Should I store my instant yeast in the freezer or refrigerator? - Food52

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Thanks for the explanation. My Inner Geek googled around for more detail about why this is so, and came up with this.
From http://www.lallemand.com/BakerYeastNA/eng/PDFs/LBU%20PDF%20FILES/1_6DRYYE.PDF
"When yeast is dried the cell membrane
becomes more porous than usual. During
rehydration the cell membrane recovers,
but while this is occurring cell constituents
can dissolve in the dough water. The optimum
temperature for membrane recovery
is about 104°F.
Warm rehydration maximizes dry yeast
performance by quickly reforming the cell
membrane. Cold rehydration hurts performance
by slowing down the recovery of the
cell membrane and allowing more cell constituents
to escape or “leach.” The effect is
not that great between 70° and 100°F, but
at lower temperatures up to half of the yeast
cells’ soluble components can be lost.
Leaching affects yeast activity because
although most of the enzymes remain, the
solubles which promoted the activity of the
enzymes are depleted. Leaching also affects
dough consistency because glutathione is released.
This contributes to dough slackening
which can be desirable at low levels in
some applications but undesirable in others."
You can put yeast doughs in a very cold refrigerator or freezer, and on being thawed/returned to room temperature, they rise just fine. Same with sourdough starters that have been refrigerated or frozen. So being in the presence of water and cold hasn't killed the yeast--or at least not all of it--in those cases. How is putting dry yeast into cold water different? I get that the yeast won't really activate until it reaches a certain temperature, but have you really killed it?
Cold water negatively impacts the yeast cells' rehydration process which must take place within a particular temperature range to be successful. In other words, it is only during the (re)hydration process that yeast is susceptible to the cold.
Freezing will not kill yeast. Not all living things are adversely affected by freezing. In fact, many microorganisms are preserved indefinitely by freezing. I always keep my yeast in the refrigerator or the freezer.