The time has come to refresh our yeast library. So time to break out the lab stuff and get to work! I need to propagate 4 types of yeast, so I need 4 plates of agar and then 8 slants. I’ll keep 2 samples of each so that one can server as master and the second as “working” sample from which the propagation will start.
But for now… I need to prepare the medium.
- Electronic scale
- Petri dishes
- Autoclave-ready test tubes
- Sterile gloves
- Isopropyl alcool
- Presto or Autoclave
In this case I need 100ml of agar solution. So here are the ingredients I need:
- 1.5 g of Agar
- 12.5 g of dry malt extract
- 125ml water
- 100ml mineral oil
- No need to be sterile for now…
- Boil the water and add the malt extract. Boil until the hotbreak forms. Cool and filter the solids (I use a coffee filter)
- Sprinkle the agar on the liquid, let it hydrate for a few minutes. Only mix when it’s all humid.
- Mix it all and slowly heat it up. Boil it for a few minutes to ensure the agar is melted.
- Slants: Transfer the liquid with a pipette. 5ml per slant in my case. Place in the autoclave
- Petris: Transfer the rest of the liquid in a mason jar with a loose cap and place in the autoclave.
- Add a mason jar with a loose cap of mineral oil. Sterilise for 20mins and let cool. The liquid has to be still warm for the pouring of the plates .
All the manipulations from here have to be aceptic!
I’ll be writing an article on aceptic technique soon. Stay tuned!
- Slants: Take the tubes out and lay them so the agar solidifies slanted (check picture). It should not touch the cap, and should not cover the entire bottom.
- Pétris: Transfer 5ml of solution in each petri. Let it set.
- Once set turn the petri dishes over so that condensation doesn’t stay on the agar.
- Keep petris and slants at room temperature until the condensation evaportates.
- They are ready to use as soon as they are dry. Seal all unused tubes or plates with tape or parafilm.
And we are ready for some streaking!
Yeast – The practical guide to beer fermentation par Chris White et Jamil Zainasheff