substrate.
Pasteurization can be divided into two categories: heat pasteurization and cold pasteurization. We’ll examine these in more detail in the sections that follow.
Heat pasteurization methods
The most popular pasteurization technique is heat pasteurization, which is also quite efficient.
In order to heat up and pasteurize substrates, mushroom producers typically utilize hot water or steam.
Here are a few common heat pasteurization techniques:
Hot water Pasteurization
For small-scale home growers, hot water pasteurization is effective, but the cost of pasteurizing large substrate increases.
It entails immersing your substrate for one to two hours in hot water that is between 149 and 167°F (65 and 75°C).
At this temperature, water kills competitors that are sensitive to heat, but certain helpful bacteria that can withstand heat are still alive in the substrate.
You run the risk of eradicating the helpful bacteria if the water becomes too hot.
Bring water to a boil, then turn the heat down until the water is within the necessary temperature range to pasteurize a substrate in hot water.
It’s ideal to use a thermometer at first, but with practice you’ll learn what setting to use on your stove or gas burner to maintain the right temperature.
When the water is the proper temperature, add your substrate, either loose or in an old pillowcase or net bag, to the hot water.
Removal and drainage are made simpler by pasteurizing chopped straw in a net bag.
A weight of some kind is frequently required to be placed on top of the substrate to keep it submerged.
Keep the water at the proper temperature and let the substrate soak for around two hours.
After the allotted time has passed, stop the heat and let the substrate cool.
In order to remove extra water from a substrate that has been placed straight into water, remove the substrate once the water has cooled.
Take the pillowcase or bag out of the hot water after use and hang it up to drain and cool.
Once the substrate has drained, remove it from the bag and spread it out on a clean surface if you want it to cool faster.
Steam pasteurization
Steam pasteurization is more expensive and less easy for home growers because it takes specialist equipment and a lot of energy.
In contrast to hot water pasteurization, producers heat the substrate with steam rather than water in this method.
In order to use this technique, you release steam into insulated rooms or containers that contain pre-moistened substrate layers or bags.
When employing this technique, take care not to overheat the substrate because doing so will sterilize it and eliminate any helpful bacteria. It is quite tricky.
Oven Pasteurization
Can a substrate be pasteurized in an oven?
Yes, and while the method is not necessarily as dependable as pasteurization using hot water or steam, it is still quite simple.
The size of your oven also restricts the amount of substrate you can pasteurize, unlike hot water and steam pasteurization, which allow you to scale up for bigger quantities of substrate.
The first step in pasteurizing substrate in an oven is to pre-heat it to 390 to 400°F (200 to 210°C).
The substrate must then be hydrated until it is just a little bit above field capacity in order to account for any water loss due to evaporation.
Place the substrate tray in the oven and wait while it pasteurizes.
Open the tinfoil after 60 minutes and use a thermometer to check the substrate’s center temperature.
160 to 180 degrees Fahrenheit (71 to 82 degrees Celsius) is the target range. If the substrate’s center reaches this temperature, you can switch off the oven and let the substrate slowly cool inside.
In that case, keep the heat on for an additional 30 minutes.
Fermentation
Fermentation is a common method for pasteurizing substrate in large-scale oyster and button mushroom farms.
The substrate is first chopped and moistened, and then it is regularly turned for the first few days as it ferments.
The fermenting substrate warms up like a compost pile during this stage of the procedure, which is known as phase one composting.
In phase two, the substrate is loaded into an insulated chamber or tunnel and allowed to pasteurize utilizing heat produced inside.
The substrate is now clean and pasteurized and prepared for spawning after phase two.
It is challenging to use this pasteurization technique on a small scale since it requires a lot of fermented substrate to reach pasteurization-safe temperatures.
Cold Pasteurization Methods
Although some people believe that hot water pasteurization is more efficient, cold pasteurization is also helpful when growing mushrooms that require less nutrient-rich substrates.
Pasteurization with cold water is often safer, simpler, and more energy-efficient than pasteurization using heat.
Since there is no need to heat a lot of water or keep temperatures high for an extended period of time, it is perfect for pasteurizing huge amounts of bulk substrate.
Here are a few common techniques for cold pasteurization:
Cold water fermentation
This technique, pasteurization through spontaneous fermentation, takes a lot longer than other approaches and can be stinky, but it is energy-efficient and suitable for processing huge amounts of straw.
Straw is soaked in non-chlorinated water for about a week in order to ferment it.
Anaerobic microorganisms, or bacteria that can live without oxygen, grow during this time and begin to degrade (ferment) the substrate.
The procedure eliminates organisms like aerobic bacteria and fungal spores that require oxygen to survive.
The anaerobic organisms dies when the straw is taken out of the water, drained, and exposed to oxygen, leaving you with pasteurized straw.
Cold water bath Pasteurization
Substrat is submerged in a solution that hydrates the straw while eradicating dangerous microorganisms during cold water bath pasteurization.
To pasteurize a substrate, you can pasteurize a variety of substrates in a cold water bath.
Although lime bath pasteurization is our preferred procedure, other options include wood ash, soap, bleach, chlorine, vinegar, and hydrogen peroxide.
Five of the simplest techniques for pasteurizing cold water baths
For those who produce mushrooms at home and for simple mushroom farms, cold water bath pasteurization techniques are ideal.
Because they use less energy and don’t require a lot of expensive supplies, growing mushrooms is simpler for beginners.
All of the techniques listed below include soaking the substrate in a cold water solution, although they each have a different mechanism of action.
Here are 5 quick ways to pasteurize cold water and how they each work:
Lime Bath Pasteurization
This approach is regarded by many growers as the most effective cold water bath treatment.
The pH of the water bath is substantially raised using hydrated lime.
The fast pH change that occurs when the substrate is immersed in the lime bath ruptures the organisms’ cell walls, resulting in their death.
Wood Ash Bath Pasteurization
By using wood ash to raise the pH of the water bath to between 11 and 14, this technique achieves the same results as lime bath pasteurization.
The benefit of wood ash pasteurization is that it is more natural and environmentally friendly than lime and frequently produces stunning flushes of mushrooms.
On the down side, finding a consistent supply of unprocessed hardwood ash might be challenging depending on where you live, and you’ll need more wood ash than lime to get the right pH for pasteurization.
You must add ash at a rate of 3% of water weight, or 30 g (1 oz) per 1 liter (0.26 gallons), to pasteurize wood ash baths.
Straw is most frequently pasteurized using cold water ash baths, however hardwood pellets can also be pasteurized using this technique.
Soap Bath Pasteurization
Pasteurization of soap is an additional simple and efficient technique.
Growers have had success pasteurizing substrate using soap solutions produced from cheap laundry or dish detergent.
Because certain liquid soaps may contain preservatives with antifungal effects, we advise using washing powder instead.
The microorganisms’ cell walls are damaged by osmotic pressure, leading to their rupture in this pasteurization technique.
When you add soap to water, you create an environment with an osmotic pressure that is significantly different from what is found inside the cells of the competing organisms.
The organism’s cell membranes rupture and it dies when the substrate is submerged in water due to the difference in osmotic pressure.
A solution that will pasteurize a substrate can be made with as little as 0.6 g (0.16 oz) of soap per 1 liter (0.26 gallons) of water.
Chlorine bath Pasteurization
To pasteurize chlorine baths, you can use household bleach or swimming pool chlorine.
Chemically, they are extremely similar, but in order to make your solution, you will typically need to add more household bleach than pool chlorine.
This technique requires soaking the substrate for 16 to 20 hours in water that has been mixed with home bleach or chlorine that contains 5.25% sodium hypochlorite.
When using household bleach, you must add it at a rate of 355ml (12 oz) per 1 liter (0.26 gallons) of water, or 0.35% of the weight of the water.
Before you inoculate the substrate, the chlorine in the water bath oxidizes, killing the majority of living organisms and gasses off, so it shouldn’t harm the mushroom mycelium.
However, to be safe, we advise adding a chlorine reducer to neutralize the solution’s chlorine concentration before draining the substrate.
Chlorine reducers are available at swimming pool supply stores, and they will lower the chlorine content of the water to levels more in line with tap water.
It’s preferable to dispose of the residual solution in an area free of vegetation when employing this approach without the chlorine reducer to avoid burning.
Vinegar Pasteurization Methods
Vinegar pasteurization method decreases the pH, which is the reverse of what lime and wood ash do.
Add 5% white vinegar to water at a rate of 2% of water weight, or 20g (0.07 oz) per 1 liter (0.26 gallons), to create a vinegar bath. When employing this technique, you desire a solution with a pH between 3.5 and 4.
Submerge the substrate in the vinegar solution and let it soak for 16 to 20 hours after checking the pH to make sure it is within the desired range.
The substrate is ready for inoculation once it has been removed from the vinegar solution and allowed to drain for about an hour.
How Long Does the Pasteurization of a Mushroom Substrate Take?
Depending on the technique utilized and the volume of substrate being pasteurized, a different amount of time is needed to pasteurize mushroom substrate.
When comparing the two processes, cold water fermentation can take anywhere between one and two weeks, depending on the amount of substrate, while hot water pasteurization takes about two hours.
Pasteurization using a cold water bath falls somewhere in the middle, and the substrate often needs to soak for 16 to 20 hours.
Mushroom Substrate Pasteurization: The pros and cons
If you wish to build up a simple mushroom farm, pasteurizing mushroom substrate is perfect and has many benefits, but it also has a few disadvantages.
The advantages and disadvantages of pasteurizing mushroom substrate are listed below.
Pros:
🍄 Sterilization is more expensive and difficult.
🍄 For spawning, a sterile environment is not necessary.
🍄 It’s an approach that is more forgiving and simpler for beginners.
Cons:
You can only grow specific shiitake species, including the button, cremini, portabella, oyster, wine cap, pioppino, and straw strains.
If pasteurized substrate is being inoculated, a greater spawn rate is frequently required.
When employing substrates with greater nutrients, a pasteurized substrate is more prone to contamination.
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