Straw: Lime Pasteurisation

Using lime, calcium hydroxide (CaHO2) to create a highly alkaline solution that effectively kills most microorganisms. By adding 12g per 100l of water you will increase the pH of the water to over 12. Care must be taken when working with such a caustic solution and neutralising the water with a base (acid) after use may be necessary depending on how you plan to dispose of it. The straw is submerged in the water for 12 hours then drained. The pH of the straw will be slightly higher (pH 7-8) but this is not a problem for Pleurotus species (oysters). To minimise the amount of waste water a pump can be used to circulate the water through a perforated pipe (see Lime Pasteurisation Bulk Processing IBC). It is important to note that not all types of lime are suitable you will need Hydrated Lime that is low in magnesium. You may want to test the water to ensure you have achieved the correct pH, if so use test strips (litmus paper), the only electronic ones that work are the expensive ones!.

The following describes how to make 10l of lime solution which treat 1kg of chopped straw.


  • Calcium Hydroxide (CaHO2) – low in magnesium 4g
  •  Citric Acid 8g
  • 2x Large Container
  • 10l Water
  • 1kg Chopped Straw
  • Mesh “onion” sack
  • pH Test strips (above pH12) (optional)
  • Gloves
  • Goggles
  • Facemask


  1. Fill container with water and ad the CaHO2. Definitely wear gloves when measuring the lime, treat it as you would when using a strong bleach. It is a fine powder so make sure you’re doing this indoors. If for any reason you are using this outdoors then a face mask and googles in case of a gust of wind.
  2. Wearing gloves, add the straw in the mesh sack and ensure it is submerged, leave for 12hours
  3. Pull out the straw and hang the mesh sack to allow the water to drain
  4. You can reuse this water for a second time adding Lime to bring the Ph back up to 12 but if not add the base (citric acid) to neutralise
  5. When straw is thoroughly drained inoculate with the required amount of spawn and fill the cropping container.



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