Sep 20, 2013

How to make malt extract agar petri dishes for yeast ranching

This year in my blogging blackout I've learned a bit more about yeast ranching. Yeast management is probably the most significant factor in beer quality so my carefully cultivated ignorance of all things science could not be allowed to stand.

Virtually all the information I've used to get going with this has come from BKYeast with some additional help from Eureka Brewing and a couple of homebrew forum threads here and there. Both those blogs are excellent reads for anyone wanting to step into the Tardis that is the world of those microscopic organisms.

Malt extract agar

So today I made up some wort-agar plates for collecting and storing both commercial and wild yeast strains.

Recipe (to make up 10 petri dishes)
200ml water
4g agar
4g dried malt extract

1. Weigh out water, agar and malt extract into a beaker, give it a stir and cover with aluminium foil.
2. Place the beaker in a pressure cooker on a wire rack to keep it off the bottom of the pressure cooker.

In the pressure cooker

3. Pour water into the pressure cooker up to the level of the rack.
4. Close the pressure cooker lid and heat on the stove. I let it go for 15 minutes in the cooker after it's steaming away.
5. Once it's done, let it cool until the beaker can be safely handled. Making sure you've got a clean space to work and a alcohol burner or butane torch nearby to create some updraft, pour into petri dishes and wrap them in gladwrap.

End product

Petri dishes all wrapped up

They're ready to go now but I'll let them sit at room temp for a week or so to make sure they haven't been contaminated. If they're clear, they'll go into the fridge ready for whenever I need them.

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