Shiitake logs will fruit just fine without any effort from you once the logs are inoculated and incubated for a summer or two, but usually that occurs just 2 times a year (spring and fall) and sometimes after a severe weather event during the summer. If you are thinking of selling mushrooms at a weekly farm market during the summer, you will need to intervene and take control of the fruiting cycle. Fortunately, you don’t have to wait for a pelleting by hail and driving rain to bring on a fruiting. Instead, you can just “force” or “shock” your logs, tricking them in to thinking it is time to fruit.
When logs are soaked (or sprinkled), three things happen: the water content in the log is increased, the gas exchange in the log is disrupted and the temperature changes. As a result, fruiting occurs.
Soaking logs in a cold water bath is a technique often used for forced fruiting - used to encourage fruiting at a time planned by the grower. When soaking, you can control the 3 conditions listed above to schedule a harvest. The soaking time you use depends upon the relationship between air (more specifically log) temperature and the temperature of water, log age and bark thickness.
Temperature gradient affects the process - the closer the log temperature is to water temperature, the longer the soak time.
For example, soaking time in the summer is usually 6 to 12 hours.
6 hours if the logs are several flushes old or thin-barked (which are tender and absorb water quickly), or longer if they are new or large logs.
In the cool spring and fall, soak time is usually 24 hours.
Sprinkling, or misting logs, can also be used to stimulate logs inoculated with cold
weather strains. Soak time can also be adjusted to control mushroom size. Usually shorter soaks increase cap size, but produces fewer mushrooms.
'Virgin' logs (newly inoculated and ready for their first fruiting), especially those inoculated with Wide Range strains, take very little stimulus to fruit. Heavy rainfall, temperature change, hail, or physical manipulation, such as walking on top of the logs or just picking one up, theoretically reallocates gas concentration in the wood that triggers fruiting.
A sprinkler or a soaker-hose placed near or over the logs and run for 24 to 48 hours, is usually enough to stimulate fruiting this way - but it is only really effective for the first few flushes.
After logs are soaked they are stacked for fruiting, which is usually done in a configuration that will ensure that all sides of each log will be harvestable.
If you are planning on soaking logs to harvest mushrooms on a weekly basis, make sure to inoculate logs with a shiitake strain that will respond to forcing. All Wide Range strains and all Warm Weather strains (with the exception of WW70) respond well to summer forcing. Logs must be acclimated to warm summer temperatures before attempting soaking, to do so earlier is a wasted effort as the logs will not respond. You’ll need at least 2-3 weeks of daytime temperatures above 65F prior to the first soak.
After soaking your logs, they will need to rest before you can soak them again. Resting insures the time for the shiitake mycelium to digest more wood for energy to fruit again, and also lets the log dry out a bit so it will respond to the soak. Logs should rest a minimum of 8 weeks (growers with lots of logs have the luxury of waiting 12 weeks). Therefore, logs are often stacked in the laying yard in an orderly fashion and batches are labeled with soak date so the grower can keep track of resting interval. In most climates, logs are soaked at least twice through out the summer in the north and three to five times in the south where summers (at least from the northerner’s perspective) lasts all year.