Types of Yeast

The yeast added to bread dough by the baker may be a commercially produced yeast or a wild yeast culture that is present in sourdough starter. The preparation, use, and handling of sourdough starters is discussed in chapter 7.

1. Fresh yeast, also called compressed yeast, is moist and perishable and is preferred by professional bakers. It is usually purchased in 1-pound (450 g) cakes. Under refrigeration and carefully wrapped to avoid drying, fresh yeast lasts up to 2 weeks. For longer storage (up to 4 months), it may be frozen. Avoid using fresh yeast that has discolored or become moldy.

   Some bakers crumble compressed yeast and add it directly to the dough in a straight-dough procedure. However, the yeast is mixed more evenly into the dough if it is first softened in twice its weight of warm (100°F/38°C) water. See chapter 6 for information on mixing procedures.

   

2. Active dry yeast is a dry, granular form of yeast. Active dry yeast must be rehydrated in 4 times its weight of warm water (105°F/41°C) before use. When using active dry yeast in a bread formula, use part of the water in the formula to dissolve the yeast. Do not add additional water.

   About 25% of the yeast cells in active dry yeast are dead due to the harsh conditions of the drying process. The presence of the dead cells can have a negative effect on dough quality. For this reason, active dry yeast has never been popular with professional bakers.

3. Instant dry yeast is a fairly new product (it was invented in the 1970s). It is also a dry granular form of yeast, but it does not have to be dissolved in water before use. It can be added in its dry form because it absorbs water much more quickly than regular dry yeast. In fact, the preferred way of incorporating it in a bread formula is to mix it with the dry flour.

   Unlike active dry yeast, instant yeast contains very little dead yeast, so less of it is needed. In general, you need only 25 to 50% as much instant yeast as fresh compressed yeast, or about 35% on average.

   Instant yeast also produces more gas, and produces it more quickly than regular dry yeast. This characteristic makes it appropriate for short fermentations or no-time doughs (explained on p. 121). For long fermentations and pre-ferments, fresh yeast may be a better choice. Fermentation times for instant yeast must be carefully monitored to avoid overfermentation or overproofing. Instant dry yeast is sometimes called rapid-rise or quick-rise yeast.

   As the illustration shows, instant yeast is nearly identical in appearance to active dry yeast. You must rely on the packaging for proper identification.