In the January Saveur issue they give some recommendations on which yeast to use when faced with the choice of fresh yeast, active dry, and rapid rise (instant). The short article advises to stay away from old-fashioned fresh yeast as it is extremely perishable and you may end up buying a block that is already dead. Active dry and instant yeast are much more reliable and can be found in most supermarkets.

The difference between active dry and rapid rise yeast is how they are prepared. Active dry goes through a harsh drying process that removes 90 percent of the moisture and kills up to 70 percent of the yeast organisms. It also produces a hard coating around the granules, which is one of the reasons you need to proof dry active yeast. In the proofing process you are dissolving the hard coating in warm water with some sugar to get the yeast moving again, but most importantly you want to see if it is still alive. No life means your bread won’t rise.

Instant rise yeast goes through a much gentler process. Fewer yeast cells are killed, but this also means that it is more potent, so many bakers will recommend using less of it. Saveur recommends using 3/4 teaspoon to one teaspoon dry active yeast, but King Arthur Flour simply recommends ignoring it and using as much as the recipe calls for regardless of type. Rapid rise yeast also does not need to be proofed in water, so it can be added directly to other ingredients.

When storing yeast, it is best to keep it in an airtight container in the freezer. It can also be stored at room temperature in a cool dark place if sealed properly, but the freezer is still a safe bet. Just make sure the yeast is not exposed to high temperatures as this will cause the organisms to become inactive, and always check the expiration date on the package.

One note of interest is that the process of making active dry yeast was developed before World War II so that troops could have fresh bread. Fresh yeast simply couldn’t make the long trips and weather the conditions under which soldiers existed. If you want to know more about all things yeast and how it works to make wonderful bread, you can go to King Arthur Flour for a more extensive article.