Emma Wilson
Mushrooms are a fun and alternative crop to grow at home, but they can be finicky. The substrate—the material that mushroom mycelium grows in—must be carefully prepared to ensure the mushrooms have the best chance of success. Sterilization is one way to prepare the substrate, and it is necessary for certain types of mushrooms. This involves heating the substrate to a high temperature to kill any living or dormant organisms that could compete with the mushrooms or cause sickness. There are several ways to sterilize mushroom mulch, and this article will outline the best methods.
| Characteristics | Values |
|---|---|
| Purpose of sterilization | To kill all living and dormant organisms and fungal spores and give mushroom mycelium a head start |
| When to sterilize | When growing fussy or medicinal mushrooms that need nutrient-rich substrates |
| When not to sterilize | When growing mushrooms that cannot be cultivated on sterile media, such as field mushrooms |
| Sterilization methods | Steam, pressure, time, and temperature |
| Minimum temperature | 121°C (250°F) |
| Minimum duration | 2 hours |
| Pressure required | 15 PSI |
| Equipment | Pressure cooker, autoclave, retort, or pressure canner |
| Alternative methods | Fermentation (submerging substrate in water for at least a week), cold pasteurization with hydrated lime |
| Materials that don't require sterilization | Wood pellets, coffee grounds |
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What You'll Learn
The benefits of sterilising mushroom mulch
Mushroom mulch is a type of substrate, which is the material that mushrooms grow on. Sterilising mushroom mulch is an important step in the cultivation process, particularly for certain types of mushrooms.
Reduces Contamination
Sterilisation kills all living and dormant organisms, fungal spores, bacteria and pathogens, giving your mushroom mycelium the best possible start. This is important because mushroom substrates are usually moist and nutrient-rich, which attracts moulds and germs that can grow faster than the mushroom mycelium.
Cultivating Fussy Mushrooms
If you want to grow more delicate, gourmet, or medicinal mushrooms, sterilising your mushroom mulch is essential. These types of mushrooms require a nutrient-rich substrate, which is more prone to contamination.
Safe Consumption
If you are cultivating edible mushrooms, sterilisation can help prevent sickness. Mushrooms grown on contaminated media can become depleted of nutrients or break down and decay, and consuming these mushrooms can make you ill.
Efficient Use of Resources
By sterilising your mushroom mulch, you can ensure that the mushrooms have the best possible chance of growing successfully, reducing the risk of wasting time, money, and resources on contaminated mulch.
Easy to Sterilise
Small-scale growers can easily sterilise mushroom mulch at home using a pressure cooker. This method is simple and straightforward, making it accessible to novice mushroom growers.
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How to sterilise mushroom mulch
Sterilising mushroom mulch is a crucial step in the mushroom cultivation process, as it eliminates potential contaminants that can hinder mushroom growth or render mushrooms unsafe for consumption. While sterilisation is not always necessary, it is particularly important when working with nutrient-rich substrates prone to mould and bacterial growth.
To effectively sterilise mushroom mulch, one must understand the relationship between steam, pressure, time, and temperature. Sterilisation involves heating the substrate to temperatures above 120°C for at least 2 hours. Specifically, a temperature of 250°F (121°C) is required, as this exceeds the boiling point of water (100°C) and ensures the eradication of bacteria and spores. To achieve this temperature, small-scale mushroom growers typically use pressure cookers, while larger operations may employ autoclaves, retorts, or pressure canners.
For those seeking a more natural and low-tech approach, fermentation is an option. This method involves submerging the substrate in water for at least a week, allowing anaerobic bacteria to proliferate. However, this technique may not be suitable for all types of mushrooms or substrates.
Another alternative is cold pasteurisation, which uses hydrated lime (calcium hydroxide) to increase the pH of the substrate, creating an environment too hostile for spores and bacteria to thrive. However, it is important to note that this method does not kill all contaminants and may not be suitable for certain mushroom varieties.
Additionally, some substrates, such as wood pellets or coffee grounds, may not require sterilisation or pasteurisation. Wood pellets, for example, are already sterilised during the manufacturing process. Coffee grounds, on the other hand, are pasteurised through the brewing process, making them a unique and low-tech substrate option.
In conclusion, the decision to sterilise mushroom mulch depends on various factors, including the type of mushroom, the substrate's nutritional content, and the grower's experience and equipment. While sterilisation offers a comprehensive approach to eliminating contaminants, it may not be necessary for all mushroom cultivation endeavours.
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When to use sterilisation over pasteurisation
Sterilisation and pasteurisation are both methods used to reduce the risk of contamination when growing mushrooms. While sterilisation kills all living and dormant organisms, pasteurisation only eliminates most competing organisms, giving the mushroom mycelium a head start.
- Sterilisation is necessary for cultivating mushrooms that are more sensitive to contaminants, such as shiitake mushrooms, and it ensures a completely aseptic environment.
- If you are cultivating edible mushrooms, sterilisation is important to prevent bacterial development, which can make you ill.
- Mushrooms that require more nutritious substrates, or slow growers with longer colonisation times, need sterilised substrates with as little competition as possible.
- If you are growing medicinal mushrooms or fussy gourmet species, sterilisation is required to kill all potential contaminants.
- Sterilisation is also necessary if you are using substrates with high levels of supplementation, such as manure, soy hulls, grains, and master's mix.
It is important to note that sterilised substrates are highly prone to contamination, so aseptic techniques must be followed during the inoculation process. Additionally, not all mushrooms can be cultivated on sterile media, so it is essential to understand the specific requirements of the mushroom species you are growing.
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What equipment is needed for sterilisation
Sterilisation of mushroom mulch is a method of preparing substrates using a combination of steam, time, temperature and pressure to kill living organisms and spores. To sterilise a substrate, temperatures higher than 120°C (250°F or 121°C) are required for at least 2 hours.
Small-scale mushroom growers generally use pressure cookers for sterilisation. The size of the pressure cooker should be big enough to hold more than one bag at a time. If you're sterilising high-nutrient substrates like manure, soy hulls, grains and master's mix, you will need a pressure cooker. However, if you're sterilising less nutritious substrates like straw, sugarcane bagasse, coco coir, hardwood sawdust and cardboard, you only need to pasteurise them.
For larger operations, an autoclave, retort or pressure canner can be used. These machines will be able to sterilise larger quantities of mushroom mulch at a time.
If you're looking for a more natural way to sterilise your mushroom mulch, you can try fermentation. This low-tech technique only requires water and no energy. It involves submerging the substrate in water for at least a week, allowing the growth of anaerobic bacteria, which will proliferate in these air-free conditions.
Another natural way to sterilise your mushroom mulch is by using hydrated lime, also known as Calcium Hydroxide or CaH2O2. This compound is made by superheating naturally occurring lime so that it bonds with extra atoms of hydrogen and oxygen. The addition of hydrated lime increases the pH of the mulch, making it too "hostile" for spores of bacteria or other fungi to germinate.
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How to prepare mulch before sterilisation
Preparing mulch before sterilisation is a crucial step in ensuring the successful cultivation of mushrooms. Here are the steps to follow:
Choose the Right Mushroom Substrate
The type of substrate you choose will depend on the species of mushrooms you plan to grow. Different mushrooms prefer different substrates, just like plants favour specific types of soil. Some common substrates include hardwoods like maple, oak, or beech, straw, sugarcane bagasse, coco coir, and even coffee grounds.
Prepare the Substrate
Before sterilisation, the substrate needs to be properly prepared. This includes adding water and potentially supplementing it with extra nutrients. For example, if you're using hardwood pellets, you can mix them with water and add wheat or oat bran to provide additional nutrients for the mushroom mycelium.
Container Selection
Once your substrate is ready, you'll need to choose the right container for sterilisation. Home growers often use mason jars or small containers, while commercial growers typically pack their substrate into large clear plastic bags.
Pasteurisation (Optional)
While not always necessary, pasteurisation is a less aggressive step that can be taken before sterilisation. It involves heating the substrate to temperatures between 65-85°C for 1.5-2 hours to reduce the population of competing bacteria. This gives your desired mushroom species a better chance to take hold.
Sterilisation
Finally, the sterilisation process involves subjecting the substrate to temperatures above 120°C under pressure for at least 2 hours. This can be achieved using a pressure cooker or more advanced equipment like an autoclave or retort, depending on the scale of your operation. Sterilisation kills all living and dormant organisms, giving your mushrooms the best chance at healthy growth.
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Frequently asked questions
Mushroom mulch is a material that mushroom mycelium can grow and establish itself in. It provides mushrooms with the nutrients, moisture, and energy they need to grow and fruit. Different species of mushrooms have their own preferences for mulch.
Sterilizing mushroom mulch kills all living and dormant organisms and fungal spores, giving your mushroom mycelium the best possible head start. It minimizes the risk of contamination-related growth issues or sickness.
Sterilization of mushroom mulch is a method of preparing mulch using a combination of steam, time, temperature, and pressure to kill living organisms and spores. To sterilize a substrate, you need temperatures higher than 250°F (121°C) for at least 2 hours. Most mushroom growers will need 15 PSI of pressure to increase the temperature of the steam to 250°F (121°C). Small-scale mushroom growers generally use pressure cookers for sterilization.
