Contamination
Contamination is the single most common problem in home cultivation. Recognising it early limits losses and prevents health risks from inhaling mould spores.
Green Mould — Trichoderma spp.
Trichoderma is the most frequent contaminant in mushroom cultivation. It initially appears as white mycelial-like growth that rapidly turns bright lime or dark green as it sporulates. It spreads extremely fast and will outcompete and destroy mycelium within days. If you see green, act immediately:
- Do not open the contaminated container indoors — spores are aggressive and will colonise nearby substrates.
- Double-bag the contaminated substrate in sealed plastic bags before removal.
- Discard into an outdoor bin; do not compost.
- Bleach-clean all surfaces the container touched.
- Review your sterilisation protocol — Trichoderma contamination almost always indicates inadequate sterilisation or a break in sterile technique during inoculation.
Black Mould — Aspergillus spp.
Black or dark grey powdery mould is often Aspergillus, which produces mycotoxins and spores that are dangerous to inhale. Handle with particular care:
- Wear an N95 or FFP2 respirator mask before handling.
- Use disposable gloves and dispose of them with the substrate.
- Do not attempt to salvage any portion of an Aspergillus-contaminated substrate.
- Individuals with compromised immune systems, asthma, or lung conditions face elevated risk — consider enlisting help or discarding without opening.
Bacterial Contamination
Bacteria cause wet rot: the substrate becomes slimy, discoloured (often yellow-brown or orange), and produces a distinctly sour or rotten smell. This is common in substrates that were too wet before inoculation or not sterilised at a high enough temperature. Bacterial contamination cannot be reversed. Discard and focus on improving substrate moisture levels (field capacity: the substrate holds no free water when squeezed firmly) and sterilisation times.
Preventing Contamination
- Sterilise grain thoroughly: Pressure cook grain substrate at 15 PSI for 90–120 minutes minimum. Brown rice flour (BRF) jars require at least 60 minutes at 15 PSI.
- Work in still air or a glove box: A still air box (SAB) built from a clear tote dramatically reduces airborne contamination during inoculation.
- Flame sterilise needle between injections: Heat the needle until glowing, allow to cool 10 seconds, wipe with alcohol before each injection.
- Use fresh inoculant: Spore syringes degrade and can harbour bacteria. Use within 6–12 months of preparation; store in refrigerator at 2–4°C.
- No light during colonisation: Colonising jars or bags do not need light and are better kept in the dark at stable temperature.