Agar is a catch all term for a two dimensional growth medium for mycellium and other microscopic organisms. In mushroom cultivation, this growth medium is generally made with agar agar. There are alternatives to agar which can be used, most notably gellan gum, which would not technically make them agar plates. A general term would be "media plates", or "plates". In common culture these are generally thought of a "petri dishes", though that is actually the name of the shallow, circular dish that comes to mind when thinking of that word.
Agar is ideal for a number of tasks when growing mushrooms. They can be used to isolate genetics, turn dirty cultures into clean ones via transfers, germinate spores, and preserve cultures over long lifetimes. Mycllium on agar can be used to start grain, create liquid cultures, or be expanded onto more agar.
Mushroom media plates are comprised of three key elemnts. Water, a nutrient source and a gelling agent. Additionally, a stain (or dye) is often added to help increase contrast when viewing wispy mycellium. Other ingredients can be added for additional nutrition, bacterial antibiotic properties, etc.
The normal process for pouring plates is to make your media, sterilize it, then pour into plates in a sterile environment once it cools enough to handle.
A variation called "no pour" involves pouring your media into plates before sterilization, ideally reducing the possibility of contamination in imperfect environments like a still air box.
- Weigh your dry ingredients
- Bring more water than you need to a low boil
- Measure out the exact amount of water you need
- Add your dry ingredients
- Add a few drops food coloring stain if using
- Swirl to disolve
- Pressure cook at 15 PSI for 45 minutes
- Remove from pressure cooker and let cool to around 125°F
- In a sterile environment, pour media into your plates
- Seal plates, and store at room temperature
- After about four days, check plates for contamination before use
- Stacking plates as they cool can help reduce condensation.