Originally, mushroom hobbyists used the PF tek to grow mushrooms at home, which was a mixture of Brown Rice Flour, vermiculite, and water that we referred to as BRF cakes. The OG infamous PF tek involved packing the BRF cake mixture into mason jars for sterilization. Then, you would inoculate directly into the mason jar and let the mycelium colonize. Once fully colonize, you would birth the jar and let the mushroom pin directly from the BRF cakes. The idea of this method was that the BRF cake provided everything necessary for the mushroom mycelia and fruiting body to grow. It had nutrition from the Brown Rice Flour, and a high moisture content from the vermiculite. However, this method was limited and cumbersome to manage all of those small 8oz mason jars.

Then the field slowly adopted to the colonized grain method, which is more widely used today. So the, what is the advantage of using colonized grain versus the traditional PF tek?

Advantages of Grain Spawn

1. Versatile: Grain spawn can be used with a variety of substrates, including sawdust, straw, and compost. You can be versatile in the types of grains you use as well depending on what is easily available in your area. Some popular options are millet, wheat berries, rye berries, and sorghum. This versatility makes it a popular choice for mushroom growers of all experience levels.
2. Faster colonization: Grain spawn has a higher surface area to volume ratio compared to other types of spawn, making it faster to colonize the substrate. The grains are also loose, and can be easily broken up during the colonization period to disperse the mycelium around and increase colonization times. The colonized grains can then further be broken up and mixed in with bulk substrate to create multiple seeding points and allow for very fast bulk colonization as well. This is an advantage over the PF tek BRF cakes in that you can easily break up the grain spawn, whereas the BRF cake would need to be grated to break up.
3. Lower risk of contamination: Grain spawn is less likely to become contaminated compared to other types of spawn, as it is sealed in a bag that helps to prevent the introduction of unwanted microorganisms. The hydrated grains are sealed in a bag and pressure sterilized to kill off all microbes and spores. And when they are inoculated, it can be through a self-healing injection port that maintains the sterilized environment inside the bag.
4. Cost-effective: Grain spawn is relatively inexpensive compared to other types of spawn, making it a cost-effective option for mushroom growers. You can purchase grains for relatively cheap prices from feed stores, or even use common household grains such as rice and oats. However, the hardier the grains (i.e. feed stores), the better it will be suited for growing mushrooms, due to the grains not becoming mush and sticking to each other.
5. High throughput: The PF tek takes a good bit of time to prepare the BRF cake mixture, and you are limited by the number of mason jars you can comfortably fit inside a pressure cooker. However with grain spawn, you can arguably fit the same amount of grains inside a pressure cooker. However, once the grains have become fully colonized, you can spawn them to a pasteurized bulk substrate and drastically multiply your mushroom fruiting blocks by at least 5 times, assuming you are seeding at 20%.
6. Easy Inoculation: Grain spawn bags are relatively easy to inoculate. You can use a syringe, cuts of colonized agar, or even grain to grain transfers. Meanwhile, the PF tek is limited to only inoculating with a sterilized syringe.

How does grain spawn increases your mushroom output by so much?

When your grain spawn is fully colonized, the next step is to spawn it to a bulk substrate. Therefore, this step is rightfully referred to as "spawn to bulk." Generally, you would spawn your colonized grain to bulk at a ratio from 1:1 or 1:10 in volume. For instance, if you were spawning 1:1, you would add equal volumes of bulk substrate and colonized grain. If you were spawning at 1:10, you would add 1 volume of colonized grain to 10 volumes of bulk substrate. A popular ratio that mushroom growers like to start off with is 2:10, a 20% seeding volume.

Therefore, if you started with a 5 lb bag of colonized grain, and you were to spawn to bulk at 20%, it would look something like this.

(1 lb of colonized grain to 4 lb of bulk substrate) x 5

This would give you 5 bags of mushroom fruiting blocks! And hopefully you would get 3-4 lbs of mushroom fruits from each block, which would total your yield to be 15-20 lbs of mushrooms. As you can see, using grain spawn is a great way to scale up your mushroom growing operation.

How to tell if your spawn is fully colonized?

Wait until the grains have become fully covered with the white mycelium. I would recommend you then wait an additional week to allow the mycelium to fully penetrate the grains and create a protective layer around the nutrient source. This will help the mycelium fight off competing contaminants when spawning to bulk.

You might also see pinning inside your grain bags or jars. This is a clear sign that the grains are fully colonized and that the mycelium have broken down the nutrients and are ready to enter the next phase of their lifecycle, which is to produce the fruiting bodies. This is the perfect time to spawn your grain to bulk, and I would not wait any longer after you see pinning.

Once the grains are fully colonized, you can safely handle them without the fear of contamination. You can break up the grains with your hands and spawn them to a bulk substrate that is either pasteurized or colonized. However, if you had supplemented your bulk substrate with a nutrition source such as wheat bran, you may have to be more careful and maintain sterile technique, as the uncolonized wheat bran can be a source of contamination.

Conclusion

In conclusion, grain spawn is a popular and cost-effective choice for growing mushrooms, and it provides several advantages over the PF tek. By following the steps outlined in this blog post, you can use grain spawn to grow your own delicious mushrooms at home.

Updated on November 15th, 2023

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