Preparing Agar (PDA)

PDA Culture Media Dishes

Preparing your Agar

For every 1 Litre of Agar Final Mixed Solution you will need the following.

  • 20 grams Bacteriological Agar
  • 200g Potato infusion
  • 4 g of Malt Extract or Yeast Extract (optional)
  • 20 g Dextrose
  • 1 Litre of Distilled Water
  • Autoclave or Pressure Vessel


  • Place your cleaned Erlenmeyer flask on a kitchen scale and turn it on. Make sure your scale now reads 0.
  • Add your dry ingredients into the flask.
  • Now add potato infusion until the scale reads 250 grams. Pick up the flask and swirl the solution until no dry matter can be seen and most of the Agar has been dissolved.
  • Return the flask to your scale and add water until your reach 500 grams. Again swirl the solution.
  • Return the flask and add water until you read 1000 grams. Again swirl the solution.
  • Cut a piece of tin foil – 300 mm by 80 mm. Roll up a piece of kitchen towel into a tight roll. Now, half way sticking over the mouth of the Erlenmeyer flask, wrap your tin foil in a tube around the glass. Place the rolled up kitchen towel in the tube and fold over the mouth of the flask to hold the paper. (This acts as a filter when autoclaving your solution. As pressure drops in your pressure vessel, the flask will balance air pressure and suck in air. For this reason we need a filter.)
  • Pressures sterilize the Agar solution for 45 minutes.
  • Open the pressure vessel, once cooled, in front of a flow hood or in a cleaned environment (glove-box).
  • Pour your agar into petri dishes (90mm) or small glass jars for use, do this rhythmically and do not linger. From 1 litre of Agar you can make 35 – 40 dishes.
  • After pouring and cooling your agar dishes, keep them in a big zip-lock bag, to ensure they do not contaminate. You can keep these in the fridge for 28 days.

agar jar cap

Prepare potato infusion: Wash two medium sized potato’s (200g) and cut them into 2.5cm cubes.  Place in a clean pot and add 1.25 litres of CLEAN water. Bring to the boil and keep the simmering temperature for 10 – 15 minutes. At this time remove the pot from the stove and allow to cool down for 5 minutes. Strain the water away from the potato’s (use a fine sieve or french press) and use this water to prepare your potato infusion.

Experiment: To train your mushroom on a specific substrate e.g. Blackwood – you can add fine sawdust from Blackwood / black wattle to your agar solution before pressure treatment. Your mycelium will grow on the woody agar and be prepared for the constituents of the wood by the time you add your spawn to the wood.

If you do not have access to agar, you can experiment with the following: Use a sealable plastic ice cream tub. Clean it well with a 10% bleach solution. Cut a square of cardboard box that can fit inside the tub and soak this in clean water. Remove one side of the cardboard to expose the grooves (use a table fork). Lay the cardboard flat in the ice-cream tub with the grooves facing up. Place your CLEAN mushroom sample on the cardboard and cover with another piece of soaked cardboard. Remember to remove one side to expose the grooves in the cardboard. You can sandwich several samples of your mushroom like this. Close the tub and allow to incubate for 5 – 10 days at 22 degrees. By now the mycelium from your mushroom sample would have run into the cardboard. You can cut this with  clean scissors and move to the next ready vessel for further culturing.

Sampling a mushroom: With clean fingers, in a clean space or glove box, split the mushroom down the middle. You will notice clean white mycelium on the inside of the mushroom that has never been exposed to air or the environment. Using a cleaned scalpel cut a piece of this mycelium and place in your readied container.

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