What Is the Best Grain for Mushroom Spawn?

One of the most common methods of growing mushrooms is using something known as grain spawn. In brief, it involves using a cereal grain to provide nutrition to the fungus as its mycelium develops.

There are several options in terms of which grain to use, each with distinct advantages and disadvantages. This article explains how to choose the best grain for mushroom spawn according to your needs. Here’s what you need to know.

What Is Grain Spawn?

Before you can produce a bountiful mushroom harvest, it is necessary to cultivate some healthy mycelium.

Mycelium is the network of strand-like structures called hyphae that make up the bulk of the fungal organism. Much like a plant’s roots, it takes up nutrition from the substrate and grows and develops until the conditions are right for the first flush of mushrooms to form.

Depending on the species, mushrooms can be grown on many different media. Wood chips, coco coir, or even coffee grounds are all popular options for the “bulk substrate,” the substance on which the mushrooms will eventually fruit. However, it isn’t simply a case of throwing some spores onto the bulk substrate in question and waiting for mushrooms to grow.

The process of cultivating mushrooms has several distinct stages. This is because home-grown fungi are very prone to contamination in the early stages of their life cycle. Therefore, it is essential to establish a healthy mycelial network before adding it to the bulk substrate.

This is why grain spawn plays a crucial role. It provides a sterile, nutrient-rich environment for the mycelium to develop with a minimal risk of contamination. Once the grains are fully colonized, the mycelium is better able to defend itself against pathogens like bacteria and mold. Therefore, can be added to the bulk substrate relatively safely.

There are many different grains that can be used to create mushroom spawn, but some are more suitable than others. Below, we will compare the options and explore which is best. But first, let’s take a brief look at the process of creating mushroom grain spawn.

Growing Mushrooms Using Grain Spawn

Below, we have summarized how to grow mushrooms using grain spawn. However, it is not a comprehensive guide, and we recommend that you thoroughly research each step before proceeding.

Washing and Soaking the Grains

The first step involves washing and soaking the grains to rehydrate them. How long this takes will depend on their size. For example, large grains like popcorn require more soaking than smaller grains like millet, with medium-sized grains like rye being somewhere in between.

Sterilizing the Grains

The grains must be thoroughly sterilized before adding the mushroom culture. Most people do this using jars or mushroom grow bags inside a pressure cooker. The pressure cooker should be set at around 15 PSI (250°F/121°C), which is hot enough to destroy the relevant pathogens.

A simpler option is to buy pre-sterilized grains from a mycology supplier or use microwavable rice bags. While many experts agree that rice is not the best grain for growing mushrooms, this quick and easy method eliminates the need for a pressure cooker and is an easy first step into the world of mushroom cultivation.

If you use pre-sterilized grains, you can skip the soaking and sterilization steps detailed above.

Inoculating the Grains

The next stage is to inoculate the grains with your mycelium. This might take the form of a liquid culture or clean, colonized agar. Adding mushroom spores directly to grain is not recommended as it increases the risk of contamination.

Good hygiene is critical to avoid introducing mold or bacteria to the grains at this stage. This means creating a sterile environment using a still air box or a laminar flow hood.

The latter option is a relatively expensive piece of kit but could be a worthwhile investment for anyone who is serious about cultivating mushrooms. It is also best practice to wear disposable gloves and a mask when handling your uncolonized grains and mycelium.

Incubating the Grains

Once the mushroom culture or agar has been added to the sterile grains, you must wait for the mycelium to colonize them. This period is known as incubation. Depending on the variety of mushrooms you are growing, the grains may need to be incubated at a specific temperature.

As the grains colonize, they will start to turn white. This is a sign that the mycelium is developing as it should. Be vigilant for signs of contamination, such as green, black, orange, or pink patches. If these appear in your grains, dispose of them immediately.

Once the grains turn completely white, they are fully colonized, and your spawn is ready to add to the bulk substrate. Colonization can take several weeks, and some experts recommend waiting an additional five days after the grains turn white to ensure they are fully colonized.

Inoculating the Bulk Substrate

Pasteurize the bulk substrate and add the spawn, breaking it up into individual grains to maximize the surface area. Mix the spawn into the substrate evenly, paying close attention to hygiene and potential sources of contamination. Cover with a lid to retain moisture and maintain optimal conditions for colonization

Finally, wait for the bulk substrate to be fully colonized before initiating fruiting conditions. The time this takes will vary depending on factors such as the mushroom species, the substrate, the temperature, and the container size.

Initiating Fruiting Conditions

Initiate fruiting conditions by introducing fresh air to the colonized bulk substrate and mist several times a day to maintain moisture levels. Within a few days, you should see your first mushrooms starting to form!

The Best Grain for Mushroom Spawn

Now that we have explained how to grow mushrooms using grain spawn, let’s investigate the best options.

Rye

Many people consider rye to be the best grain for mushroom spawn.

It is nutritionally dense, retains moisture, and has relatively small grains with a large surface area. This is advantageous because it means more inoculation points for the mycelium and, therefore, faster colonization. 

The major downside of rye is its availability. It is less common in stores than other grains, and although it can be purchased online, it may be costly.

Rye can also dry out relatively fast and should be soaked overnight for the best results. 

Wheat

Wheat (sometimes known as wheat berries or wheat seeds) is another popular option.

It is similar to rye in terms of its nutritional content and surface area. It is also more widely available in many areas, making it more affordable.

The main disadvantage of wheat is that it holds less water than rye and can, therefore, dry out even more quickly.

Millet

The main advantage of using millet is that the grains are tiny. Therefore, it has a far larger overall surface area than rye or wheat, making it faster to colonize. It is also relatively resistant to contamination.

However, millet’s tiny grains can be tricky to handle, and you should be prepared for them to bounce around and get into every nook and cranny of your workspace. They can also become mushy more quickly than other grains.

Popcorn

Popcorn is widely available and is a good option for beginners. It is relatively easy to rehydrate correctly and less prone to contamination than some other grains.

The main disadvantage is that popcorn is a much larger grain than the others we have discussed so far, meaning it has a smaller surface area and is slower to colonize. It is also one of the most expensive options on our list.

Brown Rice

As we mentioned earlier, rice is not considered the best grain for mushroom spawn. It tends to get mushy quickly and is quite prone to contamination.

However, it is very affordable and widely available. Microwavable rice also comes in pre-sterilized bags, meaning you do not need a pressure cooker for this method. If you decide to go down this route, be sure to choose whole-grain brown rice rather than white rice, which can become extremely sticky.

Wild Bird Seed

Wild bird seed contains a mixture of different grains, and it is cheap and widely available. However, it has several significant downsides for mushroom cultivation.

Because wild bird seed has various grains of different sizes, it is challenging to rehydrate evenly. Furthermore, if you use wild bird seed to create grain spawn, you should avoid brands that include sunflower seed shells or cracked corn, as these ingredients can cause issues with colonization.

Other Grains

Many other grains, including barley, oats, and sorghum, can be used to grow mushrooms. In fact, you can grow mushrooms using almost any grain you have available. While some are more suitable than others, most work well enough for small-scale operations.

The Best Grain for Mushroom Spawn: Final Thoughts

Creating grain spawn is an essential step for growing mushrooms at home. It involves colonizing a cereal grain with mycelium before adding it to the bulk substrate where it will fruit.

You can use a wide variety of grains, and each of them has pros and cons. Therefore, many experts agree that the best grain for mushroom spawn is whatever you have available. For example, while many consider rye the number one choice, it can be more difficult to find than millet, popcorn, or brown rice.

The variety of mushrooms you are growing, and environmental conditions can also have a significant impact. At the end of the day, every grow is different, and finding the best grain can often be a case of trial and error.