Every cultivator faces contamination at some point — it’s part of the learning process. Whether you’re working with agar plates, liquid culture, or all-in-one substrate bags, spotting the early signs of contamination can save you valuable time and prevent it from spreading to healthy cultures.

Why Early Detection Matters

Contamination isn’t just frustrating — it can quietly ruin weeks of progress.
By learning what to look for, you can identify problems early, isolate affected cultures, and keep your clean work clean.

Healthy mycelium is usually bright white and grows evenly across the surface. Anything that looks different — in colour, texture, or smell — deserves a closer look.

Common Types of Contamination

1. Green Mould (Trichoderma)
Probably the most common contaminant in mycology. It starts white and fluffy, turning green as it sporulates. Once it turns green, it’s releasing spores — handle carefully and dispose of the plate or bag immediately.

2. Bacterial “Wet Spots”
These appear as shiny or greasy areas on grain or agar. They often have a sour or musty smell and can stop mycelium from spreading. In agar, bacteria may cause mycelium to grow unevenly or appear wispy and thin.

3. Black or Grey Moulds
Usually fast-spreading and fuzzy. Black moulds often grow in circular patches, while grey ones (like cobweb mould) can cover a surface in hours. Both thrive in overly humid or poorly sterilised environments.

4. Yeasts and Surface Fuzz
Yeast contamination looks powdery or bubbly, often appearing on the surface of agar or near inoculation points. It tends to slow down mycelial growth and can be subtle early on.

Where Contamination Appears

Contaminants can show up anywhere — but where you see them often hints at how they got there:

Agar plates: often due to an unsterile tool, lid left open too long, or airflow disturbance.

Grain jars: may come from under-sterilised grain or unclean inoculation.

Substrate bags: usually introduced during inoculation or from weak seals.

How to Recognise It

A few simple checks can save you from losing an entire batch:

Colour: anything not bright white (green, yellow, grey, black, pink) = contamination.

Texture: bacterial spots look wet or greasy; moulds are fluffy or fuzzy.

Smell: healthy mycelium smells earthy and fresh. Sour, musty, or sweet smells are bad signs.

Speed: contamination usually spreads faster than mycelium and may overtake it in days.

How to Prevent It

Always work in a clean, still environment — ideally in front of a flow hood or still-air box.

Wipe all tools, gloves, and surfaces with 70% isopropyl alcohol before handling cultures.

Pressure-cook (PC) grain and substrate for the full recommended time.

Avoid talking or breathing directly over open plates or bags.

Label and date your cultures so you can spot slow or suspicious growth early.

When to Keep and When to Discard

It’s tempting to “wait and see” — but in mycology, that often means losing more cultures later.
If contamination is visible or smells off, it’s best to discard it carefully and start fresh.

Keep your clean agar plates, syringes, and substrate bags separate from any suspect items to prevent airborne spores spreading to your workspace.

Final Thoughts

Every cultivator encounters contamination. The key is to treat it as feedback — each case teaches you how to refine your sterile technique and improve your next batch.

With time, you’ll learn to recognise issues instantly and correct them before they spread.
If you need clean materials to restart, explore our tested and sterilised supplies:

🧫 Agar Plates & Accessories
🪴 Gourmet Cultures
💼 Substrates & Grain