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Design and Construction of a Batch Oven for Investigation of Industrial Continuous Baking Processes
Abstract
A new batch oven has been constructed to mimic industrial convection tunnel ovens for research and development of continuous baking processes. The process parameters (air flow, air temperature, air humidity, height of baking area and the baking band velocity) are therefore highly controllable and adjustable over a wide range of settings. It is possible to monitor the product weight and temperature continuously during baking. The simultaneous measuring of mass and a window allowing for visual (e.g., by video recording) control is unique for this experimental batch oven. Two validation steps have been carried out. The uniformity of heating in the oven was assessed by measurements of local heat transfer coefficients and confirmed by baking tests. The methods showed that the oven is able to heat and bake uniformly across the baking area. Hereafter, the oven was validated against a commercial 10-m tunnel oven, with a butter cookie as the test product. The investigated quality parameters for the butter cookies were mass loss and surface browning, where the uniformity of browning was evaluated subjectively against a scale of standards and objectively by L* value measurements. Good reproducibility of the baking was documented over a range of temperatures (160C to 190C).
The purpose of this paper is to describe a new specially designed pilot scale batch oven. The batch oven is designed and constructed to imitate the baking processes in continuous tunnel ovens with forced convection. Experimental work in the new batch oven will increase knowledge of how the environment and baking conditions influence the quality of bakery products in continuous tunnel ovens.
... 1. Cookies were baked at five different air velocity settings (1,3,5,7,9), all for 8 min at 180 • C. Three batches of six cookies were baked at each setting. ...
... Six bread rolls were used for each method. A French bread type was used as the model product, the dough recipe can be found in [1]. ...
... Batch oven 1) All cookies (n = 6). 2) 2 from each group (n = 2). ...
The scope of the PhD project was to increase knowledge on the process-to-product interactions in continuous tunnel ovens. The work has focused on five main objectives. These objectives cover development of new experimental equipment for pilot plant baking experiments, mathematical modeling of heat and mass transfer in a butter cookie product, and evaluation of quality assessment methods.
The pilot plant oven is a special batch oven designed to emulate continuous convection tunnel oven baking. The design, construction, and validation of the oven has been part of the project and is described in this thesis. The oven was successfully validated against a 10 m tunnel oven. Besides the ability to emulate the baking conditions in a tunnel oven, the new batch oven is designed and constructed for experimental research work. In the design options to follow the product continuously (especially weight and temperature) and control the process (air flow, temperature, and humidity) are therefore emphasized. The oven is furthermore designed to work outside the range of standard tunnel ovens, making it interesting for manufacturers of both baking products and baking equipment.
A mathematical model describing the heat and mass transfer in butter cookies during baking was formulated. The model was solved numerically by the use of a finite element method. Model optimization and validation was successfully carried out against experimental data obtained in the new pilot plant oven. The effect of the baking tray on mass transfer was examined through comparison of different modeling set-ups and experimental data. It was found that while the baking tray is likely to reduce the evaporation from the bottom surface, it is not correct to assume that no evaporation takes place at the covered surface.
Parallel to the construction of the pilot oven an advanced multi-spectral imaging method was investigated as a method for quality assessment of butter cookies. The ability of the method to assess multiple quality aspects from one image was the main focus of the study. The system was able to predict both the surface browning and the water content in butter cookies.
... Denne mekanistiske beskrivelse af stegeprocessen kan man måske nok nikke genkendende til, men faktisk har den ikke konstatere, at pilot plant-ovnen kunne genskabe det luftflow og de lokale varmeovergangstal, som hersker i en industriovn, og at bagningen var ensartet på tvaers af pladen [5]. Pilot plantovnen blev valideret over for tunnelovnen ved sammenlignede bageforsøg, som viste, at man opnåede samme farve og vaegttab ved de samme bagebetingelser (lufttemperatur og bagetid) [5]. ...
... Denne mekanistiske beskrivelse af stegeprocessen kan man måske nok nikke genkendende til, men faktisk har den ikke konstatere, at pilot plant-ovnen kunne genskabe det luftflow og de lokale varmeovergangstal, som hersker i en industriovn, og at bagningen var ensartet på tvaers af pladen [5]. Pilot plantovnen blev valideret over for tunnelovnen ved sammenlignede bageforsøg, som viste, at man opnåede samme farve og vaegttab ved de samme bagebetingelser (lufttemperatur og bagetid) [5]. ...
22 dansk kemi, 98, nr. 9, 2017 ■ FØDEVARETEKNOLOGI Forskning i fødevareproduktionsteknologi: Fysiske principper bag kunsten at lave god mad i stor skala Tilberedningen af faste fødevarer ved koge-, stege-og bageprocesser er et centralt trin i størstedelen af al madlavning, både i lille og stor skala. En mekanistisk forståelse af de fysiske og kemiske processer, som følger af opvarmningen, er grundlaget for at kunne lave realistiske, praediktive matematiske modeller af disse processer. Sådanne modeller kan lette meget af arbejdet ved opskalering til industriproduktion. Af Jens Adler-Nissen og Aberham Hailu Feyissa, Forskergruppen for Fødevareproduktionsteknologi, Fødevareinstituttet, Danmarks Tekniske Universitet Forskningen i fødevareproduktionsteknologi ved DTU har helt overordnet det formål at forstå og videreudvikle de videnska-belige principper, som ligger til grund for forarbejdning af fødevarer i industriel skala. Allerede denne brede formule-ring antyder, at skalering af processerne er et centralt emne. Fødevareindustrien, herunder catering-industrien, har brug for pålideligt og driftsøkonomisk forsvarligt at kunne opskalere forarbejdningen af nyudviklede produkter fra forsøgskøkken-skala til industri-skala og stadig opnå den ønskede kvalitet og sikkerhed. En gennemgående udfordring er her, at skaleringens effekt på produktkvalitet, produktsikkerhed og produktivi-tet kun i et vist omfang kan praedikeres gennem matematisk modellering, og der er derfor et betydeligt element af heuristik forbundet med opskaleringen og optimeringen af en ny produk-tionsproces i fødevareindustrien. Termiske processer er centrale i madlavning Ovenstående abstrakte formulering vil vi konkretisere med eksempler fra vores forskning i termisk processering af faste fødevarer. Det daekker i korthed over koge-, stege-og bagepro-cesser, som er centrale processer i størstedelen af al madlav-ning, hvad enten den foregår i husholdningen, i storkøkkener eller i industriel skala. I den klassiske udformning af disse processer transporteres varmen henover graensefladen mel-lem omgivelserne og den faste fødevare og fordeles derefter gennem ledning til det indre af fødevaren. Varmeoverførslen kan her ske ved tre forskellige fysiske principper: Ved kontakt-ledning, som f.eks. stegning på pande, ved konvektion, som f.eks. kogning i vand eller stegning og bagning i en konvekti-onsovn og ved stråling, som når man griller kød. I senere tid er de klassiske varmeoverførselsprocesser blevet suppleret med forskellige volumetriske opvarmningsprincipper, hvor energien afsaettes inde i fødevaren og her omdannes til varme, således at opvarmningen ikke begraenses af ledningen gennem produktet. Mikrobølgeopvarmning er et velkendt eksempel fra hushold-ningen, men også andre former for volumetrisk opvarmning af faste fødevarer er ved at vinde indpas i industrien. Her arbejder vi i den fødevareproduktionsteknologiske forskergruppe med ohmsk opvarmning af faste fødevarer, hvor opvarmningen sker ved at lade en vekselstrøm passere gennem produktet [1]. Den termiske processering medfører en lang raekke kemiske og fysisk-kemiske aendringer i fødevaren, hvor isaer denature-ring af proteiner, forklistring af stivelse, blødgøring af plante-cellevaegge og bruningsreaktioner som Maillard-reaktioner og karamellisering, har afgørende betydning for et gastronomisk tilfredsstillende resultat. Det er velkendt for laesere af Dansk Kemi med de traditionsrige essays om køkkenkemi, og det vil i øvrigt vaere uoverkommeligt at henvise til faglitteraturen her. Opvarmningen af den faste fødevare inducerer også vigtige transportprocesser, hvor isaer transporten af vand i flydende form og/eller på dampform er central (i brødbagning er også transporten af CO 2 vigtig). Tillige medfører opvarmningen en hel eller delvis inaktivering af tilstedevaerende mikroorganis-mer, hvilket er ønskvaerdigt og i mange tilfaelde også et hoved-formål med termisk processering. Vores forskning i termisk processering af faste fødevarer sigter på en sammenfattende mekanistisk forståelse af den rent fysiske opvarmningsproces og dens kobling med vand-og gas-transporten og de naevnte ledsagende kemiske og fysisk-kemi-ske aendringer. En daekkende mekanistisk forståelse er grund-laget for at kunne lave en trovaerdig praediktiv modellering af processen med henblik på blandt andet at kunne foretage en pålidelig ekstrapolation fra lille til stor skala. En sådan model kan imidlertid ikke opstilles på teoretisk grundlag alene-der skal kontrollerede eksperimenter til for at bestemme forskellige parametervaerdier i modellen og for i øvrigt at validere model
Modern ovens are utilized from large span of time for completing different heat treatment cycles like baking, curing, annealing, aging, drying, and so on. There are numerous sorts of industrial ovens namely batch, relieving, drying, baking, reflow, clean room, conveyor types, and so on. Conveyor oven helps to perform the heat treatment cycle in an uninterrupted flow, including the heating of the objects followed by the cooling down of the same object. A multipurpose conveyor-type industrial oven is designed using analytical approach for heat treatment process on various objects. This article presents the modeling and CFD analysis of conveyor-type continuous ovens. Simulation of the entire model of conveyor-type industrial oven is carried out in Solidworks Flow package. Since the boundary conditions of an actual industrial oven is open at both entry and exit points, same condition is maintained in the CFD analysis. With the help of the simulation model, researchers can study and observe the temperature distribution throughout the oven.
The combined surface heat transfer coefficient is a determining parameter of convective baking process time and efficiency, as well as the resulting food product quality. By this study, the combined surface heat transfer coefficient term was determined at the convective oven temperature range of 70–220°C, with fan (turbo) and without fan (static oven) applications. The methods of “Lumped Capacity” and “Time–Temperature Matching” were used. Both methods utilize the time–temperature data at a fixed position of a definite material, during unsteady state heating up period inside the convective oven. The increase in oven temperature and the fan application in the oven derived higher calculated values of surface heat transfer coefficients. Good agreement was observed between both methods and the literature values. The given methods are applicable to other oven types and heating modes.
The present study explored the possibility of using barley flour as an ingredient to incorporate soluble fibre (β-glucan) in chocolate-chip cookies. Some clinical studies have shown that β-glucan might reduce the serum cholesterol levels. The objective of this study was to determine the physical and sensory characteristics of chocolate chip cookies partly substituted with barley flour at different levels. Physical characteristics (water activity and L*a*b* colour) and sensory characteristics (descriptive and consumer analysis) were evaluated on the experimental cookies substituted with 0, 30, 40, 50, 60 and 70% barley flour for all-purpose flour. There were increases in the baked-barley aroma and flavour, thickness, colour intensity, dryness and graininess with increasing barley flour content. Consumer data showed that cookies made with 30% (0.5 g β-glucan/serving) and 50% (0.8 g β-glucan/serving) barley flour substitution were comparable in liking to the control (0% substitution) cookie and a commercial cookie. The presence of β-glucan in our chocolate-chip cookies might make them a healthier option for many consumers.
The effect of crust temperature and water content on acrylamide formation was studied during the baking of white bread. To assess the effect of over-baking, we used a full factorial experimental design in which the baking time was increased by 5 and 10 min at each baking temperature. Additional experiments were performed with steam baking and falling temperature baking. Immediately after baking, the crust was divided into the outer and inner crust fractions, and the water content and acrylamide concentration of each fraction was measured. The outer crust had a significantly lower water content and higher acrylamide concentration than the inner crust did. Crust temperature in combination with water content had a significant effect on acrylamide formation, higher temperatures resulting in higher acrylamide concentrations. However, at very high temperatures and lower water contents, acrylamide concentration was observed to decrease, though the bread colour was then unacceptable for consumption. Steam and falling temperature baking, on the other hand, decreased the acrylamide content while producing bread crust with an acceptable colour. The lowest acrylamide values and an acceptable crust colour were produced by steam baking.
Conduction heat transfer phenomena are found throughout virtually all of the physical world and the industrial domain. The analytical description of this heat transfer mode is one of the best understood. Some of the bases of understanding of conduction date back to early history. It was recognized that by invoking certain relatively minor simplifications, mathematical solutions resulted directly. Some of these were very easily formulated. What transpired over the years was a very vigorous development of applications to a broad range of processes. Perhaps no single work better summarizes the wealth of these studies than does the book by Carslaw and Jaeger (1996). They gave solutions to a broad range of problems, from topics related to the cooling of the Earth to the current-carrying capacities of wires. The general analyses given there have been applied to a range of modern-day problems, from laser heating to temperature-control systems.
Manleys technology of biscuits, crackers and cookies is widely regarded as the standard work in its field. Part one covers management issues such as HACCP, quality control, process control and product development. Part two deals with the selection of raw materials and ingredients. The range and types of biscuits is covered in part three, while part four covers the main production processes and equipment, from bulk handling and metering of ingredients to packaging, storage and waste management. Eight expert authors have joined Duncan Manley in extensively updating and expanding the book, which is now some 25% longer than the previous edition. Part one now includes a new chapter on sustainability in the biscuit industry and the discussion of process and efficiency control is more detailed. In part two the information on wheat flour has been extensively revised to reflect recent developments and there are entirely new chapters on fats and oils and packaging materials. Photographs of the major types of biscuits now illustrate chapters in part three, which also includes a newly-composed chapter on the position of biscuits in nutrition. Finally, part four has been comprehensively reviewed and revised with the assistance of an author from a major machinery manufacturer. With its distinguished editor and team of expert contributors this new edition consolidates the position of Manleys technology of biscuits, crackers and cookies as the standard reference work in the industry.
Heating heterogeneity is often observed in laboratory/kitchen ovens, medium size equipments such as rotary ovens, and industrial tunnel-type ovens. Losses of bakery products are mainly due to the effect of not a uniform heat flux delivered to the product. Discarding products of not desired shape and color, from non uniform heat fluxes, is a common practice in the bakery industry resulting in waste of energy and food ingredients. A static pilot plant oven was designed and constructed to simulate industrial continuous ovens. The oven is equipped with computerized on line control system to simulate baking parameters such as wall and air temperature, velocity and humidity of air inside the baking chamber corresponding to the real baking profile of a given commercial product. A mathematical method was developed to establish appropriate coefficients and correlations for oven performance providing a uniform baking zone. Heat fluxes in the baking zones of the oven both for top and bottom chambers at various positions were experimentally measured using a specially designed total heat flux meter, the h-monitor. Results showed an acceptable uniform heat flux of less than 5% variation within the baking zone except at the corners of the oven. Several baking trials of various industrial cake products confirmed that the desired heat flux uniformity was achieved.
Full factorial baking (drying) test was performed with five levels of initial moisture contents (0.369, 0.431, 0.539, 0.611 and 0.707 d.b.) of cake batter and four levels of oven temperatures (40, 70, 100 and 200 °C) in duplicate. The moisture diffusivity (De) was then evaluated through the first falling rate period from plotting the dimensionless moisture ratio against time on a semi-log scale. For this moving boundary problem, simple volume compensation method was applied to the analytical solution. The moisture diffusivity was 9.0×10−11 to 4.4×10−8 m2/s for the industrial cake batter during baking. As porosity (ε) and temperature (T) of the batter increased the moisture diffusivity increased. The semi-empirical model developed was De=29.6εexp(−8020.5/T).
Measurements of apparent heat transfer coefficients within a typical domestic fan oven and a commercial batch oven were performed using four different methods: back-calculation from transient temperature data; using heat flux sensors; from the mass-loss rate; a psychrometric method. The majority of the measured data ranged between 15 and 40Wm−2K−1, and were approximately twice as high as predicted by a Nusselt number correlation for laminar flow over flat-plates, which was partially attributable to radiation. Of all the methods, the heat flux sensor was the simplest to use and was the only method which revealed the time-variation in the heat transfer coefficient. However, although it was the least practical to implement, the mass-loss-rate method incorporated the effect of evaporation, and since the data measured by this method were more reliable than the data from the psychrometric method, they would be most useful for modelling cooking processes.
In this work, we study the development of browning at bread surface during baking. Computer vision is applied to follow the progress of browning at surface, while the variations of temperature and water activity are obtained by numerical simulation of a mathematical model previously validated. The formation of the bread crust is a complex process where temperature and water content change continuously during baking, making browning a non-isothermal process occurring in a non-ideal system. Minimum requirements for initiation of colour formation are temperature greater than 120°C and water activity less than 0.6. We apply a non-isothermal kinetics approach to model the browning development at bread surface during baking, where the variation of local temperature and water activity is taken into account. The methodology presented here is suitable for modelling and predicting browning during baking; model parameters can be estimated by using a non-ideal system closer to real processing conditions.
Baking conditions were observed for two different multi-zone industrial scale ovens: a gas fired band oven and an electric powered mold oven. In each zone of both ovens, parameters measured were: internal temperature profile, air velocity absolute humidity and oven wall temperature. Air temperatures were higher close to the oven wall than at the center of ovens tested. Absolute air humidity in the gas fired band oven (0.0545–0.246 kg H2O/kg dry air) was higher than in the electric fired mold oven (0.0207–0.0505 kg H2O/kg dry air). The relative air velocities in the ovens were 0–0.437 m/s, which resulted in convective heat transfer coefficients of 5.7–7.4 W/m2K and mass transfer coefficients of 3.94×10−8-5.12×10−8 kg/m2 s Pa. The average rate of total energy transferred to each product was 71992–85339 W. A proportion of 26–38.4% was the sensible heat absorbed with 61.6%–74% of the heat absorbed as the latent heat of vaporization of moisture. Radiative heat was responsible for 66.2–81.5% of the heat delivered to the top surface of products for cake baking in direct fired industrial ovens.
The influence of surface roughness on the heat transfer of a circular cylinder to the cross-flow of air has been studied. The Reynolds number was varied from 2.2 × 104 to 4 × 106. The variation of the roughness parameter was 0 < ks d < 900 × 10-5. The tests have been performed for the boundary condition T ≈ const. For each of the rough cylinders, the static pressure distribution together with the local and total heat transfer have been measured. Particular attention has been paid to the transition from a laminar to a turbulent boundary layer as a function of Reynolds number and roughness parameter.
Correlations for average heat transfer coefficient for cookie shaped objects in a hot air jet impingement oven were obtained using aluminum cookie models. The study was carried out in a pilot plant scale hot air jet impingement oven. The effects of individual cookie position, presence of surrounding cookies, air velocity, air temperature and rotation of the oven plate on average surface heat transfer coefficient were investigated. The value of the heat transfer coefficient ranged between 100–225 W/m2K and was found to be a strong function of jet air velocity. The impact of surrounding cookies on the heat transfer coefficient was more for smaller cookies, which had larger cookie-to-cookie spacing.
The axial and radial velocity components of a single jet impinging on a flat surface were measured in a commercial jet impingement oven using a laser Doppler anemometer. the measured velocity profiles had characteristics of a classical turbulent jet in its potential core region implying a local maximum for the rate of heat transfer directly under the jet center. Temperature variation at selected locations in the jet impingement oven was measured. the measured temperature field indicated that for a given set temperature of the oven, the variation of temperature within the oven cavity was dependent upon the location. Maximum of 15C variation was observed.
A static oven designed for French bread baking has been instrumented to monitor the processing conditions and record variables responsible for dough changes. Thermocouples are inserted at fixed position in the dough, mass loss is continuously weighed whereas expansion is measured by CCD video camera. Internal pressure and ambient humidity are controlled. Standard conditions for acceptable bread are checked and variable profiles measured in order to define the different sequences of variables related to the main macroscopic changes: expansion, scars opening and crust setting. This scheme is confirmed by modifying main operating conditions (temperatures and vapour injection), showing that water vapour favours expansion, reaching its maximum up to 1.7, at a crumb temperature close to 90 °C, in relation with internal pressure (90 kPa). Vault and hearth temperatures mainly influence crust, the setting of which stops loaf volume decrease (20%).
The industrial baking of cereal products is commonly performed in tunnel ovens, which give operators high flexibility for adjusting baking conditions to optimum values. This paper discusses the application of a CFD approach to predict the air temperature and velocity profiles inside the baking chamber of an industrial indirect gas-fired tunnel oven used for biscuit baking. We used two three-dimensional CFD models (one not covering the conveying band of biscuits and the other including it) to describe the complex air circulation resulting from the mechanisms of air input and exit at the ends of the oven and of air extraction through the different extraction points located along the oven length. Comparison of numerical results with experimental measurements shows a fairly close agreement in the qualitative prediction and a few inaccuracies in the quantitative prediction of the air temperature profiles within the baking chamber. Furthermore, the comparison also reveals great differences in the air velocity profiles.
Energy consumption and product quality changes are often observed as the ratio of the convection to the conduction modes of heat transfer varies in industrial baking ovens. Air and oven-wall temperature profiles as well as air velocity can affect the convection/radiation heat transfer and hence the quality of the baked products. A programmable pilot-plant oven was used to establish five baking profiles by measuring the total heat flux and the convective component using a special heat flux meter called an h-monitor. The purpose was to keep the total heat flux delivered to the h-monitor constant while varying the convective component from 27% (for the standard profile) to 11%, 22%, 33% and 37% by modifying air characteristics and wall temperatures. Industrial cupcakes were baked using the five established baking profiles and then evaluated in terms of quality parameters. Compared to the standard profile, a 10% reduction in volume expansion and a 30% increase in texture properties were observed for extreme oven conditions; top colour was always darker but more uniform for the conditions with less convection. The moisture content of the middle part of the cake was always higher than that of the top, bottom and sides. Baking industries are interested in using the pilot-scale oven to modify baking profiles for the purposes of quality improvement, product development and energy savings, rather than having to engage in high-cost trial and error practices on the production site.
A mathematical model was set up to predict browning kinetics of bread crust during baking. A bread dough was placed into a cylindrical steel mould and baked in a pilot forced-convection oven at 200 and 250°C. The sample surface temperature was measured using both a type J thermocouple and an infrared thermometer. Surface browning (ΔE) of bread crust during baking was measured by a tristimulus colorimeter. The kinetic model for bread crust browning was obtained by instant heating of dried crumb on contact with a refractory plate at 140, 150, 165, 185, 210, 235 and 250°C. At all temperatures ΔE tended asymptotically to ΔE∞ = 52, which corresponded to the burnt sample. The colour difference varies as a function of first-order kinetics. The rate constant k depends on temperature according to the Arrhenius equation (ko = 42,000 s−1; Ea = 64,151 J/mol). Kinetics was validated under dynamic temperature conditions: the experimental results were compared with those obtained from a mathematical model for heat and mass transfer during baking connected to the kinetic model for browning.
Air impingement technology is gaining popularity in food-processing operations such as baking, freez-ing, drying, and toasting. In this article, physical characteristics of impinging jets, such as turbulent mixing in the free jet region, stagnation, boundary-layer formation, recirculation, and their interactions with food products in terms of heat and mass transfer have been reviewed. The discussion includes experimental methods used for mea-surement of heat and mass transfer for single and multiple slot and circular jets. Procedures used for measurement of heat-transfer coefficient such as lumped sensor method, micro-calorimetric approach, and use of flux sensors are presented. Typical qualitative and quantitative flow-field studies using planar visualization and laser Doppler anemometry have been reviewed. Numerical modeling of air impingement systems is discussed with special consid-eration of problems arising in food-processing systems.
ABSTRACT Spatial variation of heat transfer is an important factor in air impingement systems. Temperature data were obtained when a jet at room temperature impinged on a flat object initially at −50 °C to estimate heat transfer under freeze-thaw conditions. Single and double circular jets and slot jets were examined. Temperature data were fit into empirical relationships for predicting heat transfer coefficients and their spatial variation for conditions common in impingement freeze-thaw applications. For processing conditions involving cooling, the impingement surface was initially heated to a temperature of 70 °C and allowed to cool when subjected to impingement with room temperature air.
The impact of sugar (17.6–31.2%) and fat (8.7–15.8%) levels on cookie structure was studied. Cookie diameter increased and its height decreased with increasing sugar or fat levels. X-ray microfocus computed tomography porosities and cell sizes increased with fat level, but cell size distribution, cell wall thickness and distribution were not affected by fat level, indicating that fat primarily incorporates air. In contrast, the sugar level influenced porosity, cell size, cell wall thickness and their relative distributions. Thus, the sucrose level, probably by affecting dough viscosity during baking, largely influences the baked cookie structure. Cell and cell wall anisotropy measurements indicated that the inner orientation of cells and cell walls probably depends on the horizontal spread behaviour, rather than on the maximum cookie height and collapse. Finally, the surface cracking pattern was determined by sugar level, rather than by structural collapse at the end of baking.
In addition to characterization of baking conditions during industrial cake baking, some important quality parameters, such as texture, color, density and viscosity of the cake batter were evaluated during baking in two different multi-zone industrial scale ovens: gas fired band oven and electric powered mold oven. The flow behavior of all batters was pseudo-plastic with a yield stress. The average moisture removal rates (3.59×10−4–1.40×10−3 kg H2O/kg solid s) of cakes fell between those of cookies and breads. During baking, pH increased and then decreased at the late stage of baking. Batter positions (side or center) on the band were not critical for quality parameters with the exception of moisture content. Most color changes occurred 1/4–3/4 way through the baking. After 21 days of storage, the hardness of all cakes increased 1.8–3 times the original value.
The flow field topology of a confined turbulent slot air jet impinging normally on a moving flat surface has been investigated experimentally by using particle image velocimetry (PIV). Experiments were conducted for a nozzle-to-plate spacing of eight slot nozzle widths, at three Reynolds numbers (Re = 5300, 8000 and 10,600) and four surface-to-jet velocity ratios i.e. 0, 0.25, 0.5 and 1. The measurements of the mean velocities and turbulent quantities are presented in the following main characteristic regions of the jet: the potential core, the intermediate zone and the impinging zone. It appears that the flow field patterns at a given surface-to-jet velocity ratio are independent of the jet Reynolds number in the range of 5300–10,600. A slight modification of the flow field is observed for a surface-to-jet velocity ratio of 0.25 whereas at higher ratios of 0.5 and 1, the flow field is significantly affected.
The topic of this investigation covers the study of the kinetics of colour formation during the baking of crackers in a static electrically heated oven. Methods for measuring the kinetics of variation of product temperature, water content and surface colour (assessed in CIE 1976 (L∗, a∗, b∗) system) are described. An appropriate experimental set-up was developed and experiments with increasing baking times were realised in order to reconstitute the whole baking profiles. The validity of this method was proved using continuous temperature recordings.Experimental recordings of cracker surface lightness during baking show first an enlightenment and subsequently a darkening phase. The darkening phase is initiated when the product temperature reaches a critical value in the range of 105–115 °C.A kinetic model was developed in order to predict the lightness variation of the cracker surface using the product temperature and moisture content variations during baking. The evolution of lightness appears to follow a firstorder kinetic influenced by these two parameters.
Water soluble pectin-enriched materials (PEMs) from apple pomace, were evaluated as a fat replacer in a model food system. When PEM solutions were subjected to steady-shear measurements, shear-thinning behavior was observed. The flow behaviors could be described by the Cross model (R(2)=0.99), and temperature effects were investigated by the Arrhenius equation. The addition of PEMs significantly increased the pasting parameters of wheat flour as measured by a starch pasting rheometer. Gelatinization temperature and enthalpy increased with increasing PEM concentrations. When PEMs were incorporated into cookie formulations in place of shortening (semisolid fat generally used in baked foods) up to 30% by the weight of shortening, the cookie spread diameter was reduced while an increase in the moisture content was observed. Moreover, replacement of shortening with PEMs contributed to a more tender texture and lighter surface color.
Thesis (Ph. D.)--Université Laval, 1999. Includes bibliographical references.