How to Make Grain Spawn at Home: A Step-by-Step Guide

Grain spawn is the engine of most mushroom growing. It is simply cereal grain that has been sterilised and then fully colonised by mushroom mycelium. Once you have it, you can mix it into straw, sawdust, coffee grounds or more grain, and grow far more mushrooms than a kit will give you.

Buying spawn is easy, but making your own teaches you sterile technique and saves money once you are growing regularly. This tutorial walks through the whole process, from choosing a grain to storing the finished spawn. It draws on published lab procedures, a research study and practical guides, which are listed at the end.

If you are new to the idea, our explainer on grain, sawdust and plug spawn covers what spawn is and the different types.

What makes good spawn

A lesson on spawn production from India’s National Institute of Open Schooling (NIOS) sums up the goal. Good spawn should be fully colonised by mycelium, free of contaminants, and fresh. It adds that “Fresh spawn gives higher yield” and that spawn should not be stored for more than a month. That shapes the whole process. You want clean grain, a full sterilisation, a clean inoculation and steady incubation, and then you want to use the spawn while it is vigorous.

What you’ll need

• Grain, such as wheat, rye, millet, sorghum, maize (corn) or rice
• A large pot and a sieve or colander for soaking, simmering and draining
• Calcium carbonate (garden lime or chalk) and gypsum, both optional but common
• Heat-proof jars with filtered lids, or filter-patch grow bags
• A pressure cooker or canner that can reach 15 psi
• A clean workspace, such as a still air box or flow hood
• A mushroom culture: agar, liquid culture, or a little colonised grain
• 70% isopropyl alcohol, gloves and a marker for labels

Step 1: Choose your grain

NIOS says wheat is the most commonly used grain, with sorghum and pearl millet as alternatives. The Mushroom Guide, a practical series published on Lowimpact.org, names wheat, rye and millet as common choices. Penn State’s mushroom spawn lab uses rye.

The grain affects speed. A 2023 study in Mushroom Research by Ufitinema and colleagues compared spawn for oyster mushrooms made from different substrates:

Spawn substrate	Average days to full colonisation
Popcorn maize	About 9.4
Rice	About 10.3
Wheat	About 13.2
Sawdust	About 13.4
Vermiculite	About 15.2

The authors recommended maize and rice for oyster spawn. In practice, most home growers pick whatever clean, whole grain they can buy locally. Make sure it is intact and not cracked or dusty.

Step 2: Soak, simmer and drain

The aim is grain that is moist inside but dry on the surface. The Mushroom Guide calls this “field capacity, but no more”. Too wet and the grain bursts in the pressure cooker. Too dry and the mycelium struggles to colonise it.

1. Rinse the grain and pick out broken or shrivelled grains, as Ufitinema and colleagues did.
2. Soak it in water. The Mushroom Guide soaks wheat for about 24 hours, and slightly less for millet. NIOS and Ufitinema both soak overnight.
3. Simmer briefly. Ufitinema and colleagues boiled their grain for 15 minutes, leaving it “slightly hard”. NIOS advises half-cooking the grain so it softens without splitting. The Mushroom Guide gives a quicker option: skip the long soak and simmer for 20 to 30 minutes, checking that the inside of a wheat or rye grain has turned from white to translucent.
4. Drain thoroughly. The Mushroom Guide drains its grain in a tilted sieve for at least 30 minutes. Ufitinema and colleagues spread it on a wire mesh. NIOS lets the surface water evaporate.

A 2025 study on spawn for straw mushrooms (Volvariella volvacea) by Sharifuddin and colleagues found that boiling corn grain for 3 to 5 minutes gave better mycelial growth than a 6-hour room-temperature soak. The best preparation method can depend on the grain and the species.

Step 3: Add calcium carbonate and gypsum (optional)

Many recipes add small amounts of minerals. In Ufitinema and colleagues’ study, gypsum helped keep the grains from clumping and calcium carbonate helped maintain pH.

Source	Calcium carbonate	Gypsum
Ufitinema et al. 2023	0.3% of dry grain weight	1.2% of dry grain weight
NIOS lesson	0.5%	2% (it notes calcium carbonate alone is now often enough)
Penn State spawn lab (1,000 ml flask)	2 teaspoons of lime	1 teaspoon
Sharifuddin et al. 2025 (corn, straw mushroom)	3% gave the best mycelial density	Not used

Mix the minerals evenly into the drained grain. The Penn State lab notes that its Pleurotus (oyster) spawn uses lime instead of gypsum, so recipes vary by species.

Step 4: Fill jars or bags

• Jars: fill them about two-thirds full, as Ufitinema and colleagues did with their bottles. The empty space gives the grain room to move when you shake it later. The lids need a filter, such as a filter disc, micropore tape or a polyester plug. NIOS mentions cotton or polyfill plugs.
• Bags: The Mushroom Guide suggests filling filter-patch bags so the grain sits no higher than 1 to 2 inches (2 to 5 cm) below the patch.

Step 5: Sterilise

Grain must be fully sterilised. Published procedures vary with the size of the load:

Source	Load	Sterilisation
Penn State spawn lab	250 ml flask of rye	35 minutes at 121°C
Penn State spawn lab	1,000 ml flask of rye	45 minutes at 121°C
The Mushroom Guide	A couple of jars	60 to 90 minutes at 15 psi
The Mushroom Guide	Several small bags	At least 2 hours
Ufitinema et al. 2023	Bottles	2 hours at 121°C, two days in a row
NIOS	Bottles or bags (autoclave)	2.5 hours at 22 psi

Our step-by-step guide to sterilising in a pressure cooker explains how to run the cycle safely. After sterilising, Ufitinema and colleagues shook their bottles while still hot to stop the grain clumping, then cooled them for at least 3.5 hours. Never inoculate warm grain.

Step 6: Inoculate

Inoculate in a clean space. NIOS says to work in a laminar flow hood or under fully sterile conditions. Our comparison of a still air box and a flow hood explains the options for home growers. Wipe the outside of each jar with alcohol before you start.

The Mushroom Guide describes three ways to add the mushroom culture:

• From liquid culture: shake the syringe to break up the mycelium, swab the jar’s injection port with alcohol, and inject “a couple of millilitres”.
• From agar: cut a colonised agar plate into pieces with a sterilised scalpel and divide them between several jars.
• From grain: add a small amount of fully colonised grain to fresh sterilised grain. The Mushroom Guide says an expansion of “10-20 times” is typical.

NIOS also warns against multiplying spawn grain-to-grain for more than two generations. Our agar and liquid culture guide explains how to keep a clean culture going.

Step 7: Incubate and shake

Keep the jars or bags somewhere warm and dark. Ufitinema and colleagues incubated at about 25°C, and NIOS uses 25°C for its spawn too. Penn State’s lab grows its cultures at room temperature, 22 to 24°C.

NIOS advises shaking the bottles or bags about 10 days after inoculation, and again once or twice during incubation, to spread the mycelium evenly. Ufitinema and colleagues shook frequently to stop the grain clumping. Each shake breaks up the colonised grain and spreads the mycelium to new grains.

How long it takes

• Oyster spawn in the Ufitinema study: about 9 to 13 days depending on the grain
• NIOS: complete colonisation usually in 15 to 20 days
• NIOS table for button mushroom (Agaricus) at 25°C: 20 to 21 days for mother spawn and 12 to 14 days for commercial spawn

Step 8: Check for contamination

NIOS lists green, black or other unwanted growth and a foul smell as signs of contamination. Remove contaminated containers as soon as you see them. NIOS advises autoclaving contaminated containers before emptying them, so you don’t release spores. Our contamination guide helps you identify what you’re seeing.

Step 9: Use or store your spawn

Use your spawn as soon as it is fully colonised. If you must store it, NIOS says fully colonised spawn of button and oyster mushrooms can be kept at 4 to 6°C for 1 to 2 months, but must not be frozen. It also warns that spawn of some warmth-loving species, such as Volvariella, Ganoderma (reishi) and Calocybe (milky mushroom), should not be stored below 15°C. Label every jar with the species and date, as NIOS recommends.

Troubleshooting

• Mushy, burst grain: it went in too wet. Drain longer or simmer for less time.
• Slow or patchy colonisation: the grain may be too dry, or the jar too cold. Shake to spread the mycelium.
• Contamination in every jar: sterilisation was probably incomplete. Lengthen the cycle.
• Contamination in a few jars: look at your inoculation technique and workspace.
• Grain clumped into a solid mass: shake earlier, and consider adding gypsum.

Sources and further reading

• Penn State Department of Plant Pathology: Spawn preparation (mushroom spawn lab procedures)
• Ufitinema, B., Hakizimana, M. and Niyomugabo, J. D. D. (2023). Mycelial growth of oyster mushroom in spawn made using different cereal grains, sawdust and vermiculite as substrate. Mushroom Research 32(1): 35–40
• National Institute of Open Schooling (India). Mushroom Production, Lesson 2: Mushroom spawn (seed) production/procurement
• Sharifuddin, A. S. et al. (2025). Toward improved spawn quality: Optimizing corn grain preparation for Volvariella volvacea. Asia-Pacific Journal of Science and Technology 30(6)
• Noel, B. (2019). The Mushroom Guide Part 6: preparing mushroom spawn (1). Lowimpact.org
• Noel, B. (2019). The Mushroom Guide Part 7: preparing mushroom spawn (2). Lowimpact.org

Featured image: oyster mushrooms by Charles Joynson via iNaturalist (CC0 1.0). Inline photo by Charles Joynson via iNaturalist (CC0 1.0).