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NUSC 3233 Exam 2 Latest Update @
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NUSC 3233 Exam 2 LatestUpdate @ 2024-2025
Leavening Agents - Answer • Provide gas to inflate the elastic mass of bakery products
• Without them/products heavy and compact
• Provide lightness and porosity to baked goods
Types of Leavening Agents - Answer • [1] - Steam
• [2] - Air
• [3] - Carbon Dioxide
• Yeast
• Bacteria
• Chemicals
Steam - Answer -Primary leavening agent in cream puffs and popovers
-All dough's and batters have some liquid to provide steam
-1,600 fold increase in volume when water turns to steam
-Liquid to flour ratio determines water available steam
-Ratio must be high. Water not bound to dry ingredients
-Flour vol. = liquid vol.
-Bake in hot oven: water steam
Steam Properties - Answer • Steam presses against the air cell walls and stretches cells
until
protein denatures
• Gluten in the batter is too dilute to hold steam
• Popovers and cream puffs contain eggs
• Protein in eggs contributes to hold steam
• Steam contributes always to volume
,Air - Answer -When ingredients are combined, air bubbles are incorporated
-Air expands when heated. Much smaller compared to steam
-Air bubbles: essential for the function of steam as a leavening agent
-Pound cakes use air and steam
-When air is evacuated, cakes do not rise
Techniques to incorporate air - Answer • Whole eggs, egg whites or yolks are beaten
and foams are folding into batter
• Products containing fat:
o Most commercial shortenings contain 12% air
o Creaming of fats. Work with a spoon or spatula to incorporate air
Mixing and Beating - Answer • Mixing beyond optimal stiffens the dough and can lead to
loss of air
Factors limiting incorporation of air into products - Answer •Use of liquid shortenings.
These do not trap air well
-Cold shortening - difficult to cream
-Warm batters - very fluid and trapped air can float to the top -and released
• Time: maximum air leavening if baked immediately
Carbon Dioxide - Answer -Formed by the action of yeast and bacteria on sugar
-Anaerobic metabolism of glucose to yield CO2 and H2O
-By the action of an acid on the base. Baking soda
Yeast - Answer • Saccharomyces Cervisiae: living organism that needs to stay alive for
CO2 to be produced
• Take place at RT and briefly in the oven
Forms of Yeast - Answer • Compressed yeast cakes:
• Store in the refrigerator for 5 weeks
• Dissolved in lukewarm water (32-38 C)
• Active dry yeast
• Can store at RT for 6 months. In freezer for 2 years.
• Must be rehydrated at 38-46 C
,Yeast - Answer • After mixing dough, yeast is allowed to have its action
• Glucose + OH + 2CO2 <-------> 2 CH3 - CH2
Affecting Factors - Answer Affecting Factors
• Fermentation temperature
o Affects the rate of gas production
o Ideally 25 - 27.7 C (78 - 82 F)
o If temperature too high, other micro-organisms will flourish
resulting in sour flavor. Higher temperatures kill yeast
-Type of sugar
o Glucose is preferred. Small amount present in flour
o Most yeast recipes include sugar
o Sucrose = glucose + fructose
o Maltose can be used to produce glucose from amylose
o Lactose (milk sugar) cannot be used by year
-Salt
o Negative effect on metabolism of sugar
o Influence on osmotic pressure of yeast
o Beneficial: enhances activity of amylase
o Reduces breakdown of protein by proteases
o Without salt, gluten breaks too much and bread becomes porous
-pH
o Yeast activity best between pH 4-6
o Some acid produced during fermentation
o It may cause pH of dough to drop
-Bacteria
o Can also be used for fermentation
o Used with sour dough and salt rising breads
, o Sour dough bread: characterized by sour flavor example -Rye bread
o A starter of microorganisms is used
o Salt rising bread: made from dough with both yeast and
bacteria
o Cleanliness is essential to avoid contamination with harmful bacteria
o Commercial starters are available with pure strains of bacteria
o Usually combined with yeast
Chemical Leavening Agents - Answer • A chemical reaction between and acid and a
base that can
regenerate CO2
• Effectiveness depends on amount of gas generated and speed it is produced
Baking Soda - Answer • Common alkaline ingredient included in bakery products
• Sodium bicarbonate + acid = CO2 + salt + water
-NaHCO3 + HX = CO2 + NaX + H2O
-Must be dissolved to react
-No gas produced if acid not present
-If soda is not neutralized (enough acid): bitter flavor, yellow color, coarse texture and
increased browning of crust
• Acid ingredients: soured dairy products (buttermilk, yogurt, sour cream), honey,
molasses, fruit juices, cream tartar
Baking Powder - Answer • Baking soda + acid + cornstarch formulated
• Will produce 12-14% CO2 by weight
• More reliable leavening than baking soda and acid
• Cornstarch extends shelf life by absorbing moisture
• Also dilutes active ingredient
Double action of baking powders - Answer -Some CO2 is produced from monocalcium
phosphate monohydrate
-Helps develop a textured product
-Must react at RT
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