Harold Bell asks about instant yeast vs. ordinary ("active dry") yeast, and
"Sandy in Maryland" asks about storing and using big bricks of instant yeast.
For Harold: Instant yeast is sold in most supermarkets in the same sort of
three-pack envelopes that active dry yeast is sold in. Look for brand
names, such as "Rapid Rise" or the indication that this yeast is specially
formulated for bread machines. The difference between instant and active
dry is that instant is dried more gently, so a larger percentage of its
spores are viable. In addition, a little ascorbic acid is often added to
the medium in which the yeast is embedded. Both of these factors make the
yeast more active when it is rehydrated, so you use less of it than active dry.
A second difference is that you can mix instant yeast with your dry
ingredients and it will rehydrate nicely when you mix in the liquids.
Active dry yeast must be dissolved in liquid before adding it to the dry
ingredients. In other words (to answer Sandy's question), you don't need to
"proof" instant yeast.
For most recipes, you can substitute active dry yeast for instant, but you
need to adjust the quantity. Generally, if a recipe calls for active dry
yeast, you use only 3/4 that much instant (i.e., 25% less). If it calls for
instant, then you use 1 1/3 times as much (i.e., 33% more) active dry.
For Sandy: Use it just like regular instant yeast. It keeps for a very long
time in the pantry so long as you don't open the vacuum package. Once I
open it, I like to keep my bulk yeast in the freezer in an airtight Ball
jar (use any canning jar or similar airtight container). The key things you
want to do are to keep the yeast cold, dry, and away from any more oxygen
than you can help.
If you like to spend money, King Arthur's Baker's catalogue
(http://www.kingarthurflour.com) sells a nice cannister for storing yeast,
but there's no reason not to just use whatever quart-sized canning jar is
handy. I typically keep yeast for a year in the freezer.
As I recall, the Bread Baker's Apprentice has a very good discussion of
different types of yeast, but I like the discussion in Maggie Glezer's
"Artisan Baking Across America" better. MG provides a good table of
substitutions between active dry, fresh, and instant.
Jonathan Gilligan