Practical Advice on Working with Yeast:
Answers to Five Common Questions
What are the types of yeast available to home bakers and how should I choose one?
The three types of yeast available to home cooks are fresh/compressed, dry active, and instant (aka rapid rise, perfect rise, fast rising, and bread machine yeast). Most people choose their yeast based on availability, familiarity, and shelf life (if you bake infrequently it would be better to use dry yeast, which can be stored for up to a year in an airtight container, whereas fresh yeast lasts only about three weeks). The only type that needs to be dissolved first in warm water is dry active, because the yeast grains are too big to dissolve directly in the dough. The term instant yeast refers to the fact that it dissolves instantly in the dough, as soon as liquid is added for mixing, though it can also first be dissolved in warm water if desired. Instant yeast is 25 percent more concentrated than dry active yeast due to the processing method (25 percent of the dry active yeast cellswhich are more fragile than the newer strain of cerevisiae used in instant yeastdie during packaging, whereas practically no yeast cells die during packaging of instant yeast).
How do I substitute one type of yeast for another?
The substitution formula for replacing one type of yeast with another type, by weight, is 100 percent fresh compressed yeast = 40 percent dry active yeast = 33 percent instant yeast. In other words, instant yeast is three times more concentrated than fresh compressed yeast. Unless otherwise stipulated, in most types of bread baking all three types of yeast can be substituted for each other as long as the weights are adjusted accordingly. Regardless of which type of yeast you use, as long as you make the proper replacement adjustment, the flavor of the finished bread will be the same.
Is there a difference among brands of yeast?
Almost all brands of commercial yeast are comparable to each other in strength and reliability. The only difference is in type, so be sure to ascertain whether you are using instant (which is confusing since it goes by so many names), dry active, or fresh compressed yeast, and follow the instructions on the package regarding storage and life expectancy of the yeast.
What kind of yeast works best in sweet or acidic doughs?
There is a specially cultivated strain of cerevisiae yeast that is more resistant to acidity or excessive sweetness in dough called osmotolerant instant yeast, but it’s usually available only to professional bakers (the name refers to its ability to resist the penetration of the cell walls of the yeast by sugars or acids). Some specialty catalogs and Web sites, such as King Arthur Flour, also carry it for serious home bakers. This type of yeast is especially useful for sweet, rich doughs and also for slow-fermenting doughs that develop a lot of acidity. (Yeast can process only simple, single-chain sugars, like glucose, so doughs that are high in granulated or brown sugarsucrose typescan actually overwhelm yeast and put it to sleep while the yeast waits for the dough enzymes to break down the sucrose into digestible glucose and fructose.)
I have found that regular instant yeast will do nearly as well as osmotolerant yeast if you first hydrate it in lukewarm water, as you would for dry active yeast, which seems to give it a kind of head start in the rich or sweet doughs.
What are preferments?
Artisan bakers have developed methods for adding to their doughs small quantities of old dough. The purpose of this so-called preferment is to instantly add complex fermentation flavors to the new batch of dough. Some of these prefermented doughs are called by names such as biga, poolish, sponge, pâte fermentée, or simply, old dough.
Bread-baking authority Peter Reinhart is the author of eight books, including Artisan Breads Every Day and the James Beard Awardwinning Whole Grain Breads. He’s also a baking instructor and faculty member at Johnson & Wales University and the host of the Web site Pizzaquest.com, where you can learn more about him.