Grow mushrooms the EZ way.

How to Make PopCorn Grain Spawn (Popcorn Tek).


Popcorn tek is a simple grain spawn that a lot of beginners start with before moving on to other grains (although some people swear by it).

It is a very easy spawn to prepare and most people have access to it which adds to its successes.

In this post I am going to walk through how to create popcorn grain spawn.

There are a few techniques out there so do plenty of reading before deciding which method suits you. 

You will need a pressure cooker for this preparation, if you dont have one you should checkout my post on the best pressure cookers for mushroom cultivation.

Advantages & Disadvantages of Popcorn Tek.

The Cons.

  • The large kernel size causes less inoculation jump-off points, these also have wider gaps between kernels, this causes a number of issues such as less overall mycelial growth due to less nutrients. This can be fixed by adding coffee grounds or gypsum.
  • Cost.
  • Popcorn has less nutritional value than other grains, this is coupled with there being less grains all together in one jar.

The Pros.

  • Easy tek – preparation is very easy and the grains are less messy than others. I think its a really good beginner tek.
  • Easy to shake grains – because of there weight and shape popcorn is less likely to clump up in a jar.
  • Widely available – you can get popcorn at any local super market.
  • Low contamination rate – this is normally due to the nutritional value.
  • Shorter pressure cook time.

How to Make Popcorn Grain Spawn.

Note: These steps will allow you to make 4 quart jars of popcorn grain spawn when completed. 


Prepare the Jars.

Firstly you must decide how many jars of grain spawn you are hoping to create. I have create a table which is a good estimate on how much popcorn you will need.

Popcorn Quart Jars
600g 2
1200g 4
2400g 8

Pour your popcorn grain into the jars, I filled one jar approximately halfway up (600g). This will be enough to fill 2 jars whilst leaving plenty of room at the top for shaking during colonization.

Filling jars for Popcorn Tek

I add water to the jar and leave for approximately 24 hours. This will allow time for any bacterial endo-spores on the outside of the grain to germinate before sterilization (this step is optional but be warned you may have better results with this step).

Add water to popcorn grain spawn jar

After 24 hours has passed you can see the grains have began absorbing water already.

Next, I will bring a pan of water to boil on the hob to further hydrate them.

Hydrated popcorn spawn

I pour the popcorn into the boiling water. Then turn down the boil to a simmer. 

Next, I allow the Popcorn to sit inside the simmering pot for at least 10-15 minutes.

Make sure you stir the pot keep any kernels from burning on the bottom of the pan.

When the kernels are complete you should be able to split them in half no problem with your fingernail. This is done to hydrate the grains with water for the mycelium to consume.

Boiling popcorn grain spawn

Pour out Popcorn Kernels into the colander and shake while the water evaporates off the outside. 

Spread Popcorn kernels out on a baking tray for 30 minutes while still hot (optionally this can be done by leaving them in the colander).

We do this to allow most of the water on the outside of the grains to evaporate off.

Draining popcorn in a seive

Load popcorn into your jars distributing them evenly. You want to have a gap in the top of the jars DO NOT fill jars full to the top.

As you wont be able to shake and breakup the grain.

Hydrated Popcorn up close
Pre-sterilized Popcorn

Place lids on the Jars. Check this post here on my recommended lids for grain jars if you have never done this before.

Place tinfoil over the lids and secure with elastic bands.

Tin foil wrapped around grain jar for mushroom spawn

Sterilize Jars.

Fill the pressure cooker up to the minimum line (this is normally about 3 quarts for my 23 quart presto pressure cooker).

Water being poured into a pressure cooker

Place Jars inside the pressure cooker raised from the bottom of the PC (using a rack or jar lids).

We do this so that the grains in the bottom of the jars don't burn.

Next, secure the lid.

5 grain jars in pressure cooker

Finally heat your pressure cooker on a high heat until it hits 15 psi.

Once 15 psi has been reached you should turn down the heat to maintain pressure for at least 30 minutes.

If you don't turn the heat down you risk drying outside the pressure cooker which is not advisable. 

15psi Sterilizing mushrooms

Once 90 minutes has passed, turn off the heat.

Allow the pressure cooker to cool overnight.

This is important so that the jars cool down before returning into the outside atmosphere, skipping this step can cause contamination/hydration issues.


You have now created popcorn grain spawn, next you can inoculate the grains with either liquid culture or colonized agar.

I cover this more fully in how to make grain spawn.

To do that you are probably going to need a still air box so read about how to make a still air box before beginning.

The rest of this post will be answering some frequently asked questions.

Other FAQS

When to Shake Popcorn Grain Spawn?

When ⅔ of the grain jar is colonized is when I normally shake my grains. Always ensure there is space in the top of the jar when creating them to allow plenty of space for the grains to move around during a shake.

What does Fully Colonized Popcorn Grain Look Like?

Here are some photos of fully colonized popcorn grain spawn I have created previously.

Popcorn Spawn Colonization Time?

Colonization times are usually mushroom species/genetic dependent. However at least 14 days should be expected for the average grain prep.

Popcorn vs Rye For Mushrooms.

In my opinion Rye grain is the better grain between Popcorn and Rye. This is because the size of the grain kernels creates a larger number of inoculation jump-off points when you spawn to bulk. Alongside this Rye is very nutritious for Mycelium and can colonize it very fast. However, Rye does have its downfalls, I find Rye is more likely to contaminate, the grains are slightly harder to prepare and often harder to shake when the Mycelium expands.

Popcorn on the other hand is simple to create, easy to shake and has less contamination. It is also an easier grain to source. However, when you have a fully colonized jar of popcorn grain spawn you have less volume of Mycelium growth which can result in slower results after spawning to bulk.

In the end, it normally comes down to personal preference, a lot of commercial growers use Rye grain, however, I have seen a lot of very skilled amateurs use Popcorn grain. My advice is to try both and see which you prefer.

If you are interested in creating Rye grain checkout the discussion here.

Popcorn Spawn with Gypsum/Coffee.

If you are wondering when to add gypsum and coffee grounds to a grain jar I like to sprinkle them in during the boiling of the grain. 

Not only does adding gypsum and coffee to popcorn grain spawn increase nutrition, it also fills the gaps between the grains which means the mycelium has an easier route around the jars from grain to grain.

Can Popcorn Tek be No Soak?


Popcorn grain spawn can be performed without a soak however it has mixed reception on the effectiveness. In theory Popcorn grain which is prepared for human consumption should carry a lower endospore load than something like wheat berry grain used for bird seed.

To perform a no soak tek follow the instructions described above however don’t perform a 24-hour soak before and leave the grain inside the pot to BOIL for 40 minutes during step 5.

How Long do you Pressure Cook Popcorn Grain Spawn?

Usually, this grain spawn is pressure cooked for 30 minutes as a minimum. This will allow the grains to be properly sterilized. Popcorn grain tends to burn if left in longer.

How do you Sterilize?

Place hydrated popcorn grain spawn inside a pressure cooker for at least 90 minutes.

Popcorn Spawn without Gypsum/Coffee.

This can be created without gypsum, the only difference is the mycelium will have to travel further without nutrition while jumping between popcorn grains. The tek discussed above was created without gypsum.

How to Make PopCorn Grain Spawn (Popcorn Tek)

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