Author:

Keywords:

non-uniformity, temperature distribution, thermal cooking, food safety

Abstract:

One of the crucial factors in safe food processing is the application of accurate and effective process variable settings, e.g. time-temperature integration in thermal processing systems. However, air in a ventilated process such as inside meat cooking chambers is rarely distributed uniformly due to imperfect mixing of air. This creates non-uniform micro-climate conditions and can result to non-uniform product quality and more crucially to problems on food safety. Being able to define and quantify the degree of 3D spatio-temporal non-uniformity in temperatures inside food process systems would help improve process conditions to produce equally safe and constant quality food products. This study focused on establishing knowledge on the degree of airspace temperature non-uniformity during a thermal cooking process inside a force-ventilated, laboratory-scale meat processing chamber. A 3D-matrix (2x3x6) of 36 calibrated type-T thermocouples connected to a multi-data acquisition system was used to continuously collect data. Through 3D visualization, differences in airspace temperatures (maximum 11.2 ºC) were observed to generally occur during transition stages (come-up/come-down). During holding, temperature differences were found to be consistent. With an acceptable temperature difference of ±0.5ºC, the temperature uniformity index(UI) ranged from 6%(during come-up) to 100%(end of cooling). During holding, mean UI was still relatively low at 32±12%. The cooking process did not attain UI values above 80% until 25 minutes after cooling started. Moreover, 3D visualization of the distribution of well-mixed zones(WMZs), i.e. average temperature, cold, and hot zones, and quantifying their volumes at a given process time showed that throughout the heating process, coldest and hottest zones were consistently found to be at the bottom and middle right of the chamber, respectively. This implied that imperfect(non-uniform) mixing of heating medium inside the chamber actually occurred and can be attributed to poor air circulation, lower velocity of injected heating medium, and irregular air flow pattern.