from the President
By Chris White
One of the most common questions we receive at White
Labs has to do with storing yeast in sterile water. The theorys roots
are a bit mysterious, but over the past year we have seen more and more
articles and Web postings related to this theory.
The theory goes something like this:
Store yeast in sterile water at room temperature and
it will last for years. The idea is that the yeast will go into a
hibernation state because there are no sugars or other nutrients for
them to feed on.
As one brewer recently posted on a popular Web site,
"You can store these vials at room temperature for at least 6
months, probably for years. The concept is that in distilled water with
no nutrients around, the yeast just go dormant."
At first I wanted to believe in this theory. We at
White Labs cryogenically freeze our yeast, and we have long felt that
this is by far the best storage technique. But if room temperature/water
storage worked, brewers would be able to store yeast longer.
So we put the theory to the test. Sorry for the pun,
but it just did not hold water.
Over the last year our lab manager, Lisa White, and
Kelly Correll, our senior lab technician, tested the theory in a variety
of ways. They found that the viability dropped much faster in water,
whether the yeast was washed or not washed, kept in the cold room or at
Correll explained to me that the dye she used for the
experiment was passing in and out of the cell, a sure sign of cell wall
meltdown. And when plating the colonies, Correll said she was seeing
very little growth.
"Between four and five weeks, that was the life
of the yeast at room temperature in sterile water," Correll said.
"But it was looking bad in three weeks."
Here are some typical numbers from our tests:
Percentage of viable yeast cells after two weeks of storing yeast in
sterile water at room temperature, 5 percent. The percentage of viable
cells in sterile water at cold temperatures (40 F), 25 percent. Typical
White Labs yeast after the same time period with normal storage
techniques, over 90 percent. Typical yeast viability at a commercial
brewery, 25 percent.
The experiments left Correll with one thought:
"Dont put it in water."
I might add that with small cultures, storing it in
sterile water might not hurt much because you can still get a small
amount to plate out.
But you cannot start out with, say, 10 gallons of
yeast and expect to have 10 gallons of healthy yeast later on.
If you are not using the most advanced yeast storage
techniques, the yeast cells will change. They will mutate. That is why
we cryogenically freeze the yeast. Besides our own strains, we freeze
hundreds of yeast strains for small and large breweries alike.
Keep your yeast healthy, and they will make you
Chris White is President of White Labs Inc. and is a
chemistry and biochemistry lecturer at the University of California, San
Diego. He has a Ph.D in biochemistry.