M. Migliori – 13 Marzo 2008 Rheological modelling of food production: Cereal goods Massimo Migliori Laboratory of Rheology and Food Engineering

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Summary

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Summary

M. Migliori – 13 Marzo 2008 Food Process: Technological view Raw Materials Technological specifications Technological specifications Chemical composition Chemical composition Mechanical characteristics Mechanical characteristics Unit operations Mixing Mixing Concentration - Drying Concentration - Drying Baking Baking Packaging Packaging Operating conditions Pressure Pressure Temperatures Temperatures Humidity Humidity Flow rates Flow rates Product Quality control Quality control Texture Texture

M. Migliori – 13 Marzo 2008 Modelling view Raw Materials Technological specifications Technological specifications Chemical composition Chemical composition Mechanical characteristics Mechanical characteristics Unit operations Mixing Mixing Concentration - Drying Concentration - Drying Baking Baking Packaging Packaging Operating conditions Pressure Pressure Temperatures Temperatures Humidity Humidity Flow rates Flow rates Product Quality control Quality control Texture Texture Transport phenomena Momentum balance Momentum balance Energy Balance Energy Balance Mass balance Mass balanceThermodynamic Equilibria Equilibria Boundary conditions Mechanical power Mechanical power Heat fluxes Heat fluxes Air flow characteristics Air flow characteristics Residence time Residence time Constitutive Equations Rheological properties Rheological properties Kinetic equation Kinetic equation Results Process – product interaction Process – product interaction Product development - design Product development - design

M. Migliori – 13 Marzo 2008 Rheology in food process Different mechanical behaviour Food system characteristics Multiphase complex systems: emulsion, suspensions Often aerated: Weakly Structured Strongly Structured Extrusion Pouring Sheeting Leavening

M. Migliori – 13 Marzo 2008 Dough characterisation Equilibrium spectrum Oscillatory regime Linear visco-elastic region Dough Structure Large deformation 1 Transient regime Non linear visco-elastic region Process properties Forming Bubble expansion Gas retention 1 Uthayakumaran et al., Rheol. Acta (2002), 41,

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Final remarks Final remarks Summary

M. Migliori – 13 Marzo 2008 RHEOLOGY IN BISCUIT MANUFACTURING Rheology development... Theoretical model Theoretical model Oscillatory measurements Oscillatory measurements Creep / Step shear rate test Creep / Step shear rate test Strain / Stress relaxation Strain / Stress relaxation …Industrial application… Empirical test Empirical test Uncontrolled flow field Uncontrolled flow field Viscosity measurement Viscosity measurement …Why ? Lack of theoretical knowledge (Modelling) Lack of theoretical knowledge (Modelling) Time saving analysis need Time saving analysis need Materials / process conditions variability Materials / process conditions variability R&D Laboratories Process / Product design Process control Optimisation

M. Migliori – 13 Marzo 2008 RICH TEA PRODUCTION PROCESS Process operations Mixing Mixing Sheeting Sheeting Baking Baking Packaging Packaging Dough characteristics Developed dough Developed dough Mixing time ~ 10 min Mixing time ~ 10 min Final temperature 38 ~ 41 °C Final temperature 38 ~ 41 °C Changes in dough may lead to: Machine-ability issues Machine-ability issues Biscuit roundness variability Biscuit roundness variability Biscuit height variability Biscuit height variability Moisture issues Moisture issues Colour out of control Colour out of control Recipe

M. Migliori – 13 Marzo 2008 ON LINE PRODUCTION MONITORING Dough Feed To the oven CutterRollers Sampling point Rheological test Stress relaxation out of linear range Stress relaxation out of linear range Sampling end of sheeting Sampling end of sheeting Low total testing time (~ 5 min) Low total testing time (~ 5 min) Advantages Continuous production monitoring over 8 hr Continuous production monitoring over 8 hr Fundamental measurement Fundamental measurement Dough visco-elastic properties analysis Dough visco-elastic properties analysis

M. Migliori – 13 Marzo 2008 STRESS RELAXATION TEST – SET UP AND ANALYSIS Temperature 32°C Temperature 32°C Strain 15% Strain 15% Weak Gel data treatment 2 Weak Gel data treatment 2 Time range 1 to 10 s Time range 1 to 10 s 1 Gabriele et al., Rheol. Acta (2001), 40-2,

M. Migliori – 13 Marzo 2008 PRODUCTION AUDIT RESULTS

M. Migliori – 13 Marzo 2008 Lenght MODEL PARAMETERS INTERPRETATION S Network strenght Mainly responsible for dough recovery after cutting Biscuit roundness NNetwork extension Related to dough behaviour during baking (gas retention ability) Biscuit height Moisture content Moisture content Texture Texture

M. Migliori – 13 Marzo 2008 DOUGH NETWORK STRENGHT – BISCUIT LENGTH DOUGH NETWORK STRENGHT – BISCUIT LENGTH S S Biscuit length Biscuit length Low S (Weak Dough) + Good recovery capability - Machine-ability Issues High S (Tough Dough) + Good machine-ability - Roundness control

M. Migliori – 13 Marzo 2008 DOUGH NETWORK EXTENSION – BISCUIT HEIGHT n n Biscuit height Biscuit height High value:Good gas retention ability (bulky biscuits risk) Low value:Poor rise during baking (flat biscuits risk)

M. Migliori – 13 Marzo 2008 S VARIABILITY DURING NORMAL PRODUCTION

M. Migliori – 13 Marzo 2008 n VARIABILITY DURING NORMAL PRODUCTION

M. Migliori – 13 Marzo 2008 DOUGH RHEOLOGY DURING UNOPTIMISED START-UP Cold plant increases dough toughness (low mixing temperatures) Machinability issues High waste level

M. Migliori – 13 Marzo 2008 START-UP ANALYSIS AND ACTIONS Corrections may be introduced in Recipe Recipe Process conditions Process conditions Actions Addition of SodiumMetaBisulphite (SMS) Addition of SodiumMetaBisulphite (SMS) It Acts as dough conditioner breaking sulphuric bridges (Dough weaking) Mixing time Mixing time Both to improve dough development and increase final dough temperature. Plant warm-up is speeded up Modifications in start-up

M. Migliori – 13 Marzo 2008 START-UP A Increase in SMS Improves dough toughness control (S on target straight away) Decrease in network extension (n above the target)

M. Migliori – 13 Marzo 2008 START-UP B Increase in mixing time Recover of network extension (n on target after 20 min) also as result of decreasing extra SMS Overdeveloped dough (S below the target)

M. Migliori – 13 Marzo 2008 OPTIMISED START-UP CONDITIONS Both parameters on target straight away!

M. Migliori – 13 Marzo 2008 FINAL REMARKS Application of stress relaxation test as on site measurementApplication of stress relaxation test as on site measurement Data interpretation using theoretical modelData interpretation using theoretical model Physical meaning of parametersPhysical meaning of parameters Continuous process monitoring allows determination of optimal rangeContinuous process monitoring allows determination of optimal range Start-up optimisation based on structure/process relationship knowledgeStart-up optimisation based on structure/process relationship knowledge IMPACT ON INDUSTRIAL BUSINESS Reduction of waste at the start-upReduction of waste at the start-up Rheological tool to control process conditionsRheological tool to control process conditions Support to process optimisationSupport to process optimisation Help in tackling usual raw material variabilityHelp in tackling usual raw material variability

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Strong network Strong network Weakly structured material Weakly structured material Summary

M. Migliori – 13 Marzo 2008 MACROSYSTEM Modelling approach Microsystem (Heterogeneous) Thermodynamic status (T, P, concentrations) from macrosystem balances Multi phase – Generally one is gas Mass exchange among phases Thermodynamic equilibrium at interfaces Momentum balance accounting visco-elasticity Macrosystem (Homogeneus) Continuous medium Material properties accounting of multiphase system Effect of external boundary conditions Mass and heat exchange in microsystem as sink Transport Phenomena hold in a pseudo-homogeneous system. Heterogeneity is accounted in a Microsystem MICROSYSTEM

M. Migliori – 13 Marzo 2008 Heterogeneous system Gas + Paste SPONGY CLOSED Gas Cells SPONGY CLOSED Gas Cells CRUNCHY OPEN Gas Cells CRUNCHY OPEN Gas Cells STABILISATION COALESCENCE Rheological behaviour controls the gas cells evolution BAKINGBAKING Cereal product texture is controlled by void fraction and bubbles morphology Texture of Cereal Goods

M. Migliori – 13 Marzo 2008 BAKING PROCESS - 1 FormulationProcess wrong profile time Product height optimal profile Structure development Organoleptic properties

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Strong network Strong network Weakly structured material Weakly structured material Summary

M. Migliori – 13 Marzo 2008

Objective Predict biscuit behaviour Raise Peak height - time Collapse mechanism Final biscuit height Moisture content Main Modelling issues Predict changes in rheology Account for process parameters: Oven baking profiles Raising agent amount

M. Migliori – 13 Marzo 2008 Macrosystem - Equations Macrosystem - Equations Hypothesis Cylindrycal system Axial and radial symmetry Every internal nods includes a microsystem of expanding bubbles Biscuit growth Raising agents Water evaporation Internal diffusive mechanism for energy and mass transfer From microsystem

M. Migliori – 13 Marzo 2008 Thermodynamic equilibrium of two phase multi-component system Mechanical equilibrium in biaxial extension of an aerated system Growth stops as effect of coalescence model Single bubble model R PGPG r PRPR P inf Closed Microsystem Closed Microsystem Gas - Liquid equilibrium constitutive equation (Water, R.A., Air, Dry matter) Paste Weak Gel constitutive equation

M. Migliori – 13 Marzo 2008 Expansion: rheological data

M. Migliori – 13 Marzo 2008 Coalescence implies the opening of the interacting bubbles. This phenomenon may occur in different ways: Coalescence implies the opening of the interacting bubbles. This phenomenon may occur in different ways: Thickness reaches locally a minimum value... DEFORMATION WORK REACHES A CRITICAL VALUE (RUPTURE POINT) DEFORMATION WORK REACHES A CRITICAL VALUE (RUPTURE POINT) …local stress reaches a critical value… In both cases Coalescence model Coalescence model

M. Migliori – 13 Marzo 2008 Rupture work 2 Charalambides et al, Rheol. acta (2002), 41, Under the hypothesis of affine deformation 2 max 2 R 0 h(t) R(t) h R Kinematic parameter: peak deformation

M. Migliori – 13 Marzo 2008 Model Instantaneous strain power 4 5 Constitutive equation: Weak Gel model Elastic energy (up to rupture point) 4 Williams JG, Stress Analysis of Polymers (1980), E. Horwood, Chichester 5 Gabriele et al., Rheol. Acta (2001), 40-2,

M. Migliori – 13 Marzo 2008 Device set-up Laser beam Sample Air In Heating system * Integrated as sample holder Integrated as sample holder Surface termo-couple Surface termo-couple PID Controller PID Controller * www. minco.com

M. Migliori – 13 Marzo 2008 Deformation work

M. Migliori – 13 Marzo 2008 Open microsystem Open microsystem Coalesced bubbles act as a necklace Mass exchange in an equivalent channel open toward the ambient A different mechanical equilibrium holds, based on elastic recovery Hencky Strain Kelvin Voigt mechanical model From microsystem

M. Migliori – 13 Marzo 2008 Validation – Different Baking profiles Validation – Different Baking profiles Height evolution Fast Profile Normal Profile

M. Migliori – 13 Marzo 2008 Validation – Different Baking profiles Validation – Different Baking profiles Weight loss Fast Profile Normal Profile

M. Migliori – 13 Marzo 2008 Validation – Different Rheology Validation – Different Rheology Change in flour Fast Profile Normal Profile

M. Migliori – 13 Marzo 2008 Sensitivity – Void fraction Sensitivity – Void fraction

M. Migliori – 13 Marzo 2008 Modelling View of Food Processes Modelling View of Food Processes Start up optimisation Start up optimisation Biscuit Baking Biscuit Baking Strong network Strong network Weakly structured material Weakly structured material Summary

M. Migliori – 13 Marzo 2008 BAKING PROCESS - 2 PSEUDO HOMOGENEOUS APPROACH 1.Bubble expansion (micro) 2. Bubble interaction (stabilisation) 3. Dough spreading 4. Macroscopic transport phenomena t

M. Migliori – 13 Marzo BUBBLE STABILISATION - 1 Bubble Expansion Stabilisation by Strain Hardening or h(t) void fraction void fraction

M. Migliori – 13 Marzo BUBBLE STABILISATION - 2 Cellular materials 1 1 Schjodt-Thomsen et al., Pol. Eng.Sci., 41 (2001) considering a dough, E<<P, eff 1/3, limit conditions Limit conditions Dough Cellular structure Poisson modulus Poisson modulus E Young modulus P cell pressure eff related to the cellular system

M. Migliori – 13 Marzo DOUGH SPREADING - 1 N dough layers F=Above layers weight i-th layer: internal friction UNLUBRICATED SQUEEZE FLOW F= Biscuit weight 1-st layer: no friction on band LUBRICATED SQUEEZE FLOW

M. Migliori – 13 Marzo DOUGH SPREADING - 2 UNLUBRICATED SQUEEZE FLOW Power law fluid LUBRICATED SQUEEZE FLOW Power law fluid F h Biscuit diameter H

M. Migliori – 13 Marzo MACROSCOPIC TRANSPORT PHENOMENA MASS BALANCE EQUATION (water, R.A., R.A. products) ENERGY BALANCE EQUATION CONSTITUTIVE EQUATIONS Fick law Fourier law S i : net flow bubble- paste i : water latent heat i : water latent heat

M. Migliori – 13 Marzo 2008 MATERIAL CHARACTERISATION Bubble expansion Paste Linear Viscoelastic properties Frequency sweep test, Hz; Time cure 0.1 Hz, 30°C – 110 °C Biscuit spreading Dough Steady Shear properties Flow curve 0.1 – 20 s -1 Bubble stabilisation Elongational properties Back extrusion test Dough formulation Flour, sugars, glucose syrup, liquid egg, fats, water, raising agents D1RA D2RA D3vacuum

M. Migliori – 13 Marzo 2008 LINEAR VISCOELASTIC PROPERTIES - 1 Sample D3, Time cure, 1°C/min

M. Migliori – 13 Marzo 2008 LINEAR VISCOELASTIC PROPERTIES - 2 Sample D3, Frequency sweep Weak gel model

M. Migliori – 13 Marzo 2008 STEADY SHEAR PROPERTIES Sample D2, Flow curve

M. Migliori – 13 Marzo 2008 BACK EXTRUSION TESTS Head F F eff = F - F drag Instron machine RpRp h z ReRe Dough

M. Migliori – 13 Marzo 2008 BACK EXTRUSION TESTS Sample D1-D2

M. Migliori – 13 Marzo 2008 MODEL SENSITIVITY - 1 Standard oven conditions: typical surface temperature profile

M. Migliori – 13 Marzo 2008 MODEL SENSITIVITY - 2 Raising Agent Effects lim D10.55 D20.73

M. Migliori – 13 Marzo 2008 MODEL SENSITIVITY - 3 Oven conditions EffectsStd: standard heat fluxes +5% : 5% increased fluxes