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Study of biscuit baking processes

Study of biscuit baking processes. Martin Whitworth Cereals and Ingredients Processing Department. Key processes during baking. Expansion of bubbles and structure formation Loss of moisture Colour development. Biscuit baking. Travelling oven Multiple zones

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Study of biscuit baking processes

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  1. Study of biscuit baking processes Martin Whitworth Cereals and Ingredients Processing Department

  2. Key processes during baking • Expansion of bubbles and structure formation • Loss of moisture • Colour development

  3. Biscuit baking • Travelling oven • Multiple zones • Baking by radiative and convective heat transfer Air temperature Top heat Bottom heat Heat flux probe

  4. Biscuit temperature Latent heat Start of baking Moisture loss Colour development 0 1 2 3 5 6 min

  5. Structure formation • Expansion of bubbles by raising agent

  6. Microscopy of microstructure Cream cracker

  7. Structure measurement • C-Cell imaging system • Imaging of bubble structure • Quantitative measurements Cream cracker Cell diameter: 2.3 mm Net cell elongation: 1.16 Puff biscuit Cell diameter: 3.5 mm Net cell elongation: 2.80

  8. X-ray microtomography • Coming soon... • High resolution 3-D imaging of structure Aerated confectionery product

  9. Structure during baking • X-ray tomography • Mobile medical scanner • Specially constructed oven Bread

  10. Structure during baking Fruit cakes Croissants Muffins Biscuits

  11. Biscuit moisture • Moisture added to doughs to enable moulding • Moisture removed during baking to achieve final moisture content of ~1-2%. • Uniform moisture content important. • Docking holes included to aid moisture loss from interior.

  12. Checking of biscuits • Crack formation after baking. • Associated with moisture migration • Electronic speckle pattern interferometry • Sensitive measurement of displacements to <1m • Used to study strain development in biscuits Video camera Laser beams Humidity chamber Biscuit

  13. y (mm) Horizontal strain, exx 60 13 hr 12 hr 11 hr 10 hr 2 hr 3 hr 4 hr 5 hr 6 hr 7 hr 1 hr 8 hr 9 hr 0.010 0.009 Expansion 48 0.008 0.007 Contraction 0.006 36 0.005 Expansion 0.004 0.003 24 0.002 0.001 0.000 12 -0.001 -0.002 -0.003 0 x (mm) 0 12 24 36 48 60 Measured strain after baking • Strains at surface show central contraction and peripheral expansion • Biscuit checked after 8 hours • Caused by moisture loss at centre and gain at edge. • Consistent with mathematical model of moisture migration. Crack

  14. Mapping moisture distribution and food composition • Hyperspectral NIR imaging. • HgCdTe camera sensitive to 900-2500nm NIR wavelengths. • Spectra measured for each pixel. • Field of view ~8mm to 300mm width. • Rapid: ~5s scan time.

  15. Hyperspectral image data • 3-D data structure • NIR spectra for each pixel • Absorption bands provide information on composition 2500nm Wavelength 900nm Width of deck

  16. Biscuit • Example spectra • Band assignments: • 1435nm: crystalline sucrose • 1724, 1762nm: lipid • 1925nm: water • False colour image based on 2nd derivatives for these bands

  17. Chocolate bars • Components discriminated by composition • Variations between products Chocolate Peanut Fat (CH2) Crystalline sucrose Moisture (OH) Biscuit Low High

  18. Moisture distribution • NIR calibration developed for biscuits • Biscuits sampled from oven at various stages. • Calibration applied to images to measure moisture distribution. Camera Lamp Sample

  19. Moisture distribution • Moisture is lost due to heat transfer at surfaces Control High heat flux Dough ¼ time ½ time ¾ time Biscuit Moisture (%)

  20. Colour and moisture development Cumulative heat flux (kJ/m2) 0 (dough) 253 708 1134 1495 0 (dough) 87 304 572 861 Dough ¼ baked ½ baked ¾ baked Full bake

  21. Surface moisture and colour • Good agreement for top, bottom, heat flux variations.

  22. Summary Heat transfer during baking causes: • Structure formation • Expansion of bubbles by action of raising agents • Studied by X-ray tomography, microscopy, C-Cell • Moisture loss • Uniformity important to minimise checking • Measurement by NIR hyperspectral imaging • Strain measurement to study mechanism of checking • Colour development • Final stages of baking • Related to heat flux and surface moisture content

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