Gellan Gum is an excellent alternative to traditional agar-based recipes. It tends to be clearer, more rigid, and has a higher melting temperature (great for shipping in warm climates).
The basic recipe for 500 ml of media is as follows:
5g Gellan Gum (low acyl)
8g LME (light malt extract)
0.5g Nutritional Yeast
0.5g MgSO4 (magnesium sulfate)
The total weight of 14g is added directly to 500 mL of tap or purified water. It is then sterilized (usually 45-90 minutes at 11-15 psi) before pouring into pre-sterilized polystyrene (PS) plates. It will pour 20-25 standard-size, 90mm plates, depending on the depth of media.
Alternately, the pre-mix can be thoroughly dissolved by heating and then dispensed into glass Petri dishes prior to pressure cooking/autoclaving.