Bread

Fermentation

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CONTENT
HISTORY OF BREAD Milestones in the history of bread

BREAD MANUFACTURING Worldwide per capita bread consumption

INGREDIENTS Raw Materials

BREAD PROCESSING Main steps of bread making

QUALITY CONTROL Bread quality

BAKING GLOSSARY Bread from A to Z

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BREAD FERMENTATION

• The purpose of fermentation during bread manufacturing

is converting the grain or wheat into a more functional
and consumable form.

• In contrast to dairy, meat, vegetable, or wine

fermentations, where the starting material is much more
perishable than the finished product, the raw material for
bread-making, i.e., cereal grains, are better preserved than
the bread that is ultimately produced.

• In bread fermentation, essentially none of the primary

fermentation end products actually remain in the food
product.

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FROM WHOLE GRAIN GRUEL TO MODERN WONDER

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BREAD MANUFACTURING

• Worldwide per capita bread consumption

(kg per person per year).

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Wheat Chemistry and Milling

• The most common starting material for most breads is wheat

flour.
• Breads are also commonly made from a wide variety of other
cereal grains, including rye, barley, oats, corn, sorghum, and
millet.
• Wheat kernel consists of three main constituents: the germ,
bran, and endosperm.
• The germ portion contains the embryonic plant, along with
oils, vitamins, and other nutrients. It represents 2% to 3% of
the total kernel weight.
• The bran portion, or coat, represents 12% to 13% of the kernel,
and is comprised of multiple distinct layers. The bran
contains mostly cellulose and other fibrous carbohydrates,
along with proteins, minerals, and vitamins.
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Wheat Chemistry and Milling

• The remaining portion,

about 85%, is called the
endosperm and is the
main constituent of
wheat flour. It consists
of mostly protein and
starch, along with some
water (12% to 14%) and
a small amount of lipid
(1%).

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Principles of Milling Wheat

Principles of Milling Wheat

• The object of wheat milling is to extract the flour from the wheat kernel.
• When the wheat has the appropriate composition and quality and is free of debris
and impurities, the wheat is ready for milling. Although the whole wheat flours
produced by a single-pass grinding step have wide appeal, most breads are made
using flours that contain reduced levels (or even none) of the germ and bran. It is
the job of the wheat miller to separate these wheat constituents from the main
component, the endosperm.
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Principles of Milling Wheat and Composition
Protein
• The yield is given as the extraction About 8% to 15% of wheat flour is protein. This wide
rate, and is expressed as the range reflects the various types or classes of wheat used
amount of flour that is obtained as a source of the flour
from the wheat. In general,
extraction rates of about 72% are
achieved, meaning that 72 Kg of
straight flour can be obtained from
100 Kg of wheat.
• The balance (about 28%) includes Carbohydrates
mainly bran and germ. However, Carbohydrates represent the main fraction of flour,
since 85% of the wheat is accounting for up to 75% of the total weight. This fraction
is largely comprised of starch, although other
endosperm, some of the remaining carbohydrates are also present, including a small amount
material consists of endosperm (about 1%) of simple sugars, cellulose, and fiber
that adheres to the bran layers.
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THE CHEMISTRY OF BREAD-MAKING 10
Bread-making flour must contain wheat protein of the required quantity and quality for the desired
product. Water hydrates the flour proteins, which are partially absorbed by the starch and form a
water phase in the dough, where soluble solids such as sugars, salt, and proteins are dissolved, and
yeast cells are dispersed.

The major role of yeast is leavening or aeration of the dough mass by anaerobic fermentation. The rate of
CO2 production depends on the fermentation activity, concentration, and composition of dough ingredients,
as well as on environmental factors (temperature, pH, etc.). The yeast also helps bring about essential
changes in the gluten structure, which has been developed (or has matured correctly) to allow it to retain
the gas produced.

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INGREDIENTS

In addition to Basic constiutents

• Yeast Cultures (Baker's yeast)
• Wheat Flour
• Water
• Salt
Added Ingredients
• Sugars
• Enzymes
• Fats
• Yeast nutrients
• Vitamins
• Dough improvers
• Biological preservatives
• Emulsifiers
• Gluten 12
 Yeast Cultures (Baker's yeast)
• The yeast used for bread manufacture
is Saccharomyces cerevisiae, often
referred to as simply bakers’ yeast.
Baker’s yeast is available in several
forms: yeast cakes, bulk yeast, yeast
cream, active dry baker’s yeast, and
instant active dry yeast.
• Bread strains are selected, in part, on
their ability to produce CO2, or their
gassing rate. It is the CO2,evolved • Selecting suitable yeast strains is
during fermentation, that is important to produce good bread
responsible for leavening. flavor and stability and viability of
• yeast fermentation contributes greatly cells during storage.
to the flavor of bread through the
production of complex microbial
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metabolites.
INDUSTRIAL PRODUCTION
OF BAKERS’ YEAST • The growth medium usually consists of
molasses or another inexpensive source
of sugar and various ammonium salts
(e.g., ammonium hydroxide, as a cheap
source of nitrogen).
• The yeast propagation step is performed
at optimum temperature and under pH
control (usually around 30°C and at a
pH of 4.0 to 5.0), with nutrients
provided on a continuous basis.
• At the end of the growth fermentation,
the yeast is collected by centrifugation,
resulting in a yeast “cream” that
contains about 20% total yeast solids
and a yeast concentration of about 1010
cells/g.
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Wheat Flour, Water and Salt

• Wheat flour is the main ingredient of bread,

representing about 60% to 70% of a typical
formulation. The flour contains the proteins
that are essential for dough formation and the
starch that absorbs water and serves as an
energy source for the yeasts.
• Water, added at about 30% to 40%, acts as the
solvent necessary to hydrate the flour and
other ingredients.
• Salt, at 1% to 2%, toughens the gluten, slows
dough fermentation, and gives a desirable
flavor to bread, makes dough more elastic.
• Finally, the yeast, also added at about 1% to
2%, provides the means by which leavening
and flavor formation occur. 15
INGREDIENTS
Sugars
• Sucrose or glucose (about 2% to 3%) as an additional source of
readily fermentable sugars. They also supply flavor and, when the
dough is baked, color. The Maillard reaction between reducing
sugars and the dough proteins also creates flavor products in the
crust. Wheat flour contains only modest amounts of maltose and
glucose, and although yeasts do express amylases that can release
fermentable sugars from starch, sugar availability may still be
growth-limiting.
Enzymes
• To increase the amount of free sugars in the dough, a- and b-
amylases can be added. These enzymes hydrolyze the a-1,4
glucosidic bonds of amylose and amylopectin. Flour naturally
contains both of these enzymes, but a-amylase, in particular, is
present at very low levels. These enzymes are also available in the
form of microbial preparations or in the form of malt. 16
INGREDIENTS
Fat
• The addition of 0.1% to 0.2% fat, as either a shortening or
oil, is now commonplace in most commercial breads.
Weakens gluten network, gives softer bread, stabilize gas
bubbles, increase loaf volume

Yeast nutrients
• Various nutrients can be added to the dough mixture to
enhance growth of the yeast, including ammonium sulfate,
ammonium chloride, and ammonium phosphate, all added
as sources of nitrogen.

Vitamins
• Flour currently is fortified with four B vitamins—thiamine, riboflavin, niacin, and
folic acid—and one mineral, iron. However, non-enriched flour is also available and
bread manufacturers can enrich bread by adding these nutrients directly to the
dough. 17
BREAD MANUFACTURING
PRINCIPLES

In general, bread manufacture

involves few steps.
• First the ingredients are assembled,
weighed, and mixed to make a
dough and the “bulk” dough is
allowed to ferment.
• The fermented dough is then
portioned and shaped, given a
second opportunity to ferment, and
• then baked, cooled, sliced, and
packaged.

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Bread Manufacturing Principles

Hydration and Mixing

• Once all of the ingredients are combined, they are vigorously mixed. This is a
very important step because the flour particles and starch granules are hard and
dense and water penetrates slowly.
• Mixing is the primary driving force for the water molecules to diffuse into the
wheat particles.
• Mixing also acts to distribute the yeast cells, yeast nutrients, salt, air, and other
ingredients throughout the dough. Mixing is necessary to develop the dough.
• Mixing allows the development of a protein (gluten) network to give the best
bread possible.
• too much mixing produces a dough that is very extensible with reduced elastic properties,
undermixing may cause small unmixed patches which will remain unrisen in the bread
giving a final loaf with a poor appearance inside.
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Bread Manufacturing Principles

Fermentation
• Yeast growth is initiated as soon as the
dough is adequately mixed. A lag phase
usually occurs, the duration of which
depends on the form of the yeast and the
availability of fermentable sugars.
Bakers’ yeast (S. cerevisiae) has a
facultative metabolism, meaning that it
can use glucose by either aerobic (i.e., via
the tricarboxylic acid or TCA cycle) or
anaerobic pathways

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Bread Manufacturing Principles
• As fermentation takes place the dough slowly changes from a rough dense mass lacking
extensibility and with poor gas holding properties, into a smooth, extensible dough with good gas
holding properties.
• The yeast cells grow, the gluten protein pieces stick together to form networks, and alcohol and
carbon dioxide are formed from the breakdown of carbohydrates (starch, sugars)
 Yeast uses sugars to produce carbon dioxide and water aerobically, and it needs lots of oxygen
in order to complete this type of fermentation.
 In a bread dough, oxygen supply is limited and the yeast can only achieve partial fermentation
and instead of carbon dioxide and water being given off, carbon dioxide and alcohol are
produced. This is called alcoholic fermentation.
• The carbon dioxide produced in these reactions causes the dough to rise (ferment or prove), and the
alcohol produced mostly evaporates from the dough during the baking process.
• During fermentation, each yeast cell forms a centre around which carbon dioxide bubbles form.
Thousands of tiny bubbles, each surrounded by a thin film of gluten form cells inside the dough
piece. The increase in dough size occurs as these cells fill with gas.

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Bread Manufacturing Principles

Kneading
• Kneading involves stretching and folding the dough in a rhythmical manner that
develops the gluten in the flour and releases excess gas.
• Any large gas holes that may have formed during rising are released by kneading
and so a more even distribution of both gas bubbles and temperature also results.
• The dough is then allowed to rise again and then kneaded again dependent on the
end product requirements.

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Bread Manufacturing Principles
Dividing, Rounding, and Panning
• Dividing is usually a simple process that involves cutting
extruded dough at set time intervals, such that each piece has
very near the same weight.
• The divided dough is then conveyed to a rounding station, where
ball-shaped pieces are formed. At this point the dough is given a
short (less than twenty minutes) opportunity to recover from the
physical strains and stresses caused by being cut, compressed,
and bounced about.
• A portion of the gas is also lost during the dividing and rounding
steps. However, the dough have a chance to rest and the
fermentation continues, adding a bit more gas into the dough.

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 Bread Manufacturing Principles

Proofing
• During the final proofing step, the dough is re-gassed and the fermentation is completed. For
some bread production systems the entire fermentation takes place during the proofing step.
• Proofing is usually done in cabinets or rooms between 35°C and 42°C, giving dough
temperatures near the optimum for S. cerevisiae (35°C to 38°C). Proofing rooms are also
maintained at high relative humidity (>85%).

large gas holes lined with gluten with smaller holes and After two hours rising gluten strands form a lattice as the
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ingredients in between these. dough reaches the required size.
 Bread Manufacturing Principles

Baking
• Into the oven; a glutenous, sticky,
spongy mass, with a pronounced
yeasty aroma and inedible character,
Out comes; an airy, open-textured
material, with a unique aroma and
complex flavor.

• The temperature with these ovens is not constant, but rather increases in several
stages along the route, starting at about 200°C for six to eight minutes, and then
increasing to about 240°C for the next twelve to fourteen minutes. Finally, the
temperature is reduced slightly to about 220°C to 235°C for the remaining four to
eight minutes. 25
Bread Manufacturing Principles
The baking process transforms an unpalatable dough into a light, readily digestible, porous flavourful product.

• Ovenspring;As the intense oven heat penetrates the dough the gases inside the dough expand, rapidly increasing
the size of the dough.
 Gas + heat = increased volume or increased pressure.
 A considerable proportion of the carbon dioxide produced by the yeast is present in solution in the dough. As
the dough temperature rises to about 40°C, carbon dioxide held in solution turns into a gas, and moves into
existing gas cells. This expands these cells and overall the solubility of the gases is reduced.

• The oven heat evaporates the alcohol produced.

• Heat also has an effect on the rate of yeast activity. As the temperature rises the rate of fermentation increases, and
so does the production of gas cells, until the dough reaches the temperature at which yeast dies (approximately
46°C).
• From about 60°C, stabilisation of the crumb begins. Starch granules swell at about 60°C, and in the presence of
water released from the gluten, the outer wall of the starch granule bursts and the starch inside forms a thick gel-like
paste, that helps form the structure of the dough.

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Bread Manufacturing Principles
• From 74°C upwards the gluten strands surrounding the individual gas cells are transformed into the semi-rigid
structure commonly associated with bread crumb strength.

• The natural enzymes present in the dough die at different temperatures during baking. Alpha-amylase keeps on
performing its job until the dough reaches about 75°C.

• After dying of yeast at around 46°C, extra sugars produced by enzymes are available to sweeten the breadcrumb
and produce the attractive brown crust colour (between 46-75°C)

• As baking continues, the internal loaf temperature increases to reach approximately 98°C. The loaf is not
completely baked until this internal temperature is reached. Weight is lost by evaporation of moisture and alcohol
from the crust and interior of the loaf. Steam is produced because the loaf surface reaches 100°C+. As the moisture
is driven off, the crust heats up and eventually reaches the same temperature as the oven.

• Sugars and products formed by breakdown of some of the proteins, blend to form the attractive colour of the crust
by “browning” reactions, and occur at a very fast rate above 160°C. They are the principal causes of the crust colour
formation.

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Cooling is an important part of bread making, since proper cooling is necessary before slicing and packaging to
prevent deformed loaves and undesirable moisture condensation inside the package.

The general consensus on optimum bread cooling is that the interior crumb temperature should be reduced to
35–40 ∘C in as short a time as possible without excessive moisture loss. Bread cooling is normally maintained to
the legal limit of 38% moisture.

Among the three cooling methods practiced commercially (convection, conditioned air, and vacuum) convection
cooling, which is the simplest method, is by far the most prevalent. Though this system does not provide
accurate control of moisture loss by the cooling loaf, some adjustments can be made to regulate the overall
cooling.

In conditioned air cooling, the product is exposed to conditioned air that is maintained at dry-bulb and wet-bulb
temperatures that will produce effective loaf cooling within 90 min. Recommended cooling conditions include air
temperatures (22–25.5 ∘C), humidity (85%), and air velocity to bring a temperature rise (8–11 ∘C) in the air at the
exhaust point. In this system, both temperature and humidity of the cooling medium are held constant, and thus
the rate of moisture loss from the cooling loaf is predetermined at the start of the cooling cycle.

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The vacuum cooling method involves the application of vacuum to the bread, greatly accelerating
the vaporization of free moisture from the product, and loss of the latent heat of vaporization. This
series of events has a rapid cooling effect on the product. This method of cooling is particularly
good for products that are very unstable and prone to collapse before they have cooled, but it finds
very limited application at present.

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MAJOR BREAD MANUFACTURING PROCESSES

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MAJOR BREAD MANUFACTURING PROCESSES

Straight dough process

• The homemade, one-batch-at-a-time method described above is generally referred to as the
straight method or straight dough process. Basically, the overall procedure involves mixing all of
the ingredients and then allowing the dough to ferment for several hours (with intermittent
punching down).
• The developed dough is then divided, formed into round balls, given a brief (intermediate)
proof, shaped into loaves, and placed in baking pans. Finally, after a final fermentation or proof,
the bread is baked.
• The straight dough method is little used by the baking industry, the exceptions being mostly
small or specialty bakeries.
• The process results in a bread that is chewy, with a coarse cell structure and a moderate flavor.
Although the quality of these breads is quite good, the limitation of this process is that it lacks
flexibility and is sensitive to time. In other words, when the fermentation is sufficiently complete,
the dough must soon be baked. Otherwise, if fermentation is prolonged, the bread will be yeasty,
excess air cells will be formed, and the structure will be weak.
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MAJOR BREAD MANUFACTURING PROCESSES Sponge-and-dough process
• The most commonly used method in the bread industry is the sponge-and-dough process. The
basic principle of this process relies on the use of a “sponge,” a partially concentrated portion of
a flour-water dough that is allowed to ferment and then is mixed with the remaining dough
ingredients.

• The main advantage of this method is that it is tolerant to time. In other words, once the sponge
is developed, it does not have to be used immediately, but rather can be used over a period of
time. Also, bread made by this method has a fine cell structure and well developed flavor.
• The process involves making a sponge that consists of part of the flour (60% to 70%), part of the
water (40%), and all of the yeast and yeast nutrients.
• The sponge is mixed and allowed to ferment for three to six hours at 16°C to 18°C (80°F).The
remaining ingredients are then added and mixed, and the dough is allowed to develop.

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MAJOR BREAD MANUFACTURING PROCESSES
Liquid sponge process
• One of the best examples of the quick type of process is the
continuous bread-making procedure, sometimes called the
liquid sponge process.
• The continuous mixing process involves the use of a pre-
ferment in the dough mix. The method saved time and labor
and was very economical.

• Instead of making a thick sponge (i.e., mostly flour), a thin, liquid

sponge (mostly water) is made. This mixture of water, yeast, and a
very small portion of the flour is allowed to ferment in a tank to
form a liquid “preferment.”

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MAJOR BREAD MANUFACTURING PROCESSES
Chorleywood process
This is a no-time process in which rapid mixing
is a critical feature. It has been applied to the
Chorleywood bread process in the United
Kingdom. Thus, the start to finish process takes
only two hours.
The primary purpose of the method is to circumvent
the lengthy bulk fermentation stage by imparting to
the dough the desired physical character.

The so-called no-time dough processes either involve ultra speed dough mixing or rely on chemical
dough development using reducing and oxidizing chemical agents such as ascorbic acid. They are not
subject to bulk fermentation and have been made inroads commerciallly.

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Bread Spoilage and Preservation

• Despite the fact that bread has a moderately low

water activity and pH and contains few
microorganisms when it leaves the oven, it is still,
relative to other fermented foods, a highly
perishable product. This is because the shelf-life of
bread depends not only on microbial activities, but
also on physical-chemical changes in the bread.
Specifically, it is the phenomenon called staling
that most frequently causes consumers to reject
bread products.

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Bread Spoilage and Preservation
Staling
• Staling is a complicated phenomenon. It refers to the increase
in crumb firmness that makes the bread undesirable to
consumers. In addition, staling is associated with an increase
in crust softness and a decrease in fresh bread flavor. The
reactions of staling start when the bread is baked, as starch
granules in the dough begin to adsorb water, gelatinize, and
swell. The amylose and amylopectin chains separate from
one another and become more soluble and less ordered.
Then, when the bread is cooled, amylose, in particular,
slowly begin to re-associate and re-crystallize. This process,
called retrogradation, results in an increase in firmness due to
the rigid structures that form.

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Losses resulting from bread staling are of great economic importance, and thus practical efforts to retard the
process have centered mainly on the modifications of the method of bread production

the use of antistaling agents and moisture-retaining substances in the dough formulation (emulsifiers and
amylases)

The growth of retail baking in supermarkets using the no-time dough processes

use of commercially available frozen unbaked products by in-store bakeries

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Bread Spoilage and Preservation

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Bread Spoilage and
Preservation

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Bread Spoilage and Preservation
Biological spoilage
• Microbiological spoilage of bread is most often associated with fungi, and occurs when fungal
mycelia are visible to the consumer. Some strains of Bacillus subtilis, Bacillus mesentericus, and Bacillus
licheniformis can spoil high moisture breads via production of an extracellular capsule material that
gives the infected bread a mucoid or ropy texture.

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Bread Spoilage and Preservation

Preservation
• The post-production environment (i.e., baked products) should be separated
from preproduction environments. Air handling systems should be
designed (including the use of filters or ultraviolet lamps and positive air
pressure) such that airborne mold spores cannot gain entry to the product
side.
• Bread can be exposed to ultraviolet, infrared, or microwave radiation to
inactivate mold and mold spores or packaged in modified or vacuum
atmospheres to inhibit their growth.
• Another indirect way to extend the shelf-life of bread is via freezing. Many
bread manufacturers freeze the baked and packaged breads as a means of
preserving the bread prior to delivery. Another freezing method that has
been adopted is to freeze un-baked breads.
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Bread Quality

• The criteria commonly used to assess

bread quality are based primarily on
appearance, texture, and flavor
attributes. Appearance refers both to
external (i.e., crust), as well as internal
appearance (i.e., crumb). Depending
on the type of bread, the intact loaf
should have a particular volume, or in
some cases, height and length. The
color of the crust also is an important
property, and is judged mainly on the
basis of the expected color established
by the manufacturer.

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Baking Glossary

• Crumb: The soft inner portion of bread also referring to the pattern of holes inside.
• Elasticity: The property of dough to retract to its initial position after being stretched.
• Folding: One of the best ways of encouraging gluten development in slack doughs. Folding the dough
consists of taking a wet dough out of the bowl, spreading it out a little on a clean, well-floured surface,
folding it in thirds like a letter, rotating it 90 degrees and folding it up again, picking it up and dusting
the loose flour off of it, and then returning the dough to the bowl and covering it again. Like punching
down, folding degases the dough some, but it also encourages gluten development.
• Gluten: “A strong elastic protein of wheat flour that gives cohesiveness to dough.” Gluten is what allows
bread dough to develop those long, beautiful strands and create large open pockets of air (think about
the inside of Ciabatta). Bread flours tend to be made from hard wheats that are higher in protein than
regular flour, providing more gluten.
• Proof or Proofing: (1) The final rise of the shaped loaves before baking (2) the hydration of dry active
yeast in water before it is added to the dough. Also called secondary fermentation or final fermentation.
• Sourdough: A preferment that is a culture of wild yeast and bacteria that is perpetuated by the periodic
addition of flour and water, or a bread leavened in whole or part by this culture.
• Sponge: Also known as a “preferment,” a sponge is a portion of the ingredients that is mixed ahead of
time, typically overnight. Using a sponge extends the fermentation process longer and generally releases
more complex flavors in your loaf. It can also be used to soften dry ingredients (such as whole grains)
and release sugars from the grains.
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Types of Products

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