Growing a material: a first mycelium experiment

Mycelium is the vegetative body of a fungus: a network of threads that grows through a substrate, binding it together. Grown through agricultural waste such as sawdust, hemp hurd or rice husks, then dried, it forms a light, rigid composite that has been used for packaging, insulation, acoustic panels and furniture. It is the material most students meet first in biodesign, because it is cheap, forgiving and visibly alive.

This is a guide to a first experiment. It is written for students working in a supervised studio or classroom, with a mentor, using commercially supplied, non-pathogenic fungal cultures.

What you need

• A culture of a common, safe species used in materials work, such as Pleurotus ostreatus (oyster mushroom), bought as grain spawn from a reputable supplier.
• A substrate: pasteurized sawdust, hemp hurd, or a similar lignocellulosic waste.
• Moulds: food containers, cardboard forms, or 3D-printed shapes, cleaned with alcohol.
• A clean working surface, gloves, a mask, and a mentor who has read the safety guidance.
• A notebook and a camera.

The experiment

1. Prepare the substrate. Pasteurize it (hot water, around 70°C, for an hour is a common method), drain, and cool. Record the substrate, its source and its moisture.
2. Inoculate. Mix spawn through the cooled substrate in a clean environment, at a recorded ratio by weight.
3. Pack the moulds. Press the mixture into forms, cover loosely to retain humidity while letting the fungus breathe.
4. Incubate. Keep in the dark at room temperature. Photograph daily at the same time, from the same angle. Note colour, smell, and the spread of white mycelium.
5. Dry. After roughly one to two weeks, when the surface is covered, demould and dry at low heat (around 60°C to 80°C) until the mass stops falling. Drying kills the fungus and stabilizes the material.
6. Test. Weigh it. Measure its density. Press it, drop it, cut it. Record what happens.

What a prototype should be able to answer

A grown block is not yet a design. It becomes one when it can answer questions:

• What does it do better than the thing it replaces? Lighter, compostable, locally sourced, acoustically absorbent?
• What does it do worse? Mycelium composites are weak in tension, absorb water, and vary from batch to batch.
• What happens at the end of its life? Can it actually be composted where the user lives?
• What did you change between batches, and why? The record of iterations is the design.

Safety, briefly

Work only with cultures from reputable suppliers, never with wild fungi. Mould contamination (green, black or pink growth) means the batch is discarded, sealed, not examined. Wear a mask when handling dry material. Follow your institution's rules, and if there are none, follow a published biosafety guide for community labs and classrooms.