This medium is described by Lewis (1960). The addition of phosphoric acid allows less propionic acid to be used without reducing its fungicidal effects. It is the food used at Caltech since 1955. At Caltech the food is always seeded after cooling with a yeast strain called 'Y-2 Original', which tolerates propionic acid. See Lewis (1960) for details of this yeast and its use.
|Phosphoric + Propionic acid mix (see below)||200||milliliters|
|*adjust agar concentration according to the gel strenght of the batch of agar you are using|
- Mix the agar into 13 liters of water, use the other 4 to wet the remaining ingredients.
- Add the acid mix after the food had been cooked. Stir well after adding the acid.
- Acid Mix
- A stock solution of the acid mix is prepared as follows: add 164 ml distilled water to 836 ml of propionic acid. Add 917 ml distilled water to 83 ml of phosphoric acid. Combine the two diluted acid solutions to produce the acid mix used in the recipe. Green food coloring can be added to the acid mix if desired.