From: slk6p@cc.usu.edu
Newsgroups: rec.crafts.brewing
Subject: Yeast: Freezing/Nutrients
Date: 17 Aug 92 11:53:51 MDT
Organization: Utah State University

A couple of responses to some posts in HBD 949
I can't remember who wrote them- so here they are   up for grabs.

1)  Glycerin:  It's use in storing yeast.
        For bacterial cultures we had used 10% glycerin.  I would 
agree,  use your normal culturing medium.  You won't be able to 
pipet pure glycerin (extremely viscous) so make a 50% soln and 
use that.  
        If you want to maximize viability, I would recommend a
quick freeze (so there is less chance for ice crystals to form
inside yeast cells.)  Make a dry ice/alcohol bath.  (rubbing 
alcohol is fine-  you should be able to get dry ice from the 
grocery or refrigeration supply)    Dip your tubes of cells and
medium and glycerin into them until they freeze, then place them 
in the freezer.  ideally  -70 deg C-  not likely for a home freezer.
Alternatively use a ice/rock salt bath for a quick chilling.
        In addition-  try to use a concentrated culture of yeast
from the exponential phase of growth (fastest).  They will be more
able to withstand the freeze than old bugs.  Again- ideally you
would want to concentrate the cells (but may not have the equipt)
by centrifugation.  Alternatively:  You could use a solid medium 
for growth (plates/slants), then scrape up a gob of cells and mix
into the medium in your tubes (for a thick cell slurry).
        Lastly:  Be sure to use a good plastic tube for freezing.  
Preferably one with a tight screw cap.  Glass tubes would be likely
to dismember themselves upon freezing.

2)  Yeast Nutrient:  Now I don't know exactly what goes into the 
YN we buy from homebrew suppliers, but in micro labs for yeast and
bacterial cultures Yeast Extract is a very common component of
many different types of media.  I believe it is essentially pulverized
yeast, but may have had some components separated out. (Since it is
and "Extract").  This type of stuff is available from DIFCO suppliers
and other "biologicals" supply stores.  
        Regarding "grinding up yeast" yourself (Bob D.)  I would not
recommend trying it.  The cells are microscopic, and to effectively
"pop" them open with a coffee grinder or rolling pin is quite unlikely.
You could try freezing them with liquid nitrogen and grinding with 
a mortar a pestle.  Sonication is effective.  But often enzymes are
used to degrade the cell walls of the fungi, then the cells are lysed
releasing all the goodies from inside.  (At least these are ways to
get the cells open to get their DNA).  I presume for good yeast extract
you MUST open the cells to make the proteins, amino acids, vitamins
etc available to the growing yeast.  Seems that it is easy enough to 
buy the stuff.  We generally use it in such small quantities that it
is not a financial setback, and to make it yourself might require more
expense than it's worth (anyone know the going rate on sonicators?)

        Well anyway.  Hop on ye heathens!   
        Brew on Brethren of Barley, Bee, and Vine.
_____________________________________________________________________
                                J. Wyllie (The Coyote)
                                SLK6P@cc.usu.edu
"As long as he's got 8 fingers and 8 toes, he's alright by me."  H.J.S.
_______________________________________________________________________