Tutorials/Agar/Making Plates

Agar is a gel made from seaweed. Mixed with a little sugar and nutrients, it gives mycelium a flat, clear surface to grow across, so you can actually see what's happening: whether a culture is clean, whether it's growing fast, and which part of it looks strongest. Agar is where you test, clean up, and select genetics before committing them to grain.

Recipes

All recipes are per liter of water. Halve them for a smaller batch; 500 ml pours roughly 20–25 standard 100 mm plates.

Recipe	Agar powder	Nutrients	Notes
MEA (malt extract agar)	20 g	20–30 g light malt extract	The standard. Lab recipes use 30 g; many growers prefer 20 g.
Light MEA	20 g	10 g light malt extract	Lower nutrients make contamination easier to spot and push the culture to show its vigor.
MEA + yeast (MYA)	20 g	20 g light malt extract + 2 g nutritional yeast or peptone	Faster, denser growth. Slightly cloudier.

Additions some growers use:

• Distilled water gives the clearest plates. Colorado tap water is hard and can leave a haze.
• A pinch of gypsum or a teaspoon of coir or ground grain helps the culture "learn" the substrate it will eventually eat.

Making the batch

1. Mix everything in a heat-safe bottle or jar with room to spare; a 1 L media bottle is ideal for 500 ml. Leave the cap loose or cover the mouth with foil.
2. Heat the mix in the microwave in short bursts, swirling between, until the agar powder fully dissolves and the liquid turns clear. Watch it closely; it boils over suddenly.
3. Pressure cook. At sea level that's 30 minutes at 15 psi; at Front Range elevations plan on 45–60 minutes (see pressure cooking at altitude).
4. Let the cooker depressurize naturally. Don't vent it early; the agar will boil out of the bottle.

Pouring

1. Set up in your still air box or flow hood with sleeves of plates ready.
2. Let the agar cool until you can hold the bottle bare-handed for a few seconds, around 120–140°F (50–60°C). Hotter agar makes more condensation; cooler agar starts setting in the bottle.
3. Lift each lid just enough to pour, fill the plate about one-third deep, and close it. Work in a stack so you only lift one lid at a time.
4. Leave plates to set for about an hour, then flip them upside down so condensation collects on the lid instead of dripping onto the agar.
5. Seal with Parafilm or plastic wrap, or keep them in the original sleeve.

Storage and testing

• Leave freshly poured plates at room temperature for 3–5 days before using them. Any contamination from pouring will show up as spots or fuzz, and you can throw those plates out before they waste a culture.
• Clean plates keep for weeks in the fridge, in a sealed bag, upside down.

Using plates

• Inoculating: put a drop of spore solution or liquid culture onto the center, or lay a small wedge of colonized agar there.
• Transfers: cut a small wedge from the leading edge of healthy growth with a flame-sterilized scalpel and move it to a fresh plate. Repeating this to clean up and select a culture is covered in the three-transfer method.
• Agar to grain: once a plate is clean and fully grown, a few wedges inoculate a jar of grain.
• Incubate plates upside down at room temperature, 70–78°F.

Sources

• Wikipedia, Malt extract agar: standard composition (30 g malt extract, 20 g agar per liter)
• Pouring and storage practice compiled from league members.