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  • Writer's pictureBart Acres

Making Grain Spawn from Liquid Cultures

Many home growers and smaller scale commercial growers choose to purchase pre-made grain spawn from specialist suppliers, because producing spawn from scratch can be a challenging and time consuming process, and even a single kilogram of bought mushroom spawn can be used to grow a fair quantity of mushrooms with good cost effectiveness.

Some growers, though, choose to make their own grain spawn, either for reasons of economics if they are going through lots of spawn, or in some cases just because they enjoy the process of making it, and observing the whole growth cycle.

Grain spawn is whole grains which have been hydrated and then sterilised in glass jars or mushroom grow bags (both of which are fitted with microbe-proof air filters to allow for mycelium to breathe while keeping contaminants out) in a pressure cooker. Once they’ve cooled after sterilisation, they are inoculated with live mycelium, which slowly colonises the grains over the course of about one to three weeks. Once the grains are fully colonised, they can be used to inoculate bulk substrates like pasteurised straw or sterilised sawdust based substrates.

The most common, and effective way to inoculate grain spawn with mushroom mycelium is by way of liquid culture. Liquid culture is a sterile nutrient broth which has live mycelium growing in it. Syringes filled with pure liquid culture ready to use can be bought from suppliers like MycoLogic. Liquid culture syringes can also be stored in the fridge for two or three months before use if needed.

A simplified process for making grain spawn using liquid culture is described below. Grain can also be inoculated with pieces of agar colonised with mushroom mycelium, or even with healthy, colonised grain spawn (known as 'grain to grain' transfer), using mostly the same process. Injection ports and air filters for jar lids are available from MycoLogic. Grains can usually be bought from animal feed and farming supply stores.

Materials Needed:

• Preserving Jars fitted with a silicone ‘Self healing injection port’ and a breathable air filter. Standard one quart jars can fit about 500g of grain each.

• A pressure cooker or autoclave, which can fit several jars (minimum size 6L) and which can reach at least 10PSI pressure.

• Whole grains. Common choices include oats, barley, wheat or rye. You’ll need around 700g of dry grains for each kg of finished grain spawn you plan to make.

• A big pot or bucket for soaking your grains in

• A sturdy sieve, colander, mesh, muslin cloth or bucket with small holes drilled in the bottom for draining

Grain Spawn Process:

1. Put the dry grains in a large pot or bucket. Cover with plenty of warm water so that there is a few cm of water above the grain layer. Soak for 12-18 hours.

2. Drain the grains by pouring them into a sturdy colander, muslin cloth bag, or a bucket with some small holes drilled in the bottom. Drain for 30+ minutes.

3. Load the grains into your jars. Jars should only be filled about 2/3rds full, leaving an air gap at the top to allow for air exchange, and shaking of the grains if needed.

4. Put the prepared lids on the jars and seal. Cover with a square of tinfoil to protect the filter during pressure cooking.

5. Ensure that there is a rack in the bottom of the pressure cooker so that the jars can not touch the bottom. Pour about 3 to 4cm deep of water into the bottom of the pressure cooker.

6. Load the jars or into the pressure cooker.

7. Clamp the lid onto the pressure cooker and put it on to medium-high heat on a stove or gas ring. Ensure that the steam vent is open (no weight / rocker on)

8. Once the whole pressure cooker has heated up and some steam is coming out of the vent, close the steam vent.

9. Wait for the pressure to come up to at least 10PSI (15PSI is ideal) either by looking at the pressure gauge, or when the seam valve / weight starts occasionally hissing if there is no gauge.

10. Pressure cook at this pressure for 90 minutes. Then, turn off the heat and allow for the vessel to cool naturally overnight (do not take off lid or open steam valve)

11. Once the pressure cooker has cooled to room temperature, bring it to your clean workspace (such as a still air box or clean room with smooth bench wiped down with 70% alcohol or isopropyl spray)

12. Wipe your hands (or gloved hands) down with a couple of spritzes of 70% alcohol solution. Then, take your liquid culture syringe out of its packaging. Open the sterile needle packet, unscrew the cap on the tip of the syringe, and screw the sterile needle onto the tip of the syringe.

13. Wipe the silicone injection port with some alcohol or isopropyl. Then, remove the plastic sleeve from the needle, and poke the needle through the injection port. Squirt about 5ml of liquid culture onto the grains. Aim for the top edge of the grains so that some liquid runs down the side of the glass.

14. Remove the needle and repeat the process for more jars.

15. Wrap and safely dispose of spent syringe and needle.

16. Place jars in a warm place (around 20-25°C) to colonise. After a few days you should see some mycelium starting to grow. Over the course of a couple of weeks it will spread across all of the grain. If some patches remain uncolonised, shake the jar and wait a few more days.

17. Provided that no contaminants like green or black molds, or blobs of gooey bacteria are visible, and the grain is fully colonised, it is now ready to use as grain spawn!

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