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Process Engineering Analysis of Confectionery Wafer Manufacture
[Thesis]. Manchester, UK: The University of Manchester; 2019.
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Abstract
Confectionery wafer baking is a complex process involving a series of physical, chemical and biochemical changes in the product, including water evaporation, formation of the porous structure, denaturation of protein, gelatinisation of starch and Maillard reactions. Mathematically it can be described as simultaneous heat and mass transfer operation involving processes such as conduction from the baking plate, natural and forced convection, evaporation of water and condensation of steam resulting in moisture diffusion A pressure profile analysis approach involving wafer baking experiments and mathematical modelling was proposed and used to study wafer structure formation. Wafers have a dense core and crispy structure obtained through baking between two hot plates (baking tongs with 90 degree or 45 degree reedings) in a gas-fired baking oven at temperatures in the region of 150oC for around 120 seconds. Previous work explains wafer baking through the investigation of the pressure profile that arises over the course of baking, with data collected from experiments and kitchen trials at Nestlé. The present study explains the pressure profile generated during the baking process in the context of structure formation of wafers. Three different pressure profile stages are identified: Stage 1, gas generation and expansion (bubble generation), during which the pressure increases; Stage 2, foam to sponge transition (structure formation), during which the pressure decreases; and Stage 3, drying through a porous structure (moisture diffusion), during which the pressure stays essentially constant. The focus of the work reported in this thesis is the study of these three stages in detail. A lab scale experimental rig was developed to study wafer baking between two hot plates in a temperature controlled environment. Varying compositions of water:flour ratio was used for this study. The results produced were meaningful but not reproducible due to the complexity of maintaining baking pressure within the system and achieving system stability. Further experiments were conducted with different product recipes using an industrial pilot plant baking system to achieve repeated results for data analysis. The results obtained indicated that with an increase in water:flour ratio the system retained pressure for a shorter duration due to increased viscosity of the wafer batter. Similarly increasing the quantity of enzymes and leaving agents does not necessarily result in increased system pressures as viscosity of the wafer batter plays a leading role in defining pressure retaining capability of the system for a set of defined process conditions. The experiments confirmed that change in recipe alone is not sufficient to obtain desired wafer structures rather a combination of controlled process variables such as batter deposit rate, baking temperature and baking plates operating mechanism have an impact on the final wafer structure. The results obtained were modelled using excel mathematical modelling tools. The model provided an accurate characterisation of the wafer baking pressure profiles and the modelling parameters obtained highlighted key features of wafer baking pressure profiles.