New Mailer System!

Mailer showing dividing lines, numbering & yeast deposited
on spots 1, 3, 6, 8, 9 and 11. Click for larger image.

As many of my readers know, I run an extensive yeast bank and frequently exchange yeasts with other homebrewers from around the world. In the past I've used a simple mailer system that allows yeast to be sent by letter mail. While this system worked very well, it had two major drawbacks. Firstly, it was a lot of work to prepare the mailers, taking me about an hour to prepare enough mailers to exchange 48 or so yeasts. Secondly, they did not always pack nicely into envelopes, leading to a few envelopes being returned by the post for being too thick for letter mail.

For my last few exchanges I've used a modified form of this mailer system. It is much easier to setup than the old mailers (enough mailers for hundreds of yeasts can be prepared in the time needed to make enough of the old mailers for a dozen yeast), and packs very nicely into envelopes. The only downside is that it is a little more work on the end of the recipient, as multiple yeast are now packed onto a single card.

Full details of the new mailer system can be found below the fold.

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Making the New Mailers

1. Using a pencil (not pens, as some have ink toxic to yeast), divide a card of 7.5 cm x 10 cm blotting paper (or a 4" x 6" index card) into thirds along the short-side and quarters along the long-side, creating 12 squares. These squares should be a minimum of 2.5 cm x 2.5 cm (approximately 1" x 1") in size - smaller sizes are more difficult to work with.
2. Label the top-left corner as "#1" and the top-right corner as "#4", on the same side of the card as the dividing lines drawn in step #1.
3. Cut a piece of foil large enough to fold around the paper as an envelope; foil section should be ~1 cm wider than the mailer, and 2.5 times as tall.
4. Fold the foil along the horizontal axes to form an envelope around the card which opens from the top. At this point the envelope should still be open at the sides. Once folded, open the envelope flap, but leave the envelope "body" closed around the card.
5. Seal the sides of the envelope by folding the foil tightly against the sides of the card, continuing the folds along the envelope flap. 
• Be sure to fold the sides onto the same side of the card as the envelope "flap" closes.
6. Close the flap - if folded properly the backside of the mailer should be smooth with all folds on one side - this is critical to ensure easy loading and recovery of yeast from the card.
7. Sterilise by autoclaving or pressure-cooking the envelope. If using a pressure cooker, be sure to place mailers on a surface above the level of the water in the pot - you want to steam, not soak the mailers during sterilisation. If required, dry mailers by placing in a still-warm oven.

Folding the mailer: (click for large image)

1) With the lines on the card facing upwards fold the bottom of the foil

     upwards until it meets the top of the card.

2) Fold the top of the foil downwards to form a flap, the re-open the flap.

3) Fold the sides of the foil inwards, tightly enclosing the card. Folds should

    extend through the flap.

4) Close the flap to seal the envelope around the card. Mailer is now ready to

    be sterilised.

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Loading the Mailer

Note: loading of the mailer should always be performed close to a Bunsen burner or alcohol lamp. These will provide air currents that protect the mailer from becoming contaminated with yeasts, fungi and bacteria in the air. I recommend following the guidelines in my videos on preparing a work area, building/using an alcohol lamp, and aseptic techniques to learn the best practices to use when loading mailers.

Pre-Loading Preparation:

Note: this section assumes your yeast are prepared and ready to load; specific instructions for preparing liquid and solid cultures for mailing can be found below.

1. Prepare a clean work area.
2. Light your alcohol lamp or Bunsen burner.
3. Carefully unfold the top and sides of the envelope.
4. Using forceps/tweezers steralized in the flame of your burner to fold open the bottom of the envelope, fully exposing the card. Be careful to never touch the card or inside of the envelope with anything other than flame-steralized tweezers/forceps.
5. Place the card as close as possible to the flame of your burner.

Mailer opened and loaded from liquid cultures. Burner is located
 off-image, less than 1 cm to the left of the card.

Note: If loading only a portion of squares it is best to space the yeast as far apart as possible (see image above and at top of post for an example)

From a liquid culture:

1. Setup a fresh yeast culture (e.g. in a dedicated tube, or a starter for a bew-day). Grow to completion.
2. Allow the yeast to settle to the bottom of the container and decant as much liquid as you can.
3. Transfer the yeast to a single square on the mailer, transferring as thick a yeast slurry as possible. If using blotting paper up to 150 ul of liquid can be transferred to each square, if using an index card up to 50 ul of yeast can be transferred. 
1. Always deposit the yeast in the centre of the box you are loading.
2. Stop loading once the liquid portion gets close to the edge of the box you are loading.
3. Options for transfers include:
• Use an inoculation loop to transfer slurry to the card. Most inoculation loops hold 10 ul or 20 ul of material, so multiple transfers will be required to maximise loading of the card. Be sure to use proper aseptic technique during this step - see my video on aseptic techniques if you need help in this area.
• Use a sanitised eye dropper. As with the inoculation loop, transfer the thickest slurry possible. Be sure to sanitise between yeasts if loading the mailer with multiple yeast strains.
• Use a micropipettor with a sterile tip, using a fresh tips for each yeast strain you load on the card.
4. Once loaded, immediately close fold the envelope around the card, being careful not to touch the inside of the envelope or card.
• Be sure to fold the foil back over the card - you do not want the foil to slide along the surface of the card, as this may cross-contaminate yeast.

From a solid-medium culture:

1. Setup a fresh yeast culture an an appropriate solid media (petri dish or slant). Grow until you have medium-sized colonies. See my videos on making and using petri dishes, and on making/using slants, for additional information on these culture methods.
2. Using an inoculation loop, pick a few colonies off of the plate/slant.
3. Smear the colonies onto the square of the card you are loading. Start in the middle of the square and smear in a circular direction, moving outwards to form a spiral. 
1. Attempt to cover ~2/3rds of the square with the yeast to transfer slurry to the card. 
2. If needed, additional colonies can be picked to cover the area required.
4. Once loaded, immediately close fold the envelope around the card, being careful not to touch the inside of the envelope or card.
• Be sure to fold the foil back over the card - you do not want the foil to slide along the surface of the card, as this may cross-contaminate yeast.

Mailing the Mailer:

Mailer with customs
declaration and loading guide

These card-based mailers will fit into a standard small letter envelope (2 1/8" x 3 5/8"). Up to 3 mailers can fit into a single envelope without exceeding the maximum envelop thickness or weight set by Canada Post for letter mail (check your countries regulations if not in Canada for thickness and size limitations).

While you can send the mailer(s) on their own, I recommend including a printout of which yeast is located in each square. If shipping internationally I also recommend including a shippers declaration, in case the envelope is opened by customs. My standard declaration reads:

This envelope contains dried and inactive brewers yeast sterilely deposited into protective foil envelopes. These yeasts are being shared between hobbyist home brewers and have no commercial value. These yeasts are not hazardous to humans, livestock or plants. Shipment of these non-hazardous organisms is not regulated under the UN's Recommendations on the Transport of Dangerous Goods, nor under the transportation acts of the sending or recipient countries.

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Recovering Yeast from Mailers

While preparing and loading the mailers is easier than my old system, recovering the yeast is slightly more difficult, although well within the capabilities of most home brewers. Unloading of the mailer should always be performed close to a Bunsen burner or alcohol lamp. These will provide air currents that protect the mailer from becoming contaminated with yeasts, fungi and bacteria in the air. I recommend following the guidelines in my videos on preparing a work area, building/using an alcohol lamp, and aseptic techniques to learn the best practices to use when loading mailers.

The mailer should always be stored resting on the inside of the foil envelope, or on a freshly sanitised piece of foil. Never touch the card or foil with anything other than flame-sanitised forceps/tweezers.

Removing yeast from the mailer:

1. Prepare a clean work area.
2. Light your alcohol lamp or Bunsen burner.
3. Prepare an appropriate type of agar plate or tubes of sterile 1.020 gravity wort.
4. Carefully unfold the top and sides of the envelope.
5. Using forceps/tweezers steralized in the flame of your burner to fold open the bottom of the envelope, fully exposing the card. Be careful to never touch the card or inside of the envelope with anything other than flame-steralized tweezers/forceps.
• Be sure you unfold such that the foil is pulled away from the card, and not dragged across the card. Dragging the foil on the card can lad to cross-contamination.
6. Place the card as close as possible to the flame of your burner.
7. Using scissors steralized by passing them repeatedly, but quickly, through your flame, cut out the first yeast (see image below for clarity):
1. Be sure the scissors are not over heated; if they are too hot they will kill the yeast. To cool, without contamination, simply hold them beside and slightly below your flame for 30 seconds or so.
2. Holding the card with flame-steralized (and cooled) tweezers/forceps, and starting at the yeast in square #1, cut the yeast from the card:
1. Create a flap containing the centre of the deposited yeast by making two downward cuts from the top of the card.
2. Free the strip by either cutting from the side of the card, or by folding the strip upwards and cutting across its base.
3. Hold the strip across a tube of wort or agar plate, and cut such that the middle region of the yeast spot drops into the wort or onto the agar surface of the plate.
8. Repeat for the remaining yeasts in the top row. Then cut off the residual material from the top row, and repeat for the second and third rows of yeast.

Removing yeast from card:

1) Starting from upper edge (thin dotted lines),

    cut strip containing the middle half of the yeast

2) Free the strip by either cutting from the side of

    the card, or by folding the strip upwards and

    cutting across the bottom of the strip (medium 

    dotted line)

3) Cut the centre of the yeast spot off of the tap,

    allowing the central region to drop into your liquid

   culture, or onto an agar plate.