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, 10 th 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 200 200 200 200 Gas volume / solid dough volume (%) Gas volume / solid dough volume (%) Gas volume / solid dough volume (%) Gas volume / solid dough volume (%) Final mixer pressure 180 180 180 180 5% yeast 1.5 bar 160 160 160 160 • Differences in 140 140 140 140 1.0 bar 2% yeast 120 120 120 120 initial gas 0.5 bar 100 100 100 100 entrainment in 80 80 80 80 60 60 60 60 mixer Spiral mixer 40 40 40 40 20 20 20 20 Tweedy mixer 0 0 0 0 0 0 0 0 5 5 5 5 10 10 10 10 15 15 15 15 20 20 20 20 25 25 25 25 30 30 30 30 35 35 35 35 40 40 40 40 45 45 45 45 Time (minutes) Time (minutes) Time (minutes) Time (minutes)

Effect of mixer headspace pressure • Lower final pressure gives less gas entrained Low in dough. pressure • This results in finer bread structure. 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 0.5 bar 1.5 bar (a) (b) Bubbles in freshly mixed dough

Bubble size distribution - effect of pressure • Similar range 450 1.0, 0.5 bar of sizes 1.0 bar 400 Number of bubbles / mm 3 /log 10 (bin width) 1.0, 1.5 bar • More bubbles 350 for higher final 300 mixer Mixed dough 250 pressure. 200 150 100 50 0 0.01 0.1 1 10 Bubble diameter (mm)

Measurement of bubbles in bread C-Cell bread imaging system X-ray micro CT – Image analysis of bread slices Cell area (% of slice area)  Cell diameter (mm) • …

Bubble size distribution - effect of pressure • Many bubbles 450 2.0 1.0, 0.5 bar lost during 1.8 1.0 bar 400 Number of bubbles / mm 3 /log 10 (bin width) 1.0, 1.5 bar processing 1.6 350 1.4 300 1.2 Mixed dough Bread • More bubble 250 1.0 (N.B. different y nuclei 200 scale) 0.8  coarser 150 0.6 bread 100 0.4 50 0.2 0 0.0 0.01 0.1 1 10 Bubble diameter (mm)

Mechanisms of bubble loss Freshly mixed 14 minutes 7 minutes • Damage – e.g. during moulding • Ostwald ripening – Large bubbles grow preferentially • Coalescence 50µm – Bubbles merge due to rupture of walls between them

Why do more bubble nuclei give coarser structure? More bubble nuclei Fewer bubble nuclei Same gas volume Greater likelihood of Coarser eventual Thinner walls Stable expansion Uniform structure Thicker walls coalescence 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

Effect of lipid ingredients Funded by DSM and CSM Control DATEM Lipase Spiral mix 200 Gas volume / solid dough volume (%) 180 160 140 120 100 80 60 40 20 0 0 5 10 15 20 25 30 35 40 45 Time (minutes) Tweedy

Effect of lipid ingredients Funded by DSM and CSM Control DATEM Lipase Spiral mix • Effects of Datem and lipase apparent during baking. • They help stabilise bubbles at this stage. Tweedy

Dough moulding

Dough moulding: sheeting

Dough moulding: curling Elongated Rows of bubbles bubbles within dough sheet Air trapped between layers of 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 Join between pieces Horizontal elongation within pieces • C-Cell measurements • Varies with slice position

Radical bread process Campden BRI patented process • Combine ingredients to an underdeveloped dough CBP control Radical process • Dough lamination • C-Cell contrast: Cutting and orientation of dough 0.7895 ± 0.005 0.832 ± 0.008 pieces in pan • Proof, baking and cooling 153 ± 24 g 116 ± 18 g Benefits 4.21 ± 0.07 ml/g 4.36 ± 0.08 ml/g • Finer structure • Increased softness • Increased volume

Cake structure during baking

High ratio yellow cake • Oven temperature = 180°C • Baking time = 47 minutes Relative attenuation 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

Start Temperature • Cold, dense batter 0-20 minutes Measured with thermocouples 20mm from the imaged plane • Convection Temperature /°C 25-35 minutes 100 • Temperature gradient 90 80 • Low density zone 70 93 98 85 97 88 91 95 77 83 96 95 85 97 91 86 moves upwards 60 100 100 101 101 92 86 78 76 97 98 76 90 65 65 76 76 99 82 99 90 96 40-45 minutes 50 102 101 102 102 100 100 39 96 87 72 59 48 45 59 95 39 49 83 100 102 101 42 95 43 69 47 54 86 24 40 40 39 • Contraction 30 102 102 102 101 102 102 43 99 78 29 62 91 68 40 89 29 98 51 103 103 102 75 52 91 38 99 27 26 25 25 27 45 minutes 20 • End of baking 30 minutes 40 minutes 10 minutes 35 minutes 15 minutes 20 minutes 25 minutes 45 minutes 0 minutes 5 minutes

Pressure in a high ratio cake 0.6 110 • Foam to sponge Batter added to pan conversion occurs 0.5 100 as the temperature 0.4 90 reaches ~95°C, 0.3 80 which is the starch Temperature (ºC) Pressure (kPa) Pressure gelatinisation 0.2 70 temperature in this 0.1 60 system. 0 50 -10 0 10 20 30 40 50 60 -0.1 40 Temperature -0.2 30 End of baking -0.3 20 Time (minutes)

• 190°C Sponge • 20 minutes Relative attenuation 0.4 0.3 0.2 0.1 •

• 180°C Muffins • 24 minutes Relative attenuation 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 •

Model for formation of tunnel holes Muffin • Bubbles are large enough to span a steep viscosity gradient. Growth • High viscosity at one end of the bubble prevents migration. • Low viscosity at the other end Immobile facilitates growth, • This results in tunnel holes. Tunnel holes • Hypothesis: Tunnel holes form if the rate of bubble growth is similar to the speed of a setting front.

Fruit cakes Increased water, Control Increased water no tartaric acid Fruit sinking

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.