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.     

Influence of the amount of steaming during baking on the kinetic of heating and on selected quality attributes of bread

The effect of the amount of steam injection on selected bread characteristics were investigated using a deck oven (1 m² internal surface). Baking was done at 200 °C for 20 min with steaming of 100, 200, 300, 400 and 500 ml. The temperature at center of the bread and the CO₂ concentration in the oven have been measured during baking. Specific volume, moisture loss and crust crumb ratio were measured after baking.The heating rate between 35 and 55 °C was considered to compare the steaming conditions. For low steaming (100 and 200 ml), the heating rate was significantly higher (p < 0.05) than those at higher steaming (400-500 ml). The heating rate at 300 ml was between the 100-200 and 400-500 ml groups. This difference was attributed to the condensation of steam on the loaf for higher steaming, which in turns slows down the heating rate. The largest bread volume was obtained either for low or high steaming. However, tearing of the crust was observed for low steaming. The crust-crumb ratio was increasing with decreasing amount of steaming. The amount of CO₂ released during baking was higher for the highest amount of steaming; however, this result was not statistically different except between 100 and 500 ml. This could be attributed to a slower heating rate which in turns favors the secondary production of CO₂ during baking until thermal inactivation of CO₂.     

Bread baking: Technological considerations based on process modelling and simulation

This paper presents a study of bread baking, mainly from a technological point of view, i.e. focused on transport phenomena and major quality changes occurring during the process. Such study was carried out by numerical simulation of a previously developed and validated mathematical model, which describes the simultaneous heat and mass transfer (with phase change in a moving boundary) taking place in bread during baking. Kinetic models for starch gelatinization and browning development were coupled to the transport model. Input variables to the model were oven temperature, heat transfer coefficient, and bread radius. A total of 105 operating conditions were simulated using the finite element method, and the end point of baking was established for three values of surface lightness. It is shown that an intense heating strategy can produce a browned but unbaked product, besides nutritional quality is negatively affected. Furthermore, minimization of baking time is restricted by internal resistance to heat transfer.     

An investigation of bread-baking process in a pilot-scale electrical heating oven using computational fluid dynamics

A computational fluid dynamics (CFD) model was developed for bread-baking process in a pilot-scale baking oven to find out the effect of hot air distribution and placement of bread on temperature and starch gelatinization index of bread. In this study, product (bread) simulation was carried out with different placements of bread. Simulation results were validated with experimental measurements of bread temperature. This study showed that nonuniform air flow pattern inside the oven cavity leads to uneven temperature distribution. The study with respect to placement of bread showed that baking of bread in upper trays required shorter baking time and gelatinization index compared to those in the bottom tray. The upper tray bread center reached 100 °C at 1200 s, whereas starch gelatinization completed within 900 s, which was the minimum baking index. Moreover, the heat penetration and starch gelatinization were higher along the sides of the bread as compared to the top and bottom portions of the bread.     

Computational fluid dynamics modeling of bread baking process

A computational fluid dynamic (CFD) model was developed to study the temperature and browning profile of bread. This study differs from previous work of CFD modeling reported in literature in that phase change during evaporation as well as evaporation-condensation mechanism during baking process was incorporated in this model. Simulation results were validated with experimental measurements of bread temperature at three different positions. In this study crumb temperature does not cross 100 °C due to incorporation of evaporation-condensation mechanism in this model. Baking process completes within 25 min of processing time once the temperature of crumb becomes stable at 98 °C. Formation of crust and browning of bread surface were studied using earlier reported kinetic model and it predicted more browning at bread edges than the surfaces. However, predicted browning index was well within the range (< 52).     

An instrumented oven for the monitoring of thermal reactions during the baking of sponge cake

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.     

Computational Fluid Dynamics (CFD) Modeling for Bread Baking Process—A Review

Computational fluid dynamics (CFD) modeling of entire bread baking process is very complicated due to involvement of simultaneous physiochemical and biological transformations. Bread baking is a fickle process where composition, structure, and physical properties of bread change during the process. CFD finds its application in modeling of such complex processes. This paper provides the basics of CFD modeling, different radiation models used for modeling of heating in electrical heating ovens, modeling of bread baking process along with the predictions of bread temperature, starch gelatinization, and browning index. In addition, some recent approaches in numerical modeling of bread baking process are highlighted. Moreover, current limitations, recent developments, and future applications in CFD modeling of bread baking process are discussed in detail.     

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.     

Energy demand for selected bread making processes: Conventional versus part baked frozen technologies

This article presents some results on the energy demand in conventional bread baking and in the processing of frozen part baked breads, resulting from the “EU-FRESHBAKE” European project (FP6). Bread baking is one of the most energy demanding processes (around 4 MJ/kg), compared with other thermal processes such as canning. However, there is a large variability of data in the literature. For partial baking, bread has to be baked twice. It may also be frozen after part baking, which will increase the total energy demand. Results obtained with equipment used by craft bakeries are presented. Conventional and frozen part baked processes are compared. The effect of occupation ratio on the overall energy demand is also assessed. It was observed that 15–20% of the total energy is used for heating up the dough and 10–20% for crust drying. Pre-heating of the oven represents another significant energy demand. The energy demand for freezing is comparable to that for baking. An Energy Efficiency Index is used to assess the ratio of energy effectively transferred to the dough during baking. Part baked frozen technology demands about 2.2 times as much energy as conventional bread making process.     

Characterizing the cellular structure of bread crumb and crust as affected by heating rate using X-ray microtomography

The effect of two baking conditions 240 °C and 220 °C (corresponding to heating rates 7.39 and 6.11 °C/min respectively) on the cellular structure of bread was investigated using X-ray microtomography. A comparison between helium pycnometry and X-ray microtomography was carried out and confirmed the quality of analysis in 3-D. Porosity profiles were determined in the interface crust/crumb and showed higher porosity and lower density of the upper crust when increasing heating rate and baking with steaming. The porosity profile of the whole slice bread showed differences between breads baked at 220 °C and 240 °C; that can be explained by the non uniformity in local expansion during baking resulting in different areas of variable density. Higher density was found in the bottom of the slice due to compression forces during baking. However, the upper zone of the slice was more porous, in relation with the expansion. These differences influence the texture and led to different kinetics of staling. Results of tortuosity confirm that the relative path length is shorter along the height related to the expansion of the bread during baking. Additionally, the relative path length through the pores is shorter when baking at 240 °C than when baking at 220 °C, in relation with porosity.     

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.     

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.     

Bread improvers: Comparison of a range of lipases with a traditional emulsifier

This study compares three generations of lipase enzymes with the emulsifier, diacetyl tartaric esters of mono-glycerides (DATEM), on white wheat flour bread. Baking recipes with addition of DATEM (4500 ppm), Lipopan F-BG (15 ppm), Gryndamyl Exel-16 (115 ppm), Lipopan Xtra-BG (25 ppm) and Lipopan 50-BG (27.5 ppm) were test-baked after 60 and 150 min fermentations, to study their effects on the baking characteristics of volume, oven rise, crust colour, crumb texture and colour, shelf-life, flavour and aroma. The enzymes and emulsifier preparation caused significant increase in bread oven rise and specific volume with the exception of Lipopan 50-BG, which failed to improve loaf volume in the short fermentation method. There was no significant difference between other lipase enzymes and DATEM as a bread volume improver. Increase in fermentation time resulted in increase in volume in all samples, except for Lipopan-Xtra.     

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.     

Modeling Heat Transfer During Oven Roasting of Unstuffed Turkeys

A finite element method was used to solve the unsteady state heat transfer equations for heating of turkeys in a conventional electric oven. Breast, and thigh and wing joint temperature in 5.9, 6.8, 8.6, 9.5, and 10.4 kg turkeys were simulated. A surface heat transfer coefficient of 19.252 W/m2K determined by transient temperature measurements in the same oven, was used. Thermal conductivity measured using a line heat source probe from 0 to 80°C was 0.464 W/mK. Simulated temperatures were within 1.33, 1.47, and 1.22°C of experimental values of temperature in the breast, thigh, and wing joint, respectively. Initial temperature 1,2, and 3°C lower than 4°C required additional baking time of 16,22, and 27 min., respectively for the thigh joint to reach the target endpoint temperature.     

Physical, textural and sensory characteristics of 7-day frozen part-baked French bread

Bread partially baked for 7 min at 250 °C, after cooling, was frozen until core temperature reached −18 °C and stored at this same temperature up to 7 days. Samples were removed daily from the freezer, thawed and baked at 250 °C for 6 min. Analyses were performed 1 h after final baking, and were also conducted on fresh French bread daily produced (control). Weight and specific volume of frozen part-baked bread presented significant difference (P<0.05) compared with fresh one. Sensory analysis was carried out by a trained panel using the Difference from Control test to evaluate the difference and the degree of difference between frozen part-baked French bread (FPBFB) and fresh bread regarding appearance, tactile by direct touch and mouthfeel. All scores obtained indicated that the panelists, during the studied period, considered FPBFB to be slightly different compared with fresh one. Consumer Acceptance test was applied to compare appearance (gloss, roughness and cut on bread surface), oral texture (crust crispness and crumb firmness) and overall flavor between frozen part-baked bread and a commercial brand. All sensory scores obtained from Consumer test indicated that the 4-day frozen part-baked presented a superior acceptance to the commercial brand.     

INDIVIDUAL HEAT TRANSFER MODES IN BAND OVEN BISCUIT BAKING

The individual modes of heat transfer, e.g., conduction, radiation and convection, are considered for the processing of products in conventional band ovens. A specific theoretical model is considered for the baking of biscuits in an indirect fired oven. Values of individual heat transfer constants in the theoretical model and major effects of the individual modes of heat transfer were determined using lab scale heating devices. Extrapolating these results to a band oven baking process, the model indicated a heat transfer profile of about 20% heat transferred by conduction, about 45% by radiation and about 35% by forced convection in the band oven, with about half the heat being absorbed as sensible heat, and about half as latent heat.     

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.     

Effect of crust temperature and water content on acrylamide formation during baking of white bread: Steam and falling temperature baking

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.     

Effect of baking conditions and storage with crust on the moisture profile,local textural properties and staling kinetics of pan bread

To investigate the impact of baking conditions on staling kinetics and mechanical properties, pan breads were baked at 180 °C/34 min and 220 °C/28.6 min using a ventilated oven and metallic moulds. After baking, bread slices were stored with and without crust at 15 °C in hermetic boxes for 9 days. This investigation provides a textural and physical analysis by examining the Young's modulus, crumb density and crust/crumb ratio during storage. In order to understand the relationship between firmness and moisture content, a moisture profile and a Young's modulus profile were determined during the storage of bread. To fit the staling, a first order model was used. It was found that the kinetics were faster for samples baked with a fast heating rate than for those baked with a slow heating rate. Moreover, the staling rate of bread stored with crust was faster than for bread without crust and the outer crust area staled more rapidly than the centre of the bread slice. These results suggest that the firming of the crumb is related to moisture distribution between the crumb and crust and to the impact of local baking conditions on local firmness.