From the HBD Archive
From: hpfcla!hplabs!amdahl!uunet!ingr!tesla!steve
Subject: Yeast Bank
Date: 1988-12-19 21:45:58 GMT

Here is a report on the "yeast bank" system of freezing yeast cultures for
long-term storage. I bought this system about 6 months ago, but wanted to wait
until I knew whether it worked or not before talking about it. It has worked
well for me, and here is a commentary on what it is and how it works.
The "Yeast-Bank" is sold by William's brewing in San Leandro, CA. (and maybe
others). It consists of a one quart plastic freezer container which contains
five culture tubes, a bottle of "Freeze-shield" solution, a glass eyedropper,
and instructions. The culture tubes are about 3/4" by 3", with a cap which
seals tightly, and are individually wrapped in sterile packages (like
disposable syringes). The solution is a pale blue, with no discernable odor.
The following is the way I use the system. It is mostly the same as the
directions suggest, but there are some differences. There are some assumptions
that I make when I brew and culture. One of these is that tap water is
essentially sterile. This is probably far from true, but it hasn't caused me
a problem yet. I don't like to brew with this water, but I will rinse with it
after sanitizing.I buy a bag-in-a-bag type of yeast starter and break the
inner bag. When it swells, I soak a 16 oz bottle, stopper, and airlock in
a strong bleach solution for at least 45 minutes, then rinse with hot tap
water. I prepare a solution using about 2/3 cup light DME and 1/4 tsp of
yeast nutrient by boiling the solution, then immerse the bottom of the pan
in ice water to quick-chill it. I put the solution in the bottle, pour in the
yeast starter from the bag, and put on the airlock. A few days later, when
activity has slowed, I brew a batch of beer. When it is time to pitch, I
sanitize the eyedropper, shake up the starter solution to suspend all the
yeast, (Time out for another brewing assumption. I assume that baggies out
of the box are essentially sterile. If I need to shake a carboy or bottle, I
will wipe around the top with a strong bleach solution on a paper towel, then
put a baggie over the opening, put my hand or thumb over the mouth of the
bottle and baggie, and shake.) and use the dropper to fill as many culture
tubes as I need with the starter solution. I put the caps on loosely, and
stand them up in the frig for awhile for the yeast to settle. I take the
rest of the starter and pitch it in the new beer. Later, when the yeast in the
culture tubes has settled to the bottom, I sanitize the dropper again, and
use it to remove the starter solution from the top of the yeast. I sanitize
the dropper again (to prevent ever contaminating the "Freeze-shield" solution)
and fill each tube about 3/4 full with "Freeze-shield". I put the caps on the
tubes tightly, and shake them to mix the yeast into the solution. Then I wrap
the tubes in paper towels, label them, put them in the plastic freezer
container with the lid on, and put them in the freezer. The instructions
recommend doing this to slow the freezing rate of the cultures down. The
amount of yeast sediment in each tube is about the volume of a grain of
barley. I also keep the "Freeze-shield" solution in the freezer when I'm
not using it. To re-start a culture, I make a solution as above, thaw
and shake
a culture, and add it to the starter. There is usually no activity for about
24 hours, then the starter takes off. I always make sure that the gas coming
from the airlock smells good before I pitch. It takes about 3 or 4 days for
the starter to get ready to pitch, and after pitching, I get a good
fermentation going in about 12 hours. The instructions say that you can save
cultures from subsequent starters, up to three or four generations of yeast,
but I don't do that. It's too easy to just make a bunch from the original
starter. Replacement culture tubes are 5/$2.50, and the solution is a few
bucks for 4 oz, which lasts a while. If I make six cultures from a package
of yeast, my yeast cost ends up being less than $1 a batch. It really doesn't
take much time, since I always make starters anyway. I have successfully
frozen and re-started both ale and lager strains with no problems. I hope this
helps someone. I would like to hear comments from anyone else who has used
this system. If anyone out there has the analytical gear needed to figure out
what's in freeze-shield, or is familiar with the medical world and knows where
to get the culture tubes, call me or send email.

Happy Holidays!

Steve Conklin, Intergraph Corp., Huntsville, AL 35807
W(205) 772-4013 {tesla!steve@ingr.com | uunet!ingr!tesla!steve}

Relax! Don't worry. Have a homebrew.



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