Commercial Cultivation of Wood Decay Fungi
Historically, cultivation methods for specialty mushrooms were developed using natural or "raw" logs as the substrate, however, in more recent times, production technologies have been developed to produce many specialty mushroom crops on supplemented sawdust-based media. These two methods vary greatly in costs, efficiencies and sustainability.
Natural log production is the least costly way to enter into commercial cultivation of Shiitake mushrooms, particularly if you have access to small diameter hardwood logs of suitable species. Other edible and medicinal mushrooms can be grown on natural logs, but the crop is seasonal, as strains that can be forced to fruit have not been developed for these other mushrooms as they have been for Shiitake. With log-based cultivation, you are trading low capitol input costs and high labor costs versus high capital costs and lower labor costs for sawdust-based cultivation.Log-based cultivation offers sustainability in that the logs harvested from woodlands improves forest health, are renewable, and log-based cultivation does not depend on high energy inputs for sterilization, incubation and fruiting. The use of plastics and other non-renewable resources is minimal.
Sawdust-based cultivation allows the grower to cultivate a much wider variety of mushrooms on a year-round basis. The capital outlay can be considerable if starting from scratch. A typical large scale operation that serves a year round market would need sawdust blending equipment, storage for sawdust and additives, a sterilizer or pasteurization unit, bagging equipment, and inoculation and incubation space.
Log-based Shiitake cultivation requires consistent access from year to year of logs, and depending on marketing goals, a facility for incubation and fruiting.
Natural Log-Based Cultivation
Log-based cultivation on a commercial level can be undertaken in a variety of ways either on a seasonal or year-round basis.
Seasonal production will require a large enough log population (>1500 logs), a means to stimulate fruiting, and is typically undertaken outdoors with no environmental controls.
The mix of logs should be 10% cool weather strains and the remainder split between warm and wide range strains that are capable of force fruiting.
Logs are harvested during the dormant season and inoculated during the fall or spring. After a growing season of incubation, the logs are mature enough to start a force fruiting regime late spring or early summer of the following year.
Logs are soaked on a weekly basis to produce a consistent supply for the market.
In a typical operation, the total log population is divided into eighths with a forcing interval of eight weeks. For example, in a 1600 log population, there would be eight groups of 200 logs each. Group A would be soaked first and then again nine weeks later for its second forcing of the season.
Log forcing should end a month before freeze-up to allow late season forced logs to recover before the onset of the dormant season.
Indoor Year-Round Production
This system relies on having a suitable structure capable of providing the climate to inoculate and incubate the logs indoors year-round. The advantage to this system is that inoculation can occur in the fall of the year as the logs will incubate indoors and therefore will mature earlier and be ready for production after 7-9 months of incubation. Forcing can begin as described above, but the logs are moved in a set pattern from incubation and into the soaking tank, from the soaking tank into the fruiting room, and then post-harvest back into the incubation room. The use of wide and warm weather strains that can be forced is recommended.
In this scenario, logs are inoculated and incubated indoors through the dormant season. During spring of the following year, the logs are brought outdoors and fruited in a natural environment.
Year-Round High Speed Method
This latest method utilizes a cool, temperature controlled incubation room and deliberate manipulation of the log environment with the use of plastic coverings to expedite spawn run. Using strains developed specifically for this method, logs can be brought into commercial cultivation within 4-5 months after inoculation. Field and Forest Products offers a workshop on this method in the fall of each year.
Substrate-Based Commercial Cultivation
Like log-based cultivation there are various production schemes, but in substrate-based production, many different species of mushrooms can be grown in the mushroom production room. Initial investment will be determined by the scale of the operation and the species being grown. Click here to learn more about making ready-to-fruit mushroom blocks.
Purchasing Ready-To-Fruit Blocks
The fastest way to scale up is to buy in ready to fruit (RTF) blocks. An environmentally controlled fruiting room is required to maintain temperature, relative humidity and carbon dioxide levels based upon the mushroom being grown. Due to high shipping costs, profit margins can be slim so direct sales to the end user is of paramount importance.
Wood Pellet-Based Production
Hardwood fuel pellets are now readily available throughout the U.S. and offer a readily available preprocessed substrate for commercial production of some specialty mushrooms. The pellets are manufactured under heat and pressure so the initial substrate is relatively clean from contaminant organisms. The pellets are rehydrated using hot water, bagged and inoculated at a high inoculation rate (20%) to outcompete any contaminant fungi. After the appropriate incubation period, the blocks are fruited in an appropriate environment. These blocks are typically a 'one and done' fruiting.
Conventional, High-Capacity Production
This production scheme requires the following equipment: substrate blending equipment, bagging equipment, a steam generator and sterilizer. The steam generator must be matched to the sterilizer to provide sufficient steam and pressure in a timely fashion. The use of a double door sterilizer that unloads into a clean room is highly recommended.
In addition to the equipment, environmentally controlled incubation and fruiting rooms are required. The parameters for these rooms will vary based upon the species being grown.
There are numerous mixes for each species of mushroom being cultivated but generally additives to the sawdust should be obtained locally to keep transportation costs down. The additives should serve to add nutrition to the sawdust and also to add pore space to the finished block.
A typical shiitake mix would be 79% hardwood sawdust*, 10% wheat bran, 10% grain, and 1% gypsum.
All ingredients are blended and the moisture content of the final mix should be between 60-62% moisture content. Once this moisture content is reached the substrate is bagged and sterilized for 30 minutes at 120°C.
After sterilization, the bags are cooled and aseptically inoculated by hand or via machine and then transferred to an incubation room and held until the culture reaches maturation and is capable of producing a mushroom crop. The mature cultures are then transferred to the fruiting room and generally exposed to cooler temperatures and higher humidity levels, with allowances made for fresh air exchange to minimize carbon dioxide levels.
Field and Forest Products, Inc. has 35 plus years of experience in log-based mushroom cultivation and 20 plus years of experience in substrate-based cultivation. We are available for consulting on facilities if you are in need of such a service.
*A consistent source of sawdust, preferably of a single species, is desirable to prevent variation in the mix between batches.