Making agar plates can be done a hundred different ways, there are two methods below: one for a perfectly serviceable quick plate and another more involved process to make crystal clear plates.

 

Generally you should use 10g of agar per 500ml of water, which will make 20 plates. You’ll also want to include a nutritional additive; both of these recipes use 10g of Light Malt Extract (LME). It’s best to add some food colouring to the mixture so that mycelium will standout against the background. You can use whichever colour you like but blue provides an excellent contrast for observing growth and spotting contamination.

 

Quick Method

  • Add 10g of agar powder and 10g of LME to your media bottle (if you are not using a purpose built 500ml media bottle you should ensure there is space in the top of the bottle to prevent the mixture boiling over and escaping when in the pressure cooker)
  • Add 500ml of hot water from the kettle 
  • Add around 1ml of food colouring, you may need more depending on the colour chosen and formula of the dye, you can add it by eye until the bottle is your desired colour
  • Put the lid on and shake it really well
  • Loosen the lid a quarter turn to allow air to escape as the pressure rises, otherwise it may explode
  • Place your bottle(s) in the pressure cooker, allowing space for steam to circulate around them and cook at 15PSI or 121ºc for 45mins

Using this method may result in your plates having some sediment (undissolved LME and tiny clumps of agar powder) however the mycelium will not mind and it’s relatively easy to distinguish between sediment and contamination.

 

Crystal Clear Plates

  • Add 10g of agar and 10g of LME to 500ml of cold water in a pan (you can increase these amounts to do more plates at once)
  • Bring this pan to the boil whilst stirring continuously. Stirring is key to this recipe, as it prevents the agar powder forming small clumps as it begins to melt
  • Once it has begun to boil hold it there for 1-2 mins as you add 1ml (or the required amount) of food colouring. The mixture has a tendency to foam so remove it from the heat if it looks like it may boil over
  • Pour it into media bottles (for extra protection against sediment you can pour it through a sieve lined with a coffee filter). If you are not using a purpose built 500ml media bottle you should ensure there is space in the top of the bottle to prevent the mixture boiling over and escaping when in the pressure cooker
  • Loosen the lid a quarter turn to allow air to escape as the pressure rises, otherwise it may explode
  • Place your bottle(s) in the pressure cooker, allowing space for steam to circulate around them and cook at 15PSI or 121ºc for 45mins

 

Once your agar has been sterilised you’ll need to pour your plates in a clean environment, such as a still air box or in front of a laminar flow hood. It’s best to wait until the bottles have cooled down to between 47 - 55ºc to prevent excessive condensation forming as the agar sets.