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The effects of airflow on oven temperatures and cakes qualities
Abstract
The presence of airflow during heating process is expected to increase heat uniformity in a closed heating chamber. Circulation of hot air increases the percentage of convective heat transfer. In this study, effects of airflow on oven temperature, cake temperature and several cake qualities were investigated. Experimental studies were conducted in convective oven using two different baking modes; with and without airflow. During baking, oven temperatures and internal cake temperature were measured, and images of cake expansion were captured. Results of the study showed that the presence of airflow could maintain the oven temperature within a small range of set point temperature. Temperature in the oven exhibited ±5.5°C fluctuation, approximately 3.5% overshoot that occurred continuously during baking with airflow. On the contrary, higher overshoot (ranging from 15 to 30%) was observed in oven temperature without airflow. Airflow also showed a significant effect (p<0.01) during the second stage of baking. The presence of airflow increased the heating rate and resulted in a faster volume expansion, which was 3.21mm/min, as compared to 2.88mm/min without the airflow. However, airflow dried off the cake surface, resulted in quicker browning, higher weight loss and lower moisture content of cakes.
... The percentages of moisture content in the air fryer baked-cake and convection oven-baked cake was found within the range of 26% to 28% on a wet basis while the initial moisture content of the batter was 31.03 ± 1.12%. Similar with previous study by Shahapuzi et al. (2015) found that when baking with and without airflow, the moisture content of cake batter ranged from 25.27% to 33%. Although different process conditions, the moisture contents of cakes baked still lies within the range of accepted moisture content of moist cakes which is 25-30% (Cauvain and Young, 2010). ...
Rapid airflow in oven will influence the heat transfer in baking process therefore the purpose of this study is to experimentally and numerically investigate the effects of operating conditions on the heat transfer mechanism and volume expansion during baking. Cakes are baked in an air fryer and convection oven with constant speed 5.11 m/s and 0.88 m/s respectively at 150, 160, 170 °C in different baking times. A heat transfer model was defined to describe the influence of baking temperature on internal cake temperature by Fourier’s law. It was observed that the presence of rapid airflow (air fryer) and increment in oven temperature yielded an increase in volume expansion but produced a less moist product. Cakes baked in the presence of rapid airflow at 150 °C were moister but with little volume expansion in the cakes compared to convection oven-baked cakes. Significant correlation between the numerical models with experimental temperature profiles were recorded during complete cake baking process.
Baking temperature and time are among the conditions for producing good quality cakes. The aim of this study was to investigate the effects of baking temperature and time on the volume expansion, moisture content, and texture of moist cakes baked in either an air fryer or a convection oven. The cakes were baked under different conditions: (1) baking temperature of 150 °C, 160 °C, and 170 °C for both air fryer and convection oven and (2) baking time of 25, 30, 35 min for air fryer and 35, 40, 45 min for convection oven. Baking temperature and time were found to have a significant (p < 0.05) effect on the relative height, moisture content, firmness and color of the product but no significant effect on the springiness of the product. Based on the numerical optimization method, the optimum condition in an air fryer was 150 °C for 25 min. These optimized conditions resulted in higher relative height (37.19%), higher moisture content (28.80%), lower crumb firmness and chewiness (5.05 N and 1.42 N respectively) as well as higher overall acceptance score (5.70) as compared to optimum condition in convection oven (150 °C at 55 min). Moreover, baking in the presence of rapid air flow in an air fryer may be declared that it is possible to produce high-quality moist cake with minimum baking temperature and shorter baking time.
Experimental data concerning heat and mass transfer phenomena during the baking process of a sponge cake batter are presented, namely the surface and internal temperatures profiles, the surface and mean water contents and the cake expansion curves, for different process temperatures and batter thicknesses. The product textural evolution during the process was also investigated by photography and image analysis. By means of these data, two baking periods and the corresponding main transfer mechanisms were described, namely the “heating up” period and “crust and crumb” period, delimited by the formation of a dry crust at the batter heated surface. During the heating up period, water migrated from the core to the surface by diffusion in liquid phase and heat was transferred from the surface to the core by conduction and by water vapor evaporation, diffusion and condensation. During the crust and crumb period, the main resistances for heat and mass transfer are located in the dry crust where heat was transferred by conduction and water vapor migrated by convection under a gradient of total gaseous phase pressure.
Particle Image Velocimetry (PIV) was used to map the internal airflow of a domestic kitchen oven. Oven cooking performance is dependant on the airflow within the cavity. Previous flow measurement techniques such as hot wire anemometry and pitot probes are very time consuming and prone to error in the hot recirculating flow in an oven. The oven cavity, a commercially available mid-range oven, was modified for optical access. The PIV system consisted of a CCD camera, light sheet illumination from a pulsed Nd:YAG laser, and propanediol droplets and hollow glass spheres with a Stokes number of less than 0.055. Experiments were conducted in an empty oven at room temperature and at 180oC, and at 180oC with a single cooking tray installed. Velocity fields were measured in seven adjacent, coplanar object planes each on four different planes in the oven. The velocity data was averaged to yield mean flow fields, and the seven coplanar data fields were subsequently collaged to produce a full cross-sectional velocity map for each oven plane. In the cold and hot empty cavity a single vortex centred on the fan axis was seen, with strong radial flow. The maximum measured velocity in the cold oven was 1.8ms-1, which compared well with earlier hot-wire measurements. When a tray was introduced, the single vortex was replaced by three circulatory features. Shear flow was seen on both upper and lower sides of the tray, with a lower velocity and a stagnation point on the upper side.
Experimental and computational fluid dynamics (CFD) analyses of the thermal air flow distribution in a 3-zone small scale forced convection bread-baking oven are undertaken. Following industrial bread-making practise, the oven is controlled at different (constant) temperatures within each zone and a CFD model is developed and validated against experimental data collected within the oven. The CFD results demonstrate that careful selection of the flow model, together with implementation of realistic boundary conditions, give accurate temperature predictions throughout the oven. The CFD model is used to predict the flow and thermal fields within the oven and to show how key features, such as regions of recirculating flow, depend on the speeds of the impinging jets.
A multiphase model for simultaneous heat and mass transfer in porous medium was developed to simulate the baking process of a bread product. The model was based on Fourier’s law for conductive heat transfer and Darcy’s and Fick’s laws for mass transfer of liquid (water) and gas (water vapour and CO2) phases. Explicit formulation was adopted for the evaporation rate allowing direct solution of the system of equations. The use of the non equilibrium approach, allowed the implementation of the model in commercial software. Numerical Finite Element Method (FEM) scheme was used to solve the equations. The model was compared with experimental results reported in literature. Results show a good agreement between experimental and numerical results. Sensitivity analysis of the effect of the evaporation rate constant and process operating conditions on the temperature and moisture content were conducted and showed that the baking process was affected mainly by the convective heat transfer and the product initial moisture characteristics.
This paper discusses the validation of a Computational Fluid Dynamics (CFD) model to calculate the heat transfer in an industrial electrical forced-convection oven. The CFD model consists of the continuity, momentum and energy equation with the standard k–ε approach to model the flow turbulence. Density effects are accounted for through a weakly compressible formulation. Time-dependent boundary conditions and source terms are derived from a simplified lumped model, which results in a good qualitative agreement of the calculated oven temperatures and the measured temperature distribution. The average oven temperature difference between measurements and predictions is 4.6°C for a set point of 200°C. The heating uniformity of PVC bricks in different configurations was calculated with the CFD model, but the wall functions in the k–ε model limit the accuracy to a qualitative agreement. A correlation was established between the calculated flow field variables and measured surface heat transfer coefficients.
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.
A high temperature humidity sensor was used to monitor the absolute humidity inside an electrically heated conveyorized, food service-scale, two-zone, air-jet impingement tunnel oven as commonly used by pizza chain restaurants. The oven was first operated empty, then loaded with dummy loads consisting of pans of water in perlite while baking layer cakes, and finally when baking cakes with added dummy loads. Temperature and loading affected humidity, and humidity affected final product quality. High humidity lightened cake crust color, increased volume, and raised the final moisture content of the cake. There was no significant effect of humidity on the heat transfer coefficient as determined by a standardized metal target plate. In this study, one pan of perlite approximated three pans of cake. Adding perlite dummy loads was shown to be a useful technique to quantitatively measure and to demonstrate the effect of humidity during baking. It is also a convenient way to accelerate oven load-testing without producing and discarding a large number of samples.
There are well-known difficulties in making measurements of the moisture content of baked goods (such as bread, buns, biscuits, crackers and cake) during baking or at the oven exit; in this paper several sensing methods are discussed, but none of them are able to provide direct measurement with sufficient precision. An alternative is to use indirect inferential methods. Some of these methods involve dynamic modelling, with incorporation of thermal properties and using techniques familiar in computational fluid dynamics (CFD); a method of this class that has been used for the modelling of heat and mass transfer in one direction during baking is summarized, which may be extended to model transport of moisture within the product and also within the surrounding atmosphere. The concept of injecting heat during the baking process proportional to the calculated heat load on the oven has been implemented in a control scheme based on heat balance zone by zone through a continuous baking oven, taking advantage of the high latent heat of evaporation of water. Tests on biscuit production ovens are reported, with results that support a claim that the scheme gives more reproducible water distribution in the final product than conventional closed loop control of zone ambient temperatures, thus enabling water content to be held more closely within tolerance.
INTRODUCTION BAKING STAGES HEAT TRANSMISSION OVEN SPRING REACTIONS DURING BAKING ROLE OF OVEN STEAM OVEN PROBLEMS ENERGY REQUIREMENTS OVEN
To simulate the dynamics of an industrial continuous baking process where dough was conveyed continuously into the oven chamber as a first-in-first-out system, a three-dimensional computational fluid dynamics (CFD) model with moving grids was developed. With a transient state assumption, the model could predict the dynamic responses during the continuous baking. By integrating it with the mathematical models developed earlier by the authors, variations in bread quality due to changes in the oven load were estimated. The results were consistent with the actual measurements from the industrial baking process. The model was further used to investigate the oven operating conditions which could produce the optimum baking condition. According to the simulation results, the heat supply could be reduced whereas the airflow volume should be increased. With this modification, the weight loss of bread could be reduced by 1.4% with an acceptable crust colour and a completed baking as indicated by its internal temperature.
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.
An electric convective oven was conceived and equipped to allow monitoring thermal reactions during the baking of sponge cake. High total heat fluxes of between 6000 and 9000 W m−2 were recorded under baking temperatures of 140–200 °C. The mapping of thermal conditions indicated satisfactory thermal homogeneity, with average temperature variations of 5 °C and maximum relative variations of the convective heat transfer coefficient of 15% on the thermal domain investigated. Internal heat and mass transfers, the extent of thermal reactions within the sponge cake and repeatability of the baking operation were all characterized by experimental measurements. Some of the main operating variables were monitored in the cake (core and surface temperatures, moisture content, levels of chemical reactants and products) and others in the baking atmosphere (temperature, humidity and concentrations of volatile compounds). Specific non-disruptive sampling devices were designed to extract data from cakes and the oven atmosphere in order to follow the kinetics of thermal reactions during the baking operation. Three phases could be identified during baking, corresponding to the relative importance of conductive and evaporative internal heat transfer regimes and to macroscopic changes in the cake structure with formation of a crust. The progress of thermal reactions was monitored with satisfactory precision in both the cake and the baking vapors: relative standard deviations of 2% and 8.7% were obtained respectively for the water content and hydroxymethylfurfural (HMF) content of three replicates during a baking operation.
In this study, response surface methodology was used to design gluten-free cakes made from rice flour to be baked in infrared-microwave
combination oven. Two types of cake formulations containing different types of gums were used in the experiments, which were
xanthan gum and xanthan–guar gum blend. The independent variables were emulsifier content (0, 3, and 6% of flour weight),
upper halogen lamp power (50, 60, and 70%), and baking time (7, 7.5, and 8min). Specific volume, surface color change, firmness
and weight loss of the cakes were determined for optimization. Cakes formulated with xanthan gum had better quality characteristics
than cakes containing xanthan–guar gum blend. Cakes formulated with xanthan gum and 5.28% emulsifier and baked using 60% halogen
lamp power for 7min had the most acceptable quality.
A dynamic height profile method using digital imaging of cakes at 2min intervals during baking was used to analyze changes
in volume during baking for cakes made with three different flour types (plain flour, heat-treated cake flour, and strong
white flour) and baked at three different temperatures (175°C, 190°C, and 205°C). The cakes made from the different flours
showed, with some exceptions, a similar trend in the shape and development of the top contour during baking. In the first
4–6min of baking, there was relatively little expansion followed by a period of rapid expansion to the maximum volume and
a period of contraction up to the end of baking. For the three flour types, volume peaked at 16–17min for the medium and
high baking temperatures and at 20min for the low baking temperature. Cakes made from heat-treated cake flour and strong
white flour baked at low and high temperatures produced cakes where the center of the cake was lower than the surrounding
pins resulting in a final undesirable dimpled cake contour. A higher baking temperature caused the cake to rise more rapidly.
Baking at high temperature produced cakes which shrank the most (P < 0.001) during cooling. Among all combinations of flour type and different temperature treatments, cake made from heat-treated
cake flour baked at the middle temperature produced the best final cake in terms of a final dome-shape contour, an appreciable
volume during baking, less volume shrinkage during baking, and maximum cross-sectional area of the half cake after 1h cooling.
KeywordsCake-Dynamic height profile-Baking temperature-Cake shrinkage-Batter viscosity-Cake firmness
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.