Lab 7 Flashcards
Yeast acts as a ___ in bread by producing what?
A leavening agent, producing zymase
What does zymase do?
An enzyme that converts glucose and fructose into CO2, alcohol and other flavour components.
How does CO2 leaven dough?
By producing a light, airy product.
What else does yeast do?
Produces a number of other chemicals which that contribute to the unique flavour of dough and brings about changes in the structure of gluten.
Name the 3 kinds of yeast
Active dry
Instant (rapid rise/bread machine)
Compressed
When was active dry yeast invented?
in WWII, used by the armed forces.
How is the activity of dry yeast decreased? How can this be prevented?
Decreased when exposed to oxygen, heat and humidity. Therefore should be refrigerated and stored in a closed container.
What is used when making sourdough bread?
sa sour starter
How can yeast be tested for viability?
If they dissolve in a small amount of water and sugar.
How must traditional dry yeast be used?
Must be rehydrated in a small amount of warm water (43-46 C) with sugar prior to use. Then, it is added directly to the dry ingredients.
The using traditional dry yeast, the presence of surface foam means that the yeast is ___
viable
What temperature will kill traditional dry yeast? What temperature will cause leeching for glutathione?
kill yeast: >60 C
leaching of glutathione: >38 C
Why is the presence of glutathione not desirable?
Limits gluten development
What is instant yeast?
Newer, more soluble form of yeast that does not have to be rehydrated, and added directly to the dry ingredients
What temperature can instant yeast withstand?
As high as 50C since the flour mixture will absorb heat, and cool the overall mixture.
What is instant yeast used in? When is it added?
Bread machines, and added on top of flour to protect it from the liquid heating at the bottom of the pan
What is compressed yeast?
Must be softened for a short period of time in warm water (27-30C) prior to mixing in with the dry ingredients.
What is a sourdough starter?
a mixture that was used in making bread prior to the reliable availability of yeast.
What is a sourdough starter sometimes referred to?
A sponge
What is a sponge (sourdough starter)
A living culture of acid-tolerating yeast and lactobacillus bacteria in a symbiotic relationship, since they rely on different sugars,
How is the sponge made?
My mixing flour, water and yeast - then left to ferment at room temperature for a few days.
What kind of sugar does Lactobacillus use? What kind of acids does it ferment?
Uses saccharides in flour and produces lactic and acetic acids.
Whats the result of fermentation by Lactobacillus?
Low pH which is favourable for the yeast to produce CO2
Can the starter be reused?
Yes, the rest can be refrigerated and replenished with water and flour, while removing old water and flour to keep it indefinitely.
Why does sourdough bread have a more coarse texture?
because acidity (from the fermentation of the bacteria) breaks gluten strands.
What are the two major acids in sourdough bread?
Lactic Acid
Acetic Acid
What are the four minor acids in sourdough bread?
Propionic
Butyric
Isovaleric
Valeric
What is unique about sourdough bread?
Less gluten and longer shelf life
What is the fermentation of yeast dependent on?
Environmental temperature and food source.
What is the optimal temperature for yeast growth? The practical temperature at home?
Optimal: 30-35C
Practical: 27-30 C
At what temperature its fermentation slow?
below 24 C
At what temperature does the dough rise before it has a chance to mellow(soften)?
above 37C
which sugars are used by yeast in food?
Glucose
Fructose
Sucrose
Maltose
In the absence of sugar, glucose can be slowly ____ from ___ by the yeast
hydrolyzed from flour
What sugar can yeast NOT utilize?
Lactose (galactose)
What do sugars provide?
Flavour, tenderization, browning
What is a consequence of too much sugar being added?
Decrease gluten formation and will draw water away from yeast.
Name the 7 steps to bread making (HMF-PP-BO)
1) Hydrating + Solubilizing flour and yeast
2) Manipulating via stirring, beating, kneading
3) Fermentation
4) Punching down
5) Proofing
6) Baking
7) Oven spring
How can water and flour become hydrated and solubilized when making normal bread?
When water is initially added, a sticky mass forms.
How can water and flour become hydrated and solubilized when making sourdough bread?
The sponge method only adds PART of the flour, (less sticky, more liquid), and lets the liquid stand which improves final flavour and texture.
Name the 4 ways to manipulate bread
1) Hand
2) mixer
3) Food processor
4) Tiny blade in bread machine
What is important to keep in mind when manipulating bread?
Keep dough soft and and not add too much flour.
Upon manipulation, the dough becomes ___
stiffer and less sticky
What are the gluten proteins?
Glutenin and gliadin
What does the development of glutenin and gliadin do to dough?
Increase elasticity, allows dough to retain gas and water vapour during fermentation.
Gluten forming proteins absorb (more/less) water and form a better gluten network when (hot/cold)
- More
- cold
Why do some bakers add a small amount of crushed ice prior to kneading?
Since gluten network is better formed at cold temperature.
A mature or ripe dough has an optimal balance of what?
-Extensibility and resistance with maximum gas retaining capability
When should extra ingredients, such as nuts and raisins be added?
At end of kneaded so they do not interfere with gluten development
How can we tell when dough has been sufficiently kneaded? When can we tell that is has been under or over mixed?
Sufficient: When an indentation made with 2 fingers allows for doughs shape to retire (memory foam)
Over/Under mixed: Too extensible or resistant. and will produce coarse and compact beads.
Describe fermentation
yeast cells use available sugars for energy and produce CO2 and ethyl alcohol.
What happens to the properties of dough after fermentation?
Gluten becomes more elastic, and the acidity and volume increase (pH decrease)
What does the time for fermentation depend on?
type of flour
room temp
type of yeast
concentration of sugar and salt
Instant yeast results in a __
shorter fermentation time
What is the usual time range of fermentation? For instant yeast?
Usually 1-1.5 hours, but instant yeast needs only 10 minutes.
High temperatures create a __ dough thats is ___ and facilitates growth of ___ producing undesirable flavours
sticky
hard to handle
bacteria
Name some characteristics of under fermented dough
coarse
small
compact
paler in colour and sour odour
What is the pale colour and sour odour due to in under fermented dough?
Pale colour form depletion of sugar by yeast (some sugar is needed for maillard rxn)
Sour odour is form over production of lactic acid.
What is the ideal fermentation temp? How can we create this environment?
26-30C
A pan of hot water in the oven with the light on will produce this ideal environment.
How can we tell that the dough is properly fermented?
Indentation of two fingers to the dough should not retain its shape.
How can the fermented dough be punched down? why?
Gently push and fold dough after it as double will release gas and prevent hair holes form becoming too bug and forming an uneven grain.
What are the consequences to gluten during the punching down process?
Prevents gluten form over stretching and will re distribute the yeast nutrients and heat so yeast is now surrounded by a new food supply.
What is proofing?
Final shorter rising period after the dough has been shaped, the dough should double in size.
What does insufficient proofing cause?
Causes product to tear along its sides during the first few minutes of baking during oven spring.
Oven proofing creates bread with ___ and a ___ texture
Large holes
crumbly
How can we tell when proofing is complete?
When dough partially regains shape after pressed with fingers
Can bread dough be frozen? When? What happens to yeast?
Can be frozen BEFORE final rise (proofing stage). Some yeast may die, so adding a bit more will help. Frozen dough must be thawed for 3 hours before proofing.
During baking, how can we prevent steam from becoming trapped under the surface of the crust?
By slashing the top
How is french bread baked?
Oven is full of steam, and will form a softer crust.
Steam applied after baking evaporates (quickly/slowly) and causes the crust to be (drier/softer)
quickly
drier
Where should bread be baked in the oven? Why?
At a spot where the top of the bread is no higher than the centre of the oven.
What is the oven spring?
The considerable increase in volume that occurs during the first 10-12 minutes of baking.
What causes the oven spring?
rapid expansion of gases, evaporation of alcohol into gas and increased yeast fermentation, enzymatic activity and softening of gluten as the tempo rises.
Inadequate fermentation produces a ____
poor oven spring and a small loaf
Too much oven spring results in _____
unload with a flat top that ballots over the side of the pan and crumb with a “moth eaten” appearance.
What can too much oven spring be caused by?
Too low oven temp
insufficient salt
over fermentation
What happens when dough reaches 60C during baking?
Starch granules between gas bubbles begin to gelatinize, and the yeast is killed.
What happens to dough at temperatures > 60C?
-Enzyme activity CEASES due to denaturation and gluten proteins coagulate
How is the semi-rigid, self supporting structure of bread formed?
From the combination of coagulated gluten and partially gelatinized starch.
What are some indicators that the bread is done baking?
- Comes away from edge of pan
- Gold brown
- Sounds hollow
When bread is done, its internal temperature should read ___ on a thermometer, then __
93C
removed immediately from pan to cool
How can a soft crust be achieved?
By brushing butter/margarine on crust.
How should bread be stored? What happens to amylose?
Should be kept in the freezer or at room temperature. Amylose turns into a hard crystalline for at refrigerator temperature, and results in faster staling.
Describe the effects upon addition of barley/malt syrup to bread
Provide enzymes that help break down flour into food for yeast
What needs too be added after kneading to prevent damage to gluten strands?
Coarse grains and seeds.
Describe the effects upon addition of dried ground beans to bread. Given an example
Increase yeast growth, dough performance, flavour and nutritional quality.
i.e Chickpea flour
What provided minerals to increase yeast activity, protein, tenderization while enhancing crust colour AND acting as a buffer?
Milk
How does lactose provide sweetness to bread?
Since yeast cannot utilize lactose
Why is important to use milk as a buffer?
Prevents changes ina acidity that make damage the yeast
Why is scalding of milk important prior to adding to mixture?
heat will denature why proteins which reduce loaf volume
What ingredient contains propionic acid? What is it?
Grape juice, acts as a mold inhibitor.
Describe salts effect on gluten, what else does it do? What does it promote?
Tightening effect on gluten.
Slows yeast activity, contributes flavour, controls bacterial growth.
Sea salt will add more minerals which will promote gluten development.
Name two ways to add more minerals to dough to promote gluten development
Milk and sea salt
Which spices will increase yeast activity?
caraway cardamom cinnamon ginger mace nutmeg
What does cinnamon and cloven contain? What does this act as?
Contain aldehyde and eugenol, which acts as preservatives inhibiting mold growth.
What does dry mustard do?
Inhibits yeast activity
What does vitamin C do?
chances gluten development, can be added through a crushed tablet.
If __ is added to flour before liquid, it coats gluten forming proteins and (promotes/reduced) gluten formation, therefore (increasing/decreasing) the glutens gas holding ability
Fat
reduced
decreasing
What do eggs told do in dough?
Bind and emulsify, keeping fat and moisture together and softens and deceases staling.
Wha sugar us found in honey?
Fructose
Fructose is more ___ than ____ therefore retaining moisture in bread
hygroscopic (absorbs more moisture in air)
sucrose or glucose
Why is spend and sugar twin used in baking?
Less heat labile
What are some disadvantages of using artificial sweeteners in baking?
Texture may be dense
less tender
less brown / crispy
The product may be acceptable if only a ___ of the required sugar is replaced with an artificial sweetener
portion
Name some sugar substitutes approved for use as food additives in pre-packaged foods in Canada
- Acesulfame potassium
- Aspartame (Equal)
- Stevia
- Sucralose (Stevia)
Name some sugar alcohols
Sorbitol, isomalt, matitiol, mannitol and xylitol
Which AS is 200 x sweeter than sugar and can tolerate baking temperature?
Acesulfame-pottasium
Is acesulfame-pottasium carcinogenic?
No, or mutagenic.
In north america, acesulfame-pottasium is approved for use in ___
tabletop sweeteners chewing gum non dairy creamers puddings soft drinks
Which AS is 200 x sweeter than sugar, clean taste but cannot tolerate baking temperature (will loose sweetness)
Aspartame (equal)
Which AS the most widely used?
Aspartame
Which individuals should not consume aspartame? Why?
Those with PKU
Aspartame is a methyl ester of aspartate/phenylalanine dipeptide
Where is stevia from?
From the leaves of the stevia rebaudiana Bertoni plant
How many times sweeter is stevia than sugar?
300 x
Has any toxicity been reported from the use of stevia?
No
Which AS is the sweetest?
Splenda (Sucralose)
600 x sweeter
Does splenda break down with heat?
No, can be used in cooking and baking.
When splenda is consumed it is excreted ___
unchanged
the main advantage and disadvantage of artificial sweeteners is ____
ADV: few or no calories, put provide sweetness
DADV: limited in baking
What do AS not perform in baking?
Browning
Tenderizing
Leavening
How does browning occur upon addition of sucrose?
With heat and acid, sucrose breaks down to fructose and glucose to provide browning through the maillard reaction, providing colour and enhancing flavour.
How does tenderization occur upon addition of sucrose?
Sucrose combines with flour proteins to prevent gluten formation.
What can sugar substitute for a tenderizer?
fat
How can we make low fat baked goods?
Adding more sugar instead of fat (not actually healthier)
How does sugar leaven?
Helps incorporate fine air bubbles into the batter in the creaming step.
