Wednesday, 26 February 2014

A Beautiful Sight

Eighteen new yeasts, all on agar, ready to be grown up and frozen down in the yeast bank.  Where did this bounty of yeastie goodness come from you ask?  The answer is brewers like you - these are the product of three exchanges with fellow yeast bankers.  Yeast exchanges are easy and cheap.  So common - share those yeasts!

And to Brian, Richie & Nick, I say thanks for the yeast!

5 comments:

  1. Where is a good source for the slant tubes?

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    1. Those tubes are not being used for slants, but rather for a liquid culture. I get them from ThermoFisher, but you can often find them on ebay. They are 14ml polypropylene round-bottomed tubes.

      For slants I would recommend getting some equivalently-sized glass tubes - its easier to prepare slants in them (you can sterilize/pressure cook the media right in the tubes, instead of having to pour media into the tubes after sterilization) and they are reusable which cuts long-term costs. Again, ebay is a good place to look. Generally, for glass, you want to look for screw-cap glass culture tubes.

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    2. Do you freeze in the liquid culture tubes, using glycerin?

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    3. Ted,

      Yes, I freeze my yeast using glycerol (AKA glycerin). I'm planing a series of videos on showing the home brewer how to do it, but in the mean time I hope this description will suffice:

      1) Prepare (using a pressure cooker) a sterile mixture of 20% glycerol dissolved in 1.020 wort.

      2) Grow up some yeast in sterile 1.040 wort, under the best growth conditions you can achieve. Ideally you want this on a stir-plate. You will only need 50-100ml of wort/yeast for this.

      3) Once the yeast have grown completely, place the yeast culture in the fridge for three days. This will settle the yeast and allow them to produce some compounds that protect them during freezing.

      4) After the 3 day refrigeration decant the spent wort from the cooled yeast and then add-in a minimum of 5 yeast-pellet volumes worth of the glycerol/wort mix prepared in step 1. Suspend the yeast and transfer to your freezing tube. I would recommend a 15ml polypropelene screw-capped tube; these can be purchased pre-steralized on ebay. The glycerol/wort mixture should be at the same temperature as the yeast.

      5) Place the tube of yeast into a small cooler placed inside of your deep-freeze. The cooler should contain ice-packs in order to protect the yeast from the freeze-thaw cycles used by frost-free freezers, and the cooler/ice packs should be pre-cooled in the cooler for at least a day. The cooler/icepacks are not required if using a non-frost free freezer.

      Stored like this, yeast are stable for a few years - so long as you've protected them properly from your freezers frost-free cycles.

      I run a research lab, so I keep my yeast in a -80C lab freezer (but still in 1.020/20% glycerol). Stored like that, yeast are stable for decades, if not longer.

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  2. *sigh*, I have trouble keeping my kitchen privileges, but to have a research lab! Thank you!

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