This will be a three-part "Beer Geek Techneeks" on culturing yeast. Part 1 will consist of equipment and supplies needed as well as preparing your blank slants. Part 2 will deal with slanting yeast and preparing starters. Part 3 will deal with obtaining a pure culture from a suspect yeast source.
Why culture yeasts? What you gain is indefinite (practically speaking) storage, assured maintenance of the original generation, and ease of sharing yeast with brewpals. Also, when it comes time to make up a starter to pitch into a batch of beer, you get 500 ml of active starter within 4 days every time. If you are doing slants, when someone sends you a sample of yeast, or you get one from some other means, you can make yourself a renewable lifetime supply from that sample. Finally, using a new package of yeast every time you brew is expensive. After your initial set-up costs, yeast cost per brew will plummet when you propagate your yeast this way.
Minimum Equipment:
1. A bunch of glass vials or test tubes which have caps that can: (a) withstand pressure cooker temperatures or boiling water temperatures; and (b) form a tight seal.
2. An inoculation loop to transfer yeast.
3. Some type of flaming mechanism for sterilization (an alcohol lamp or a butane pencil torch).
4. Something to use for your starter vessel, like an old-style milk bottle, an Erlenmeyer flask (that's what I use), or other glass vessel that has a mouth to which you can affix a rubber-stopper and airlock.
5. The other hardware you will already have if you brew beer: a scale, a big pot to boil in, kitchen stove, refrigerator, and spoons. Additionally, a pressure cooker is ideal for sterilizing solutions (that's what I use).
Minimum Materials:
1. Either agar or gelatin, to use as a growth medium. I use agar and it works great.
2. A bag of dried malt extract. One bag will last you the rest of your life as far as keeping a full supply of yeast slants on hand is concerned.
3. An additional item which is a terrific time saver is mini-yeast starters. These are 10 ml of sterile wort in 50 ml vials. Brewers Resource sells them, and they're really a must if you culture yeast.
Preparing "Blank" Slants
Bring 1 cup (about 250 ml) water to a boil. Remove from heat, add 2 tablespoons of dried malt extract, and stir till dissolved. Put back on the heat and boil for 5-10 minutes to ensure sterility. Remove from heat. Add 1 1/2 tablespoons agar (or a package of gelatin) into this "wort" and stir till completely dissolved. Pour this mixture into as many of your vials/test-tubes as you can; a small funnel is useful for this step. Fill the vials about 1/2 full - do not fill them all the way up. Screw the caps on. Now either boil the tubes for 30 minutes or place in a pressure cooker and "cook" for 15 minutes at 15 PSI. The pressure cooker will do a more complete job of sterilization.
Remove from the heat, and have a couple homebrews while it cools off. When the vials have cooled enough to handle (still hot however), loosen the caps a bit and place them at an angle of about 40-45 degrees. When you do this, the surface of the still-liquid-but-cooling agar and malt extract will of course stay horizontal. Let the vials sit like this for 12 hours, after which time the agar and malt will be somewhat solid (still a bit soft and yielding--ideal for this purpose). After cooling, the surface of the medium is at an angle giving a greater surface area, hence the name "slant". These are now ready to be "inoculated" with cells of your favorite yeast. Store these in the refrigerator until you're ready to use them.
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