Cold Water – Sterilize with Calcium Hydroxide

pinning oyster mushrooms

I recently had quite a large order to fill, growing oyster mushrooms. The time I was given to complete the project was slim and I decided to use straw as a substrate instead of wood shavings. I found myself in a pickle, since I have not used hot water pasteurization for a while and the steaming vessel I use was too large for the amount of straw needed. It was time for a new plan.

I set off to Game and purchased 6 X 56L Black tubs with lids. I was going to try my hand at using Calcium Hydroxide as a sterilizing agent to prepare the straw for my Oyster mushrooms.

Here is the procedure I followed:

As with all other mushroom related work, remember to keep everything clean, wash all equipment with a bleach solution before use. Make sure your clothes are clean and the room used for inoculation is clean, and the air is scrubbed with a bleach solution (10% bleach + water = 100 ml + 900 ml water).

Calcium Hydroxide:

  1. The straw bales were chipped into pieces using my electrical wood chipper.
  2. Add 150 g of Calcium Hydroxide to each 56L tub + 50g of Gypsum.
  3. Fill the tubs 3/4 way with clean rain water – this produced a milky white liquid. (MIX WELL)
  4. Next I stuffed as much straw into each tub as would comfortably fit, and filled with water to the brim. Once I closed the lid, all the substrate was submerged in the milky water.
  5. Leave the tubs standing like that for 16 hours. (Any time between 14 and 18 hours.)
  6. After this time, the tubs were turned on their sides to drain the water. I left them like this for 2 – 3 hours.
  1. Next was time to shower and put on some freshly ironed clothes, just to make sure that I was not the source of any contamination 😉
  2. Wear some latex gloves when working with the straw and wash them down with a water/bleach solution or Isopropol alcohol from time to time in between completing each bag.
  3. I washed down the surfaces I would be working on and sterilized the air twice with a 10% bleach/water solution using a misting bottle (avoid breathing in the mist!)
  4. Use fresh good quality spawn only for inoculation.
  5. The substrate was bagged and inoculated using the sandwich spawn method (layering straw and spawn seeds).

The completed bags were punctured with my pocupine quil (rinse the puncturing tool with a bleach solution in between use for each bag to avoid cross contamination). Each bag received 30 – 40 holes on average. The bagged substrate was placed in my incubation room at a steady temperature of 21°C.

After 6 days incubation, the smaller bags I made for testing purposes were completely white with mycelium and there was no sign of contamination.

The mycelium seemed to run with extra vigor through this substrate. (This may be a result of the added calcium)

The above pictures were taken 9 days after inoculation. (The bag is weighing in at 4 Kilogram)

The above pictures were taken 5 days after placing the bags in my grow room.

Tomorrow, on day 11, I will start harvesting the first oyster mushrooms from these bags. (Total – 20 DAYS to harvesting my first flush)

In conclusion: I really like the Calcium Hydroxide method of sterilizing. I will post more regarding this project as we go along.

Some huge oyster mushrooms ready for harvest on my second flush. We have harvested 14 kg of usable mushrooms this far, with more to come.

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