Lecture 18 Flashcards
What is the purpose of yeast?
Leaven baked dough products
What are the essential ingredients in yeast breads?
Flour
Liquid
Yeast
Salt
What kind of food system are yeast products?
Foam food system
Gases dispersed in dough mix
What are examples of lean doughs?
French/italitan bread
Hard-Crust rolls
What is an example of rich doughs?
Brioche
What are examples of fish sweet doughs?
Croissant
Danish
Cinnamon Roll
What is a fried yeast dough?
Doughnut
What is the texture like with yeast breads?
White bread has fine crumb, thin cell wall, uniform grain
Shape of cells vary
Crumb is elastic, and springs back when touched
What kind of breads tend to be more dense and why?
Breads made with 50% whole wheat flour are more dense
What is the appearance of yeast breads?
White bread looks golden brown crust
Well shipped load as rounded top, side it smooth and even
What factors affect the shape and volume of dough?
Stiffness of dough Strength of dough Fermentation Proofing Baking Temp Position in oven
What is the flavour of yeast breads like?
Yeasty
Other flavours are dependent on the type of bread
Sometimes sour taste due to time of fermentation
What is yeast?
Living unicellular organism
-a fungi
Can have many strains
What is the scientific name for bakers yeast?
Saccharomyces cerecisiae
Is yeast live when purchased?
Can be made formant after growth by drying or low temp
-can become active again once it is mixed into dough
What did people use before bakers yeast?
natural wild yeast
-equalt was flour and water was used to trap bacteria from the air and that’s what they use as the culture
Can yeast grow with or without O2?
Can to both
-begining stage is aerobic, later stage of baking is anaerobic
How does yeast work with bread?
Metabolizes fermentable sugars and ferments then anaerobically
-produces ethanol and CO2
What sugars can yeast readily metabolize?
Glucose
Fructose
Sucrose
Maltose
What happens to the alcohol (ethanol) when baked?
Evaporated and contributes to volume
What roles do acetic and succinct acids have on baking?
The acids impact gas holding capacity
CO2 trapped in flour gluten network
What does damaged starch turn into?
Hydrolyzed to maltose by alpha and beta amylase
What does yeast convert maltase and sucrase into?
The conversion hydrolyzes starch into maltose and sucrose
Why is sugar added to dough?
Speed up gas production
-but if its more than 10% sugar by wt then it will have a negative effect on yeast bread and can delay fermentation
What is the optimal fermentation temp and pH for yeast?
38C
4.8-5.5
What is the thermal health point of yeast?
54.4C
How is commercial yeast made?
- Healthy yeast are selected from he desired strain
- Yeast is placed with nutrients for budding to occur (multiplication)
- Culture is transferred to a medium called the wort
- After the yeast have multiplied, it is ready for fermentation
- After fermentation yeast is separated from wort
What are the nutrients in the wort?
Carbs
Vitamins
Minerals
What are the difference kinds of yeast you can find?
Active dry yeast Instant quick rising active yeast Bread machine yeast Inactive dry yeast Compressed (cake) Yeast
What is active dry yeast?
Dried dormant live yeast cells
Activated by specific temp, hydration, food
Should not be added directly to dry ingredients
Mostly for home use
Larger cell
How long can yeast be stored?
1-2 years if unopened
-if unopened store in fridge
What destroys yeast cells?
Moisture
Warm Temps
What is instant quick rising active yeast?
Added directly to dry ingredients (no need to rehydrate)
50% reduction in dough rising time
High instability in air and must be packed with inert gas (O2) or vacuum
Smaller cell
Home or bakers
What is bread machine yeast?
Same as instant quick rising active yeast BUT with added:
-ascorbic acid (dough conditioner) to promote dough extensidbility (Stretching) during rising
What is inactive dry yeast?
Same as nutritional yeast
Dough conditioner, not a leavening agent
Inactivated by pasteurization during drying on steam heat roller dryers
Breaks gluten sulphide bonds (gluten reducing agent), resulting in a more extensible dough (optimizes CO2 retention)
What is inactive dry yeast a good source of nutrient wise?
Protein
B vitamins
What is compressed (cake) yeast?
Blend of wet years cells, water, emulsifier and oil
Shorter shelf life of 10 days refrigerated due to 70% moisture
Softened in water (29C)
Powder will be 60% wt if compressed
Commercial bakeries
Which yeast is the most consistent in quality?
Compressed (Cake) yeast
-minimally processed
What will happen to compressed (cake) yeast if left out?
Will lose leavening power if left out at room temp for several hours
What does too much yeast cause?
Undesirable:
- odor
- Flavour
- Coarse texture
- Grey colour
- Distorted shape in bread
What causes a sour flavour in bread?
Natural starters or Sours from wild yeast bacteria collected from the air
What does lactic bacteria do to bread?
Increase AA content due to the break down of protein and add more flavour
(Flour proteolysis)
What kind of flour has the highest gluten protein?
Bread flour
Why do we need a stronger flour?
Weakening effect due to fermentation on the gluten
What leads to cell rigidity?
Starch from the flour gelatinizes during backing f
What is the role of pentosans?
They are gums in the flour and allow for increase water absorption
-leads to goof volume of loaf
What kinds of flour has better hydration capacity?
Strong
High protein flours
-alter liquid addition
When do you need to add more flour to dough?
When baking on a hot and humid day
Why is liquid added to dough?
Water needed for yeast activation (40-46C)
Dissolves sugar and salt and binds water
Used for lean dough and crips crust
What temp do liquids need to be heated to before being added to dry mix?
120-130F
What kind of liquids can be added to dough?
Milk (scalded to denature protein)
Eggs
Cooked potato Starch
-provides gelatinized starch flavouring fermentation
Whey
What does the addition of milk or eggs as liquid do to bread?
More tender Better dough handling Crust colour Flavour Shelf life
What happens when you have too much or too little liquid?
Much: Dilute gluten yielding decreased loaf volume
Little: dry, stiff, ineleastice, slow to rise, limited gluten development
Why is salt added to dough?
Flavour enhancer
Firming effect on gluten structure
Slows fermentation
Increases time required for rising
What happens if your dough has no salt or excessive salt?
No= crumbly
Excessive= .3% flour wt leads to stiff dough and difficult to work
What does sugar do to dough?
Fermentation time increased
Yeast metabolizes sucrose before maltose
-sugar comes from flour and added
What happens when you have too little or too much sugar?
Little: Rises quicker
Much: Delays action of yeast
What does fat do to the dough?
Makes breads softer, increases shelf like
Improved dough handling
Increase gluten extensibility for increase load volume and better texture
Not an essential ingredient
What does vital wheat gluten do?
Increases:
- dough strength
- water absorption
- dough tolerance
- loaf volume
- crumb texture
What do yeast nutrients to to dough?
Monocalcium phosphate or Calcium sulfate Supply nitrogen or phosphate for improved yeast growth
What re pH regulators?
Help to lower pH for optimal yeast growth
- Calcium carbonate
- Calcium Sulfate
Why are oxidizing agents sometimes added to dough?
Helps with gluten development
Stripping H atoms from sulfhydryl linkages, making sulphur available for disulphide bonding in gluten
Ascorbic is most popular
Why are reducing agents sometimes added to dough?
Breaks disulphide bonds
Affects stretchability of dough
Can combine with oxidizing agent to optimize gluten development and increase volume
L-cyseine and inactive yeast act on gluten to increase extensibility while also shortening mix time
What do emulsifiers do in dough?
Enhance: Stability Soften hough for flexibility Finer Softer crumb
What are some examples of emulsifiers?
Lecithin
Mono and diglycerides
Polysorbate 60
Why are enzymes used in dough?
Slow staling
Enhance bread crust colour
Oven Spring
Softer crumb
What is oven spring?
Final burst of rising after thee loaf has been put into the oven
What are some examples of enzymes used?
Alylases Diastatic malt syrup Malt Flour Oxidase Carbohydrase Proteases -mostly from fungi or bacteria
Why is mixing important ?
Air is incorporated into the dough creating many small ag nuclei leading to gluten development
Helps moisture distribute throughout the dough
Does yeast crease new nuclei in dough?
Yeast produces CO2 which increase the size of nuclei but does. not crease new gas cells
What does fully kneaded dough look like?
Smooth
Not sticky
Can stretch to think film (windowpane test)
What doe over mixed. dough look like?
Sticky
Excessively soft
-usually happens with mechanical mixer
Why do we knead dough?
Aligning of gluten and gliadin molecules
-the swollen particles of both result in the alignment from the kneading
Starch granules for flour entrapped en developing gluten
What happens during the fermented stage with eh first rising?
Dough is ripened
What are the control factors for fermentation?
Time Temo Environment Atitude Gluten Strength Yeast
What kind of fermentation doe sit start and finish as?
Begins as aerobic (20% O2 and 80% nitrogen) and then become anaerobic (only nitrogen remains)
What does the run of glucose and yeast produce?
Ethanol and carbon dioxide
What is also produced during fermentation that contributes to flavour?
Organic acids
AA
Others
What is the purpose of Organic acids, AA andOther compounds produced during fermentation?
Decrease pH from 6-5 promoting fermentation nd amylase activity
Greater dispersion of gluten with loss of elasticity
At what degree do you get the best flavour development?
26-32C
-become cold temp inhibits yeast activity
What happens when dough is exposed to air and what should you do to prevent that?
Creates a film, and can lead to streaks and forms a hard crust
- cover with damp cloth
- Place in proofing cabinet
- Grease surface of dough
How long does it take for the Dough to double in size and what does it depend on?
1 hour
- Yeast
- Temo
- Salt
- Sugar
- Dough stiffness
What happens when you have over fermentation?
Weakened gluten strands (dense coarse grain)
Sour odor
What happens when you have under fermentation?
Less tender
Small volume
What is punching down dough?
Subdivide the gas cells to:
- produce smaller cells
- redistribute yeast cells
- redistribute food substrate
- Equalize temp
When should you shape/mold the dough?
After letting dough relax for a bit after punching
What happens when you shape the dough
Removes large gas bubbles on pans or baking sheets
What is scaling?
When dough is divided into portions
What is proofing?
The final rising stage in the pan
- 30-35C and 85% humidity
- size doubled after 30-60 mins
What happens when you have an under or over proofed dough?
Under: Small and dense after baking
Over: collapse in oven
When do you know a dough is ready to be baked?
When dough doesn’t spring back its done proofing and ready to bake
What is oven spring?
Sharp rising of dough when it first goes in the oven from gas production and dough expands
What happens if you have too hot of an oven?
Initially can set the bread before optimum oven spring occurs which reduces volume
Why is steam injection good?
Is at the start of baking and allows crust to remain soft and expand giving a thin hard crust
No steam injected: crust formed early resulting in thicker and heavier crust
What happens when temp of dough increases?
Yeast is killed
Enzymes inactivated
Fermentation stopped
What temp should the dough reach to be done?
91-93C
-can reach 100
Does mailer or caramelization take place in baking dough?
Both
What is a high fibre dough?
Bran is detrimental to gluten and produces low volume dense bread
Pre soaking brann and finely grinding and adding shortening help overcome this effect on gluten
Vital wheat gluten and conditioners can help as well
What are bagels?
Proofed, shaped, boiled and baked
Dense, chewy, tough
Boiling expands due to increased gas production and sets outer crust (partial gelatinization)
Baking browns the bagel
What is staling?
Crust toughening
- water migration rom crumb to crust
- starch responsible for staling
What happens when crumb firms?
Amylopectin retrogradation: starch molecules bind together in an ordered structure after gelatinization
Monoglycerides form a complex with amylose decreasing retrogradation and softening the crumb
Interaction with starch and gluten could be the cause of staling
What prevents staling?
Fat
Emulsifiers
Amylase
Can you reverse staling?
Yes, can toast or freeze
-fridge promotes staling
How do you know when bread has spoiled?
Rope bacteria, their spores aren killed in baking
- will have overripe melon odor
- ropey inside
Why does bread spoil?
Moisture and Temperature
How can you prevent spoilage?
Calcium propionate as ate-molding additive
Calcium or sodium proionate
Acidify dough with vinegar or buttermilk
