Browse by title articles:

Shiitake Mushroom Production:Fruiting, Harvesting and Crop Storage

by Stephen M. Bratkovich, Ohio State University Extension    

Fruiting

Shiitake logs are ready to fruit when the shiitake has colonized the outer cylinder of available sapwood. At this point (6-24 months), the mycelium has stored enough nutrients to form mushrooms.

An obvious sign of mature logs is the appearance of mushrooms. Other signs that indicate a readiness for fruiting are: elastic and spongy bark, logs that no longer "ring" when struck, and (under moist conditions) white mycelium appearing on log ends that are traceable to inoculation holes near the log ends.

Log Soaking

Temperature and moisture changes trigger the shiitake fungus to produce mushrooms. Therefore, log soaking is often used for "forced fruiting" and is done at a time planned by the grower.

Log soaking (complete immersion in water) can be done by various methods, such as using stock tanks, ponds or streams. The length of soak depends upon air and water temperature, log age and bark thickness. As a rule, the closer the air (log) temperature to water temperature, the longer the soak. For example, soak time in the summer is usually 6 to 24 hours with 2-3 days the rule in the cool spring or fall. Older logs and thin barked logs absorb water quickly and do not require as long a soaking time as younger or thick barked logs.

Log Stacking and Protection

After logs are soaked they are stacked for fruiting, normally using the X frame or lean-to configuration. Regardless of the stacking arrangement, all sides of each log should be accessible for harvest (Figure 1).

Logs stacked outdoors can use a protective covering to minimize wind and rain, stabilize temperatures and localize humidity around the logs. Burlap and plastic should be used with care and are recommended only for experienced growers. Fruiting (humidity) blankets, which are a better choice for the grower, are porous, white, synthetic, felted material that hold water, allow air movement and provide some insulation.

Environmental Conditions

"Pinning," which is the development of very small mushrooms, occurs as the logs dry. Whereas well-colonized soaked logs can have moisture contents as high as 80 percent to 90 percent, pinning requires a log moisture content of 35 percent to an optimum of 60 percent.

Optimum temperatures for pinning are between 55 F and 65 F with relative humidities of at least 85 percent.

Light is not required for spawn run, but is required for fruiting (enough light to read a newspaper at arm's length). If shiitake is fruited indoors, approximately 30 foot-candles of light should be used.

Fruiting Period

Once the "pins" have emerged (3-10 days after soaking), the protective covering should be removed to expose more of each log and to produce dry, firm mushrooms. Depending on the temperature and shiitake strain, the fruiting period usually lasts from one to two weeks. A grower can extend the natural outdoor fruiting season through use of combinations of different strains (cold weather, warm weather and wide range), soaking and log coverings (to prevent natural irrigation and unplanned fruiting).

After mushrooms are harvested, logs should be placed in a laying position and rested for one to three months. Log moisture content should be maintained from 30 percent to 40 percent to promote mycelial growth while inhibiting pinning. Warm temperatures (60-77 F) speed recovery of the logs, after which time they can be soaked (forced) for another flush or crop of mushrooms.

Harvesting

Shiitake mushrooms, growing on one log or a group of logs, will not usually develop at the same time. Therefore, logs must be checked frequently and mushrooms harvested at just the right time to maximize quality.

Shiitake should be picked when the cap is opened approximately 50 to 75 percent (Figure 2). At this stage the gills are exposed but the cap edges are still rolled under the cap. Harvesting mature mushrooms (cap 100 percent opened) can lead to reduced shelf life, a longer delay before the next flush and increased pest problems.

Picking

Shiitake are picked by grasping the lower portion of the stem and, with a slight twisting motion, pulling the mushroom from the log. Shiitake can also be harvested by cutting them as close as possible to the log surface with a sharp knife or scissors. Since bruises on the caps and gills will discolor rapidly, only the stems should be touched during picking.

Picking mushrooms from the bottom of the log and working up can minimize the accumulation of bark flecks and other debris on unpicked mushrooms. Also, after shiitake are picked, the stems can be trimmed to remove debris.

Picked mushrooms can be put into a basket, box, paper bag or other suitable container. Air vents in the container are recommended so the shiitake can be cooled rapidly. To prevent bruising and promote rapid cooling, picking containers should not be filled more than four to six inches deep with shiitake.

Storage

The immediate objective after picking is to cool the shiitake to 33-36 F as rapidly as possible. The use of plastic "crates" or baskets that are slatted on all sides are recommended for refrigerator storage. Mushroom shelf life is reduced dramatically by using containers that do not allow rapid cooling. Also, frost-free refrigerators tend to dry mushrooms excessively.

The storage life of shiitake is similar to that of Agaricus (common button mushroom) and is highly dependent on temperature. For example, at 32 F Agaricus can be stored for 17 to 20 days but at 37 F the storage life is 7 to 10 days.

References

Kozak, M., and Krawczyk, J. (1989). Growing shiitake mushrooms in a continental climate. Peshtigo, WI: Field and Forest Products Inc.

Leatham, G. F. (1982). Cultivation of shiitake, the Japanese forest mushroom, on logs: A potential industry for the United States. Forest Products Journal, 32(8), 29-35.

Przybylowicz, P., and Donoghue, J. (1988). Shiitake growers handbook. Dubuque, Iowa: Kendall/Hunt Publishing Co.

Schroeder, G. (1989). Harvesting, post harvest handling, and packaging of shiitake. In Shiitake Mushrooms: Proceedings of a National Symposium and Trade Show (pp. 83-86). St. Paul, MN: University of Minnesota, Educational Development System, 405 Coffey Hall.

Figure 1. X frame log stacking to facilitate fruiting and harvesting.

Figure 2. Shiitake mushroom with cap opened approximately 75 percent.


-----------------

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-1868