The date that is posted on packages of yeast is for storage at room
temperature. Stored in the fridge, yeast will last at least 6 months beyond
the expiration date. Stored in the freezer, yeast will last 10-12 months
beyond the expiration date.
Some people say that you should store the bulk of your yeast in the freezer
and just keep a small jar in the fridge to help prevent moisture build up
in the container you store it in. But I've never had a problem with this,
but I live in a really dry climate. I always keep mine in the freezer.
Roxanne