What agar does in a mycology lab
Agar is a gel made from seaweed extract. On its own it has almost no food value. Mixed with a nutrient source and poured into a petri dish, it becomes a flat, clear surface where mycelium can grow and be watched. That is the whole point. You can see what is growing, judge how it is growing, and cut out the parts you want.
In practice agar does three jobs. It isolates clean mycelium, because you can cut a wedge from the healthy edge of a colony and leave any contamination behind. It reveals contamination early, because moulds and bacteria show up on a plate within days, long before they would show in a grain jar or grow bag. And it stores a culture, because a colonised plate kept cold will hold a strain for months.
Most of the gourmet cultures sold on Culture Cave started life on a plate. Vendors isolate, test and expand on agar before anything goes into a syringe or a bag.
MEA, PDA and other recipes
The two common recipes are malt extract agar (MEA) and potato dextrose agar (PDA). MEA uses light malt extract as the sugar source. It is cheap, easy to make and suits most gourmet species, including oyster and lion's mane. PDA uses potato starch and dextrose. Some growers find it gives faster, denser growth with wood-loving species such as shiitake and reishi.
Beyond those two, you will see recipes with added yeast extract for nitrogen, peptone for protein, or a pinch of activated charcoal to make white mycelium easier to see against a dark background. Antibiotics are sometimes added to suppress bacteria when cleaning up a dirty culture. None of this is essential for a beginner. Plain MEA at roughly 2 percent malt and 2 percent agar will do nearly everything you need.
Whatever recipe you use, the plates must be sterilised. The mixed liquid goes into a bottle with a loose lid and is pressure cooked at 15 psi for about 30 minutes, then poured once it has cooled enough to handle but is still liquid.
Pre-poured plates or pour your own
Pouring your own plates is cheap per plate but needs a pressure cooker, a clean workspace and some practice. The first few batches often come out too thin, too thick or contaminated. Pre-poured agar plates arrive sterile, sealed and ready to use. They cost more per plate but remove the biggest source of failure for a new lab.
If you are starting out, buy a sleeve of pre-poured agar plates and learn the transfer and reading skills first. Pour your own later, once you know what a good plate looks like.
Still air box and flow hood basics
Every time you open a plate, the air in the room can drop spores and bacteria onto it. The still air box (SAB) and the laminar flow hood exist to stop that.
A still air box is a clear plastic tub with two armholes. The air inside is allowed to settle so that nothing is drifting. You work slowly inside it with wiped-down tools. It costs very little and is enough for plate-to-plate transfers, as long as you move with care and do not stir the air.
A flow hood pushes filtered air across the work surface in a steady stream. Anything that falls off your hands or tools is blown away from the open plate. It is faster and more forgiving than a SAB, and it is the right choice if you plan to pour plates or do a lot of transfers. Both options, along with scalpels, alcohol lamps and parafilm, are listed under lab equipment.
Transferring a wedge
A wedge is a small triangle of colonised agar, usually about the size of a fingernail, cut from one plate and moved to another. This is the core skill.
- Wipe the outside of both plates and your hands with 70 percent isopropyl alcohol. Flame the scalpel blade until it glows, then let it cool for a few seconds.
- Lift the lid of the source plate just enough to get the blade in. Cut a wedge from the leading edge of the mycelium, where growth is youngest and cleanest.
- Lift the lid of the fresh plate, drop the wedge in the centre with the mycelium side down, and close it straight away.
- Label the plate, seal it, and put it somewhere warm and dark.
The same tools and method are used to move mycelium from a plate into a jar of broth to make liquid culture, or onto grain to make spawn. The liquid culture guide covers that step.
Reading a plate
A plate tells you more than a jar ever will. After a week at room temperature you should be able to judge it.
Rhizomorphic and tomentose growth
Rhizomorphic mycelium grows in thick, ropey strands that fan out from the centre. Tomentose mycelium is fluffy and cotton-like with no clear structure. Neither is wrong. Rhizomorphic growth is often faster and is favoured by many growers, but plenty of good gourmet strains run tomentose. What matters is that it is white, even and moving outward.
Sectoring
Sometimes one slice of the colony grows differently from the rest. It may be denser, faster or a different texture. This is a sector. Each sector is a slightly different genetic expression. You can cut a wedge from the sector you like and plate it on its own. Done a few times, that is how an isolate is made. This is why the genetics and isolates category exists: a vendor has already done the selecting for you.
Common contaminants
- Green mould (Trichoderma). Starts white and turns bright green within a day or two. It spreads fast and outcompetes almost everything. Bin the plate.
- Black or grey mould (Aspergillus and others). Dark, powdery spots. Do not open the plate indoors, as the spores are a health risk. Bag it and dispose of it.
- Bacteria. Shiny, wet-looking patches, often cream, yellow or pink. They may smell sour. Mycelium will usually refuse to grow over them.
- Cobweb mould. Grey and wispy, grows very fast and lies flat. Easy to mistake for mycelium at first, but it looks dirty and climbs the sides of the dish.
If a plate has a small spot of contamination well away from the healthy mycelium, you can cut a wedge from the clean side and move it to a fresh plate. Two or three transfers will usually clean a culture up.
Labelling, parafilm and storage
Write the species, strain, source and date on the base of the plate, not the lid, because lids get swapped. Use a permanent marker. Then wrap the join between lid and base with parafilm. This stops the plate drying out and keeps airborne spores from creeping in. Store colonised plates upside down so condensation does not drip onto the surface.
Once a plate is fully colonised it can go in the fridge at around 2 to 4 degrees Celsius. Growth almost stops, and the culture will keep for three to six months, sometimes longer. When you need it, cut a wedge to a fresh plate and let it recover at room temperature for a week before using it for anything else.
Buying colonised plates and isolates
Many vendors on Culture Cave sell colonised plates, often the same isolate they use for their own liquid cultures and spawn. A plate from a reputable vendor skips the cleaning-up stage and gives you a known strain to work from. The genetics and isolates listings show the species, the strain, the vendor's country and the regions they ship to, alongside real customer reviews. The vendor guide explains what to check before ordering.
Plates travel well in a padded envelope but should be unpacked and transferred within a week or two. If a plate arrives with a small contamination spot, cut from the clean edge as described above. If it arrives overgrown with green, tell the vendor. With 29 vendors across the USA, UK, Australia and South Africa, there is nearly always someone close enough to post a fresh one. Start from all vendors and filter by country.