How To

How To: Build your bioreactor

Full instructions for large bioreactors can also be found here:

Due to file size limitations and bandwidth issues the video has been temporarily removed.

Why do we ask for money? We rely on volunteers for all our work. We're incorporating as a not-for-profit: But we are doing science! And, for our science to progress we need things like Microbiometers (to measure soil carbon and fungi:bacteria ratios), pallets, wire, BRIX refactors (which measure sugar in leaves which tells nutrition levels) and other groovy stuff. Your money pays for all of this. Which keeps our science going. Thank you!

How to build your bioreactor will look at two methods: the Large Bioreactor and the Home Bioreactor.

In this, the large bioreactor build, Scott has made some improvements to the design which you may wish to compare to the original bioreactor build instructions linked to under the video.

For home bioreactor instructions see our Home Bioreactor build here.

Buy your bioreactor starter kit here. Remember, your ONfdc bioreactor starter kit adds a rich bounty of fungal spores right from day one. This will help your fdc build a much richer fungal count.

Large Bioreactor

Follow the steps:

Step one: Gather Materials

  • material list: wire mesh, pallet, liner, plastic sheet

Step Two: Assemble Materials

  • steps to assembly: see following

Step Three: Fill the bioreactors



Cage materials:

Wire mesh:

There are a variety of wire fence meshes you can use. Corn crib mesh is also excellent. Typically we use 2″ x 4″ 10g wire mesh in 5′ by 100′ rolls. These are found for around $220 at farm stores.
We cut the roll at 12’6-10″ for a 4′ circum. This way we get 8 bioreactors from each roll.

Cage lining:

In our last build we used donated landscape screen from a road construction site. Others have used landscape fabric, hemp fibre, jute, etc. From our experience, this fabric tends not to last very long and may not have enough “breathability.” I personally recommend using burlap. Its biodegradable and earth friendly. Note: the home bioreactor uses a finer mesh and doesn’t require cage lining.

Liner clips:

Either way we attach the fabric and seal the cage with
rabbit cage clips — these are available online and at most farm stores. You can also use twist ties, some even just fold the material over the top of the bioreactor and fill carefully.

Pallet for bottom:

4′ wood pallet covered with plastic 6mil.

The pallet at the bottom is a subject of debate. We use a 4′ pallet (bit bigger works) and has a seven hole design. One in the middle and then six holes around the circumference.

You can skip the pallet bottom and we are doing tests with no pallet summer 2022. The benefit is worms can come and go from your bioreactor more easily. The downside? Tree roots can easily enter the mass and eat your compost! Maybe this is a good thing as the roots support a wide range of life (ie. protozoa, fungi, nematodes, etc).

Breathing tube supports:

For best results the bioreactor needs airways that allow the compost material to breath but not get so much air that bacteria are overly stimulated.

The material in the bioreactor should be within 7-12 inches of air.

To make these breathing passages we use 4″ PVC tubes. These are placed before filling and removed after the filled bioreactor mass has settled. Usually within a few days to a week.

We have also used down pipes from rain gutters; tubes of fencing mesh (which can be left in!).

For building smaller bioreactors some have used corrugated drainage pipe with holes drilled or preexisting. These are laid in horizontally. Not sure how that works as the biomass settles.

Pallet Tips:

  • In the pallet, cut your hole just slightly larger than the tube you use to make removing the tubes easier.
  • use plastic on the bottom to separate the pallet wood from the biomass. Pallet wood can be treated with chemicals and it will last for many bioreactor fillings if protected from the soggy biomass.

Top tips for maximum performance:

  • use worms. If you have access to red wigglers or other worms get them into the bioreactor after it has settled and the breathing tubes are ready. This will greatly enhance the fungi to bacteria ratio!
  • keep your biomass at 70% humidity. Not too much, not too little moisture!
  • use the ONfdc bioreactor starter. The started has a proven high fungal ratio and will enhance and expand the number of fungal types in your fdc right from day one. This is a top tip!

Note: if you build a bioreactor please please please send us pics and results. This will help many many people. Share the love!

The key features of ONfdc
  • Very high 3.7 to 1 fungal dominant ratio
  • production site is close to a remaining stand of old growth forest; a rich source of fungal spores
  • Scott’s many years of experience and care is proven to create a better fdc — ONfdc

Citizen Scientist and Regeneration Influencer


  • David Kroetsch

    Is there a PDF or a better video for building a home bio-reactor.

    Can you give some specifications for the the aeration tubes? Size and do you drill holes to allow air exchange?

    When you are preparing your fillings for the reactor can you list the ingredients. I get the chopped leaves and compost but what else are you adding – the video doesn’t show. It looks like bone meal but I want to verify.

    I currently have 4 active composters and have prepared compost tea but I am intrigued to try this system.

    I am a retired soil scientist (Pedologist) and have worked on Soil Quality and Health research.

    • admin

      Hi David,
      To help start your FDC compost on its journey we recommend adding one “experimental kit” (available from our new ONfungi shop) to the water you soak your compost material in. The other amendments are largely part of the more is more male mentality. smile.
      We will have better instructions coming. Please remember that we’re a group of volunteers. On the communications side there is only our delightful Kelvin Hodges. He could use some help. Volunteers with writing and education material development happily sought.

      • admin

        Thanks Terri, I have added the link to the .edu instructions under the video. Do compare to Scott’s notes as he’s made some improvements to the process. We have further videos in progress to make things even easier.

  • Richard Bull

    Is your pallet 48″ x 40″ i.e. 4ft x 3ft 4in?

    I know pallets are most common in that size, but that obviously cannot give a 4ft diameter bioreactor.

    Other pallet sizes are: 42” x 42” and 48” x 48”

    Thanks for clarifying!

    • admin

      Yes. We have had good results using all wood structures. Scott opts for the fabric wrapped bins as its easier to build and he’s using “repurposed” waste fabric from a construction site. So the cost is low for us. Good luck. And reports of your results appreciated. We also have kits of the Microbiometer and starter compost coming soon.

  • Stephen Newport

    Thank you for your hard work and commitment to this – just ordered a few starter kits to get me going!

    I’m really taken by Dr Johnson’s work, so I watch his presentations whenever I come across them. In the last presentation at the Soil Food Web symposium, I noticed Scott asked a tough question about his break from California State Chico. His response was (not suprisingly) careful but interesting. I guess his point is that perfectly designed studies that meet the standards of academia might not respect the complexity of nature and, I guess, NOT being able to meet that bar does not mean you aren’t producing outcomes. “Just ask the farmers”, he said in response to Scott’s question. Bravo.

    Thanks for asking that question Scott. Very brave.

    Now on to my question: the duo of Johnson-Su often mention that the reactor cannot freeze. I’m struggling to negotiate placement of my reactor indoors ;-). What is the best way to address this? I do have a heated utility building, but I assume that a reactor would shed a lot of water + worm smells.

    • admin

      Scott replies:

      Hi Stephen,
      Thank you for your kind comments about the question posed to David J.
      Regarding freezing:
      Freezing does slow down the rate of curing/decomposing such that what David gets done in 12 months in NM, we get done in 19 months from a late fall start near Ottawa Ontario.I have been able to get a 3:1 F:B ratio on our fungal dominant compost.
      If you have a warm space and can conveniently load and unload in that space, I’d use it to buy time. You will have leakage to manage.
      If your outdoor space is not limited, the effect of waiting 7 extra months disappears after filling your “pipeline” in the first year.
      Check this article:,has%20large%20potential%20for%20growth.

      • Brady

        I was wondering the same as Stephen about allowing the reactor to freeze. Do you add worms to your reactors and if so do they die or cause problems with the compost after a winter freeze?

        • Kelvin Hodges

          Brady, We don’t seem to find any negative effects of freezing. The fungal / bacteria ratio is still excellent, as measured by the MicroBiometer. We did try to get some microscopy done this spring on a slowly unfreezing bioreactor. Unfortunately I have no results for you at this point.
          We do add worms, whether they leave the pile before freeze up we don’t know. Worms are highly mobile and can easily move out of the bioreactor.

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