Discover the process used to grow shiitake mushrooms in bags, which involves steaming, cooling, inoculation, incubation, and fruiting

This article is the second part of a two-part series on growing shiitake mushrooms in bags from a professional’s standpoint. Check out part-one if you want to read from the start. Below we start on step #5 of the process for how to grow shiitake mushrooms in bags. This is a commercial strategy used for indoor shiitake mushroom cultivation.

Step #5 for how to grow shiitake mushrooms in bags: Steaming

The next step in indoor cultivation is steaming. One method is autoclaving. This involves using an autoclave or pressure cooker to bring the temperature of the substrate up to at least 250 degrees Fahrenheit and maintaining that temperature for at least two hours. The other option is to use the atmospheric steaming method. This involves steaming at atmospheric pressure up to temperatures around 208 degrees Fahrenheit for about 16 hours. This method is very inexpensive compared to an autoclave and is efficacious. Contamination levels can be maintained below 5% using proper technique with atmospheric steaming. Steaming at Fungi Ally was done using a 9 kw sauna steamer that was on continuously.

Step #6 for how to grow shiitake mushrooms: Cooling

Cooling is best done in a positive pressure lab. After the 16-hour steaming is complete, bags are rolled into a positive pressure hepa-filtered lab to cool. Bags are left to cool for 24 hours before inoculating. During this time, bags are sucking air in so it is important to be in a clean environment. Some farms do the entire process of steaming and cooling outside. This is possible, but for a long incubating species like shiitake, contamination rates will increase.

Step #7 for how to grow shiitake mushrooms: Inoculation

If this process was a wave, inoculation would be the point as the wave crests and is getting ready to crash. This is the point when you either catch the wave and ride or fall of the surfboard. Of all the steps, inoculation is the most precise and technically demanding. Understanding the seven vectors of contamination, proper technique for sterile lab work, and workflow dynamics are all critical for a successful inoculation process. First, the cooled bag is opened in front of a laminar flow hood. Next, a small amount of spawn is dropped into the bag. Finally, the bag is sealed so air exchange only happens through the filter. After inoculation is complete, bags are shaken to distribute the spawn more evenly. grow shiitake mushrooms

Step #8 for how to grow shiitake mushrooms: Incubation

Time to kick back and watch the mycelium work its magic! During incubation the mycelium jumps off the spawn and begins inhabiting all the new substrate. Watching the leading edge of the mycelium to ensure it stays healthy and that no contamination shows up is important.

Ideal temperatures during incubation are around 73 degrees Fahrenheit but anywhere from 55-75 degrees will work. As temperatures rise above 75 degrees, internal overheating can occur. There are two key things to be aware of during incubation with shiitake:

  • First, when placing bags onto shelving, be sure there is a gap between each bag so popcorning can happen effectively. If bags are touching, popcorning will not happen and fruiting will not occur in that section of the block. Especially after about 2 weeks, it is critical that bags are not touching.
  • Second, shiitakes are sensitive to temperature swings. If incubation temperature drastically drops, the blocks can start fruiting in the bag. This leads to malformed mushrooms and an overall loss in yield. CO2 levels, lighting, and humidity do not need to be controlled during incubation. Shiitakes are also sensitive to physical disruption, so after week 4 or 5 bags should be handled minimally until they are ready to fruit.

Step #9 for how to grow shiitake mushrooms: Browning

Typically it takes about 7-8 weeks for shiitake blocks to be fully mature. They are ready to fruit once the outside of the block has popcorned and browned fully. Bags can be fruited with 50% or more browning, but generally yield is decreased when browning is less than 50%.

During incubation, the mycelium goes through three phases.

  • First, the mycelium inhabits all of the new substrate.
  • Next, popcorning creates ridges and valleys on the outside of the substrate making it extremely textured.
  • Finally, the outside of the shiitake mycelium turns brown and makes a skin-like area from which the pins develop and emerge. Because of this browning, shiitakes are the only specialty mushroom for which the bag is completely removed for fruiting.

Step #10 for how to grow shiitake mushrooms: Fruiting Initiation

Fruiting for shiitake is typically initiated with a temperature change. After 50-100% browning, shiitake blocks are transferred to a walk-in cooler for a 12-24 hour cold shock. This cold shock initiates the shiitake into a fruiting cycle. Blocks are stripped of the plastic bags and placed into the grow room. It is extremely helpful to spray the blocks down with a hose in the grow room 2-3 times a day for the first 3 days of fruiting.

Step #11 for how to grow shiitake mushrooms: Fruiting

The fruiting room is a place of transformation on any mushroom farm. Mycelial blocks turn into sellable fungal fruit bodies. During fruiting, monitoring four key environmental parameters is essential. CO2 levels, lighting, humidity, and temperature should all be monitored and adjusted to maintain optimal conditions for fruiting.

During the first 4 days of fruiting, pin set is occuring. This is when little baby mushrooms start emerging from the substrate. Size and quantity of mushrooms is determined at this point; If there are an excessive amount of pins that create little mushrooms, which happens with strain 3782, some pins can be knocked off to encourage fewer larger mushrooms.

During these first 4 days, air exchange and high humidity are extremely helpful to create a good pin set. If CO2 levels are above 1000-1200 ppm, pin set can be adversely affected. Likewise, if humidity drops below 70%, pin set can be adversely affected.

To maintain high humidity at Fungi Ally, shiitake blocks were sprayed directly 2 times per day for the first 3-4 days until pins were the size of a thumb nail. After pin set, mushrooms are a little more durable to environmental fluctuations. The best measure of proper environmental parameters is the mushrooms themselves. If they look good, taste good, and store well, environmental parameters are great! In general, temperatures between 55-70 degrees Fahrenheit, CO2 levels below 1200, sufficient lighting to read comfortably, and humidity between 80-95% are ideal. Shiitakes, however, are much more tolerant to high CO2 levels and low light than oyster mushrooms.

This next part of this series on growing shiitake mushrooms talks about the harvesting process and drying shiitakes. Visit this article here now.

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