bubble structure formation in bread and cakes · underdeveloped dough • dough lamination •...
TRANSCRIPT
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Bubble structure
formation in bread and
cakes
Martin WhitworthBritish Society of Baking Spring Meeting,
10th April 2019
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Bread and cake structure
• Bubbles are a key aspect of the
product structure.
• Important for:
– Product volume (~75-80% air)
– Softness
– Whiteness (diffuse scattering)
• Recipe, ingredient and process
variations can be used to achieve a
wide range of structures for different
product styles.
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Bread structure
• Expanded foam structure
• Bubble nuclei created in mixer
• Expanded by gas production in
proof and baking
• Converted to set sponge structure
during baking
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Factors affecting structure formation
• Bubble nuclei
– Mixing
• Gas production
– Proof
• Gas retention
– Proof and baking
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Gas volume measurement
• Calculated from
dough density
• Buoyancy method
• Dynamic
measurement for
doughs proved in
warm oil.
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Gas volume production
• Differences in
initial gas
entrainment in
mixer
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35 40 45
Gas
vo
lum
e /
solid
do
ugh
vo
lum
e (%
)
Time (minutes)
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35 40 45
Gas
vo
lum
e /
solid
do
ugh
vo
lum
e (%
)
Time (minutes)
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35 40 45
Gas
vo
lum
e /
solid
do
ugh
vo
lum
e (%
)
Time (minutes)
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35 40 45
Gas
vo
lum
e /
solid
do
ugh
vo
lum
e (%
)
Time (minutes)
2% yeast
5% yeast
Tweedy mixer
Spiral mixer
1.5 bar
Final mixer pressure
1.0 bar
0.5 bar
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Effect of mixer headspace
pressure
• Lower final
pressure gives
less gas entrained
in dough.
• This results in
finer bread
structure.
Low
pressure
High
pressure
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Measurement of bubbles
in dough
• Samples frozen in liquid nitrogen
• Microscopy
– Imaging of cross-sections
• X-ray micro CT
– Non-destructive 3D imaging
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Effect of mixer pressure
(a) (b)
0.5 bar 1.5 bar
Bubbles in freshly mixed dough
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Bubble size distribution - effect of
pressure• Similar range
of sizes
• More bubbles
for higher final
mixer
pressure.
Mixed dough
0
50
100
150
200
250
300
350
400
450
Bubble diameter (mm)0.01 0.1 1 10
1.0, 0.5 bar
1.0 bar
1.0, 1.5 bar
Num
ber
of
bubble
s / m
m3/log
10(b
in w
idth
)
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Measurement of bubbles in bread
• …
X-ray micro CT
Cell
are
a (
% o
f sli
ce a
rea)
Cell diameter (mm)
C-Cell bread imaging system
– Image analysis of bread slices
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Bubble size distribution - effect of
pressure• Many bubbles
lost during
processing
• More bubble
nuclei
coarser
bread
Mixed dough
0
50
100
150
200
250
300
350
400
450
Bubble diameter (mm)0.01 0.1 1 10
1.0, 0.5 bar
1.0 bar
1.0, 1.5 bar
Num
ber
of
bubble
s / m
m3/log
10(b
in w
idth
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Bread
(N.B. different y
scale)
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Mechanisms of bubble loss
• Damage
– e.g. during moulding
• Ostwald ripening
– Large bubbles grow
preferentially
• Coalescence
– Bubbles merge due to rupture
of walls between them
Freshly mixed7 minutes14 minutes
50µm
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Why do more bubble nuclei give
coarser structure?More bubble nuclei Fewer bubble nuclei
Thinner walls Thicker walls
Same gas
volume
Greater likelihood of
coalescence
Stable expansionCoarser eventual
structure
Uniform structure
Hypothesis
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Bubble structure during proof and baking
• X-ray CT scanning
• Oven placed inside scanner
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Structure development during bread
production
• Gas retention
important
• Determined by
flour quality and
dough
development
Breadmaking flour Non-breadmaking flour
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0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35 40 45
Gas
vo
lum
e /
solid
do
ugh
vo
lum
e (%
)
Time (minutes)
Control DATEM Lipase
Effect of lipid ingredients
aaa
Funded by DSM and CSM
Tweedy
Spiral mix
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Control DATEM Lipase
Effect of lipid ingredients
• Effects of Datem and
lipase apparent
during baking.
• They help stabilise
bubbles at this stage.
Tweedy
Spiral mix
Funded by DSM and CSM
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Dough moulding
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Dough moulding: sheeting
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Dough moulding: curling
Air trapped
between layers of
dough sheet
Elongated
bubblesRows of bubbles
within dough
sheet
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Single piece moulding effects
Start of proof End of proof Bread
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Single piece moulding effects
Start of proof End of proof Bread
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Four-piece moulding
• sss
Time
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Cell elongation in a 4-piece loaf
• C-Cell measurements
• Varies with slice position
Horizontal
elongation
within pieces
Join between
pieces
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Radical bread processCampden BRI patented process
• Combine ingredients to an
underdeveloped dough
• Dough lamination
• Cutting and orientation of dough
pieces in pan
• Proof, baking and cooling
Benefits
• Finer structure
• Increased softness
• Increased volume
CBP control Radical process
C-Cell contrast:
0.7895 ± 0.005 0.832 ± 0.008
153 ± 24 g 116 ± 18 g
4.21 ± 0.07 ml/g 4.36 ± 0.08 ml/g
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Cake structure during baking
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High ratio yellow cake• Oven temperature = 180°C
• Baking time = 47 minutes
0.1
0.2
0.3
0.4
0.5
0.7
0.6
Relative
attenuation
0.8
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TemperatureStart
• Cold, dense batter
0-20 minutes
• Convection
25-35 minutes
• Temperature gradient
• Low density zone
moves upwards
40-45 minutes
• Contraction
45 minutes
• End of baking
Temperature /°C
20
30
40
50
60
70
80
90
100
Measured with thermocouples 20mm from the imaged plane
40 39 42 24
27 25 26 25
0 minutes
29 29 27
39 39 43
5 minutes
43 40 38
48 45 47
10 minutes
62 51 52
59 49 54
76 65 76
15 minutes
78 68 75
72 59 69
78 65 76
20 minutes
91 89 91
87 83 86
86 76 82
85 77 85
25 minutes
99 98 99
96 95 95
92 90 90
88 83 86
30 minutes
102 101 102
100 100 100
97 98 96
93 91 91
35 minutes
102 102 103
102 101 101
100 100 99
97 95 95
40 minutes
102 102 103
102 102 102
101 101 99
98 96 97
45 minutes
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Pressure in a high ratio cake
• Foam to sponge
conversion occurs
as the temperature
reaches ~95°C,
which is the starch
gelatinisation
temperature in this
system.
20
30
40
50
60
70
80
90
100
110
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
-10 0 10 20 30 40 50 60
Tem
per
atu
re (º
C)
Pre
ssu
re (
kPa)
Time (minutes)
Pressure
Temperature
Batter added to pan
End of baking
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Sponge
• aaa
0.1
0.2
0.3
0.4
Relative
attenuation
• 190°C
• 20 minutes
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Muffins
• aaa
0.1
0.2
0.3
0.4
0.5
0.7
0.6
Relative
attenuation
0.8
0.9
1.0
1.1
• 180°C
• 24 minutes
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Model for formation of tunnel holesMuffin
• Bubbles are large enough to span a
steep viscosity gradient.
• High viscosity at one end of the
bubble prevents migration.
• Low viscosity at the other end
facilitates growth,
• This results in tunnel holes.
• Hypothesis: Tunnel holes form if the
rate of bubble growth is similar to
the speed of a setting front.
Growth
Immobile
Tunnel holes
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Fruit cakesIncreased water
Increased water,
no tartaric acid
Fruit sinking
Control
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Conclusions
• Methods such as X-ray tomography enable us to study the
mechanisms of structure formation in bread and cakes.
• Bread:
– The number of bubble nuclei formed in mixing is critical;
– Gas retention during proof and baking depends on flour quality
and dough development;
– Ingredients such as Datem and Lipase have their effect during
baking.
• Cakes:
– The structure depends on the balance between the rates of
bubble growth and setting. Tunnel holes occur when the rates are
similar.