Grow mushrooms the EZ way.

Best Grain Spawn For Growing Mushrooms

Many different grains can be used as a nutritious substrate to inoculate  mycelium spawn. This is done to allow the mycelium to multiply and create a strong network with a large surface area; once  grains have 100% colonized a grain they are comparable to seeds in the plant's life cycle.

Using grain spawn reduces the chance of contamination and increase the speed of colonization of the bulk substrate.

So…which is the best grain for growing mushrooms?

In short, Rye is the best grain for growing mushrooms; the small kernel size means there is more total surface area for the mycelium to grow out of when it is placed into a bulk substrate. Alongside this Rye is a very nutritious grain for the growing mycelium and is widely available.

Rye Grain


Holds lots of water – for the size of the grain Rye can hold a lot of water, the berries can swell 3X normal size or larger without bursting.

Highly Nutritious – this grain holds high levels of magnesium, B vitamins, copper and proteins that most of the other grains. Coupled with its size this makes it a mighty grain.

Large Surface Area – as discussed earlier due to the size of the grain, more kernels can be fit into a smaller sterilization chamber. As a result, there is a large surface area from your inoculated spawn to grow from inside the bulk substrate. This also means less goes a longer way when creating grain spawn.

Widely available – it is easy to purchase rye grain online as it is used for artisan organic cooking, get some here.


Cost – Rye grain can be costly in places as it is a popular product in organic food stores.

Drying out – the grain tends to dry out easier than other grains which can cause troubles during a spawn run.

Preparation time – Rye grain needs an overnight soak to germinate the endospores which may be found on the grains and a wash to remove debris from the grains.

How To Prepare Rye Grain



Step 1: Rinse and wash through grain until drained water is no longer discoloured.

Step 2: Soak Grains in water for 12-24 hours.

Step 3: Cook the grains for 20-30mins.

Step 4: Drain off water/grain in a colander and allow excess moisture to evaporate off the kernels until they are dry to touch.

Step 5: Load the Rye grain into mason jars and sterilize at 15psi for 75+ minutes

Step 1 Rinse and Wash Grain

Measure out the amount of Rye grain you wish to use in your spawn run and place it into a sieve or bowl. Wash the grain under a tap to wash away any debris which is left. Make sure to mix up the grain and ensure the run-off water is no longer coloured.

Step 2 Soak Grain in Water (optional)

Take the cleaned grain kernels and soak them in a container of warm water overnight, this will allow endospores to germinate making them more susceptible to sterilization. 

This step is often contested as unnecessary on various forums but I like to do it anyway as a precaution.

Step 3 Cook The Grains For 10-20mins

Take the soaked grain and place it inside your pressure cooker or a boiling pot and cook for about 10-20minutes. 

Step 4 Drain Grain and Dry

After the grain has been cooked and is hydrated, allow it to dry out on a large surface (I like to use baking trays for this stage.). Because the grain is hot coming out of the boiling pot the water should evaporate off the surface of the kernels. Make sure to spread the kernels out  and move them around regularly to ensure that all sides are dry. 

The grain should be dry to touch but still swollen on the inside when complete, this is important as if the grain is too wet it could cause issues.

Step 5 Load Grain into Jars

Next, take the swollen kernels and place them into your mason jars ready for sterilization. Sterilize at 75+ minutes inside your pressure cooker at 15PSI. When sterilization is complete allow the jars to cool inside the pressure cooker overnight before opening the PC.

Can I Add Coffee Grounds into Rye Grain?

Yes! Coffee can be added into the mix during step 3 to increase nitrogen in the grain spawn and increase colonization times. However, make sure you have done a few runs of Rye only grain jars before adding coffee grounds as often the introduction of coffee creates more contamination factors inside the jars.

When is My Grain Spawn Ready To Use?

Once the whole grain jar has turned white  wait an extra 5 days for good measure to ensure the inside of the grain (which you cannot see) has had a chance to fully colonize as well. It is recommended to shake the grain to break it up and spread the spawn around the jar if it is stalling.

How To Use 100% Colonized Grain?

Using the grain spawn is as simple as placing the grain into a sterilized or pasteurized bulk substrate. Some strains such as Oyster mushroom will eat a large variety of bulk substrates including recycled waste paper, alongside this it is   quite a contamination resistant strain so it is easier on beginners.

Alternatives To Rye Grain for Growing Mushrooms?

Wheat Berry grain is a good alternative to Rye grain; it has a similar nutritional profile and surface area. It is prepared in the same way as Rye also so it is a perfect substitute if Rye is not available. 

Wheat Berry is more commonly grown and available in the UK than Rye grain so it may be cheaper to purchase for people who are growing outside of the US. 

In the UK it is possible to purchase Wheat Berry in health food shops and pet stores. For ease, you can also purchase it on amazon.

Easiest Grain For Beginner Mushroom Growers?

PopCorn Grain Spawn – In my opinion popcorn is the easiest grain to prepare and use for beginner mushroom growers. It usually takes about 40 minutes to prepare and getting correctly hydrated grain is not hard at all. Popcorn spawn is usually widely available and can be found cheap in Asian supermarkets. The downside for Popcorn spawn is it is a larger grain and as a result, you can fit less inside your jars which means you will have a smaller amount of overall grain spawn to inoculate the bulk substrate with. 

I have a full post discussing Popcorn Grain spawn here.