I use a lot of yeast. I buy it at Sam's Club in the bulk packages. I freeze it and use it right out of the freezer. I am using yeast that I found in the freezer for over two years and it is still good. Did you know the more you bake yeast bread the more good spores will be in the air making homemade starter thrive. I keep a starter of sourdough going, this last batch is over three years old, survived two house moves. My grandmother told me her grandmother would soak a piece of muslin in starter and let dry. Then she would revive if she lost her starter or give it to those that needed a starter. You can buy starter now that is good.