Fermentation is the process by which yeast acts on carbohydrates and changes them into carbon dioxide gas and alcohol.This release of gas produces the leavening action in yeast products.The alcohol evaporates completely during and immediately after baking.
Yeast is a microscopic plant.As a living organism, it is sensitive to temperatures.
70° to 90°F (20° to 32°C) Best growth;proofing temperature for bread doughs.
Yeast is available in three forms:
1. Fresh yeast, also called compressed yeast, is moist and perishable and is preferred by professional bakers. It is usually purchased in 1-lb (450-g) cakes.
2. Active dry yeast is a dry, granular form of yeast.Active dry yeast must be rehy-drated in 4 times its weight of warm water [about 110°F (43°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.
3. Instant dry yeast 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. It also produces more gas than regular dry yeast, so less of it is needed. Instant dry yeast is sometimes called rapid-rise or quick-rise yeast.
In this book, when yeast is required in a formula, fresh yeast is specified.To substitute dry yeast, use the following guidelines.
To convert fresh yeast to regular active dry yeast, multiply the quantity by 0.5. For example,if the formula calls for 1^2 ounces fresh yeast, multiply by 0.5 to get % ounce active dry yeast.
To convert fresh yeast to instant dry yeast, multiply the quantity by 0.35. For ex-ample,if the formula calls for 40 g fresh yeast,multiply by 0.35 to get 14 g instant yeast. Yeast contributes flavor in addition to leavening action.
Chemical leaveners are those that release gases produced by chemical reactions.
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