Everything You Need to Know About Mushroom Substrates

Everything You Need to Know About Mushroom Substrates

Are you curious about mushroom substrates? If so, you've come to the right place! In this blog post, we'll discuss everything you need to know about mushroom substrates, from what they are to how to create your own. We'll also go over some of the most popular substrates on the market and explore the pros and cons of each. By the time you're finished reading, you'll have a better understanding of mushroom substrates and be able to make informed decisions when selecting a substrate for your mushroom growing needs. So let's get started! 



What is Substrate and What is it Used For?


A mushroom substrate serves as a medium for mushroom mycelium to establish and grow in, providing essential nutrients, moisture, and energy for the mushrooms to thrive. To ensure successful growth, it's important to match the correct substrate with the specific species of mushroom.


A good mushroom substrate should be dense in woody, fibrous materials containing a high amount of carbon. It should also contain a small amount of nitrogen, magnesium, potassium, calcium, sulfur, and phosphorus, have a slightly acidic pH level of about 5-6.5, good structure for air exchange, and a moisture content of 50-70%. Additionally, it must be free from competing organisms to provide a clean environment for the mycelium to flourish.


Before inoculating with mushroom spores or mycelium, the substrate must be prepared by adding water and extra nutrients if necessary. It should then be sterilized or pasteurized to eliminate any competing mold or bacteria.


Mushroom substrate can be placed in various containers, such as large plastic bags for commercial growers or smaller jars or buckets for home growers. After inoculating, the mycelium will need several weeks or even months to decompose and spread throughout the substrate. Once colonization is complete, the entire substrate will be covered in mycelium and ready to fruit.



Commonly Used Materials For Substrate


Mushroom growers use a variety of materials as substrates for growing mushrooms. The commonly used substrates are coffee grounds, straw, coco coir and vermiculite, hardwood pellets, manure, and logs.


Coffee grounds are easy to obtain and pasteurized during brewing, so they are suitable for growing mushrooms.


Straw can be bought from farm stores and prepared using a heating method.


Coco coir and vermiculite are mixed in equal parts to make a substrate.


Hardwood pellets are a low-cost option that can be supplemented with bran to add nutrients to the substrate.


Manure, although not ideal, is necessary for some mushrooms and is combined with coco coir.


Logs are also used as a substrate for growing mushrooms outdoors, with hardwood varieties such as beech, poplar, and oak being the most suitable.



Pasteurizing and Sterilizing Mushroom Substrate


Learning how to make mushroom substrate involves not only selecting the right substrate but also deciding when to pasteurize or sterilize it. While some growers may use complex setups with cleanrooms and expensive equipment, a low-tech approach is often sufficient as long as basic procedures for sterilization or pasteurization are followed and surfaces are kept clean.


The main difference between pasteurization and sterilization is the temperature at which the substrate is exposed. Pasteurization involves heating the substrate up to 185 degrees F, while sterilization requires temperatures above 250 degrees F and pressure.


For pasteurization, there are two methods: hot water bath pasteurization, where the substrate is submerged in boiling water for at least one or two hours, and cold water lime pasteurization, which involves soaking the substrate in a bath of hydrated lime-treated cold water for 24 hours.


Sterilization, on the other hand, requires a pressure cooker or similar equipment to expose the substrate to high temperatures and pressure.


Alternatively, tyndallization or fractional sterilization can be used by boiling jars or bags for a certain length of time over several days in a row.


However, sterilizing the substrate in an oven or autoclave may cause it to dry out or burn, and rehydration with sterile distilled water may be necessary.



Is it Necessary to Pasteurize or Sterilize Substrate?


Mushroom growing substrates are often rich in nutrients and moisture, which makes them an ideal environment for mold and bacteria to thrive. These contaminants can outcompete the mycelium and hinder the growth of mushrooms. To give mushrooms the best chance to establish themselves, pasteurization or sterilization is necessary.


Pasteurization removes most of the contaminants from the substrate, much like pulling weeds from a garden before planting vegetables. Sterilization, on the other hand, kills all living organisms in the substrate.


The decision to sterilize or pasteurize depends on the nutrient content of the substrate. High-nutrient substrates like manure, rye grain, popcorn, brown rice, and wheat berries should always be sterilized. Less nutritious substrates like straw, coco coir, logs, and cardboard can be pasteurized.


When supplementing substrates with more nutritious materials, sterilization may become necessary. If unsure, sterilizing any substrate will guarantee that contaminants are eliminated, albeit with additional effort and equipment.



Straw Fermentation: A Pasteurization Alternative


Instead of pasteurizing straw, mushroom growers have the option to ferment it. This process involves submerging a bag or bale of straw underwater for around a week, or even two weeks for larger bales. Anaerobic organisms break down the straw during fermentation, eliminating other oxygen-dependent organisms. Once the fermented straw is exposed to air, it becomes essentially pasteurized.


However, one drawback of this method is the strong odor it produces, similar to the process of fermenting foods like sauerkraut or kombucha. It can be difficult to remove the smell from clothes or skin, so precautions must be taken. Additionally, fermenting requires more time and planning than pasteurizing, which can be completed in just a few hours.



How to Mix Your Substrate


Mixing substrate can be a simple process, as using your hands is an easy way to do it. However, it's important to wash your hands thoroughly before starting and to consider wearing disposable gloves.


For larger batches, you could use a big spoon or a shovel, depending on how much substrate you're handling. A compost tumbler, which is what we utilize at Nublume, is also an option. Alternatively, you can use a commercial substrate mixer.



Which Substrates Work Best and For Which Mushrooms?


Throughout this guide, we have alluded to the fact that different mushroom species require different kinds of substrates. Unfortunately, there is no one-size-fits-all answer to the question "What is the best mushroom substrate?" If it were that simple, every mushroom grower would use the same ultimate substrate.


Some mushrooms, like oyster mushrooms, are very aggressive and can colonize a wide variety of materials, while others prefer wood-based substrates. Some, like truffles, even prefer to grow on the roots of living trees, which makes them notoriously difficult to grow commercially.


Choosing your substrate comes down to a few factors: your available time and money, the substrate materials that are available locally, and the mushroom species you want to grow.


If you want to keep your time and money input low, pasteurized substrates without supplementation are a good option, and oyster mushrooms are a good choice.


If you want to grow a wide range of gourmet mushrooms on a commercial scale and are willing to invest more time and money, supplemented substrates and sterilization methods are necessary.


If you choose to go the low-tech route, good substrate options include straw, straw pellets, sawdust pellets, sugar cane mulch, and coffee grounds.


Straw is not very nutritious, but it can be effective for growing oyster mushrooms, as well as other species like agaricus, wine cap, shaggy mane, and enoki.


Logs or sawdust can be used for wood-loving mushrooms like shiitake, maitake, turkey tail, lion's mane, and reishi. Supplemented sawdust mixes, such as Masters Mix or a mix of hardwood sawdust, wood chips, bran, and gypsum, can also be used.


Manure is not an ideal substrate for most edible mushrooms, except for button, crimini, and portobello mushrooms. Coffee grounds are recommended only for oyster mushrooms, while vermiculite can be mixed with other materials for better moisture retention or other qualities.


If you are thinking of growing mushrooms commercially, you may want to supplement your substrate with materials like bran or seed derivatives, which can increase the yield of mushrooms. Pellet forms of high-protein animal feed are preferred since they are already pasteurized.


Experimentation is necessary to determine the amount of supplementation to add, which will also depend on whether the material is sterilized. We recommend starting at 5% and working your way up.



What Can You Do With Used Substrate?


As an experienced mushroom cultivator, you will inevitably accumulate significant quantities of spent substrate.


At this point, you might wonder about the best way to dispose of it. Composting is the most popular solution among mushroom growers. You can either mix the substrate with an existing compost pile or create a new pile solely composed of spent substrate, which will gradually decompose into a nutrient-rich compost.


Alternatively, if you have a garden, you can blend the used substrate directly into the soil. Some large commercial growers take it a step further and process their spent substrate into compost, which they then sell to home gardeners.


By utilizing your compost pile or garden, you may even be able to coax a few extra flushes of mushrooms out of the substrate. Some mushroom species, such as oyster mushrooms, are capable of thriving and spreading in this environment, giving you free mushrooms year after year.


Additionally, you can use some of your spent substrate to inoculate a new batch of substrate, which eliminates the need to purchase mushroom spawn from suppliers and allows for a fully self-sufficient operation. However, keep in mind that this Low Tech Mushroom Farm approach may result in a slightly higher risk of contamination.


For those growing mushrooms in urban areas, finding a way to dispose of used substrate can be challenging. However, many cities now have composting programs in place that offer a solution. Used substrate can be placed in compost bins that are collected weekly, or dropped off at city depots that handle yard waste, compost, and other recyclables.


In the event that a city doesn't have a composting program, farmers in the surrounding area may be willing to accept used substrate to add to their own compost piles. This service could be offered for free.


Additionally, studies have explored the possibility of using mushroom substrate as an ingredient in feed mixes for chickens and cattle. So, even if composting isn't an option, there may be other ways to make use of the substrate.



Concluding Remarks


Your success in growing mushrooms depends on selecting the appropriate substrate and preparing it correctly for the specific species you're growing.


While some mushrooms, such as oyster mushrooms, can grow on a variety of substrates such as straw and even cardboard, other species require specific substrates to produce high yields.


Once you have chosen the appropriate substrate, you need to pasteurize or sterilize it to minimize the risk of mold and bacteria growth. This step is crucial in ensuring that your mycelium can establish itself successfully.


After harvesting your mushrooms, you can dispose of the spent substrate by composting it.


Now that you understand how to create the ideal substrate for your mushrooms, you're ready to start growing!

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