Liquid culture

Liquid culture is mycelium grown in a sterilised nutrient solution rather than on a surface. One jar inoculates a dozen jars of grain, colonisation starts from hundreds of points instead of one, and the whole thing is drawn up in a syringe in seconds.

It is genuinely convenient and it has one serious weakness, which is worth stating before the recipe.

The weakness

You cannot see bacterial contamination in a liquid culture.

A jar of cloudy liquid with mycelium in it looks much the same whether it is clean or carrying a bacterial population. By the time it is obvious — usually a sour smell on opening — you have already inoculated grain with it.

This is why serious growers keep their genetics on agar and use liquid culture as a working intermediate, not as a library. See agar work.

The recipe

Keep it simple. Elaborate liquid culture recipes are mostly folklore.

4% sugar solution:

4 g light malt extract, honey, or plain sugar
100 ml water

Scale as needed. Malt extract performs best; honey is fine; corn syrup works and is cheap. Do not go above about 4% — excess sugar inhibits growth rather than accelerating it, which is the most common recipe error.

Fill jars no more than half full. Add a magnetic stir bar if you have one.

Sterilise at 15 psi for 30 minutes. Longer caramelises the sugars and produces a darker, less effective medium.

Let it cool completely — inoculating warm liquid kills the culture.

Lids

The lid does more work here than people expect. You need gas exchange and an injection point, and both must exclude contaminants.

Drill two holes in a mason jar lid.
Cover one with a synthetic filter disc or a few layers of micropore tape for gas exchange.
Fill the other with self-healing silicone, or fit a proper injection port. This is where the needle goes.

Purpose-made lids are inexpensive and better than most home versions. This is not where to economise.

Inoculating

From agar: cut a small wedge from the leading edge of a clean plate and drop it into the jar, working in a still air box or in front of a flow hood.

From another liquid culture: 2–3 ml through the injection port, needle flame-sterilised and cooled first.

Then leave it at 70–78°F in the dark. Growth appears as small white clouds suspended in the liquid, expanding over 7–14 days.

Stirring

Agitation breaks mycelium into fragments, and each fragment becomes a new growth point. It substantially speeds colonisation.

Magnetic stir plate: 15–30 minutes daily is plenty. Continuous stirring shears the mycelium and does more harm than good.
By hand: swirl firmly once a day. Do not shake hard enough to wet the filter — a wet filter is an open door for bacteria.

Judging it

Ready: even white cloudiness or small distinct clumps distributed through clear liquid. Smells faintly of mushroom, or of nothing.

Contaminated: any colour other than white or cream. Cloudy and uniformly turbid with no visible mycelial structure. Anything sitting as a film on the surface. And above all, sour smell.

Uncertain: streak a few drops onto an agar plate and wait 48 hours. If anything other than mycelium grows, you have your answer, and you have found out for the price of one plate instead of twelve jars of grain.

That test costs almost nothing and is skipped by almost everyone.

Using it

2–5 ml per quart jar of grain. More than that adds free water without adding much speed.

Flame the needle, let it cool for a few seconds, wipe the injection port with alcohol, and inject at an angle so the liquid distributes rather than pooling in one spot.

Storage

Refrigerated, a healthy liquid culture keeps 6–12 months. It will separate — mycelium settling, liquid clearing above it. That is normal. Swirl to redistribute before use and let it come to room temperature first.

Colonised liquid culture goes into grain spawn.