What is liquid culture?

Liquid culture is faster than spores because its mycelium is already growing. GroCycle says liquid culture often shows visible growth on grain a couple of days after inoculation, while spores can take up to a month (GroCycle). Our syringes guide and buyer's guide go deeper.

Make liquid culture by pressure-cooking a weak sugar broth in a jar with an injection port, then adding clean culture. These steps follow GroCycle unless another source is named (GroCycle):

1. Mix the broth. For a pint (473 mL) jar, dissolve 16 g of light malt extract or honey in 400 mL of water, a 4% broth. La Mycosphère aims lower: "2% (4% max)" (La Mycosphère).
2. Sterilize. Close the jar with a port-and-filter lid and pressure-cook it 30 minutes at 15 PSI, following your cooker's instructions. Leave the jar in the cooker to cool.
3. Inoculate. Once the broth is at room temperature, wipe the lid with alcohol and inject culture through the port, in a still air box or in front of a flow hood. A wedge of agar works too, but the lid comes off, so do it in front of a flow hood.
4. Agitate and wait. Swirl, stir or shake the jar once a day. Started from culture or agar, growth shows in 2–7 days and the jar colonizes within 3 weeks.
5. Test a drop on agar. At 68–77°F (20–25°C), growth from a drop shows in 4–10 days (Mycoboutique). La Mycosphère calls this test "the number one safeguard".
6. Inoculate grain. Inject 1–2 mL per quart jar of grain spawn through the port, working in a still air box or, with a self-healing port, a clean room away from drafts (GroCycle).

Contaminated liquid culture usually turns cloudy, smells foul or grows a scum, while healthy liquid culture "is clear with clean white blobs of mycelium floating in it". GroCycle's warning signs (GroCycle):

• Cloudy all the way through, with nothing growing: bacteria.
• A foul smell and a slightly pressurized jar: bacteria.
• A green, moldy scum on top: mold.
• Fast-growing white clumps with erratic shapes: possibly white mold.

A clean-looking syringe proves little: contamination in one "looks very similar to the strands of mycelium" (GroCycle). For contamination on grain, see the contamination ID guide.

Liquid culture keeps for months in the fridge but is best used early. Store it sealed at 35–46°F (2–8°C), never frozen, and warm it to room temperature before use (GroCycle). GroCycle says it can last 6–12 months, but growers recommend using it within a month or two, "when it's most viable" (GroCycle). North Spore rates its own liquid cultures at up to 2 months. It says pink oyster cultures can't be refrigerated: keep them at room temperature and use them within a month (North Spore help center).

• Expanding liquid culture into liquid culture again and again. La Mycosphère warns that repeated expansions "increase the risk of genetic drift and a decline in vigor" and advises keeping a mother culture on agar (La Mycosphère).
• Losing track of lineage. In Hypha, create each jar as a transfer from its culture, so every grain jar traces back to its source.