Isolating Yeast

July 2, 2016

agar plate yeast

This post continues from the previous instructions for making agar plates, so be sure to read that first, you’ll need the plates for what comes next.

The finished agar plates should be a sterile way to observe the development of yeast colonies. The gelatinized wort forces yeast to sit on the surface of the “liquid” rather than floating freely throughout the wort. As the yeast consume sugars present in the wort, they will multiply, and visible blob-like colonies will appear along the areas of the wort that were exposed to the yeast. Becasue yeast multiply like crazy, we only want to add the tiniest amount of yeast to the plates—through a process called streaking. As before, visit Bootleg Biology for more information and to order supplies.

Equipment:

  • Paper clips
  • Lighter or butane flame
  • Agar plates
  • Saran Wrap or medical tape

 

Instructions:

  1. Unbend a paper clip and sterilize one end of it until glowing red.
  2. Let cool 30-60 seconds (to avoid killing the yeast on contact).
  3. Dip the end of your paper clip into a sample of yeast or beer sediment.
  4. Streak the sample across one side of the agar plate in a series of quick parallel lines.
  5. Sterilize the paper clip again and let cool.
  6. Streak the plate perpendicular to your first lines, dragging through the original streaks.
  7. Repeat two more times forming a diamond, with each round dragging out a bit of yeast form the previous streaks, essentially thinning out the already minuscule amount of material (see diagram below for a visual guide).
  8. Cover the plate and wrap it in plastic wrap or medical tape to create a good seal.
  9. Store in a room temperature dark environment for several days until you see yeast colonies start to develop.
Agar plate streaking instructions

Sterilize clip between each round of streaking and drag through the previous marks to gradually thin out sample.