Same lesson, with the figures in motion.
Mastering Agar Plates
Why keep plates?
This is the Academy’s biggest step in both equipment and patience — plates take a couple of days to grow and a chosen colony a few more. But it is also what lets a strain live with you for years instead of for a handful of generations.
1. The Magic Gel
Agar is basically a gelatin-like substance made from algae. Mixed with ordinary starter wort (DME and water) and pressure cooked for 15 minutes at 121 °C, it becomes a solid, sterile food surface for yeast to grow on. An ordinary boil is not enough — the plates sit for days, and that gives the spores time to catch up.
2. Pouring Plates
In a draft-free room (next to an open flame to create a sterile updraft that pushes dust away), carefully pour the hot liquid into sterile Petri dishes. Let them cool and solidify.
3. Streaking for Isolation
Dip your sterilised loop into a yeast sample. Gently drag it across the agar surface in a zig-zag pattern. Sterilise the loop, drag it through your first lines, and make new zig-zags. This spreads the cells thinner and thinner.
Want to try the streaking yourself – in the game Streak Plate?
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4. Harvesting a Colony
Incubate the plates in the dark at room temp. After a few days, individual white dots appear — each dot is a pure colony grown from a single yeast cell! Scoop one up and either pitch it into a tiny test-tube starter, or streak it onto a slant and keep the strain in your yeast library.