Bread machine yeast can be mixed directly into the dry ingredients of recipe before the bread is baked, usually in a specialized appliance. Unlike active dry yeast, a baker does not need to proof bread machine yeast before using it, and the dough will need to rise only one time. The yeast is similar to instant or rapid rise yeast. Bread machine yeast is finely granulated and is designed to rehydrate more quickly than active yeast. It also usually has added ascorbic acid.
The primary difference between active dry yeast and bread machine yeast or instant yeasts is the level to which the yeasts are dried. Bread machine yeast is finer than active dry and contains less moisture before it is rehydrated. The lower moisture level means that a baker can mix it into dry ingredients without rehydrating it first. Active dry yeast needs to be dissolved in water before it is mixed in with the rest of the dough ingredients, or it will not rehydrate fully.
Another difference between bread machine yeast and other types of yeast is the rate at which the yeast leavens the bread. Instant or bread machine yeasts are designed to leaven the bread quickly — up to twice as fast as active dry yeasts — so a baker can bake the dough after allowing it to rise only one time. The smaller size of the yeast granules and the addition of ascorbic acid, also known as vitamin C, encourages a rapid rise.
Although they are different types of yeast, a baker can use bread machine or active dry yeast interchangeably by making some adjustments to the bread recipe. If a baker replaces bread machine yeast with active dry yeast, he or she will need to dissolve the active dry yeast in half a cup (60 ml) of water with a small amount of sugar before adding it to the recipe. Usually, active dry yeast must proof, or foam in the water, before it is added to the dough.
When bread machine yeast is used to bake bread in a bread making appliance, it is sprinkled on top of the dry ingredients. When the water is added, it should be 80°F (27°C). A baker should use half a teaspoon (about 1.5 g) of yeast for every cup (450 g) of flour in a bread machine recipe.
The yeast also can be used to make bread in the traditional way, without a special appliance. Although the yeast still should be added directly to the dry ingredients, the water temperature needs to be considerably higher — 120°F (49°C). When used for traditional recipes, a packet or 2.25 teaspoons (7 g) of yeast will leaven up to 4 cups (1800 g) of flour.
