Chocolate lecture abingdon school-2010

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This presentation on the cold extrusion of chocolate was given to Abingdon School in 2010

Transcript of Chocolate lecture abingdon school-2010

  • 1. FxleleibScience Innovation EN GI N EE R I N ImaginationCcla!h ot o eG ENC IE SCMelting,The ingredientscasting,and structure extrudingof chocolate N O TI TEC NE HNIN V O L New ideas inProcessing shape-forming Ochocolate to G Y chocolateform shapesRY O VEB P fMlc lm ak yy r a o Mcle oD I SC

2. Fellow of Robinson College 3. Professor of Process InnovationDepartment of Chemical Engineeringand BiotechnologyUniversity of Cambridge 4. 1965O Levels; Gravesend Technical High School1967A Levels; Bath Technical College1969BSc Physics; Leicester University1972PhD; Polymer Physics; Bristol University1976Lecturer in Material Science; University of Sussex1979Department of Chemical Engineering, University of Cambridge1994 Chocolate 5. The scientific mindR YB 1 LB = 2 12 w X 6. The inventive mindThe Patent Self-Operating Napkin 7. Theimaginativemind 8. C ocoa plantation 9. Harvesting cocoa 10. C ocoa pods 11. Structure of chocolateCocoabutterSugarcrystalsCocoa solidsMilk solidsabout 0.1 mm 12. Cocoa butter - melted 13. Cocoa butter - solid 14. MeltingChocolate100 liquid8060 solid softProportion of 40fat that is liquid 20hardsolid( percent ) 0-10 010 20304050Temperature of chocolate (degrees.C ) 15. Traditional chocolate formingi mxingixinheating toabout 400Cpouri cooling tunnelsfrom300C to 180C ng eating! de-moulding The chocolate m be heated ust to m the fat so that it elt can be poured into moulds. It m then be cooled to about 18oC ust before it can be removed fromthe mould. The whole process takes about thirty minutes. 16. Extrusion processingPolyethyleneColdMeltExtrusion ProcessingH 50 100150 200 Temperature 0CChocolateColdMeltExtrusion ProcessingH 10 20 3040 0 Temperature C 17. Extrusion processGo to movie on chocolate cold extrusion process 18. knotting Go to movie on Chocolate cold extrusion knotting 19. moulding Go to movie on chocolate cold extrusion moulding 20. Extruding a tubeextrusion"torpedo" 21. Axisymmetric ram experiments UD0 / 2 pressure transducer pressure end ofD/2 piston motion L time 22. Cold extrusion of semi solid chocolate Typical Pressure v/s Time trace Piston/(ram) A Yield pressureChocolate feed Pressuretransducer DieP(bar) B Extrusion pressureCCompaction (no flow)Milk choc at 20 oCt (s) 23. 15Ex trusion 10Pre ssureM Pa5010 15 20 25 30 Te mp e rature 0C 24. Mechanism.Rate of doing work = Rate of heat generation P A x = A x Cp T PA = pressure x area = forcex= velocity= densityCp = Specific heatT = temperature increasePT = Cp100 10 5T == 6.9 0C 1, 200 1,200 25. Temperature doesnt change!So where does the work go? 26. Another calculation P Ax PRate of work done/kg == Ax Work done/kg in melting mass fraction of cocoa butter = = latent heat of melting / kgEquateP=P 10 7 ==3 = 5.5% 1,200x150x10 27. 100%LiquidFat50Microstructurechangeadiab atic heating0 102030T e m pe ra ture Centigrade/ 28. Themechanism1: BeforeflowLiquid fat inisolated sub-micronregions Sugar crystals 29. Themechanism2: As flowbegins Sub-micron internal slip planes allow plastic flow. Some crystals melt Some fat migrates to walls, reducing friction and easing flow 30. Themechanism3: Duringflow Liquid fat slip planes make the chocolate flexible 31. Themechanism4: Some time later.... As liquid fat reverts to its original regions and cocoa butter recrytallises, so the chocolate hardens 32. The scientific mindR YB 1 LB = 2 12 w X 33. The inventive mindThe Patent Self-Operating Napkin 34. Theimaginativemind