Case Study BAKERY
The science of
SLICED
BREAD
Sliced bread is an everyday product familiar to
most homes throughout the UK; over 4 million
units of bread are baked every day throughout
the country.
The role and functionality
of ingredients in sliced
bread
Despite having many
culinary uses, bread is
often taken for granted.
However, sliced bread
production has evolved
over time and is constantly
being reviewed and
challenged by the baking
industry to deliver
improvements in eating
quality and flavour. When
deciding on the attributes
of a finished sliced loaf the
baker and manufacturer
consider a number
of factors.
This case study explains the
role of the ingredients and
the manufacturing process
used in order to deliver
the desired bread structure,
flavour, colour and texture.
Flour
The bakery will set its protein
quantity and quality target for the
flour miller and will typically be
looking for a specification which is
high in protein (around 10.5%-13%),
as this is most likely to perform
well during mixing stage of the
Chorleywood Bread Process.
Quantities of flour enzymes are
monitored as too much naturally
occurring amylase will give the
sliced loaf sticky slices and
excessive volume.
The bakery is also interested in the
damaged starch levels. Damaged
starch naturally occurs during the
milling process and is caused when
part of grain becomes cracked or
damaged; this will directly influence
water absorption properties of
the flour. Each loaf of bread flour
delivered to the bakery will arrive
with a specification to identify levels
of protein, damaged starch and
water absorption.
Water
Water added to the dough during
mixing is directly related to the
water absorption rate of the flour.
Water absorption levels can be
variable dependent on the time
of day, the age of the flour and
storage conditions.
The main role of water is to hydrate
the dry ingredients to allow dough
to be developed in the mixer. The
dough temperature can be controlled
by the water temperature; if dough
temperature increases the water
temperature can be reduced to
compensate.
Yeast
The function of yeast in bread
making is to:
produce carbon dioxide gas to
enable the dough to rise;
form the cellular network found
in bread crumb;
give bread its characteristic aroma.
The yeast also helps develop lactic
and acetic acid which deliver both
aroma and flavour to the final
baked loaf.
Salt
Salt is an important ingredient,
not only for its flavour but for its
action as a regulator of the growth
of the yeast. Salt retards the action
of the yeast, slowing the process
and preventing the dough from
over fermenting or developing a
sour taste if slow rising. Salt also
helps the retention of moisture
in the dough, but too much
makes the crust very hard.
Ascorbic acid
Ascorbic acid is used to strengthen
the dough and help it rise. It has
a beneficial effect on the volume,
Case Study BAKERY
crumb structure and softness of the
bread. Without this ingredient the
bread can collapse and be dense
in structure.
Fat
Fat is used in production to
improve the overall eating quality
and texture keeping the bread soft.
Fat lubricates the flour proteins
during mixing allowing the dough
to pass more easily through the
production process.
Enzymes
Enzymes are naturally occurring
proteins. The main types used in
bakery are protease, amylase and
lipase obtained from flour and
yeast sources. Enzymes have played
a significant role in production of
bread over the last 20 years, they
are actively functional in the
production process but are not
present in the final baked product.
Enzymes work on flour lipids and
starch to enhance the texture and
volume to the bread; however the
most significant benefit is the
delivery of additional softness and
reduction in staling.
Emulsifiers
These are typically used in sliced
bread to provide strength to the
dough and volume to the finished
product. Emulsifiers also help to
deliver improved texture, softness
and reduced staling. Emulsifiers are
normally labelled with an E-number,
unless they are soya lecithin based.
They also function within the
production process however,
unlike enzymes, are present in the
final baked goods and therefore
are declared on the label.
Mould inhibitors
These are added to control the
growth of mould over the given life
of the bread. Calcium propionate is
commonly used, however, other
mould inhibitors can be used. The
challenges of food storage requires
the use of mould inhibitors for some
types of sliced breads as it supports
the growth of many types of mould
given the pH is around 5.5 and the
available water in the product is
above 0.93.
The average bakery
production line would
use 24,000kg of flour
The process explained
1. Mixing
Mixing is the most important part
of the bread making process; if this
stage goes wrong then no matter
how accurate and controlled the
rest of the process, the final product
will be affected.
The Chorleywood Bread Process
(CBP) is the most common way
to mix dough. This process was
developed in the UK in the 1960s
and is still widely used to make sliced
sandwich bread. The essential feature
of the CBP is that it delivers a fixed
amount of energy (for kneading) in
a short space of time, usually 2-5
minutes. The required energy will
vary according to the properties
of the flour being used.
The main purpose of mixing is
to input energy into the dough
mechanically (i.e. kneading the
dough), rather than by hand. This
fast mixing process develops the
protein in the flour to produce a
gluten network which forms the
structure of the bread.
Firstly, all ingredients are placed
in the mixer. The average bakery
production line would use 24,000kg
of flour, 14,160kg of water, 1,200kg
of yeast, 360kg of improver, 450kg
of salt, 240kg of fat every single
day of production.
Flour, yeast and water are
automatically delivered to the
mixer before the kneading process
commences. This hydrates the flour
and other ingredients and produces
dough of a correct consistency
for the next stage. The dough is
mechanically mixed at high speed
for 2-5 minutes.
Dough temperature should be
between 26-31C once mixing has
finished, allowing the yeast to work
efficiently. If the temperature is too
low the yeast will not be able to
produce a sufficient amount of
carbon dioxide gas, resulting in a
loaf with a very low volume. However,
if the temperature is too high the
yeast will start to produce gas too
early resulting in a loaf which is over
the desired volume.
Storage of Ingredients
Flour is kept in a silo adjacent to the bakery which is filled via an automatic
tanker delivering around 24,000kg a day.
Fresh yeast is kept in chilled tanks and is piped through an automatic
dosage system directly into the mixer.
The rest of the ingredients are pre weighed in large covered storage tubs
after they arrive on site in 1,000kg bags. The fat arrives in boxes and is cut
and weighed into a separate tub; it is then transferred to the bakery line
and added manually to the mixer.
Case Study BAKERY
Dough piece
folded at entry (time
slowed down 5 fold).
Bread divider and
moulder
Typical rounder
Shearing on entry
(time slowed down
3.3 fold).
2. Moulding and Dividing
Once the dough is mixed it is then
tipped into a large hopper on a
divider. The dough is divided into
equal amounts and moulded into a
ball shape. The weight of the pieces
is strictly controlled to comply with
legislation. For example, a sandwich
loaf must weight 800g.
3. Proofing
The dough is then transferred into a
prover with a temperature of around
38C and a relative humidity of
85%. The correct temperature and
humidity provide the yeast with the
right environment for it to produce
carbon dioxide. Yeast is most active
between 35-40C.
The dough pieces prove for the first
time on a conveyor for around 8
minutes. The first proofing process
allows the dough to relax preventing
it from springing back to its original
shape. This allows further moulding
and shaping to take place.
The carbon dioxide expands
the dough; the gluten network
developed during mixing retains the
gas in the dough structure enabling
the dough to rise in the sandwich tin.
The dough spends around 45-50
minutes in the prover and rises to
within 2-3 cm of the top of the
sandwich tin. The sandwich tin
is then lidded before it reaches
the oven.
After proofing the dough piece is
then sheeted (shaped into a flat
piece of dough) by forcing the dough
through rollers and over a drum.
The sheet of dough then travels on a
mechanical belt under a pressurised
plate, this is called the moulder.
The moulder rolls the sheeted dough
into a Swiss roll shape. Finally, as the
dough exits the moulder, the dough
piece travels between two rollers
before being cut into four almost
identical pieces and then dropped
into baking sandwich tins.
It is important that the dough has
been extended and developed so
that the protein structure is flexible
and can withstand the moulding and
dividing process. Damage to the final
product can take place at this stage;
this may include crust damage,
holes in the bread and poor colour
and texture.
The transition from the prover to
oven is a critical stage in the bread
making process. The young loaf
needs to be protected from damage
during this phase; the slightest
impact can destroy the fragile
structure.
4. Baking
Crumb structure, yeast activity,
starch gelatinisation, enzyme
activity, baked core temperature,
crust formation and crust crispness
are all key factors of the baking cycle.
The ovens have a series of chambers
set at different temperatures, and
typically fit 800 sandwich loaves.
Baking takes around 23 minutes at
temperatures exceeding 250C.
Creasing on exit
(time slowed down
5 fold).
Torn dough base
on exit (time slowed
down 3.3 fold).
Case Study BAKERY
between 60-75C, but will be
destroyed at 85C. At this stage the
loaf crust formation will almost be
complete. The bread exits the
oven with a core temperature
of 90 - 95C.
In the first chamber of the oven the
dough continues to expand as the
yeast produces more carbon dioxide,
as a result the bread becomes square
in the pan. Yeast is inactive by the
time the core temperature of the
dough reaches 55C, but the stability
of the dough structure is maintained
because the trapped gases expand
as they warm.
Wheat starch in the flour starts to
gelatinise at 60C. This gelatinised
starch eventually becomes selfsupporting and is not reliant on
the protein (gluten) developed at
the mixer stage.
Enzymes naturally present in the
flour (and sometimes added to the
ingredients) act on the lipids present
in the flour and on the starch chains,
converting starch to dextrin. This
improves and stabilises the bread
structure. During baking these
enzymes will be most effective
First leaf
emerges
Young
wheat
5. Cooling
On exit from the oven the 800g
sandwich loaves are removed from
the baking pan within 20 seconds
and are then sent through an
automatic cooler.
This takes around 2 hours 30
minutes; the bread loses weight due
to the loss of moisture during this
process. Typically a loaf of bread
can lose around 45g in weight from
leaving the oven to exiting the cooler.
The target temperature on exit from
the cooler is around 25C, if it is
too high it can cause problems with
automatic slicing and also impact on
the shelf life (if the bread is too warm
when it is packed bacteria and mould
will grow at a quicker rate). Shorter
more aggressive cooling times and
temperatures can increase weight
loss and result in bread which does
not meet legislation.
machines. These slicer units contain
high tension blades to slice through
one loaf every 1.5 seconds. The
number of slices can vary dependant
on the brand and the slice thickness
desired. The bread is then
immediately presented to the
automated bread bag unit. The bread
is automatically pushed through into
a pre-opened plastic bag and then
sealed with a bread tag which
carries the best before date and
production details. The bread is the
automatically picked and placed
within a bread basket ready to be
dispatched. The bread will normally
be on the shelf for the customer
within 24 hours of leaving the oven.
Marks and Spencer plc 2012
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6. Slicing and wrapping
After cooling the bread is transferred
on a conveyor to automatic slicing
Wheat
starting to turn
Close up
ripe wheat
Harvested
wheat
