The Yeast Page
(scroll down for new additions 12/22/04)
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This is a scanning electron micrograph of a Saccharomyces cerevisiae, (brewers
yeast) cell. This haploid
parent cell has produced at least 6 daughters as shown by the polar contiguous
array of circular bud scars.
Photograph by Anna Cosney and John Forsdyke, (from a Microbiology calendar).
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Sterile tubes with various yeast strains, waiting to be used as is or recultured.
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Some Yeast Farming Notes...
A clean bench is a fair alternative to an expensive HEPA filter unit.
Isolating Bottle Conditioned Strains of Yeast
Flaming bottle just before opening and decanting off beer. Then sediment (yeast,
etc.) is poured into
a sterilized container full of sterile wort. This should begin to ferment
within a few days.
(Be sure to keep caps loose during fermentation, to avoid exploding
the containers.)
Here is the 800mL sterile wort starter ready to "plate out" for
the first time. Later when the plate is
ready, one or two single isolated colonies can be picked out and restuck on
another sterile plate.
Then this second plate is used to make slants for long term storage, and/or
to inoculate or "pitch"
directly into small starters to be later stepped up for a larger amount of
clean yeast.
I pick one to three colonies of yeast and transfer to a 10mL sterile wort
tube. When this tube is
actively fermenting (~2 days), I then pitch to 800mL sterile wort. When the
800mL is at full
krausen it is ready to pitch into 5 gallons. Or you may let it ferment out
and then cool down
overnight. The yeast will drop down, and you can decant off the beer and pitch
the thick slurry
of yeast directly to the 5 gallons of wort.
These 10mL tubes are showing active fermentaion.
Boiling the previously prepared wort agar, in order to pour new plates.
Always have an open and clean area when sterile technique is desired. Two
small jars of hot agar are allowed to
cool a bit, (until you are just able to hold them without burning your hand).
Pouring warm agar into sterile petri dishes. About 25-30mL for each plate.
I leave lids cracked for a few minutes after pouring to let some condensate
escape. Then the covers
are tapped on and the plates are allowed to fully solidify (~20min) before
stacking upside down.
Plates are labelled with the date made, and the type of agar medium used.
When a plate is struck out
it should labelled immediatly before continuing futher, to avoid mix ups.
After new plates have solidified they are stored upside down to avoid "drop
ins" and moisture pooling.
Flame the loop before and after each transfer.
When striking out plates, hold the dish at an upside down angle. This helps
keep dust and those free-loading
microorganisms from infecting your plates. Keep covers face down on clean
surface while streaking.
This shows early yeast growth, about 2 days at 68F.
When plates are "grown up", they should be wrapped with parafilm
or tape (too prolong drying out),
and kept cool until needed.
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Microscopy
Yeast cells as viewed through my microscope.
MORE LATER...