Agar – What You Need To Know

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Working with agar might seem like a bit of a scientific dark-art, reserved for men in white coats with severe expressions and clipboards.  

But it’s not nearly as mysterious or exclusive as it might seem.  You can – and should – be working with agar.  It’s an incredibly useful tool for the aspiring mycologist!

This, the first in our Agar mini-series, will aim to explain what agar is, what the different types of agar are for, and how you can use it to step up your mushroom growing game.

You can work with agar, and you’ll be glad you took the plunge!

There are just a few things you need to know.

Let’s break it down…

Table of Contents

Coming soon…
  • Preparing Agar
  • Working With Agar
  • Storage
  • What You’ll Need

What is Agar, and why do we use it?

‘Agar’ in mycology terms is a mixture of sugar (Malt Extract, Dextrose, Honey etc) and a gelling agent (agar agar).  This creates a nutritious gel upon which we can grow our mycelium of choice.

When we pour the agar into a petri dish, we create a flat two-dimensional surface upon which we can grow out mycelium.  This way we can easily spot contaminants or desirable qualities in the mycelium we might wish to isolate.  A petri dish prepared with agar in this way is often called a ‘plate’.

Many aspiring mushroom growers initially shy away from agar, and the scientific side of mycology it represents.  But the fact is that if certain procedures are followed, and techniques practiced, agar is an incredibly useful tool which will help you better understand the fungi you are working with – and ultimately, improve your growing!  (We’ll cover the what and how in the next guide!)

A range of different things can be used to inoculate an agar plate; a spore streak or swab, a drop of liquid culture, a wedge of agar, colonised grain, mushroom tissue sample… the list goes on!  We’ll cover how to use agar in a little more depth in the next guide.  

But first we need to know what sort of agar to use…

Types of Agar

MEA, MYA, PDA, PDYA, PDG, DFA, WTF?

It can seem a bit overwhelming being faced with a list of acronyms when you’re not sure what they mean.  

Below is a list of some of the most common types of agar used for growing fungi.  You may have come across others elsewhere which are used for other areas of microbiology, but for our purposes the list below will cover just about everything you’ll need to get started.

Types of Agar for Growing Fungi

  • MEA (Malt Extract Agar) – A standard for coprophilous (manure-loving) species.  Some say it is less suited for lignocolous (wood-loving) species.  Often produces a plate with good clarity for easily observing growth. MEA is also a more acidic medium than PDA, so is (somewhat) less hospitable to bacteria.

  • MYA (Malt Extract Yeast Agar) – As above, with the addition of Yeast for extra nutrition.  The trade-off is that the yeast often leaves the agar cloudy and reduces clarity making identification of mycelium and contaminants less easy.

  • PDYA (Potato Dextrose Yeast Agar) – An industry-standard formula for many mycologists.  Dextrose is a simple sugar, easily metabolised by mycelium, which encourages rapid initial growth.  The potato provides broader nutrition through more complex starches, and helps to sustain the mycelium for longer term storage.  The tradeoff is a plate with considerably less clarity than MEA.

  • PDA (Potato Dextrose Agar) – As above, without the addition of nutritional yeast.

  • Activated Carbon Agar – This can be any of the above formulae, but with the addition of Activated Carbon.  This turns the agar black which not only looks sharp, but offers brilliant contrast and has naturally antibiotic properties!

  • PDG (Potato Dextrose Gellan) – A new addition to our lineup (coming to the shop soon!), and one you may not have come across before.  Gellan is a gelling agent just like agar, but offers greatly increased clarity.  PDG combines the unparalleled clarity of gellan with the nutritional benefits of PDA.

  • DFA (Dog Food Agar) – Yes… really.  Dry dog food is used, providing a broad range of nutrition.  Clarity can be very poor, with lots of ‘bits’ present, and the more scientifically-minded may prefer to know exactly what the nutritional makeup of the medium is – which is harder to do with a proprietary dog food recipe.  Also, you probably don’t want your kitchen smelling of boiling dog food…

MEA Plate (uncoloured)

MEA Plate Blue

MEA Plate (blue)

Carbon Agar Plate

Activated Carbon Agar (PDYA)

PDG Gellan

PDG (Potato Dextrose Gellan)
How’s that for clarity?

Which to choose?

It depends on what you want your agar to do for you!  The short answer is – you can’t really go wrong.  All fungi you’re likely to want to cultivate will grow on all the recipes mentioned in this guide.  

If in doubt, you can’t go wrong with PD(Y)A – it contains a broad range of nutrients, and will work for short-term isolation work, or for longer term storage.  It is suitable for both lignicolous and coprophilous fungi.

Once you’ve decided on your formula, you might then decide to add a colouring for contrast, or antibiotics to deal with a bacterial contamination. 

Or even go for black activated carbon agar plates, which offer excellent contrast, as well as naturally antibiotic properties of activated carbon.  Our Black Carbon plates use a PDYA base with the addition of Activated Carbon. 

Summary

Hopefully this guide has taken a little of the mystery away from Agar, and you’re feeling like you might take a crack at it.

In the next part, we’ll go into how to prepare agar, and how to work with it to up your mushroom growing game!

You can do it!


If you want to get stuck in right away, you can find our range of Pre-Poured Agar Plates here.
And Black Activated Carbon Plates here.

Is there anything you’d like to see us cover in future guides?

Feeling a bit stuck on something? Drop us a line!  

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