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The rate of yeast fermentation is affected by several important ______.
factors
Fast fermentation is desirable when ______ is a constraint.
time
Yeast is dormant at ______34F (01C).
32
The typical amount of ______ in yeast doughs is 1.82.5 percent (baker's percentage).
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Small quantitiesup to 5 percent (baker's percentage)of ______ increase yeast activity.
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The optimum pH for yeast fermentation is an ______ 4 to 6.
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Certain ______ agents slow or stop yeast fermentation.
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Most ______, including cinnamon, have strong antimicrobial activity and can slow yeast fermentation.
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A large amount of ______ can add an undesirable yeasty flavor.
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Some yeast products sold to bakers contain fast fermenting ______, good for no-time doughs.
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Yeast cells break down ______ for energy.
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The biological or organic production of carbon dioxide results primarily from ______ fermentation.
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Approximately 15 trillion of yeast cells are in one pound of compressed ______.
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Yeast lacks ______ and cannot break down starch into sugar.
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Malted barley flour is the most common means of adding ______ into lean doughs.
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The process of breaking down sugars to carbon dioxide is called ______.
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Alcohol evaporates to a gas and expands during the early stages of ______.
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Some yeast strains grow well in ______ doughs, doughs that are high in sugar.
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The term ______ is still sometimes used to refer to the many enzymes in yeast that take part in the breakdown of sugars.
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The name osmophilic comes from the fact that sugar increases the ______ pressure in dough by tying up water.
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Bread can be made from a traditional, naturally fermented ______ starter, called levain in French.
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Starters are prepared by mixing flour and water and allowing wild ______ and lactobacilli bacteria from the flour and air to ferment the mix.
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French sourdough bread (pain au ______) is usually milder.
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A small amount of starter is mixed with fresh flour and water and saved for the next day's ______.
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All yeast purchased for bread baking consist of ______ yeast or Saccharomyces cerevisiae.
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The three main forms of yeast available to the baker today are compressed, active ______, and instant.
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Compressed yeast lasts up to two weeks when stored wrapped in ______ and refrigerated.
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Active dry yeast is dried in a spray drier to less than 10 percent ______.
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Dead and damaged yeast release a substance—______—that is detrimental to the quality of gluten in dough.
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Active dry yeast is not popular with professional bakers because it tends to produce ______ doughs and dense loaves.
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When using active dry yeast, it should be dissolved in ______ times its weight in very warm water.
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Instant yeast was developed in the ______.
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Instant yeast is sold ______ and vacuum-packed.
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Instant yeast is more ______ than either compressed or active dry yeast.
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When using instant yeast, initial dough temperatures should be between ______ and ______ degrees Fahrenheit.
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Unopened instant yeast will last up to ______ year at room temperature without loss in activity.
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Study Notes
Yeast Fermentation
- Yeast fermentation is a process in which yeast cells break down sugars for energy, producing carbon dioxide and alcohol as byproducts.
- Yeast uses the energy for survival and reproduction.
- The rate of yeast fermentation is affected by several factors, including temperature, amount of salt, amount of sugar, type of sugar, pH of dough, presence of antimicrobial agents, and amount of yeast.
Yeast Cells
- Yeast cells are very small, single-celled microorganisms, with approximately 15 trillion cells in one pound of compressed yeast.
- Yeast cells reproduce by budding, and visible scars from previous buddings can be seen on the yeast cell.
Enzymes and Fermentation
- Yeast can be thought of as tiny enzyme machines, breaking sugars into smaller and simpler molecules with every step.
- Yeast lacks amylase and cannot break down starch into sugar, which is why amylase is an important additive in bread baking.
- The overall process of fermentation involves multiple steps, controlled by separate enzymes, and produces carbon dioxide, alcohol, and small amounts of flavor molecules.
Factors Affecting Yeast Fermentation
- Temperature: Yeast is dormant at 32–34°F (0–1°C), active at 50°F (10°C), and slows down at 120°F (50°C), with an optimal temperature of 78–82°F (25–28°C).
- Amount of salt: Salt retards yeast fermentation, and the optimal amount of salt is 1.8–2.5% (baker's percentage).
- Amount of sugar: Small amounts of sugar (up to 5%) increase yeast activity, while large amounts (above 10%) slow fermentation.
- Type of sugar: Sucrose, glucose, and fructose are fermented rapidly, maltose is fermented slowly, and lactose is not fermented at all.
- pH of dough: The optimal pH for yeast fermentation is an acidic 4 to 6.
- Presence of antimicrobial agents: Certain antimicrobial agents slow or stop yeast fermentation.
- Amount of yeast: The more yeast, the faster the fermentation, but excessive yeast can add an undesirable yeasty flavor and exhaust dough of sugars.
Types of Yeast
- Compressed yeast: Fresh, moist cakes or blocks with 30% yeast and 70% moisture, lasts up to two weeks when stored wrapped in plastic and refrigerated, and three to four months when frozen.
- Active dry yeast: Dried granules with less than 10% moisture, sold in vacuum-packed jars or pouches, and lasts several months at room temperature, longer if frozen or refrigerated.
- Instant yeast: Developed in the 1970s, instant yeast can be added directly to dough without first hydrating in water, and is more vigorous than compressed or active dry yeast.
Sourdough Starters
- Sourdough starters are prepared by mixing flour and water, allowing wild yeast and lactobacilli bacteria to ferment, and can be used to leaven bread.
- Fresh starter does not need to be made for each new day's production, and can be saved for the next day's bread by mixing it with fresh flour and water.
- Some bakeshops pride themselves on the number of years they have continued to bake from their original starter.
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Description
Learn about the process of yeast fermentation, how yeast cells break down sugars, and the factors that affect the rate of fermentation. Discover the role of yeast cells in producing carbon dioxide and alcohol.
