formation in bread and cakes Martin Whitworth British Society of - - PowerPoint PPT Presentation

Bubble structure formation in bread and cakes

Martin Whitworth

British Society of Baking Spring Meeting, 10th April 2019

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.

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

Factors affecting structure formation

• Bubble nuclei

– Mixing

• Gas production

– Proof

• Gas retention

– Proof and baking

Gas volume measurement

• Calculated from

dough density

• Buoyancy method
• Dynamic

measurement for doughs proved in warm oil.

Gas volume production

• Differences in

initial gas entrainment in mixer

20 40 60 80 100 120 140 160 180 200 5 10 15 20 25 30 35 40 45

Gas volume / solid dough volume (%) Time (minutes)

20 40 60 80 100 120 140 160 180 200 5 10 15 20 25 30 35 40 45

Gas volume / solid dough volume (%) Time (minutes)

20 40 60 80 100 120 140 160 180 200 5 10 15 20 25 30 35 40 45

Gas volume / solid dough volume (%) Time (minutes)

20 40 60 80 100 120 140 160 180 200 5 10 15 20 25 30 35 40 45

Gas volume / solid dough volume (%) Time (minutes)

2% yeast 5% yeast Tweedy mixer Spiral mixer 1.5 bar Final mixer pressure 1.0 bar 0.5 bar

Effect of mixer headspace pressure

• Lower final

pressure gives less gas entrained in dough.

• This results in

finer bread structure. Low pressure High pressure

Measurement of bubbles in dough

• Samples frozen in liquid nitrogen
• Microscopy

– Imaging of cross-sections

• X-ray micro CT

– Non-destructive 3D imaging

Effect of mixer pressure

(a) (b)

0.5 bar 1.5 bar Bubbles in freshly mixed dough

Bubble size distribution - effect of pressure

• Similar range
• f sizes
• More bubbles

for higher final mixer pressure.

Mixed dough

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

Number of bubbles / mm3/log10(bin width)

Measurement of bubbles in bread

• …

X-ray micro CT

Cell area (% of slice area) Cell diameter (mm)



C-Cell bread imaging system

– Image analysis of bread slices

Bubble size distribution - effect of pressure

• Many bubbles

lost during processing

• More bubble

nuclei coarser bread

Mixed dough

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

Number of bubbles / mm3/log10(bin width)

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)

Mechanisms of bubble loss

• Damage

– e.g. during moulding

• Ostwald ripening

– Large bubbles grow preferentially

• Coalescence

– Bubbles merge due to rupture

• f walls between them

Freshly mixed 7 minutes 14 minutes

50µm

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 expansion Coarser eventual structure Uniform structure

Hypothesis

Bubble structure during proof and baking

• X-ray CT scanning
• Oven placed inside scanner

Structure development during bread production

• Gas retention

important

• Determined by

flour quality and dough development

Breadmaking flour Non-breadmaking flour

Gas volume / solid dough volume (%) Time (minutes)

Control DATEM Lipase

Effect of lipid ingredients

Funded by DSM and CSM

Tweedy Spiral mix

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

Dough moulding

Dough moulding: sheeting

Dough moulding: curling

Air trapped between layers of dough sheet Elongated bubbles Rows of bubbles within dough sheet

Single piece moulding effects

Start of proof End of proof Bread

Single piece moulding effects

Start of proof End of proof Bread

Four-piece moulding

• Time

Cell elongation in a 4-piece loaf

• C-Cell measurements
• Varies with slice position

Horizontal elongation within pieces Join between pieces

Radical bread process

Campden 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

Cake structure during baking

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

Temperature

Start

• 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

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

0.1 0.2 0.3 0.4 0.5 0.6

• 10

10 20 30 40 50 60

Temperature (ºC) Pressure (kPa) Time (minutes)

Pressure Temperature Batter added to pan End of baking

Sponge

• 0.1

0.2 0.3 0.4 Relative attenuation

• 190°C
• 20 minutes

Muffins

• 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

Model for formation of tunnel holes

Muffin

• 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

Fruit cakes

Increased water Increased water, no tartaric acid Fruit sinking Control

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.