Malt Extract Agar vs Potato Dextrose Agar: Which Should Beginners Use?
A grower emailed me last winter, halfway through pouring his first plates, worried he had bought the wrong thing because a video told him potato dextrose agar was the only real option. He had not bought wrong. For legal gourmet and functional mushrooms, malt extract agar and potato dextrose agar both grow mycelium well, and there is no universal winner.
If you are choosing one to start with, use malt extract agar. You weigh it, dissolve it, sterilize it, and pour, so your plates come out the same every batch. Reach for potato dextrose agar when you are germinating spores, comparing how colonies look, or you simply cannot get malt extract where you live.
Out-Grow Quick Answer
- 🍄 Both malt extract agar and potato dextrose agar grow mushroom mycelium well. There is no universal winner.
- ✅ Start with malt extract agar. You weigh, dissolve, sterilize, and pour, so batches stay consistent.
- 🥔 Reach for potato dextrose agar when you germinate spores, compare colony appearance, or cannot source malt extract.
- ⚗️ Per liter: malt extract agar is 15 to 20 grams malt extract plus 15 to 20 grams agar. Potato dextrose agar is 200 to 300 grams potato, 10 to 20 grams dextrose, and 15 to 20 grams agar.
- 🧫 Your sterile technique decides contamination, not which of the two you pick.
What Is the Difference Between Malt Extract Agar and Potato Dextrose Agar?
The first potato dextrose agar I ever made, I stood over a pot of simmering potatoes near midnight, wondering why I had not just used the malt extract powder sitting in the cabinet. That night is the whole difference in one scene. Malt extract agar is a powder you dissolve. Potato dextrose agar starts with cooking.
Both are rich, non-selective nutrient media that set into a firm surface where you can grow, isolate, and clean up mushroom cultures. They differ in three practical ways: how you prepare them, how repeatable they are, and small differences in how colonies look and grow.
A gelling agent taken from seaweed that sets liquid nutrient media into a firm plate you can grow mycelium on. The agar itself adds almost no nutrition. The malt extract, or the potato and dextrose, is what actually feeds the fungus.
Malt extract supplies fermentable sugars, amino acids, vitamins, and minerals in a soluble, even form, which tends to give smooth, uniform colonies that are easy to read. Potato dextrose agar leans on starches and complex carbohydrates from the potato plus simple dextrose, a rich mix many fungi exploit fast, and the potato can bring out more colony character that is useful when you are comparing strains.
Where they really part ways is prep time. Malt extract agar is usually under thirty minutes of hands-on work before it goes in the sterilizer. Potato dextrose agar adds twenty to thirty minutes of simmering potatoes and then filtering the infusion, so you are often looking at forty to sixty minutes of active work.
Which Agar Is Best for Beginner Mushroom Growers?
A woman I helped get set up last spring poured her first ten plates of malt extract agar in one afternoon and had clean transfers running inside a week. That is the case for malt extract agar as a beginner's first plate. Fewer steps, nothing to filter, and a recipe you can repeat exactly, which means when something does go wrong you can rule the medium out and look at your technique instead.
Potato dextrose agar is not harder to succeed with, it just has more moving parts up front. If you are comfortable in a kitchen, simmering and filtering will not slow you down, and the ingredients are cheap and easy to find. My honest recommendation is to start on malt extract agar, get your pouring and transferring clean, then bring in potato dextrose agar for the jobs it suits.
Malt Extract Agar
Weigh, dissolve, sterilize, pour. Fast and repeatable batch to batch. Best for routine transfers, tissue work, and culture maintenance where clean, consistent growth is the goal.
Potato Dextrose Agar
Simmer and filter potatoes first, then add dextrose and agar. Cheap from grocery ingredients. A classical, broadly used medium favored for spore germination and reading colony morphology.
This is the same reason a working lab keeps both on the shelf. It is not about one recipe being better. It is about matching the plate to the job in front of you.
How to Make Malt Extract Agar and Potato Dextrose Agar
The step that trips people up is never the weighing, it is the potato. The first time I filtered a potato infusion I used too fine a cloth, clogged it, and wore half the batch on my hands. Both media follow the same arc though, and once you have the rhythm it is the same afternoon either way.
- Malt extract powder, or potatoes plus dextrose or plain table sugar
- Agar powder, the gelling agent for either recipe
- A pressure cooker or pressure canner that reaches 15 psi
- Sterile petri dishes or clean jars to pour into
- A still air box or a flow hood to pour in front of
- A kitchen scale that reads in grams
Malt extract agar recipe per liter
Dissolve 15 to 20 grams of malt extract and 15 to 20 grams of agar in one liter of water. That is the whole mix. Stir so nothing cakes on the bottom, cap loosely, and it is ready for the sterilizer.
Potato dextrose agar recipe per liter
Simmer 200 to 300 grams of peeled potato in water for twenty to thirty minutes, then filter to keep the clear infusion and discard the solids. Bring the infusion back to one liter, then add 10 to 20 grams of dextrose and 15 to 20 grams of agar. Same agar amount as before, since the agar is what sets the plate.
Here is every number from both recipes gathered in one place, so you are not scrolling back up while you are standing at the scale.
From there the two recipes merge. You sterilize, you cool, and you pour the same way. Here is the shared workflow start to finish.
Before you tuck plates into the refrigerator, it helps to know what a plate looks like once it is past its window.
None of that comes down to which recipe you poured. It comes down to storage, which brings up the bigger question growers ask me at the counter.
Does the Agar You Choose Affect Contamination or Yield?
I have watched a beautiful malt extract agar plate turn into a green science experiment in three days, and the medium was not the problem. My glovebox work that day was sloppy. That is the honest answer to whether agar type drives contamination. It does not. Both malt extract agar and potato dextrose agar are rich and non-selective, which means they feed molds and bacteria just as happily as they feed your mushroom mycelium.
Contamination comes down to clean inoculum and sterile technique, not the recipe. If anything, a richer medium grows contaminants faster once they land, which makes a dirty plate obvious sooner. As for yield, the agar plate is a starting culture, not the fruiting substrate, so the plate you choose is not a yield lever. It is a place to build clean, vigorous mycelium that you carry forward.
| Medium | Prep ease | Repeatability | Low cost | Beginner friendly |
|---|---|---|---|---|
| Malt Extract Agar | ||||
| Potato Dextrose Agar |
Read that table as tendencies, not laws. Malt extract agar wins on prep and repeatability. Potato dextrose agar wins on cost if you already have potatoes in the pantry. Both grow gourmet and functional mycelium well, so neither column is a wrong answer.
The fuller side by side below covers the same ground with the specifics.
| Factor | Malt Extract Agar | Potato Dextrose Agar |
|---|---|---|
| Prep difficulty | Lower. Weigh, dissolve, sterilize, pour. | Higher. Simmer and filter potato first, then add dextrose and agar. |
| Active prep time | Under thirty minutes before sterilizing. | Roughly forty to sixty minutes before sterilizing. |
| Ingredient cost | Moderate. Malt extract and agar powder. | Low. Potatoes and sugar from the grocery store, plus agar. |
| Repeatability | High. Standardized powder, same result each batch. | Moderate. Potato batches vary a little. |
| Colony morphology | Smooth and even, easy to read for contamination. | Slightly more variable, can bring out strain character. |
| Contamination risk | Same. Rich and non-selective. Technique decides. | Same. Rich and non-selective. Technique decides. |
| Best use | Routine transfers, tissue work, culture maintenance. | Spore germination, morphology and strain comparison. |
Is Potato Dextrose Agar or Malt Extract Agar Better for Spore Germination?
Every so often someone tells me their spores will only take on potato dextrose agar, and then they germinate the same print on plain malt extract agar the next week and look a little betrayed by their own results. The tradition that potato dextrose agar is for spores and malt extract agar is for tissue is exactly that, a tradition. It is built on grower habit, not on broad experimental proof across gourmet species.
Spores are not fussy about which rich medium they land on. They will germinate on many low-nutrient and rich media, including plain water agar. If you have potato dextrose agar and you like it for prints, use it. If all you have is malt extract agar, germinate your prints on that and move on. The bigger levers are the freshness of the print, a clean pour, and steady incubation, generally in the 20 to 28°C (68 to 82°F) range, with many growers keeping gourmet plates toward the cooler end of that to hold contamination down.
Common Bad Advice About Choosing Mushroom Agar
The claim I run into most is that malt extract agar is somehow "for bacteria" and potato dextrose agar is the only true fungal medium. It gets repeated with real confidence, and it is simply not how these media work. Here are the two corrections worth carrying with you.
Potato dextrose agar is the only correct medium for fungi, and malt extract agar is mainly for bacteria.
Both are standard, widely used media for filamentous fungi, including mushrooms. Malt extract agar is not a bacterial medium, and neither one is uniquely required. Either grows gourmet and functional mycelium well.
A rich medium like malt extract agar lowers contamination because the mycelium outruns competitors.
Rich, non-selective media feed contaminants just as well as mycelium. Contamination comes down to clean inoculum and sterile technique, not nutrient richness. More nutrients can actually let a stray mold take off faster.
Relevant Out-Grow Supplies
If you would rather not stand over a pot at all, here is what we stock for agar work, and an honest note on where each one fits.
- Ready-poured agar plates in our mushroom culture collection. Fit note: these are the same media styles discussed here, already sterilized and poured, so you can start isolating and transferring cultures without a pressure cooker session of your own.
- Culture media if you want to mix and pour your own. Fit note: this is where the malt extract, agar, and prepared blends live. Buy the ingredients if you plan to pour in any real volume, since mixing your own is cheaper per plate at scale.
- Liquid culture syringes for the next step after a clean plate. Fit note: agar and liquid culture work together. A lot of growers keep a master culture on a plate, then expand a clean wedge into liquid culture to inoculate grain.
The Bottom Line on Malt Extract Agar vs Potato Dextrose Agar
Malt extract agar and potato dextrose agar both grow mushroom mycelium well, so you are not choosing between right and wrong. Start with malt extract agar because it is fast and repeatable, and it lets you build clean technique without fighting the recipe. Add potato dextrose agar for spore prints, for reading colony character, or when malt extract is hard to get. Whichever you pour, remember that your sterile technique, not the medium, is what keeps a plate clean.
About the author
Mike Wiberg is the founder of Out-Grow, a mushroom cultivation supply company he has run since 2009. He developed the original all in one mushroom grow bag in 2014, a format now used across the hobby, and over more than 20 years of hands-on mycology he has grown hundreds of species and researched substrate formulations from the lab bench. He maintains one of the largest commercial culture libraries online, including a working collection of more than 300 species under a USDA permit. His cultivation work has been cited in peer reviewed research published in Frontiers in Cellular and Infection Microbiology, and he is one of only a handful of growers with a documented successful clone of Matsutake, one of the most difficult species in cultivation. He has helped growers troubleshoot cultivation problems for nearly two decades, and he writes from the lab and the grow room, not from a keyword list.