Preparing some plates and slants

IMG_0003The 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.

Equipment checklist:

  • Electronic scale
  • Pipette
  • Petri dishes
  • Autoclave-ready test tubes
  • Burner
  • Sterile gloves
  • Mask
  • 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!

  • _MG_6334Slants: 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

See the yeast section in our links


Leave a Reply