"An ounce of prevention is worth a pound of cure." 

Benjamin Franklin

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How to Prevent Contamination When Growing Mushrooms at Home

Beginner Sanitation Checklist

Contamination kills more first-time mushroom grows than any other mistake.

The good news?

You do not need a laboratory. You need consistent habits at the right moments.

But I'm going to be real with you now so as not to set you up for disappointment when you have your first contam....

It is impossible to avoid contamination as a grower!

In fact, you might as well consider it a right of passage as a mushroom cultivator!

BUT...there are things you can do to minimize contam in your grows...

Here is a simple checklist organized by stage: 

how to prevent contamination

BEFORE YOU START

Clean your workspace first.

Wipe down every surface with isopropyl alcohol (70% works better than 91% for killing contaminants).

Let it dry completely before you touch anything.

Wash your hands.

Wash your hands.

Wash your hands.

Then wash them again.

Use gloves if you are working with agar or liquid culture. Nitrile gloves are cheap and worth it.

Turn off fans and close windows.

Moving air carries mold spores.

Dead still air is your friend during inoculation.

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WHEN PREPARING YOUR SUBSTRATE

Pasteurize or sterilize based on your method.

Straw gets pasteurized with hot water for a simple bucket grow for gourmet species. 

Substrate for magic mushrooms is also pasteurized with hot water (grab my book for step-by-step). 

Grain jars get pressure cooked at 15 PSI for 90 minutes minimum.

Skipping or rushing this step is the number one beginner mistake.

Let your substrate cool completely before inoculating.

Hot substrate creates condensation inside your container and can damage your spore/cultures genetics.

Condensation invites bacteria.

DURING INOCULATION OF GRAIN BAGS

Work fast. Every second your container is open is a second contaminants can enter.

The best way to prevent contam at this stage is to make your own grain bags (vs. buying them already sterilized from a grower). 

Make sure you have everything you need before starting (alcohol, spores/cultures genetics syringe with needle, masking tape (to cover injection hole), grain bags)

Wash your hands for 30 seconds.

Clean the injection site of your grain bag for 30 seconds with alcohol.

Do not talk, cough, or sneeze over your work. Seriously. Wear a mask if you have to.

DURING COLONIZATION

Store colonizing jars or bags somewhere dark and undisturbed.

Check them daily but do not open them.

Learn what healthy mycelium looks like.

It is white and fluffy, and can grow in a beautiful rhyzomorphic pattern (resembling ropes).

Green, black, pink, or orange patches mean contamination.

Remove contaminated containers immediately and away from your grow area.

how to prevent contamination

DURING FRUITING

Wash your hands for 30 seconds before you open your mono tub grow.

Maintain humidity without pooling water.

There should only be beadlets of water on your substrate. 

Standing water breeds bacteria.

Use a spray bottle and mist the walls of your fruiting chamber, not the substrate directly.

Fresh air exchanges matters here.

Crack your chamber or fan it briefly two to three times per day, preferably with each FAE (fresh air exchange).

THE QUICK REFERENCE CHECKLIST

  • Wipe surfaces with 70% isopropyl alcohol
  • Wash hands thoroughly before every step
  • Wear gloves during inoculation (remember you have to wash your gloves, too, every time you step away from your grow...so it's best not to do it)
  • Sterilize or pasteurize substrate properly
  • Cool substrate fully before use
  • Work in still air
  • Remove contaminated containers immediately
  • Mist walls, not substrate
  • Fan your fruiting chamber daily (ideally with each FAE) 

ONE THING TO REMEMBER

Good-enough cleanliness at every stage beats perfect cleanliness at one stage.

Most contamination happens because someone rushed or skipped a step they thought did not matter.

Build the habit. Your success rate will climb fast.

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