Yeast breads
Food Guide Pyramid
Yeast bread outline
• Yeast
– Compressed
– Dry active
• Functions of other yeast bread ingredients
• Yeast bread cookery
• Spoilage of baked goods
– Microbial
– Staling
• Prevention and “unstaling”
Yeast
• A one celled microorganism
• Saccharomyces cerevisiae
– Compressed
• Moist, living cells
• Very perishable
– Dry active
• Dried to a granular form
• Very shelf stable
Compressed and dry active
Dry active
Compressed
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Basic yeast reactions
• Yeast + sugar
CO2 + alcohol
Yeast function depends on
• Food
– Needs a minimum of 1% sugar
• Home -- add sugar to yeast during initial
hydration
• Commercial -- alpha-amylase added to bread
flour. This releases D-glucose from starch to feed
the yeast.
– Note: Too much sugar will dehydrate the
yeast, causing it to stop working
Yeast function depends on
• Water
– Needed to hydrate yeast and start the fermentation
• Proper temperature
– Ideal fermentation temperature is 80-90oF
– If temperature is a little too high (~100oF), you will
get a sour dough, i.e., the bread rises too fast and too
much carbon dioxide and alcohol are produced
– Temps > 120-130oF kill the yeast
Yeast “wake-up” temperature
• This is different than the fermentation
temperature and applies only to active
dry yeast
• You need to “wake-up” this type of yeast
by hydration with warm water
• This should be done at 105-110oF
Yeast bread ingredient
functions
• Flour
– Bread flour is high in protein because you
want lots of gluten development
– Can also use all purpose or whole wheat
flour (partially)
– Whole wheat may limit loaf volume by
puncturing gas sacs in dough
Yeast bread ingredient
functions
• Liquid
– Water may be used, but more commonly
milk is the liquid in breads
• Note: Milk contains a protein that makes the
dough very sticky and hard to work. This
normally will limit loaf volume.
• To avoid this problem, scald the milk to denature
the protein
• But remember to cool the milk before combining
with the yeast or it will be killed
Specific functions of milk in
breads
• Hydration of protein and starches
• Dissolves sugars and salts
• Higher L-lysine content tends to offset
the low L-lysine content of wheat flour
• Improves texture and loaf volume and
delays staling
• Provides good crust browning
Yeast bread ingredient
functions
• Salt
– Flavor
– Also, and more importantly in this
application, salt moderates (slows) the action
of yeast and allows the yeast to produce
carbon dioxide at a more desirable rate
– This produces a fine textured bread with
small to medium air cell sizes
Yeast bread ingredient
functions
• Sugar
–
–
–
–
Yeast food
Flavor
Tenderizer
Maillard browning
• Fat
– Tenderizer
– Increases loaf volume
Yeast bread ingredient
functions
• Enzymes
– Fungal alpha-amylase is added to produce
D-glucose from wheat starch to feed the
yeast during fermentation
– These heat-stable amylases also have a role
in delaying bread staling
• Lightning Quiz
Ingredient combining
techniques
• Straight dough method
– Mix all ingredients together, let rise
• Sponge method
– Mix ingredients, reserving part of the flour
– Let rise to form a sponge
– Then add the rest of the flour
• These two methods produce breads with
somewhat different flavors and textures
Mixing techniques
• Kneading is done to develop gluten
• Can be done by
– Hand
– Mixer (Kitchen-Aid, Hobart)
Hand kneading
Kneading
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Heavy duty mixer
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Fermentation or proofing
• Let double in volume
Ideal proofing temperature is 80-90oF
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Fermentation or proofing
• Punch down
– Disadvantages
• Some loss of carbon dioxide
– Advantages
• Introduces oxygen needed for the next rise
• Makes shaping the loaf easier
• Redistributes carbon dioxide for the final rise
Punching down
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Scale and shape
• Scaling is the process of dividing the
dough into loaf size pieces
• Shape dough
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Fermentation or proofing
• Proof again to double in volume
• Bake
Bread baking
• The loaf rises more during baking
• This increase in volume is called oven
spring
• Oven spring is due to
– An increase in the volume of trapped carbon
dioxide during baking
– Before the yeast dies it produces carbon
dioxide very rapidly up to about 120-130oF
Oven spring
375-400oF
Baked bread
Raw dough
This increase in volume is known as oven spring.
Bread baking
• General rule
– The larger the loaf, the lower the baking
temperature
• Loaf
• Roll
375-400oF
400-425oF
– The reasoning here is the same as for the loaf
cake/cupcake case and involves balancing
the baked good cooking all the way through
and yet being nicely browned on the surface
Bread spoilage
• Mold
– A low moisture type of growth
– Commercially, mold inhibitors are added, i.e.,
calcium propionate
• Rope
– Caused by a fungus
– Observed as a yellow, sticky substance running
through the loaf
– Inhibitors will prevent this
Bread spoilage
• Staling
– A huge economic problem for the baking
industry
– In spite of intense study of this problem for
many, many years, we still don’t fully
understand the processes leading to the
changes observed as staling, or how to stop
them
Staling characteristics
• Staling is not just loss of water!
• Some minor changes occur in the gluten
fraction of bread
• There is a redistribution of water from
the crumb to the crust
• Starch retrogradation occurs
– Bread firming is due primarily to
retrogradation of amylopectin, not amylose
Staling retardants
•
•
•
•
•
Monoglycerides
Fat
Milk
Note that these are “rich” ingredients
Eggs
Sugar
Storage to prevent staling
• Best long term - freeze
• Short term - room temperature is OK
(however, mold growth may be more of a
problem for longer term storage at room
temperature)
• Don’t store at refrigerator temperatures!
• Lightning Quiz
Storage to prevent staling
refrigerator
Staling
rate
room temperature
freezer
Temperature
“Unstaling” of stale bread
• Warm (toast) the bread (60-70oC), serve warm,
and use immediately
• This unstaling reflects the reversibility of
amylopectin retrogradation
• The retrogradation of amylose is completed by
the time the loaf has cooled to room
temperature and is not reversible
• Thus, amylose could not be involved in the
temporary unstaling of bread by heating