|A yeast mailer loaded & read-to-roll|
One problem faced by many yeast banks is the sharing of yeasts over long distances. Yeast plates, frozen cultures, slants, etc, can be expensive to send and are highly temperature/time sensitive. There is a better way!
Since the mid-1990’s I’ve been using a simple & cheap method to mail yeasts. I cannot take credit for this – I think I first came across this method in rec.crafts.brewing (for the young whippersnappers out there, this is a usenet brewing group), or perhaps on the ol’ home brew digest. It works very well, requires no special tools, is relatively resistant to swings in temperature, and relies on regular letter mail instead of expensive package mail or couriers.
The concept is simple – a foil envelope is built around a piece of absorbent paper. This packet is then sanitized, then liquid yeast is sterilely dropped onto the paper & allowed to dry. The foil envelope is then sealed & mailed. The recipient recovers the yeast (ideally) by placing it on a wort-agar plate and selecting the colonies that grow, or (less ideally) by placing the paper in a tube of media and letting the yeast grow out of that.
Details below the fold…
Preparing the mailers
|Step 1: Cut a small piece of absorbent paper (1cm x 1cm is more then enough). Place it in a piece of tin foil large enough to form an envelope around the paper.|
Here I have used laboratory filter paper, but any thick absorbent paper will do.
|Step 2: Fold an envelope around the paper, making sure the paper is freely moving within the envelope. Use masking tape (or autoclave tape, if you got it) to seal the edges. Do not use a plastic tape like scotch tape.|
Also make a tape tab (bottom of image) to hold the top shut. Make sure this tape tab will stick onto tape, not foil. Foil is too weak, and will tear when you try to open the envelope.
|Step 3: Close and tape shut the envelope. We now need to sterilize the envelope. This can be done using an autoclave on the dry cycle, or by steaming 20 minutes in a pressure cooker. If using a pressure cooker make sure the envelope is in the steam, not in the liquid!|
If you use a pressure cooker, dry the envelopes by placing them in your over at its lowest setting. Depending on the absorbency of the paper you use, they need to bake for 30-60 minutes.
Preparing & mailing the yeast
Sample Customs Letter:
This envilope contains brewers yeast sterilely deposited into protective foil envelopes. These yeasts are being shared between hobbyist home brewers and have no commercial value. These organisms 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.
Note: letters such as these are not generally required for shipments within a country. If your shipping from/to countries other than Canada or the USA you should check the veracity of last statement.
Recovering the yeast using an agar plate
|Step 1: Sanitize the surface of the packet using starsan or 70% ethanol. Don’t soak the packet, as the sanitizing agent may enter the envelope and kill the yeast. Excess sanitizing agent should be dabbed off using a lint-free cloth. Next, working near a flame, open the foil envelope.|
|Step 2: Working near a flame, remove the paper and place it on a prepared YPD or wort agar plate. Add a few drops of sterile water to the paper. Let sit 30-40 minutes, then remove the paper. The paper in the image (left) is about as big as you would want it to be (1.5cm x 1.5cm) – larger pieces should be cut smaller using sanitized scissors.|
EDIT: we have found that placing a few drops of sterile water onto the paper at this stage, and leaving the whetted paper on the agar plate for at least 24 hours, greatly improves the success of the recovery.
|Step 3: Allow the yeast to grow overnight to a few days at room temp. You should get individual colonies of yeast. Pick a colony and grow it up using the same methods described for a starter. Keep the plate in the fridge, just in case there is something wrong with the colony you have chosen.|
|Step 4 (optional): If the density of the yeast is too high, streak out the colonies on the plate using a sterile wire loop, sterilizing the loop between each streak (video):|
Each streak dilutes the yeast; eventually leading to single colonies
|Plate after streaking (left). Individual colonies are visible at the bottom of the plate. Pick a colony and grow it up using the same methods described for a starter. Keep the plate in the fridge, just in case there is something wrong with the colony you have chosen.|
Recovering the yeast using wort
The risk of infection can be reduced by adding penicillin (100U/ml) and streptomycin (100ug/ml) to the wort – if you have them.
|Step 1: Open the packet as described in step 1 of the agar plate method|
Step 2: Using tweezers which have been sterilized by heating to red-hot in a flame and then cooled by shaking in the air (obviously, do this in a clean, low-dust room), remove the paper and quickly transfer it to a prepared flask/tube of wort. For a piece of paper the size of a hole-punch, 10ml of wort is sufficient.
|Step 3: Let grow overnight, or until media is cloudy with yeast.|
Step 4: Pour off wort into a larger starter, leaving the paper behind in the culture tube.
That’s it! Using nothing more than a few cents worth of materials plus a stamp, you can send yeast nearly anywhere in the world. And let me point out at this time that I am very interested in sharing my yeasts with other yeast bankers around the world. So lets get mailing!