Liquid culture

What it is

Liquid culture is mycelium grown in a nutrient broth instead of on a solid. A jar of sterilised broth is inoculated with clean mycelium, usually from agar, and the growth is later drawn out with a syringe and injected into sterilised grain.

In research on shiitake spawn, liquid spawn was easy and efficient to inoculate into sawdust, faster to produce than grain or sawdust spawn, and grew vigorously in 3 to 5 days¹. The same work found its main drawback: a tendency to degenerate and mutate after repeated subculturing¹.

The other catch is visibility. On agar you can see contamination as a separate colony; in a cloudy jar you cannot, so careful growers test a drop of a new jar on agar before trusting it.

What it suits

Any species you already have as a clean culture. The research cited here was on shiitake.

Equipment

• Pressure cooker that holds 15 psi
• Jars with a lid that has a filter and a self-healing injection port
• A simple sugar or malt broth
• Sterile syringes and needles
• Still air box or flow hood
• Clean agar culture to start from

Time to first harvest

3–5 days of growth, then 10–20 days on grain. Liquid shiitake spawn grew vigorously in 3 to 5 days in the cited research¹. Grain inoculated from it then needs the usual 10 to 20 days to colonise².

Contamination and other risks

• Strain degeneration and mutation after repeated subculturing, which is hard to spot before fruiting¹.
• Bacterial contamination hiding in the broth, which shows up later on grain.
• Contamination through the needle or port if they are not flamed and wiped.

Steps, in overview

1. Make broth. Mix a weak sugar or malt solution in a jar fitted with a filtered, ported lid.
2. Sterilise. Pressure-cook the jars and let them cool completely.
3. Inoculate. In the still air box, add a small piece of clean agar culture through the lid.
4. Grow. Keep the jar warm and swirl it now and then to break up the growth.
5. Test. Put a drop on an agar plate. If it grows clean, the jar is ready to use.
6. Use. Draw the culture into a sterile syringe and inject it into sterilised grain.

Common mistakes

• Making each new jar from the last jar, generation after generation, instead of going back to a clean agar plate¹.
• Trusting a jar without testing it on agar first.
• Using a lid without a filter, so the jar either suffocates or breathes room air.