Yeast Fermentation and Cell Biology
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Questions and Answers

Match the following terms with their definitions:

Amylase = An enzyme that breaks down starch into sugar Zymase = A term used to refer to a single enzyme responsible for fermentation Glycolysis = The process of breaking down sugars to carbon dioxide Fermentation = The process of yeast cells breaking down sugars for energy

Match the following statements with their corresponding facts:

15 trillion yeast cells are in one pound of compressed yeast = Yeast cells are very small Yeast uses energy for survival and reproduction = Yeast cells break down sugars for energy Alcohol evaporates to a gas and expands during baking = Fermentation produces as much alcohol as it does carbon dioxide Malted barley flour is used to add amylase in lean doughs = Yeast lacks amylase and cannot break down starch into sugar

Match the following processes with their descriptions:

Fermentation = The process of yeast cells breaking down sugars for energy Glycolysis = The breakdown of starch into sugar Budding = The process of yeast cell reproduction Baking = The process of breaking down sugars to carbon dioxide

Match the following elements with their roles:

<p>Yeast = Tiny enzyme machines breaking sugars into smaller molecules Amylase = Enzyme breaking down starch into sugar Louis Pasteur = Scientist who proved that living yeast is necessary for fermentation Malted barley flour = Means of adding amylase into lean doughs</p> Signup and view all the answers

Match the following terms with their characteristics:

<p>Yeast cells = Very small single-celled microorganisms Fermentation = A process that produces carbon dioxide and alcohol Glycolysis = A process with multiple steps and separate enzymes controlling each step Lean doughs = Doughs consisting of little more than flour, water, salt, and yeast</p> Signup and view all the answers

Match the following statements with their corresponding results:

<p>Yeast cells break down sugars for energy = Production of carbon dioxide and alcohol Yeast lacks amylase = Inability to break down starch into sugar Alcohol evaporates to a gas and expands during baking = Rise of dough during baking Yeast reproduces by budding = Formation of new yeast cells</p> Signup and view all the answers

Match the following processes with their importance:

<p>Amylase addition = Crucial in lean doughs for starch breakdown Glycolysis = Necessary for the production of carbon dioxide Fermentation = Important for yeast cell survival and reproduction Budding = Important for yeast cell reproduction</p> Signup and view all the answers

Match the following elements with their relationships:

<p>Yeast cells = Produce carbon dioxide and alcohol through fermentation Amylase and starch = Interact to produce sugar Yeast and sugar = Interact to produce carbon dioxide and alcohol Glycolysis and enzymes = Interact to break down sugars into smaller molecules</p> Signup and view all the answers

Match the factors that affect yeast fermentation with their effects:

<p>Temperature of dough = Increases yeast activity between 50°F and 120°F (10°C and 50°C) Amount of salt = Retards or inhibits yeast fermentation pH of dough = Has an optimal range of 4 to 6 Type of sugar = Influences fermentation speed</p> Signup and view all the answers

Match the type of yeast with its primary characteristic:

<p>Active Dry Yeast = Produces slack, sticky doughs and dense loaves Instant Yeast = Is less vigorous than compressed or active dry yeast Fresh Compressed Yeast = Has the same high level of dead and damaged yeast as Active Dry Yeast</p> Signup and view all the answers

Match the sugar types with their fermentation rates:

<p>Sucrose = Fermented rapidly Maltose = Fermented slowly Lactose = Not fermented Fructose = Fermented rapidly</p> Signup and view all the answers

Match the type of yeast with its recommended usage:

<p>Active Dry Yeast = Conventional or no-time doughs Instant Yeast = Extensible dough is desirable Fresh Compressed Yeast = Short fermentation time doughs</p> Signup and view all the answers

Match the effects of yeast fermentation with their descriptions:

<p>Alcohol production = Leavening gas in yeast-raised baked goods Carbon dioxide production = Fast rising of bread during baking Flavor molecule production = Distinctive aroma of freshly baked yeast bread Acid production = Low pH ideal for yeast fermentation</p> Signup and view all the answers

Match the type of yeast with its production process:

<p>Active Dry Yeast = Requires hydration in water before adding to dough Instant Yeast = Gentler drying process than Active Dry Yeast Fresh Compressed Yeast = Vacuum-packed and sold dried</p> Signup and view all the answers

Match the yeast-related terms with their descriptions:

<p>Preferment = A mixture of yeast and some ingredients fermented before final dough Sponge = A type of preferment for sweet doughs Instant yeast = Fast-fermenting yeast for no-time doughs Lean dough = Dough with low levels of added sugar</p> Signup and view all the answers

Match the factors that slow yeast fermentation with their effects:

<p>High sugar levels = Inhibit yeast fermentation above 10% High temperature = Kills yeast cells above 140°F (60°C) Antimicrobial agents = Slow or stop yeast fermentation Low salt levels = Increase yeast fermentation</p> Signup and view all the answers

Match the type of yeast with its shelf life:

<p>Active Dry Yeast = Up to one year at room temperature without loss in activity Instant Yeast = Has an indefinite shelf life at room temperature Fresh Compressed Yeast = Has a shorter shelf life than Instant Yeast</p> Signup and view all the answers

Match the type of yeast with its usage ratio:

<p>Active Dry Yeast = Use the same amount as Instant Yeast Instant Yeast = Use one-quarter to one-half the amount of fresh compressed yeast Fresh Compressed Yeast = Use the same amount as Instant Yeast</p> Signup and view all the answers

Match the yeast fermentation outcomes with their characteristics:

<p>Fast fermentation = Desirable for time-constrained bakers Slow fermentation = Develops flavor and gluten strength Optimum fermentation = Occurs at temperatures around 78°F-82°F (25°C-28°C) Inhibited fermentation = Caused by high sugar levels or antimicrobial agents</p> Signup and view all the answers

Match the type of yeast with its desirable temperature range:

<p>Active Dry Yeast = Between 70F (21C) and 95F (35C) Instant Yeast = Has a wide temperature tolerance Fresh Compressed Yeast = Has no specific temperature range</p> Signup and view all the answers

Match the yeast amounts with their effects:

<p>Large amount of yeast = Adds an undesirable yeasty flavor Small amount of yeast = Suitable for long fermentation times Optimal amount of yeast = Balances fermentation rate and flavor No yeast = Prevents fermentation</p> Signup and view all the answers

Match the type of yeast with its specific use case:

<p>Active Dry Yeast = Pizza or tortilla production Instant Yeast = Where extensible dough is desirable Fresh Compressed Yeast = Short fermentation time doughs</p> Signup and view all the answers

Match the dough conditions with their effects on yeast fermentation:

<p>Acidic pH = Ideal for yeast fermentation Basic pH = Slows yeast fermentation High salt levels = Retards yeast fermentation Low sugar levels = Increases yeast fermentation</p> Signup and view all the answers

Match the type of yeast with its unique characteristic:

<p>Active Dry Yeast = Is more vigorous than compressed or active dry yeast Instant Yeast = Can be added directly to dough without hydration Fresh Compressed Yeast = Has a shorter shelf life than Instant Yeast</p> Signup and view all the answers

Match the yeast products with their characteristics:

<p>Fast-fermenting yeast = Suitable for no-time doughs Instant yeast = Used in commercial bread production Active dry yeast = Requires rehydration before use Wild yeast = Found naturally on fruits and grains</p> Signup and view all the answers

Match the baking practices with their effects on yeast fermentation:

<p>Short fermentation = Suitable for high-sugar doughs Long fermentation = Develops flavor and gluten strength Multiple preferments = Enhances yeast activity and flavor High-temperature baking = Kills yeast cells and stops fermentation</p> Signup and view all the answers

Match the following types of yeast with their characteristics:

<p>Osmophilic yeast = Grows well in high-sugar environments Regular yeast = Takes an hour or more to adapt to high-sugar environments Compressed yeast = Comes as dry granules Active dry yeast = Has a light grayish tan color</p> Signup and view all the answers

Match the following yeast strains with their suitable environments:

<p>Osmophilic yeast = Rich doughs with high sugar Regular yeast = Lean doughs Compressed yeast = Warm water (100°F; 38°C) Sourdough yeast = Flour and water mixture</p> Signup and view all the answers

Match the following attributes with their corresponding yeast forms:

<p>Moist cakes or blocks = Compressed yeast Dry granules = Active dry yeast Pleasant yeasty aroma = Fresh compressed yeast Vacuum-packed jars or pouches = Instant yeast</p> Signup and view all the answers

Match the following yeast storage methods with their corresponding shelf life:

<p>Wrapped in plastic and refrigerated = Up to two weeks Frozen = Three to four months Room temperature = Several months Spray-dried = Less than 10 percent moisture</p> Signup and view all the answers

Match the following yeast characteristics with their potential issues:

<p>Darkened extensively and turned gummy = Bacterial contamination Uneven distribution = Crumbling directly into dough Off aroma = Dead yeast cells Low moisture = Extends shelf life</p> Signup and view all the answers

Match the following sourdough bread characteristics with their countries of origin:

<p>Notably sour = San Francisco Milder = French Rich doughs = Rye flour Leavened with a sponge = Traditional sourdough</p> Signup and view all the answers

Match the following sourdough starter preparation methods with their ingredients:

<p>Flour and water = Basic mixture Rye flour = Added ingredient Onion or potato = Additional source of food Wild yeast and lactobacilli = Naturally fermented</p> Signup and view all the answers

Match the following yeast handling methods with their benefits:

<p>Caring and feeding the starter = Affects flavor Adding a portion of starter to the sponge = Leavens the bread Saving a small amount of starter for the next day = Consistent source Mixing fresh flour and water = Ready to use</p> Signup and view all the answers

Match the following bread-making techniques with their characteristics:

<p>Using a sourdough starter = Naturally fermented Using pure yeast cultures = More consistent source Baking with compressed yeast = Warm water (100°F; 38°C) Baking with active dry yeast = Several months shelf life</p> Signup and view all the answers

Match the following yeast-related terms with their definitions:

<p>Levain = French term for sourdough starter Osmotic pressure = Increased by sugar in dough Sponge = Mixture used to leaven bread Baker's yeast = Saccharomyces cerevisiae</p> Signup and view all the answers

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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Learn about the process of yeast fermentation, factors affecting the rate, and the biology of yeast cells. Discover how yeast cells break down sugars and produce byproducts.

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