One of the biggest troubles that first time mushroom grower run into is contamination. This might not seem like it’s going to be a problem at first, you know how to keep things clean right? Unfortunately, contamination can sneak into your mushrooms in all sorts of ways and most of it is undetectable until it’s too late.

So what does this mean for you? It means your best bet to reduce contamination is through prevention!

What is Aseptic Technique?

Aseptic technique is the process in which you work to reduce microbial contamination. It’s not just one thing you do, it’s your whole methodology. This comes down to the way you clean surfaces, how you put on gloves, and even the kinds of assumptions you’ll make about what is and is not clean.

The most basic principles of aseptic technique are simple:

  • Use sterile or sanitized equipment.
  • Don’t touch sterile surfaces or equipment with non-sterile objects.
  • If you don’t know if something is sterile, assume it is not.
  • Work in areas that prevent airborne contamination (like a hood.)

For the most part these are the only general rules you need to follow. If you were working in a professional setting where aseptic technique mattered, you would have strict procedures set out to follow. This way you can ensure everything that needs to stay clean stays clean.

Do I Really Need to Use Aseptic Technique to Grow Mushrooms?

Honestly, no you don’t. However, if you’re raising your own grain spawn from spores there are a lot of steps that can be messed up by introducing contamination. To keep yourself from wasting time and money you want to do whatever you can to minimize unwanted microbial invaders.

Aseptic technique, even if followed to varying degrees, will always help you reduce the chance of contamination. Ultimately how strict you are is up to you, and how strict you need to be is dependent on what you’re doing.

Sanitizing vs. Sterilizing

This is a slight, but important difference any mushroom grower should know.

Sanitizing is cleaning particles and removing most micros from something.

Sterilizing is removing or kill all the microbes on something.

Why does this matter? Because mold spores are tough. They’re so hard to kill in fact that sanitizing can often make them more difficult to get rid of by removing other microbial competitors. When you’re growing things on Agar or other nutrient medium any contaminate that can grow will grow.

Cleaning and Preparing Surfaces

The world is a disgusting place. You’re covered in microbes, many of which are supposed to be on your body and help you survive. The surfaces in your house likewise are covered in bacteria, spores, and other microorganisms all trying to survive.

The first and most basic aseptic technique you can get familiar with when cultivating mushrooms is to clean your surfaces and equipment. In most cases you can get by with placing equipment in boiling water. This will kill many, but not all microbes. If you do have the need to make sure your equipment is absolutely sterile you can use any pressure cooker that can get up 15 PSI and maintain pressure for at least 90 minutes. If you have the budget you can even get an autoclave for your home!

If you have access to proper ventilation you can use certain cleaners to remove bacteria, viruses, and mold spores also. When I used to do lab work we used Spor-klenz; a horrible chemical, but highly effective. These are not ideal for home use, but can really do wonders in a dedicated space for growing mushrooms.


It should go without saying you need to wear gloves when handling sterile equipment. Not as obvious is that you need to make sure your gloves are sterile and you need to be aware that to moment you touch something with them that isn’t they’re dirty. Once contaminated, even if it’s just a chance, your best bet is to put on a new pair of clean gloves.

When Do I need to Use Aseptic Technique for Mushroom Cultivation?

Good question! Aseptic technique is typically only required when growing spores on agar or when making or propagating grain spawn. You can of course contaminate your fungi at any time, but those two stages are when the process is most susceptible. Once you have a strong mycelium growth built up your fungi can do a decent job of defending themselves from foreign microbial invaders.

In some cases sterilization of certain materials, such as compost, can be almost impossible to do at home. Really what this comes down to is knowing when it’s necessary. Most commercial button mushrooms are gown on compost that is in no way sterile, but is instead optimized for mushrooms over other types of organisms.

The Takeaway: Aseptic Technique is Always a Good Idea

While it is recommended that you always wash your hands, surfaces, and equipment, there are still plenty of times you can get away without any fancy technique. Just be aware that you are trying to keep your crops contamination free or you could be wasting tens or even hundreds of dollars in materials.