Producing shiitake mushrooms can be broken down into three specific and straightforward phases: fruiting, harvesting, and storage. This fact sheet provides insights into these three phases, providing strategies for improving your shiitake mushroom production activities.
Shiitake logs are ready to fruit when the shiitake has colonized the outer cylinder of available sapwood. At six to 24 months post-inoculation, the mycelium has stored enough nutrients to form mushrooms.
When mushrooms appear, you know the log has fully colonized. Before a log begins producing mushrooms, growers often notice elastic and spongy bark, logs that no longer “ring” when struck, and the appearance of white mycelium on log ends.
Temperature and moisture changes trigger the shiitake fungus to produce mushrooms. Therefore, log shocking (or soaking) is often used for “forced fruiting” and is done at a time planned by the grower. Keep in mind that forced fruiting can reduce the production life of the log.
Shocking can be done by various methods, such as using stock tanks. Water should be clean and have a significantly different temperature compared to ambient temperatures. The length of soak depends on the air and water temperatures, the log’s age, and the log’s bark thickness. As a rule, the closer the air (log) temperature is to the water temperature, the longer the soak. For example, soak time in the summer is usually six to 24 hours, while soak time is usually two to three days in the spring or fall. Older logs and thin-barked logs absorb water quickly and do not require soaking times as long as younger or thick-barked logs.
Log Stacking and Protection
After logs are shocked, they are stacked for fruiting, normally using the high A-frame or lean-to configuration (see fact sheet “Shiitake Mushroom Production: Logs and Laying Yards” (F-0041) for more information on stacking configurations). The stacking arrangement should make it easy to access all sides of each log for harvest (Fig. 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 materials that hold water, allow air movement, and provide some insulation.
Environmental Conditions for Pinning
“Pinning” refers to early mushroom development. It often occurs as the logs dry (Fig. 2) three to five days after shocking, but can also occur naturally after a week. At this stage, mushrooms are highly vulnerable to cold and windy conditions, which may inhibit growth.
Whereas well-colonized soaked logs can have moisture contents as high as 80–90%, pinning requires a log moisture content of 35%to an optimum of 60%. Optimum temperatures for pinning are between 55–65 F with relative humidity of at least 85%. Avoid rain during this period— shiitakes can act like sponges and soak up rainwater, which reduces their value.
Keep in mind that while light is not required for the spawn run, it is required for fruiting. Enough light to read a newspaper at arm’s length should be sufficient.
Once the “pins” have emerged, the protective covering or fruiting blanket over the logs should be removed. Exposing more of each log produces dry, firm mushrooms. This typically takes seven to 10 days following shocking. 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 by using different combinations of strains (cold weather, warm weather, and wide-range).
After mushrooms are harvested, the logs should be placed in a laying or stacking position that works best for your site and rested for one to three months. Log moisture content should be maintained from 30–40% 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 (crop) of mushrooms.
Each shiitake mushroom on a log will develop independently compared to other mushrooms on the same log. Therefore, logs must be checked frequently, and mushrooms need to be harvested at just the right time to maximize quality.
Shiitake should be picked when the cap is opened approximately 50–75% (Fig. 3). At this stage, the gills that are exposed by the cap edges are still rolled under the cap. Harvesting mature mushrooms with the cap 100% opened can lead to reduced shelf life, a longer delay before the next flush, and increased pest problems.
Shiitakes are picked by grasping the lower portion of the stem and pulling the mushroom from the log with a slight twisting motion. Shiitake can also be harvested by cutting them as close as possible to the log surface with a sharp knife or pair of 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 shiitakes 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. Avoid plastic bags as they can hasten mushroom decomposition. Air vents in the container are recommended so the shiitake can be cooled rapidly. To prevent bruising and promote rapid cooling, containers should not be filled more than 4–6 inches deep with shiitake mushrooms.
The immediate objective after picking is to cool the shiitake to 33–35 degrees Fahrenheit 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 shiitakes is similar to that of Agaricus bisporus (common button mushroom) and is highly dependent on temperature. For example, at 32 F, Agaricus bisporus mushrooms can be stored for 17–20 days, but at 37 F, the storage life is seven to 10 days.
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