Abstract
Few studies concerning contact heating of food products were found in the literature despite the importance of this mode of heat transfer in many operations (grilling, pan-frying) and its drastic impact on product quality change during heating. An original heating device to measure continuously contact heat flux and heating surface temperature was therefore developed and applied to the contact heating of turkey meat with a heating surface at 128°C, 215°C and 255°C. Based on the experimental results obtained, a simplified heat transfer model was developed and allowed the calculation of the parts of the total energy received by the product (i) used to raise its temperature (ii) used to evaporate water exuding from its lower surface during heating and (iii) lost by heat exchange with the surroundings. In the experimental conditions covered by our experiments, the part of energy used to evaporate water exuding from the product was found to vary between 55% and 67% of the total energy received. The precise evaluation of the kinetics of variation of the contact heat transfer coefficient (quantifying the quality of thermal contact between the lower surface of the meat sample and the heating plate) was also made possible. At 215°C and 255°C, this coefficient ranged from 500 to 100 W⋅m−2⋅K−1 between the start and the end of the cooking, these values being in the same order of magnitude as those measured in previous studies concerning single-faced grilling of meat.
Highlights
From industrial production to final preparation in the kitchens of consumers, food products undergo a large number of heat treatments
In order to perform contact heating experiments under controlled conditions, a contact heating device previously developed in our laboratory by Cernela et al (2015) was modified in order to meet the objectives of the present study, which included continuous measurement of the contact heat flux exchanged between the heating surface and the heated product
The kinetics of the rise in temperature in the three zones of the meat sample are shown in Fig. 2 for the tests performed at a set-point temperature for the heating surface of 215 ∘C
Summary
From industrial production to final preparation in the kitchens of consumers, food products undergo a large number of heat treatments. Many studies in the literature have been devoted to convection and radiation during the heating of food products (Erdoğdu, 2008; Rastogi, 2012), very few have focused on contact heat transfer. This seems paradoxical because contact heat transfer is the principal mode of heat transfer in many operations (single- or double-faced grilling, pan-frying) and is known to induce drastic quality changes in the zone of the product close to the heating surface, as studied for example by Kalogeropoulos et al (2006), Sioen et al (2006), Haak et al. As proposed by Incropera et al (2007), the effect of the geometry of this complex interface upon heat transfer between the two solids in contact can be globally described by the use of a thermal contact resistance Rct defined according to equation (1): Rct
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