I started growing oyster mushrooms. A really small batch really. One bucket with almost 3 gallons of the substrate and spawn.

  • I bought my spawn online and stored it in the fridge, sealed in its container.
  • I pasteurized my substrate of sawdust, woodchips and oat bran with very hot, almost boiling water.
  • I sprayed my surfaces with 95% isopropyl alcohol. Also sprayed alcohol on my working area, mixing bucket and growing area.
  • I have drilled holes in a 4-gallon bucket with a few inches of space and also sterilized that bucket.
  • I had put my substrate in with sterilized gloves and drained excess water.

It has been about a week now and the spawn is spreading however there was spawn left uncovered at the top which started growing to the upper side of the bucket which looks kinda spongy and weird but I don't think that's an issue as it looks like a mushroom spawn. The issue is there is a heavy mushroomy, spawny smell but my concern is that is very heavy and I am doing this indoors.

  1. What may cause a heavy smell?
  2. Is it normal and Do I have to bear with it until mushrooms grow?

Any further information can be given if you request.

  • pasteurisation is a technique of removing microbes through steam not water. Items are steamed at temperatures of about 63° C (145° F) maintained for 30 minutes. Pouring hot water, almost boiling water does not achieve the same things.
    – GardenGems
    Commented Dec 24, 2019 at 20:21
  • @GardenGems Almost boiling as in boiling. Do you suggest that this is a contamination issue?
    – user27663
    Commented Dec 25, 2019 at 11:02
  • If I were to guess, I would think your contamination is wild yeast that have started to ferment your oats and sawdust. Pouring almost boiling water is not the same as holding a consistent temperature for 30 min. Even if you cleaned everything the act of adding hot water just gave yeast and mildew a warm wet place to start to grow. You have built this to grow a fungus, but you might be growing the wrong kind or maybe both.
    – GardenGems
    Commented Dec 25, 2019 at 12:53
  • Will it be a problem for my oyster mushroom?
    – user27663
    Commented Dec 25, 2019 at 13:10
  • BTW I am not sure about your bacteria claim. There is no visible bacteria colony all of it looks like my spawn. There is a mushroom smell but very heavy. There is no other smell other than the mushroomy smell.
    – user27663
    Commented Dec 25, 2019 at 13:40

2 Answers 2


From experience the smell is normal. The heat-treating of the substrate is mostly to kill certain other fungi, especially Trichoderma. I treat my substrate in the microwave without contamination problems. In the future the fungi may produce drops of yellow honey-like liquid - its not a problem.


Oyster mushroom mycelium produces a fairly strong mushroom smell as it grows. This is good. You would worry if you smelled anything other than this, in fact. If you smell sweet or especially sour or vinegary you'd probably want to toss the batch.

Typically you would want to sterilize, not just pasteurize, sawdust/chips that were supplemented with nitrogen rich bran. This would require putting it through a pressure cooker at 15psi for 90 minutes or so depending on the quantity or bag size. I would expect a grow to experience a bacterial contamination problem without this sterilization in a supplemented substrate.

The only other reliable method I know of preventing contamination in supplemented substrate without sterilization is to use the hydrogen peroxide method as described by Dr. Rush Wayne.

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