How To Make Agar Plates.


This is what we are going to be making:


Why Make Agar Plates?


The benefits of using agar are numerous. To name a few:

  • You can conserve mushroom strands for later use.
  • For growing mushrooms you get the benefit of seeing whether you have any contamination before innoculating your substrate. Even if there is some contamination going on you can cut out the healthy mycelium and discard the rest.
  • You can also use a wedge of agar from one petri dish to propagate further agar plates.

I hope this is enough to convince you that it is well worth doing!

Time To Make Some Agar Plates


To make 20 agar plates you are going to need:

  • a pressure cooker that can reach 15 psi
  • an Erlenmeyer flask or glass bottle that can hold at least 750ml of liquid.
  • 23 grams of your Malt Extract Agar (MEA) mix
  • Sterile Petri dishes
  • Parafilm
  • 500 ml of Water
  • Tinfoil
  • Scales
  • Latex gloves
  • Disinfectant solution or alcohol wipes
  • Clean working area – Still air box (you can learn how to make one of those here) or flow hood

As the sterile petri dishes come in packs of 20 it is worth making up the whole lot at once as once the bag of sterile dishes has been opened, it will be hard to keep them sterile. You can always wrap them up with the parafilm and store them for later use if you are not able to use them straight away.

To make 20 agar plates you are going to need about 23 grams of your MEA mix. Weigh this out on your scales and mix with the 500ml of water in your flask or bottle. You can cover the top and give it a good shake. Then cover the top with some tinfoil so that no condensation can get into your mix while it is being sterilised like so:

Put water into your pressure cooker about an inch from the bottom and make sure you have a stand to put your agar mix onto so that your flask/ bottle isn’t sitting on the bottom of the cooker and isn’t in contact with the water in your pressure cooker. Turn your heat source on and once your pressure cooker is up to temperature you will need to leave it to sterilise for 45 minutes. You don’t want to leave it any longer as the sugars in the mix will start to caramelise and you will have to start again.

Once it has been cooking for 45 minutes, turn it off and let the pressure cooker get down to a safe temperature before opening it up. Some people advise to cover the pressure cooker with a wet towel as when the cooker is cooling it will be sucking air inside, potentially contaminating your mix. Once you have your agar mix out you will need to leave it for a while so that it cools down enough for you to be able to pour into your petri dishes. You need to leave your agar mix long enough that when you pour your plates the amount of condensation will be minimal, but not so long that your mix will start to solidify. This will take approximately 45 minutes.

In the mean time you can be getting your petri dishes ready for action. Regardless of where you are pouring your dishes you want to make sure everything is nice and clean including you. Get your gloves and face mask on. Clean everything your using including your hands with your alcohol. Once you have cleaned the sleeve of your petri dishes, get it in your work area and remove the sleeve. Stack your petri dishes in piles of 5 – 7 in your work area like so:


Once your agar mix has cooled down enough to comfortably pour, start pouring in a quick and efficient manner, keeping the amount of time the inside of the petri dishes are exposed to the air to a minimum. Work your way from the bottom of each stack, lifting up from the lid of the first petri dish, pouring, lowering the stack back down and lifting up from the lid of the second petri dish, until you have worked your way up the stack to the top. Do this until you have used all your petri dishes.

Once all the plates have been poured leave them to fully cool before going on to use them or parafilming them up for later use. They can be stored for up to 1 month. You can learn how to use parafilm here.

And that is pretty much it.

Happy Mushrooming!

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