Pasteurization and Sterilization

There are 2 main ways to kill off contamination in mushroom substrates, these are Pasteurization and Sterilization. Pasteurization is a more simple form as it does not require high-tech equipment however it does not kill off all contamination. Sterilization is a superior method as it kills off all contamination when done right, however, it will require an Autoclave and autoclavable containers for the substrate.

 

Hydrated lime pasteurization, also known as lime Pasteurization or alkaline pasteurization, is a method used in mushroom cultivation to prepare certain types of substrates by raising the pH level and creating an unfavorable environment for competing organisms. It involves the use of hydrated lime, also known as calcium hydroxide (Ca(OH)₂). This is commonly done with hardwood sawdust and straw, other richer substrates like masters mix will not work well.

Here's an overview of the hydrated lime pasteurization process:

  1. Substrate Selection: Choose a substrate that is suitable for lime pasteurization. This method is commonly used for substrates like straw or agricultural waste.

  2. Preparing the Substrate: Prepare the substrate by cutting or shredding it into small pieces. It is important to ensure the substrate is clean and free from contaminants.

  3. Soaking the Substrate: Submerge the substrate in water and soak it for a specific duration, usually between 12 and 24 hours. This step helps hydrate the substrate and prepare it for the lime treatment.

  4. Drain and Mix: After soaking, drain the excess water from the substrate. Transfer the substrate to a suitable container or mixing vessel.

You can also just add hydrated lime to the substrate and mix thoroughly to ensure even distribution. The amount of hydrated lime to use depends on the substrate type and desired pH level. Generally, a common ratio is 1-2% of hydrated lime by weight of the substrate.

Hydrated lime pasteurization can help create a favorable environment for mushroom mycelium growth while reducing the chances of contamination. It is important to follow proper safety precautions when handling hydrated lime, such as wearing protective gear and avoiding inhalation or contact with the skin or eyes. Additionally, it's recommended to consult reliable cultivation resources or seek guidance from experienced mushroom cultivators to ensure the accurate application of hydrated lime pasteurization.

 

Sterilization, in the context of mushroom cultivation, refers to the process of eliminating or killing all living organisms, including bacteria, fungi, spores, and other microorganisms, from the substrate or growing medium. The goal of sterilization is to create a sterile environment that is conducive to the growth of mushroom mycelium without competition from unwanted organisms.

There are different methods of sterilization commonly used in mushroom cultivation:

  1. Heat Sterilization: This method involves subjecting the substrate to high temperatures to kill microorganisms. It can be done using various techniques, such as pressure cooking, steam sterilization, or dry heat sterilization. The temperature and duration of heat treatment depend on the specific requirements of the mushroom species and substrate composition. This is commonly done in an Autoclave, pressure Cooker or Pressure Canner, you can learn more about this here.

  2. Chemical Sterilization: Chemical sterilization involves the use of chemical agents, such as hydrogen peroxide or bleach, to kill or inhibit the growth of microorganisms. Chemical sterilization is typically used for small-scale operations or in specific situations where heat sterilization may not be feasible or practical.

  3. Radiation Sterilization: Radiation, such as gamma radiation or ultraviolet (UV) light, can be used to sterilize substrates. Gamma radiation is often used on a commercial scale, while UV light sterilization can be suitable for smaller setups or surfaces.

The choice of sterilization method depends on factors such as the type of mushroom being cultivated, the substrate composition, the scale of cultivation, and the available resources. Each method has its advantages and considerations in terms of effectiveness, cost, time, and equipment requirements.

It's important to note that after sterilization, the substrate needs to be handled in a sterile manner to prevent recontamination. This includes working in a clean environment, using sterile equipment, and taking precautions to prevent contact with airborne contaminants.

Sterilization is a critical step in mushroom cultivation as it helps create a clean and favorable environment for the growth of mushroom mycelium. Proper sterilization techniques significantly increase the chances of successful cultivation and the production of healthy mushrooms.