Jean-Yves Monteau

Transport properties of a high porosity model food at above and sub-freezing temperatures. Part 2: Evaluation of the effective moisture diffusivity from drying data

Abstract The moisture diffusion during freezing of porous medium has been widely studied for low porosity matrix (i.e. concrete, rocks, …), whereas very few works are available for materials with high porosity. This work focuses on the evaluation of moisture diffusion of a model food (sponge) with a high porosity (in the range of porosity 0.90–0.94). The drying data has been obtained at positive temperatures (10–30 °C) for selected water content (25–142 g H 2 O/100 g DM). Then, the effective diffusivities have been estimated by using two different methods. Finally, moisture diffusivity in the sub-zero domain has been extrapolated by using an Arrhenius’s model. During drying, the diffusivity increases as the average moisture content decreases. The temperature plays a significant role on the diffusivity. One of the two methods gives better results for the estimation of the effective diffusivity.

Transport properties of a high porosity model food at above and sub-freezing temperatures. Part 1: Thermophysical properties and water activity

Abstract Few data are available on the thermophysical properties of high porosity foodstuff in the freezing domain. This paper presents some data obtained with a cellulose sponge used as a model food. The fraction of unfreezable water was obtained from differential scanning calorimetry data, using two different methods with a very good agreement. Water activity was experimentally determined at positive temperature. Experimental data were modeled by the Guggenheim–Anderson–de Boer (GAB) model, and a model deduced from the Clausius–Clapeyron equation. The GAB model was used to extrapolate these data in the subzero domain. It showed a good agreement until a water activity of 0.9, whereas the second model is usable only up to the value of 0.75.

Effect of external conditions on the rate of post-baking chilling of bread

Abstract Effects of chilling conditions on moisture and cooling rate of bread were evaluated. Chilling time and water losses were assessed for four air temperatures between 5 and 20 °C. Results showed that high air temperature increased chilling time and decreased water loss. Cooling rate was high at the beginning of the cooling and decreased with time during chilling. Intense evaporation–condensation in the crumb combined with radiation was proposed as an explanation for this non-linear behaviour. A higher cooling rate was observed at surface than at centre and was confirmed by a higher water loss at surface of the product.

Effective Thermal Conductivity Evolution as a Function of Temperature and Humidity, During Freezing of a High-Porosity Model Food

The modelling of heat transfer within materials with high porosity is complicated by the evaporation–condensation phenomenon. The aim of this work is to develop a model of apparent thermal conductivity in these products. The effective thermal conductivity of a porous food model (sponge) having 0–60% moisture content and 0.92–0.94 porosity was measured by a line-source heat probe system in the range –35–25°C. Two predictive models of the effective thermal conductivity of porous food were developed (Krischer and Maxwell models). The effective thermal conductivity predicted by the Krischer model was in good agreement with the experimental data. Also, it was shown that the model, including the effect of the evaporation–condensation phenomenon in addition to heat conduction, was useful in predicting the effective thermal conductivity of foodstuffs.

Numerical modeling of heat transfer and pasteurizing value during thermal processing of intact egg

Abstract Thermal Pasteurization of Eggs, as a widely used nutritive food, has been simulated. A three‐dimensional numerical model, computational fluid dynamics codes of heat transfer equations using heat natural convection, and conduction mechanisms, based on finite element method, was developed to study the effect of air cell size and eggshell thickness. The model, confirmed by comparing experimental and numerical results, was able to predict the temperature profiles, the slowest heating zone, and the required heating time during pasteurization of intact eggs. The results showed that the air cell acted as a heat insulator. Increasing the air cell volume resulted in decreasing of the heat transfer rate, and the increasing the required time of pasteurization (up to 14%). The findings show that the effect on thermal pasteurization of the eggshell thickness was not considerable in comparison to the air cell volume.

Effect of Temperature on the Solubility of CO2 in Bread Dough

Dough expansion during fermentation is caused by CO2 production by yeast, and its transfer from liquid state in the dough liquor to gaseous phase in the gas cells. The liquid-gas equilibrium is controlled by the solubility of CO2 in the dough and by the Henry coefficient. The solubility of CO2 in bread dough was measured for different temperatures with a specific device based on the evolution of the pressure during fermentation at constant volume. The measurements range from 15 to 40°C. Data obtained was extrapolated to 0 and 50°C. Values were found between 1.6 × 10−5 and 5 × 10−6 g CO2 kPa−1 g−1 LPD, at 0 and 50°C, respectively (LPD: Liquid Phase of Dough).

Post baking bread chilling; evaluation of water pulverisation on bread surface to control weight loss and cooling rate

ABSTRACT Post baking chilling of bread is an important part of the bread making process. However, it is quite often underestimated in comparison to formulation, mixing or baking. During post baking chilling, the bread matrix that switched from dough to crumb during baking undergoes a solidification phase due to temperature decrease. The heat transfer associated with the cooling kinetic is largely influenced by evaporative cooling, especially at the beginning of the cooling process. This evaporative cooling corresponds to a significant water loss. This work presents original numerical and experimental results concerning the use of mist (water) spraying on the bread surface during post baking chilling. A numerical model has been developed with finite element software (FEMLAB). It accommodates the coupled heat and mass transfer in the bread during post baking chilling of French part-baked baguettes. Water diffusion in the crumb has been modelled using specific moisture diffusivity previously determined experimentally. The model was validated against experimental results. The main results showed that spraying water on the surface of the bread can help to limit the weight loss caused by evaporation but has a limited effect on the cooling rate of the bread (in our conditions). Comparison with other techniques, such as vacuum chilling, is discussed.

Coupled Heat and Mass Transfers in a Solid Foam with Water Phase Transitions: Application to a Model Foam and Bread

Abstract Industrial manufacturing of bread is made of empirical practices without precise knowledge of mechanisms that govern heat and mass transfer during the processes. The objective of this work is to develop a coupled heat and mass transfer model for solid foams. The model was first designed for a solid model of foam (cellulose sponge), and then applied to a real product (bread). The heat and mass transfer model was validated against experimental results. For the foam model in freezing, the transfer model revealed an inverse water content profile (more water at the surface than in the centre). Use of this model for bread reveals the concentration of ice crystals to be more important under the crust than elsewhere at the end of freezing.