Cake yeast is slightly moist, compressed fresh yeast. Because it doesn’t have a very long shelf-life, most grocery stores only carry active or instant dry yeast.
Cake yeast requires refrigeration and has to be used within one or two weeks. Freezing it extends its shelf life for a few months. Some bread makers insist on using cake yeast, stating that the resulting bread is slightly sweeter and milder. Others, however, find no discernable difference between cake yeast and dry yeast. Cake yeast is more expensive than dry. Substitute one packet, or 2-1/4 teaspoons, dry yeast for one block of cake yeast.