white oyster mushrooms

Steam Sterilizer for Mushroom Production

One of the most challenging things for a small scale speciality mushroom farmer is the ability to produce enough bags of sterile substrate at one time to be cost-effective and time conscience. When starting a mushroom farm many of us buy our mushroom spawn from spawn producers and we inoculate logs and wait for our mushrooms to grow.


But what if you want to expand your production and start growing mushrooms indoors all year round? There are many sterilizing alternatives available. Most are expensive, size limiting or you need to be an engineer to set it up and run. Well, needless to say, I’m not an engineer, I tend to be thrifty (or should I say cheap) and I want to produce a minimum of 25 – 42 bags of substrate at a time.

The solution we found was a 55-gallon drum with a sauna steam generator hooked into it. Quite simple yet very effective. We used a 6kw generator and wired it to use the dryer receptacle. All we need to do is unplug the dryer and plug in the steam generator. We ran a dedicated copper water supply with a shutoff valve and filter to the generator.

55 gallon drum and steam generator

The 55-gallon barrel requires three holes to be drilled into it. One for the steam inlet coming from the steam generator. The second hole is for a drain in the bottom of the barrel. The third is a small hole for a temperature probe. The barrel should be food grade and properly cleaned before installing. The barrel should have a properly fitting lid and retainer ring. NOTE the barrel is not to be pressurized.

When doing a test run I reached a temperature of 212° F. We maintained that temperature for over 3 hours. My total run time was about 8 hours. The temperature continued to climb to 212° F after shut down, as the stored heat penetrated the substrate bags. It took 3 days to cool the substrate to room temperature before opening the barrel.

This article is not a tutorial or how to, this is just to share what we’ve done.