Denard Brewing

Better brewing through science.

Simple Yeast Cultivation

I know yeast cost is a big factor in brewing. I’ve got a bit of a secret. I haven’t bought yeast in years. I have a yeast bank. I know that may sound a bit intimidating, but it is really easy.  Go over to Amazon and buy this stuff:

  1. Liquid Propane Bunsen Burner
  2. Neoprene Bunsen Burner Hose
  3. Bunsen Burner Control Valve Regulator
  4. Standard Propane Fuel Cylinder
  5. Hardy Diagnostics Inhibitory Mold Agar Slant
  6. Inoculating Loops, Metal
  7. Borosilicate Glass Culture Flask (125 ml): the ones with Stainless Steel Closure are preferred, but you can use tin foil as a top if they are unavailable. 
  8. Tripod 9” with mesh screen for burner. 
  9. Gram Scale

I know you are thinking: All that’s expensive! Yes, but consider this: You will only buy a new yeast once, then have it forever banked. All except agar slants are a one time cost. Great, so how do you use this stuff? 

First, you need to brush up on Aseptic Technique:

Banking Yeast

  1. Obtain yeast(s) that you want to bank. 
  2. Turn on Bunsen Burner; perform everything under the flame to avoid contamination. 
  3. Flame your loop until red hot; Allow to cool. 
  4. Open yeast. 
  5. Without touching the outside of the pack, put the cooled loop in the yeast. 
  6. Open the agar slant and briefly pass the top of it through the flame of the Bunsen Burner. 
  7. Streak a zigzag on the surface of the agar with the yeast containing loop. 
  8. Pass the slant top and cap through the flame briefly to sterilize and cap. 
  9. Allow yeast to grow at room temperature until visible. Generally, 16-24 hours. 
  10. Label and store slant in refrigerator. 

If you are more visual, this video may be helpful:

Sterilizing a Starter Flask

Warning: The glass will reach >500 F in this process. Pull your hair back, keep kids and dogs away and don’t touch!

  1. Turn on Bunsen Burner.
  2. Place your 125 ml flask with the top (or tin foil) on the mesh stand. 
  3. Place the flame underneath and allow to heat for 5-10 minutes. 
  4. With oven mitts, remove flask from heat. Allow to cool to room temperature. 

Note: This flask will remain sterile until you remove the top so do it ahead of time! I do several batches at a time so they are ready to go. 

Making a Starter from Yeast Bank

  1. Pull agar slant from refrigerator. Allow to warm up while your are preparing your starter flask. 
  2. Turn on Bunsen Burner; perform everything under the flame to avoid contamination. 
  3. Remove flask top and place flask on gram scale. 
  4. Add ~18 grams of honey and 100 mg of Fermaid O to flask. Exact amounts are not so important here. I use a flamed butter knife for the Fermaid O and guesstimate 100 mg based on previous experience. Measure or guess is your choice. 
  5. Fill flask with sterile/bottled water to 100 ml mark. 
  6. Flame cap/flask top and affix cap. 
  7. Mix well by swirling. 
  8. Remove and flame top of both flask and agar slant. 
  9. Flame loop, allow to cool and use the loop to obtain a very small amount of agar yeast. 
  10. Inoculate starter flask by swirling loop in liquid. Be sure not to touch the sides of anything. 
  11. Flame and replace caps. 
  12. Restore agar slant to refrigerator. 
  13. Place starter flask at fermentation temperature. 
  14. Starter is ready in 2 days. 

I use this starter for beer and mead. It’s a lot easier than the DME beer starter and most appropriate for mead. 


You will need to restreak new agar slants about once every 2 years. I’ve had some last longer if they are not frequently used. You will know it needs to happen because the agar will start to dry out. 

This storage method also works for bread yeast! Just make a starter with 1 tsp of sugar and 100 mg Fermaid O in 100 ml water. It’s good to use in a day or two.

by denardb on May 17, 2020, 11 a.m.