Many varieties of mushrooms thrive when grown on logs. Logs made of most hardwood tree species like beech, poplar, oak, birch and elm work well.

Mushroom growing substrates need to be sterilized and pasteurized before being inoculated with mushroom spawn. This will eliminate competing organisms and ensure that the mycelium colonizes it successfully.

Pasteurization

When it comes to growing mushrooms, you want to make sure your substrate is as contaminant-free as possible. Otherwise, it will not be the blank canvas your mycelium needs to thrive. Pasteurization is one of the primary ways to do this.

Many mushroom cultivators use this technique to sterilize straw before inoculating it. The straw becomes less hospitable to foreign organisms after being pasteurized, making it more likely that your mycelium will take root and grow.

Typically, you’ll mix a straw pasteurized with other non-sterilized materials such as manure, soy hulls, grains, master’s mix, and nutrient-rich substrates. If you’re just dipping your toes into the world of home mushroom cultivation, pasteurization is a great place to start. It’s less energy-intensive than sterilization, and can be a little more forgiving for beginners.

Sterilization, on the other hand, is a much more rigorous process that involves heating the substrate to extremely high temperatures. This can be a challenge for some home mushroom cultivators, as it requires specialized equipment like a pressure cooker or an autoclave. It also takes a longer time to complete, and it can be hard on your substrate.

The main difference between pasteurization and sterilization is that pasteurization only reduces the number of organisms in the substrate, while sterilization eliminates them completely. This makes it important to determine which method is right for you, depending on your specific circumstances.

Most people who are just getting started with growing mushrooms use a supplemented substrate, which consists of hardwood sawdust pellets, bran, and other ingredients. This mix is usually supplemented with gypsum and gypsum-calcium carbonate for added minerals. Since wood pellets are already sterilized during the manufacturing process, they don’t need to be pasteurized or sterilized again before using them for mushroom growth.

However, non-straw and supplemented substrates do need to be pasteurized or sterilized before they are inoculated with mushroom spawn. This is because the non-straw material may be home to other species of fungus that could potentially produce poisonous mushrooms. This can be avoided by utilizing a heat-based sterilization method such as tyndallization, which uses a series of boiling temperatures over the course of an hour and a half to kill off contaminants in the substrate.

Sterilization

Mushrooms thrive on a substrate that is moist and full of nutrients. This helps preserve their freshness and potency. Unfortunately, there are many other organisms that also love these conditions, including bacteria and molds. They tend to grow faster than mushroom mycelium, and if they colonize the substrate first, the mushrooms will have a difficult time overtaking it. To give mycelium a leg up in the race to the surface, it is important to sterilize the substrate.

There are a number of different ways to sterilize mushroom substrates, but most of them require some form of heat. Using a pressure cooker is the best way to ensure that the substrate will be hot enough to kill off bacteria and molds. However, there are other methods that can be used if the grower does not have access to a pressure cooker. One way is to soak the substrate in water for one or two hours. This is a less effective method, but it can still help to reduce the number of contaminants in the substrate.

Another method is to use household bleach to sanitize the substrate. This works by adding 5.25% sodium hypochlorite to the substrate and submerging it for 16 to 20 hours. This method does not remove all of the contaminant spores from the substrate, but it is very effective at reducing the number of contaminants that are present. After using the bleach method, it is important to neutralize the solution by drenching it in water.

Some growers supplement their substrate with bran, as it can be more nutritious than wood alone. This is done because wood pellets typically have a low nutrient content, and the supplemental bran can make up for this. Adding bran to a substrate will mean that the entire block of substrate needs to be pasteurized or sterilized.

Sterilization is the most thorough technique for preparing a substrate, as it uses steam, time and temperature to eradicate all living organisms and spores from the substrate. This can be achieved with boiling, but the temperature of 212degF at sea level is not high enough to completely sterilize the substrate. Using a pressure cooker to raise the temperature to 250degF for a few hours is a more effective way of sterilizing a substrate.

Supplementation

Many cultivators use bulk substrates like straw, sugarcane bagasse, coco coir or hardwood sawdust as the foundation of their mushroom growing operations. These materials are rich in minerals and nutrients that mushroom mycelium can easily absorb. They also provide a structure that allows for good air exchange, which is necessary to the health of mushroom colonization. Bulk substrates typically need to be sterilized before they can be inoculated with mushroom spores or mycelium.

The goal of sterilization is to eliminate competing organisms like bacteria and mold in the substrate, leaving a blank canvas for mushroom mycelium to grow and colonize the substrate. For low-nutrient substrates that require a relatively slow colonization process, sterilization is critical to ensure that the mycelium does not compete with other microorganisms for food and nutrients. Sterilization is more effective than pasteurization in this regard, since the latter does not eliminate all living organisms in the substrate but instead simply reduces their population to levels that are not detrimental to the mushroom growth process.

For high-nutrient substrates, however, sterilization is not always necessary. Some types of mushrooms, particularly those that grow well on logs, will thrive in a low-nutrient environment. For this reason, it is possible to grow a variety of different mushrooms using low-cost and readily available materials like coffee grounds and sawdust. Regardless of the specific material used, however, any substrate that is rich in nutrients should be sterilized before being inoculated with mushroom spores to give the desired species of mushroom a clean slate and a head start.

When using these high-nutrient substrates, it is important to supplement them with other ingredients that can help boost growth and fruiting. For example, nitrogen is a key nutrient for most fungi, and it is commonly added to the substrate by using protein supplements like soybean meal or cottonseed meal. These supplements can be mixed into the substrate in addition to the mushroom spores and mycelium or they can be added separately, depending on the grower’s preferences.

The proper amount of water is also critical for promoting growth and full colonization of the substrate. If the substrate is too dry, the mycelium will struggle to overtake it and may not colonize the entire substrate. Similarly, if the substrate is too wet, it may encourage bacterial growth and inhibit mycelial colonization. The ideal moisture content for most mushroom-growing substrates is between 50 and 70%, which can be achieved by mixing in additional ingredients that can help to retain the water.

Composting

 

Sterilization is a process that exposes the substrate to high temperatures, killing living and dormant organisms that could compete with mushroom mycelium for nutrients. It’s important to sterilize higher nutrient substrates, such as supplemented hardwood sawdust fruiting blocks, so that the mycelium has an advantage over competing organisms in its race to colonize the material and begin producing mushrooms.

In contrast, lower nutrient substrates like straw, sugarcane bagasse, coco coir and logs only need pasteurization, rather than sterilization. Sterilizing a substrate involves heating it at very high pressure and can be a time-consuming process. It can also damage the material, making it less desirable for use as a growing medium.

Many growers add a small amount of millet to their mushroom compost to help it retain water and promote nutrient uptake. This grain is inexpensive and readily available at most feed stores. It also helps prevent scalding during heat shock, which can kill mushrooms.

Other popular ingredients for mushroom substrate include soy hull pellets, which are made from the stem portion of various grains and are a great source of protein and nitrogen. These pellets have good moisture retention, and they’re commonly added to hardwood sawdust to produce fruiting blocks. They can also be used to inoculate logs for incubation.

Another common ingredient is vermiculite, which helps to absorb excess moisture from the substrate and allows the mycelium to break it down easily. This mineral is often kiln-dried and sold for use as a soil amendment in garden centers.

For larger operations, it’s possible to speed up the sterilization process by using a steam pressure cooker. This method can sterilize large blocks of mushroom substrate in a matter of hours, which is much faster than sterilizing them by boiling them. It’s important to note, though, that even this method of sterilization doesn’t completely eliminate contaminants.