Producing grain spawn is one of the fundamental skills of every mushroom grower. Grain spawn is grain that has been colonized by mycelium, serving as a nutrient source and starter for your substrate. Compared to liquid culture or pure agar transfers, grain spawn offers several advantages: The grains provide a larger surface area for faster mycelial growth, are easy to incorporate into substrate, and allow for uniform colonization of larger quantities.
Before inoculating, please read the safety notice regarding steam pressure sterilization and the safety notice regarding mushroom spores below – both are an essential part of any grain spawn production.
1) Choosing the right grain
Choosing the right grain is the first step. Wheat (wheat berries) and rye are classic and reliable, while oats and corn also work excellently.
You can purchase prepared grain spawn bags directly from Meisterpilze – these come pre-prepared and ready for inoculation – or you can start with whole grains from a health food store.
Important: Use untreated varieties to rule out pesticides and fungicides.
2) Preparing the grain (Rinsing & Soaking)
Preparation requires care:
- Rinsing: First, rinse the grain thoroughly to remove dust and debris.
- Soaking: Soak the grain in water for about 12 to 24 hours until the kernels are fully saturated.
- Moisture: The moisture content should be about 65–70% – the grain should be wet, but not dripping wet.
- Draining: Let the grains drain well after soaking.
3) Sterilizing
Sterilization is crucial for a clean culture. The classic method involves using a pressure cooker or autoclave:
- Fill the moistened grains into Mason jars or filter patch bags (bags with microfilters).
- Closing: Close jars loosely (only place the lid on top / do not seal airtight) to allow for pressure equalization. For bags, a filter patch (microfilter) is suitable as it allows for the necessary gas exchange – do not seal airtight with tape.
- Duration/Pressure: Sterilize at 15 PSI (approx. 1 bar) for about 2.5 to 3 hours. Larger quantities require correspondingly longer times.
- Cooling: Let everything cool completely after sterilization – ideally overnight at room temperature – before you inoculate.
⚠️ Safety notice – Steam pressure sterilization (Risk of scalding & bursting)
When working with a pressure cooker/autoclave, there is excess pressure (approx. 1 bar) and hot steam is generated. There is a risk of scalding and bursting.
- Use only a pressure-tested, intact device with a functioning safety valve and observe the manufacturer's instructions for your pressure cooker/autoclave (filling capacity, max. pressure, operating time).
- Do not overfill the device and do not operate it unattended.
- Never seal glass lids airtight (risk of bursting) – only place the lid on loosely.
- Release the pressure completely and let the device cool down entirely before opening it. Only remove hot jars/bags using suitable protection (gloves).
4) Inoculation
For inoculation, you need a starter culture: either from a healthy agar plate or from a liquid culture. The process should take place under the most sterile conditions possible.
- Small quantities can be inoculated in front of a laminar flow hood or alternatively in a glovebox / Still Air Box; work with distilled water and ethanol to disinfect hands and surfaces.
- Larger quantities: Here, injection/inoculation ports on the bags (self-healing ports) are recommended – these are easy to use with accessories from Meisterpilze (see product CTA below).
- Rule of thumb: About 5–10% of the grain mass in starter culture is sufficient.
Cleanliness first: Contamination is the most common cause of failure. Work quickly, with disinfected hands and surfaces.
5) Incubation
Incubation takes between two and four weeks, depending on the mushroom species:
- Temperature: Keep it constant at 20–25 °C and avoid direct sunlight. (Rule of thumb; the optimal incubation temperature may deviate slightly depending on the mushroom species.)
- Progress: Over time, the grains will become whiter as the mycelium grows over them.
- Full colonization: This is achieved when all grains are covered with a dense white network and the entire container appears to be fully colonized.
6) Storage & processing
Once the grain spawn is ready, it remains storable for several weeks – optimally in the refrigerator between 4–10 °C. This grain spawn is now your base for the substrate, which initiates the next phase of your cultivation.
⚠️ Identifying contamination – do not use, dispose of safely
Check your culture regularly. Do not continue to use or consume moldy or otherwise contaminated grain spawn (green, black, pink, or slimy coating, unpleasant odor). Contaminated grain can form harmful molds/mycotoxins.
- Dispose of affected jars/bags while closed and do not stir up spores.
- For the continuation of cultivation, use only cleanly colonized, contamination-free grain spawn.
⚠️ Safety notice – Mushroom spores (Respiratory tract)
Mature mushrooms release spores. Inhaling large amounts of spores can irritate the respiratory tract and lungs and, with repeated exposure, trigger allergic reactions up to extrinsic allergic alveolitis ("Mushroom Worker's Lung").
- Allow fruiting in well-ventilated rooms; do not place in bedrooms or living areas.
- Harvest mushrooms just before they release their spores to reduce the spore load.
- Sensitive, allergic, or pre-existing individuals, as well as persons with constant exposure: Wear respiratory protection (FFP2/FFP3).
- Never consume contaminated or moldy cultures; dispose of the bag closed and do not stir up/inhale spores in the process.
Material for your cultivation
Need material for your cultivation? Get the right grain spawn and accessories directly in our online shop:
- Grain spawn & sterile substrate – pre-prepared and ready for inoculation for your own mushroom cultivation.
- Accessories – bags with injection/inoculation ports, microfilter bags, and liquid culture.
➜ sterile wheat substrate · To the shop
Related mushroom species: Pink Oyster Mushroom · Shiitake · Lion's Mane · Reishi · Chestnut Mushroom / Pioppino