autoclaves large capacity steam autoclaves by priorclave

Mycology Laboratory Equipment
& Mushroom Autoclaves

top loading autoclave by priorclave

Mushroom cultivation—for profit, for research, and as a source of natural dietary supplements and “nutraceuticals”—is booming. According to the U.S. Department of Agriculture specialty mushroom sales alone expanded by 32 percent in a single year (the 2021–2022 growing season).

Mushroom growing doesn’t have big barriers to entry or high equipment demands. But in order to get consistent results and higher yields while creating less waste, most mushroom growers ultimately invest in an autoclave sterilizer and other purpose-built, precision machined mycology lab equipment. Contamination is the most common source of failure in any mushroom lab. Almost invariably, that contamination comes from improper preparation of bulk substrate prior to inoculating it with mushroom culture. So, whether it’s for research or cultivation, properly preparing your fungus substrate is a vital first step.

Reducing the Risk of Contamination in Mushroom Cultivation

Contamination is the most common source of failure in any mushroom cultivation operation. Almost invariably, that contamination comes from improper preparation of bulk substrate prior to inoculating it with mushroom culture. So, whether it’s for research or cultivation, properly preparing your fungus substrate is a vital first step.
But there are many complicating factors: Different substrates (and even different batches of the same substrate) have different compositions, densities, microbial loads, nutrient concentrations, chemical profiles, etc. But every bulk substrate will arrive with its own natural load of competing organisms and dormant spores that you need to reliably reduce or eliminate, lest they crowd out your mushrooms.

In order to meet these challenges, it’s extremely important to establish a validated, consistently reproducible mushroom substrate preparation procedure. Having a self-contained, programmable laboratory autoclave makes it significantly easier to develop such a procedure.

Options for Mushroom Substrate Preparation: Pasteurization vs. Sterilization

You have many options when preparing your mushroom substrate. These tend to break into two broad categories:

  • true sterilization (e.g., steam autoclaving)
  • pasteurization (e.g., “traditional” heat-based pasteurization or “cold pasteurization” methods like lime bath, peroxide bath, or cold-water fermentation)

An important distinction here is that pasteurization seeks only to weaken microorganisms and kill pathogenic bacteria present in the substrate. Pasteurization does not actually remove/kill/deactivate all forms of life present in the substrate (e.g., fungi, bacteria, viruses, spores, unicellular eukaryotic organisms, and so on). Sterilization, on the other hand, uses high temperature and pressure to achieve complete elimination of microorganisms and spores.

Pasteurization is favored by many edible mushroom growers, because it scales easily and demands no specialized equipment. Provided you’re working non-supplemented straw substrate, it’s both effective and forgiving. But supplemented substrates (and especially denser ones, like hardwood sawdust) cannot be prepared using pasteurization. They harbor mold spores that easily survive pasteurization, and will take over the substrate long before most mushrooms have a chance to gain a foothold.
Supplemented substrates—and even plain straw substrate, in some applications—need to be fully sterilized.

Steam sterilization is, by far, the most common approach used in mycology labs. (Some fungus cultivators do use dry heat for their non-straw mushroom substrate, but that’s only in special cases; in general, sterilizing substrate with dry heat is counter-productive, as you will then need to rehydrate the substrate to cultivate fungus).

Autoclaves for Mushroom Cultivation Labs

Steam is the most reliable way to sterilize mushroom substrate. While mushroom hobbyists rely on something as simple as a kitchen “pressure canner” or pressure cooker (and may graduate up to an atmospheric pressure sterilizer unit), most labs are better served by autoclave-based steam sterilization. This is likely the most important piece of mycology lab equipment.

It is cost-effective, consistent, and quick (relative to other solutions). It’s also the simplest to validate (which is important, as undesirable resting spores can be so resilient in mushroom substrate).

Laboratory autoclaves work by flooding a sealed chamber with high-pressure steam while monitoring the temperature and pressure, and then holding the chamber under those conditions for a specified period. Programmable mushroom autoclaves make most lab sterilization tasks extremely easy.
Most autoclaves designed for research will sterilize equipment and supplies (probes, beakers, agar plates, etc.) in just 15 to 20 minutes. Growth media preparation is another common task. With a programmable lab autoclave, preparing agar, bulk nutrient/growth media, or agar plates takes between 15 and 45 minutes (depending on volume). These cycles can be safely run overnight.

That said, substrate sterilization is trickier, because of the variety of substrates, and because the sterilization time varies wildly (and not necessarily linearly) by substrate volume. For example, hardwood sawdust in small volumes can be sterilized in under 20 minutes, while the same sawdust in blocks or large bags of substrate could take upwards of 2.5 hours. Jars of grain spawn can likewise take from 45 minutes to two hours. Grain bag sterilization times may vary by weight, volume, and grain type.
Regardless of your sterilization task, every lab needs to develop and validate several substrate sterilization protocols (for the various substrates, sizes, and preparations).

Reduce the Risk of Contamination with Good Mycology Lab Practices

Autoclaves use pressurized steam to sterilize mushroom substrate or grain. A reliable autoclave sterilizer ensures consistent pressure and heat, forcing the steam to evenly penetrate the substrate for sterilization.

In addition to your mushroom autoclave, you will also need quality biological indicators, such as Self-Contained Biological Indicators (SCBI), Mini Self-Contained Biological Indicators (MSCBI), or self-contained spore ampoules. These are used to validate your sterilization process.

To develop your mycology lab’s standard sterilization procedure:

  1. Layer 2–4 inches substrate evenly in identical metal trays
  2. Embed biological indicators (BIs) throughout the sample
  3. Process the tray in a mushroom autoclave for 30 min at 121°c or 20 min at 135ºc
  4. Incubate your BIs
  5. If the BIs show no activity your procedure is validated
  6. If the initial sterilization procedure did not inactivate the BIs, repeat with an identical tray of substrate, but process it for twice as long as the first. If biological activity remains, process again for three times the original cycle time.

Some mushroom cultivators advocate routing steam from their autoclave back into their fruiting rooms. It can be a temptingly cost effective way to maintain the heat and high humidity mushrooms like, but we advise against. Serious mushroom growers should treat their autoclave effluent just as labs do: vent your steam outside, above ground, using heat-resistant pipe. The risk of contamination is too great, and creating positive pressure in the fruiting room increases the likelihood of dispersing mushroom spores throughout your lab. Contact us to discuss your lab needs.