Mushroom Spawn is a fundamental component of mushroom cultivation. It is often compared to “mushroom seed” as it is what mushroom growers utilize to “plant” (inoculate) their mushrooms. While these botanical comparisons are compelling parallels for communicating the purpose of spawn, it is good to clarify the biology of fungi is entirely distinct from that of plants.
So, what is mushroom spawn?
Spawn is a pure culture of mushroom mycelium grown on grain or sawdust, which is utilized to inoculate a bulk substrate. After inoculation, mycelium spreads from the spawn onto the substrate of choice.
Fundamental Qualities Of Spawn
- Pure Culture: Spawn contains a sterile culture of mushroom mycelium. It should not contain any contamination or dormant spores that could compromise the fungus's future growth. For this to be achieved, it must be prepared under sterile laboratory-like conditions.
- Spreadable: Spawn is made of easily fragmentable materials that can be broken up and spread onto the new substrate. By distributing the spawn throughout the substrate provides many “inoculation points” from which mycelium can spread.
- Nutritious: Spawn is generally grown on nutritious materials that promote vigorous growth once placed onto their new substrate. In some cases, such as in outdoor cultivation, low-nutrient sawdust spawn can also have benefits.
- Vigor: Spawn should contain fresh mycelium that is actively growing and in a state of vigor. If your spawn is old or weak, it will cause slower growth and inferior yields.
The Importance Of High-Quality Spawn
High-quality spawn is quintessential to mushroom cultivation. Even if you have the best technique and state-of-the-art equipment, everything sits on the shoulders of your spawn. While good spawn ensures quick growth and high yields, low-quality spawn can cause the opposite, or even complete failure.
While spawn can be produced by anyone (and we’ll teach you how), keen attention to detail is required to get it right. Most methods to make spawn require a sterile environment and sterilization equipment, which may not be readily available for many folks. The exception is if you purchase pre-sterilized grains and inoculate them with a liquid culture. Anyone can do this with no additional equipment.
Generally speaking though, it is recommended that first-time growers purchase their spawn from a trusted producer. After all, it’s best to get experience with the latter stages of the process before embarking on producing spawn yourself. This way, you can really dial in your process before taking on this additional challenge.
Consider that many serious mushroom cultivators, if not most, do not make their own spawn. They purchase it from a trusted producer to ensure consistency and quality.
What To Look For In High-Quality Spawn
Below are some features you should look for in high-quality spawn to ensure the inoculation is successful.
| Good Spawn | Things to Look Out For | |
|---|---|---|
| Color | Completely white, indicating healthy mycelium growth. Note that Pink oysters and a few other species may have distinct colors to their mycelium. | Any discoloration or odd colors may suggest contamination. |
| Colonization | The entire spawn should be thoroughly colonized by mycelium. | Uncolonized areas provide opportunities for contaminants to establish themselves post-inoculation. They may also indicate areas that are already contaminated. |
| Freshness | The spawn should be easy to break apart, indicating freshness and vitality. | Difficulty in breaking apart or the presence of pins (tiny mushrooms or primordia) suggests the spawn is old and may be less vigorous. |
| Absence of Contaminants | No visible signs of mold, bacteria, or other unwanted organisms. | Contaminants compete with the desired mycelium, potentially hindering mushroom growth or rendering the spawn unusable. |
| Smell | A fresh mycelium-like aroma. | Any off or foul odors could indicate contamination or spoilage. Yeasty, alcohol, or dusty smells are bad signs. |
Types Of Spawn
There are three main types of spawn:
- Grain Spawn: This is the most commonly used in mushroom cultivation. Since grains are high in nutrients, they give the mycelium ample vigor and strength for rapid colonization. Grain spawn can be made of various grains, including wheat, rye, millet, sorghum, and popcorn. We will discuss the differences between these grains later.
- Sawdust Spawn: Sawdust spawn is low in nutrients, making it perfect for outdoor cultivation or inoculating logs. In these contexts, grain spawn could get easily contaminated or attract insects/animals wanting to eat it. You can also utilize sawdust spawn for inoculating straw or more sawdust, but growth may be slower, and your yield lower when compared to grain.
- Plug Spawn: These are wooden dowels colonized with mycelium utilized explicitly in log cultivation.
How To Make Mushroom Spawn
There are many different ways to make spawn. Some of these methods, like pre-sterilized grains, are easy and suitable for beginners. On the other hand, making spawn from scratch can be a bit trickier (but perfectly doable).
There are four essential steps to producing spawn.
- Preparation: Preparing your grain or sawdust (soaking, boiling, drying, etc.) and fill it into jars or bags.
- Sterilizing: Sterilization requires heating your materials at 121°C (250°F) for 90-120 minutes. This is typically done in a pressure cooker or autoclave.
- Inoculation: This is either done with agar, liquid culture, or existing spawn. Liquid culture can be inoculated under almost any conditions utilizing proper sanitation protocols. Other methods may require a flow hood or a still-air box, plus familiarity with the aseptic technique.
- Incubation: The last step is to keep your inoculated spawn in adequate conditions for the growth of the inoculated mycelium.
Making Grain Spawn
Grain spawn is the spawn of choice for most mushroom growers and hobbyists. Since it is naturally nutrient-rich, it gives the mycelium an extra boost for quick colonization and high yields compared to sawdust spawn.
Grain spawn can be made with a number of different grains, including wheat, rye, millet, sorghum, brown rice, popcorn, and oat. While some are arguably better than others, they all accomplish the same goal. Growers often have a preference based on accessibility, cost, and grain experience.
| Grain | Comments |
|---|---|
| Wheat | Readily available, good nutrient profile. Can be prone to clumping and bursting. |
| Rye | Preferred by many cultivators and considered gold standard. Excellent nutrient balance and relatively low risk of bursting. |
| Millet | Can be challenging to source in bulk. Many home cultivators like it for no-soak no-boil techniques. |
| Sorghum | Some cultivators like sorghum due to its cheap cost. The downside is that it may require additional cleaning. |
| Brown Rice | Not recommended in most cases as it is prone to becoming mushy and clumping. |
| Popcorn | Easily accessible and many growers like it. It is more expensive than other grains. |
| Oats | Similar to wheat, and prone to clumping. |
Classic Grain Prep
Below are the classic instructions for preparing grain which precedes sterilization. Like almost every step in mushroom cultivation, there are many other ways to go about it. Some techniques skip soaking, boiling, or even cleaning, and while this might be completely suitable in some cases, these processes are conducted to ensure consistency and a reduced risk of contamination.
- Cleaning Grain: Depending on the grain you purchase, it may have some impurities. These can be small stems, husks, rocks, and even garbage. This is particularly true for grains produced for animal feed, such as sorghum. It is recommended that these be removed manually. You can also winnow the grains in front of a fan to blow away lighter impurities. Afterward, rinse the grain to remove any fine sediments or dust.
- Soaking Grain: While there are many methods for “no-soak” grains if you are in a rush, it is generally recommended to soak the grain for about 8 - 12 hours. This not only hydrates the grain, but promotes the germination of endospores (potential contaminants) which become less resistant to sterilization after germination.
- Boiling Grain: This process requires careful attention as you do not want to overcook grains. Oat, wheat, and rye typically take around 30 minutes of boiling, while popcorn can take up to 45 minutes. The goal here is to have the grains “al dente” without them bursting. Essentially, it should be soft enough for the chew without bursting or being mushy.
- Strain and Dry: Once boiled, strain all the water and let them dry. I like to lay them out on a clean table with a fan. Move them every 15-30 minutes as moisture tends to accumulate on the underside of the grains. Once they are dry on the surface, give them another 30 minutes to be certain they do not have excess moisture.
- Fill Jars/Bags: Once dry, you want to fill your jars or bags. Only fill jars about 2/3 full so that when shaken, you can effectively mix the grains. If using jars, make sure your jar has a hole/filter for breathing (if not they can burst in the pressure cooker).
- Sterilize: The final step of the process before inoculation is to sterilize your grains. This is typically done for 90 to 120 minutes at 15 PSI. For smaller portions of grain (<1lbs) 90 minutes is typically fine, while large bags/jars may be done at least 120 minutes for safe measure.
A Word On Sawdust Spawn
Sawdust spawn has traditionally been used for mushroom cultivation despite it having some downsides compared to grain spawn.
| Pros and Cons of Sawdust Spawn | |
|---|---|
| Pros | Cons |
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Sterilizing Spawn
Sterilization aims to eliminate any living organisms, or their propagules, from the substrate. It is essential to conduct proper sterilization when making spawn as contamination can compromise its viability. Grain spawn in particular is very vulnerable to contamination due to its high nutrient content.
To sterilize spawn, it requires cooking your materials at 15 psi for about 90 to 120 minutes. This is typically done in a pressure cooker or autoclave. This process can take 3-4 hours in total, considering the time it takes to reach 15 PSI and then eventually cool down.
Inoculating Spawn
There are three main methods for inoculating sterilized grain or sawdust. Using a liquid culture is considered the most accessible, as it is less delicate and does not require a sterile environment. Inoculating spawn via agar or with colonized spawn is considered more advanced.
- Liquid Culture: For this process you are simply injecting your sterilized spawn with a liquid culture syringe. While doing this in a relatively clean environment is recommended, it does not require a flow-hood or SAB (still-air-box).
- G2G (Grain to Grain): Grain to grain is a method in which colonized spawn is multiplied. One portion of colonized grain can be utilized to inoculate 6-10 equal portions. While this method is often referred to as “Grain to Grain”, it is also applicable to sawdust spawn.
- Agar: Inoculating with agar is considered an advanced technique and does require a sterile environment provided by a SAB or a flow-hood.
- Spores: Spores are rarely used for inoculating spawn as they are rarely clean enough for this process. It is recommended to take spores to agar before inoculating spawn, so the culture can be cleaned up via various isolations. Few species are vigorous enough to colonize substrates properly from spores.
Conclusion
Like almost every step in the cultivation process, spawn is a much more complex topic than can be discussed in a single article. While anyone can make it, mastering the process takes hands-on experience. This being said, we encourage anyone with the enthusiasm to give it a shot! Consider starting with small quantities before scaling up your production.
