Bakery product characteristics as influenced by convection heat flux

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.     

Effects of Heat Transfer by Radiation and Convection on Browning of Cookies at Baking

The effects of modes of heat transfer (radiation or convection) on the baking color development of food were studied. An experimental baking oven that could be altered to two heat transfer modes was designed; the ratio of heat by radiative transfer to total heat transferred was about 30% or 70%. The glucose-glutamate solutions were heated at different air temperatures to measure the browning rates to calculate the activation energies. Cookies were baked at 200°C to measure the lightness of color on the surface and the surface temperature. It was clarified that the development of color depended on the temperature only.     

Apparent Heat Transfer in a Forced Convection Oven and Properties of Baked Food

Parameters for expressing the heating performance and baking results of sponge cakes dependent on heating performance in a forced convection oven were studied. The heating performance of a forced convection oven may be expressed by the apparent heat transfer coefficient which was measured at various air temperatures and velocities. Both the air velocity and temperature of the circulating air affected the apparent heat transfer coefficient in a forced convection oven and determined the final properties of the baked food. The effects of these parameters on sponge cakes baked in the forced convection oven were observed.     

Baking of Sponge Cake: Experimental Characterization and Mathematical Modelling

Sponge cake is a sweet bakery product that begins as a fluid batter and, during baking, transforms into a porous solid, presenting an important volume expansion. The aim of this work was, first of all, to study experimentally the influence of operative conditions (natural and forced convection; oven temperature, from 140 to 180 °C; steam addition) on volume expansion and the heat transfer dynamics during baking of sponge cake. It was observed that an increase in oven temperature, airflow and steam injection produces an increase in volume expansion. Secondly, a mathematical model was developed to simulate heat transfer coupled with volume expansion. Both experimental and simulated temperature profiles verified that the last region to achieve a correct degree of baking is the one near the crust around the axial axis. In consequence, the minimal baking time was defined as the average time at which this region reaches 95–98 °C. The baking time was strongly affected by the effective oven temperature, with a slight influence of the convection mode.     

Computational fluid dynamics (CFD) modeling of an electrical heating oven for bread-baking process

Radiation is the most dominant heat transfer mode in an electrical heating oven. A 3D CFD model for an electric heating baking oven was developed. Three different radiation models namely, discrete transfer radiation model (DTRM), surface to surface (S2S) and discrete ordinates (DO) were employed for the simulation of the electrical baking oven. All models predicted almost similar results, which tallied well with the experimental measurements. During the full heating cycle, the oven set-point temperature was reached after 360 s. Lower temperature zones occurred near oven wall due to lower air flow. Based on preliminary evaluation of applicability, the DO radiation model was selected for bread baking simulation and validated with the experimental measurement of bread temperature. Bread simulation was carried out to study the profiles of temperature and starch gelatinization of crust and crumb of the product. This study indicated the baking process to be complete at 1500 s when the temperature of bread-center reached 100 °C.     

A quality comparison of breads baked by conventional versus nonconventional ovens: A review

Undesirable qualities of breads baked in nonconventional ovens have been observed by most researchers. The altered heat and mass transfer patterns and much shorter baking times associated with microwave radiation resulted in a crustless product with tougher, coarser, but less firm texture. Insufficient starch gelatinization, microwave-induced gluten changes, and rapidly generated gas and steam caused by the heating mode could be reasons for quality changes in the microwave-baked breads. Although breads baked in an electrical resistance oven did not brown, their interior characteristics and shelf-life were superior to those of products baked in a conventional oven. Bread with a superior keeping quality was obtained using an air impingement convection oven. The determination and explanation of the physical and biochemical changes that occur in products during baking in conventional versus nonconventional ovens are fruitful areas for future research.     

Baking of muffins: Kinetics of crust color development and optimal baking time

Baking is a decisive stage in the production of bakery products, in general—muffins, in particular—for most of the quality attributes of the final products depend on it. The aim of this work is to model the kinetics of muffin crust color development during baking and to evaluate the feasibility of this kinetic model to predict the baking times. Surface color is represented by the Browning Index, and the effect of baking temperature (from 140 to 220 °C) and process convective characteristics (natural convection, forced convection, and steam-assisted forced convection) are analyzed. Minimal baking times are calculated from experimental core temperature measurements. The modeling of browning kinetics, which incorporates the optimal crust color determined by sensory analysis, allows the estimation of optimal baking times. For all the tested conditions t _op?>?t _min, assuring a product whose inner structure was already totally baked. Finally, minimal, half, and optimal baking times present an exponential dependence with the oven temperature. Besides, there are no significant differences between both forced convection modes.     

CFD modeling of heat transfer and flow field in a bakery pilot oven

A bakery pilot oven is modeled using computational fluid dynamics software. This approach relies on integration of an instrument into modeled geometry. The instrument is a heat flux measuring device that can be used in the industrial baking process. All three heat transfer mechanisms are considered and coupled with turbulent flow. Turbulence is taken into account via the k–ε realizable model whereas the surface-to-surface model simulates the radiation. Additionally, buoyancy forces are introduced by means of a weakly compressible formulation. The model predictions show a good qualitative agreement with the experimental measurements. A quantitative agreement was obtained to some extent. Limitations came from the difficulty to measure the temperature of the radiant surfaces of the oven. Operating conditions used are typical of bakery products and, as expected, radiation was the dominant mode of heat transfer. The integration of the instrument was useful for assessing the model. Since it is designed for industrial use, it may be a valuable tool for future challenges in the field, such as simulation of an industrial scale oven.     

Heat Transfer Coefficients on Cakes Baked in a Tunnel Type Industrial Oven

Using an h-monitor, surface heat flux and effective surface heat transfer coefficients were evaluated during baking of two cakes in a tunnel-type multi-zone industrial oven. An average 75–80% of total heat flux was counted as radiation heat. Air-mass temperature outside the boundary layer was determined from the experimental temperature profiles over the h-monitor top plate. In the range of baking temperatures (186–22 5°C), relative air velocities (0.02-0.437 m/s) and absolute humidities (0.0267–0.0428 kg H₂O/kg dry air) heat transfer coefficients were 20 to 48.0 W/m²K. A simple regression model was developed based on experimental data.     

EXPERIMENTAL COMPARISON OF NATURAL CONVECTION AND CONDUCTION HEAT TRANSFER

Magnitude of fluid motion is significant in convective heat transfer (the faster the fluid motion, the greater the heat transfer), while in conductive heat transfer, there is no physical movement of objects undergoing heat transfer. Due to this statement, it is a real fact that convection can be many times faster than conduction. The objective of this research was to compare natural convection and conduction by creating both heat transfer mechanisms in the same product. For this purpose, canned water and 1% agar-gelled water were used in the experimental and further computational fluid dynamics studies. Experiments were conducted at 70C and in boiling water, and ANSYS V.10 (Ansys Inc., Canonsburg, PA) was used in the numerical simulations. The results showed that addition of agar prevented the natural convection phenomena in the gels resulting in pure conduction while the effect of natural convection, which occurred due to thermal buoyancy effects in the given gravitational force field, was obvious in the case of water. Creation of both natural convection and conduction heat transfer mechanisms in the same medium is an important contribution as the effect of natural convection over the conduction heat transfer can directly be emphasized.

PRACTICAL APPLICATIONS

Creation of both natural convection and conduction heat transfer mechanisms in the same medium would be an important contribution as the effect of natural convection over the conduction heat transfer can experimentally be emphasized. The results of this study are significant to show the significant difference between these heat transfer modes as both mechanisms were created in the same medium, and these results will be useful especially for teaching heat transfer purposes.     

Impact of Infrared Broiling on the Thiamin and Riboflavin Retention and Sensory Quality of Salmon Steaks for Foodservice Use

Salmon steaks were broiled using infrared radiation and compared to convection oven baking. Total percent cooking losses of moisture and fat content were not significantly different. Samples broiled by infrared oven retained 87.2% and 92.6% of thiamin and riboflavin content, respectively. There were no significant differences for vitamin retention by both methods. Appearance and color of salmon steaks baked in the convection oven were rated significantly higher than infrared broiled samples. Tenderness and juiciness scores for infrared broiled steaks were significantly higher than those for convection oven baked steaks. There were no significant differences in panel scores for odor, flakiness, flavor and overall acceptability of steaks prepared by both methods.     

Cake Baking in Conventional, Impingement and Hybrid Ovens

White layer cakes were baked in three types of air impingement ovens, a hybrid (microwave/air impingement) oven, and a reel oven. Cakes were evaluated based on volume, crust color, and texture. Oven heat transfer rates were measured directly, and ranged from 22.8 to 84.8 J/s m²C° for top and from 17.4 to 110.9 for bottom surfaces, exposed in the different ovens, with the conventional reel oven having the lowest values. An RSM design was used to establish optimum baking conditions for each oven. For air impingement ovens, baking time was reduced by almost half but produced cakes very similar to those from the control (reel) oven. Incorporating microwaves enabled a further reduction in baking time, to one fourth. Cakes baked with microwaves had similar color, but had 15% less volumes and firmer textures than control cakes.     

Modeling of simultaneous heat and mass transfer during convective oven ring cake baking

The convective oven ring cake baking process was investigated experimentally and numerically as a simultaneous heat and mass transfer process. The mathematical model described previously by the authors for cup cake baking was modified to simulate ring cake baking. The heat and mass transfer mechanisms were defined by Fourier’s and Fick’s second laws, respectively. The implicit alternating direction finite difference technique was used for the numerical solution of the representative model. Prior to the utilization of the developed model in predicting the temperature and moisture profiles for ring cake baking, the results of the numerical model were compared with analytical results involving only heat or mass transfer with constant thermo-physical properties. Excellent agreement was observed. The numerical temperature and moisture contents predicted by the model were compared with the experimental profiles. They agreed generally reasonably well with the experimental temperature and moisture profiles.     

Baking kinetics of muffins in convection and steam assisted hybrid ovens (baking kinetics of muffin…)

Effects of oven type and baking temperature on acrylamide concentration, surface browning, temperature profiles and drying rates of muffins were investigated. Muffins were baked in convection and steam assisted hybrid ovens at 145, 160 and 175 °C for different baking times. For all oven types, the acrylamide concentration of muffins increased with increasing baking time and temperature (p < 0.05). The formation was considered as the first order reaction kinetics except for the lowest baking temperature at natural convection and steam assisted hybrid ovens. The reaction rate constant, k was found to be in the range of 0.027–0.078 (min⁻¹). For the forced convection oven, the effect of baking temperature on acrylamide concentration followed the Arrhenius type of equation; with activation energy of 36.35 kJ/mol. The minimum drying rate was observed by the steam assisted hybrid oven, at all conditions. Steam assisted baking resulted in lower acrylamide concentration at all baking temperatures, while providing the average moisture content not significantly different.     

A Finite-Difference Model for Heat and Mass Transfer in Products with Internal Heat Generation and Transpiration

A finite-difference numerical model for heat and mass transfer in products with respiration and transpiration is presented. Besides conduction and convection, the model also accounts for evaporative cooling due to transpiration and radiation heat transfer. The model is more accurate than currently used finite-difference models and requires larger time steps.     

Convection and radiation combined surface heat transfer coefficient in baking ovens

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.     

Two-dimensional CFD modeling and simulation of crustless bread baking process

A special type of baking oven was developed where crustless bread was made by gently baking the dough at controlled temperature by spraying water at prefixed intervals on the surface of the dough. In this study, a two-dimensional (2D) CFD model for crustless bread during baking has been developed to facilitate a better understanding of the baking process. Simultaneous heat and mass transfer from the bread during baking was successfully simulated. It was found that core temperature of the bread reached at 95 °C at the end of baking where as moisture of the bread satisfies the normal bread quality. The model can be successively applied to study the unsteady heat and mass transfer from the crustless bread during baking.     

Development of an improved heating system for industrial tunnel baking ovens

This objective of this work was to develop, test and optimise the design of a novel gas-fired radiant burner suitable for incorporation into industrial tunnel ovens. Computational fluid dynamics (CFD) simulations have been used to model the burner and baking chamber environment, and in particular to predict radiation heat fluxes incident on the top surface of the food, both across the width of the baking chamber and along its length. Data from thermocouple sensors attached to a full-scale 40 kW prototype burner have been used to validate the CFD model. Initial results presented here show that CFD model predictions agree with experimental data to within 10%. CFD simulations have indicated that the new burner is capable of delivering irradiation to a travelling conveyor more uniformly than existing radiant burner designs. The effects of oven chamber humidity and surface emissivity on radiation heat transfer have been quantified.     

Acidulant and oven type affect total anthocyanin content of blue corn cookies

BACKGROUND: Anthocyanins, pink to purple water‐soluble flavonoids, are naturally occurring pigments with claimed health benefits. However, they are sensitive to degradation by high pH, light and temperature. Blue corn (maize) contains high levels of anthocyanins. Cookies are popular snacks and might serve as a vehicle to deliver antioxidants. A cookie formula with a high level of blue corn was developed with added acidulents and baked in ovens with different heat transfer coefficients. RESULTS: The best whole‐grain blue corn flour/wheat pastry flour ratio (80:20 w/w), guar gum level (10 g kg^?1, flour weight basis) and water level (215 g kg^?1, flour weight basis) were determined based on response surface methodology analysis. The interactions of citric and lactic acids and glucono‐δ‐lactone with three oven types having different heat transfer coefficients (impingement oven 179 °C/4 min, reel oven 204 °C/10 min and convection oven 182 °C/4 min) influenced the total anthocyanin content (TAC) remaining in blue corn‐containing cookies after baking. CONCLUSION: Cookies baked with citric acid in the convection oven retained the maximum TAC (227 ± 3 mg kg^?1). By baking rapidly at lower temperatures and adding acidulents, it may be possible to increase residual natural source antioxidants in baked foods. Copyright © 2010 Society of Chemical Industry     

MODELING HEAT AND MASS TRANSFER DURING THE OVEN ROASTING OF MEAT

The roasting (baking) of meat involves both heat and mass transfer. A mathematical model which describes the roasting process as it occurs in a conventional oven is presented. Numerical solutions are presented for several different roasting conditions and the results are compared to available experimental results. A significant fraction of the energy required for roasting is associated with the evaporation of water and this needs to be considered in modeling the roasting process. Water losses due to mass transfer from the product depend on oven humidity and temperature. The mathematical model considers the variation of oven humidity with time during roasting. The implicit alternating direction finite difference method is used to obtain the numerical solutions.