Easy Home Yeast Banking - and a Video!

Wow, two videos in as many weeks - that has to be a new production record for me! This time around the video is on my most requested topic - an easy to implement home yeast banking system. The video outlines a method, based on the use of slants, to store yeast for future use. Managed carefully this method will allow the average home brewer to easily maintain stocks of up to 2 dozen strains with minimal cost or effort.

Because of the length of the video, and the presence of multiple separate methods, I have provided written instructions, below, to complement the video.

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Overview

Storing yeast on agar slants is an easy and inexpensive way to maintain a yeast bank. Practically, at home, you can maintain 1-2 dozen strains this way; more than that can become laborious to manage. It is important to perform all steps in an appropriate work environment, and using the best aseptic techniques you can manage. If you are not experienced with these methods, I'd recommend you watch the relevant videos in my Your Home Yeast Lab Made Easy video series

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Preparing Slants

Equipment:

• 16 mm x 100 mm (or similar size) screw-cap glass culture tubes
• Suitable growth media such as 1.005 gravity wort + 2% agar
• Measuring cup
• Small funnel (optional)
• Pressure cooker
• Cookie sheet
• "Wedge"

Procedure:

1. Pre-fill the pressure cooker to half the depth of the tubes and begin heating on the stove.
2. While the pressure cooker begins to heat, dissolve the agar into the media by microwaving in short (20-30 second) bursts. Stir the media between bursts. It is not necessary to boil the media for any length of time; stop heating once the agar is completely dissolved.
3. Fill the culture tubes half-full with the hot media, cap loosely, and place in a tube rack
4. Once all tubes are filled, place the tube rack & tubes into the now-hot pressure cooker.
5. Seal the pressure cooker and turn up the heat. Steam at maximum pressure for 15 minutes.
6. Let the pressure cooker cool, while still sealed, until it is below 80C (generally 30-40 minutes). Remove tubes & tighten the caps.
7. Place the tubes on a cookie sheet wedged 10-15 degrees above horizontal, with the cap-side "uphill".
8. Let the media solidify; as soon as it is solid, but while still warm, invert the tubes into your tube rack. Let cool in the fridge over night.
9. The next morning, working near a flame, remove the caps and flick out the condensation which has collected overnight. Re-seal the tubes and keep refrigerated until needed.

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Inoculating & Storing Yeast on a Slant

Equipment:

• Slants, prepared above
• A source of yeast (tube of yeast, bottle sediment, top- or bottom-cropped yeast, etc)
• Bacteriological loop
• Alcohol lamp or Bunsen burner
• Vinyl (electrical) tape or parafilm
• Optional: Distilled water or pharmaceutical-grade mineral oil, sterilized using your pressure cooker.

Procedure:

1. Flame your loop and the opening of your yeast-source container.
2. Cool the loop on the inside of the yeast source container (not on the yeast itself), then grab a loopful of yeast.
3. Open the slant, flame the opening (but not your loop!), and starting at the bottom of the slant, wipe the yeast off of the loop onto the slant media, using a zig-zag pattern to cover as much of the slant surface as possible.
4. Re-flame the slant tube opening and cap, then close the tube loosely (so that gas can escape) with the cap.
5. Let sit in a dark, warm location (20C/68F to 28C/82F) for 24 to 72 hours, or until large (3-6 mm diameter) colonies have formed.
6. Optional: Once growth is complete, open and flame the opening to the yeast slant, and open & flame the opening of the sterile mineral oil (or distilled water). Fill the slant with the mineral oil (or distilled water), and recap the slant tightly.
7. Tightly seal the cap with vinyl (electrical) tape, or with parafilm.
8. Store in a refrigerator between 3C and 6C (37-42 F).

Notes:

• Yeast stored in a tape-sealed slant should be stable for 8 - 24 months. Reculturing is recommended every 6 months if storing yeast in this manner.
• Yeast stored under sterile distilled water should be stable for 18 to 24 months. Reculturing is recommended every 12 months if storing yeast in this manner.
• Yeast stored under sterile mineral oil should be stable for 3 to 30+ years. Reculturing is recommended every 18 to 24 months if storing yeast in this manner.

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Reculturing Yeast

Equipment:

• Slant(s) in need of reculturing
• Fresh slants
• Bacteriological loop
• Alcohol lamp or Bunsen burner
• Vinyl (electrical) tape or parafilm
• Optional: Distilled water or pharmaceutical-grade mineral oil, sterilized using your pressure cooker.

Procedure:

1. Flame your loop and the opening of the old yeast slant.
2. Cool your loop by dipping it into the mineral oil (or water) filling the old yeast slant. If water or oil was not used, cool the loop on the inside glass surface of the tube (not on the agar).
3. Insert the loop to the bottom of the old slant and drag it outwards, across the slant surface. You want to grab yeast from as many colonies as possible.
4. Open & flame the new slant. Insert the loop to the bottom of the slant and inoculate as per step 3 of "Inoculating & Storing Yeast on a Slant", above.
5. Grow, seal and store the new slant as per steps 4-8 of "Inoculating & Storing Yeast on a Slant", above.

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Beginning a Starter from a Slant

Equipment:

• Slant containing the desired yeast
• Bacteriological loop
• Alcohol lamp or Bunsen burner
• Tube containing 5 to 10 mL of sterile 1.040 wort

Procedure:

1. Flame your loop and the opening of the yeast slant.
2. Cool your loop by dipping it into the mineral oil (or water) filling the old yeast slant. If water or oil was not used, cool the loop on the inside glass surface of the tube (not on the agar).
3. Grab several colonies with your loop, but leave enough behind for future use of the yeast and reculturing. Flame the lip of the slant and seal with the tube cap.
4. Open and flame the tube of wort (but not the loop).
5. Vigorously swirl the loop in the wort; remove and flame the loop.
6. Flame the lip of the container of wort and the cap; recap tightly.
7. Shake the tube of wort vigorously to oxygenate, then loosen the cap and place in a warm location  (20C/68F to 28C/82F). 
8. Re-seal the slant with vinyl tape or parafilm, and return to the fridge for future use.
9. A minimum of two times each day tighten the lid on the tube of wort and shake vigorously; then loosen the cap and return to the warm location.

In 2 to 4 days the yeast should grow, providing you with a tube of yeast at ~10 million cells/mL. A 5 to 10 mL starter tube can be used to pitch a 250 mL (1 cup) to 500 mL starter, providing ~35 or 75 billion cells. This can then be stepped upto pitchable amounts following conventional starter calculators.