Commercial Growing

Overview

Historically, cultivation methods for specialty mushrooms were developed using natural wood logs as the substrate. 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.

The Pros and Cons of Each

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 capital input costs and high labor costs as opposed to high capital costs and lower labor costs for sawdust-based cultivation.

Log-based cultivation offers sustainability in that logs harvested from woodlands improves forest health, are renewable, and do not depend on high energy inputs for sterilization, incubation and fruiting. The use of plastics and other non-renewable resources is also minimal. However, seasonality becomes an issue with log-based cultivation as well as the access to a consistent supply of good quality wood.

Log-based cultivation also requires more planning. A shiitake log can take anywhere from 9 to 18 months to produce mushrooms when using the standard outdoor method. However, a log will last approximately one year per inch in diameter, so a 4-inch diameter log will give you several years of harvest.

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.

Sawdust blocks are also generally a "one-and-done" product that requires a large area for block disposal/composting once growing on a commercial scale.

Natural Log-Based Mushroom 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 Basis

Seasonal production will require a large enough log population (>1500 logs), a means to stimulate fruiting (i.e. water tanks), and is typically undertaken outdoors with no environmental controls. With either seasonal production or year-round methods (see below) we highly recommend investing in one or several of the Okuda Tools. These tools will greatly increase your efficiency and cut down on labor costs.

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 (see our Tips on Harvesting Mushroom logs page). After a season of incubation, the logs are mature enough to start a force-fruiting regime late spring or early summer of the following year, where 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.

Year-Round High Speed Method

This 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 as opposed to the typical 9-12 months required for outdoor incubation. This method allows you to take advantage of the times that spawn run wouldn't occur (ie the winter for northern states and the summer for southern states) and utilize it so you're not missing out on several months of growth. Field and Forest Products offers a workshop on this method in the fall of each year.

Sawdust-Based Commercial Cultivation

Like log-based cultivation there are various production schemes, but in sawdust 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. While bag (or block) cultivation can have more upfront costs in infrastructure, it's often a necessity for year-round production.

Purchasing Ready-To-Fruit Blocks

The fastest way to scale up is to buy in ready-to-fruit (RTF) blocks. These are blocks made from a producer and arrive ready to open and fruit mushrooms. 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. Field & Forest Products offers bulk block sales (a minimum 175), but as of now we only offer pallet shipments to shipment zones that are economical for the customer (zones serviced by SpeeDee Delivery). Please request our pamphlet on the bulk block program if you are interested and meet the qualifying criteria of amount and shipping zone.

Low-Tech Wood Pellet-Based Production

Hardwood fuel pellets are now readily available throughout the U.S. and offer an inexpensive 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. See our Hardwood Pellet Kits if you want to get your toes wet.

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. See our Ready-to-fruit mushroom block instruction sheets for specifications.

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 of raw materials 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 (anywhere from 2 to 12 weeks depending on species). 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.

*A consistent source of sawdust, preferably of a single species, is desirable to prevent variation in the mix between batches.

Hybrid Cultivation Method

Depending on your resources and set-up a hybrid method can prove the best of both worlds. For a year-round production schema we would recommend a timeline as follows for a northern climate.

Winter weather would require all production to be done indoors for the months of November through May. This phase would require the use of ready-to-fruit blocks. If you are making your own blocks be sure to build in the proper incubation times (anywhere from 2 to 12 weeks) to ensure your blocks are ready to open upon outdoor production slowing.

For the months of May through October you can depend on outdoor production for shiitake. Supplemental specialty mushrooms such as chestnut, oyster, nameko, etc can also transition to outdoors, but the fruiting times of these mushrooms is tied to weather patterns and cannot be forced in the same way that shiitake can. By transitioning shiitake production to outdoors you can cut down on infrastructure requirements and raw material costs for several months out of the year.