The Difference Between Still and Rotational Motion of Complex Shape Chicken Carcasses

Abstract

In the food processing industry, particularly where naturally formed products are processed, complex shapes are frequently encountered. For example, in poultry processing, the shape of the products (chicken carcasses) is always a challenge. During processing, carcasses are transported, heated, cooled, washed, and cut. The thermal treatment of food requires the cooling and heating process be designed to meet certain conditions. This is despite the fact that products with heterogeneous properties and various sizes, shapes, and thicknesses are processed at the same time. Thus, the transport and thermal process cannot simply be predicted from previous work for well-defined shapes and sizes. Although more work is needed to understand the contribution of all the factors involved in processing, the current work focuses on the heat transfer and the complex geometry effect. The chilling process is a vital component of poultry production for both quality and safety. In order to prevent bacterial growth, the carcass core temperature needs to be cooled from 37–40 °C to 4 °C. Different poultry chilling systems exist within the industry to accomplish this task. Auger chilling is the most common method used in the United States, which is a process in which poultry carcasses are chilled by water immersion in a large tank with an auger. This has been the traditional method due to its efficiency in space along with its ease of implementation. Although auger chilling has been the traditional chilling method, in-line water chilling systems can be an alternative. In-line water immersion chilling creates a condition where a continuous line of carcasses hangs on shackles throughout the process. Potential benefits include enhancements in food safety, worker safety, economic, and processing labor requirements. Despite these benefits, inline chillers require a much larger spatial footprint due to the required dwell time. The objective of the current work is to improve a method of cooling by introducing relative motion between the carcass and the cooling medium (rotational kinematic component). Faster cooling reduces the dwell time of carcasses in the chiller, eventually reducing the footprint required which is the major drawback of in-line chillers. This experimental work will attempt to establish the difference and significance of two cooling conditions: 1. Cooling of complex shapes (chicken carcasses) in a still bath, and 2. Cooling of chicken carcasses under rotating motion. The experiment is designed to suspend chicken carcasses on shackles in a cooled ice water bath. The ice water is used to keep the temperature at a constant 0 °C. The built ice bath container mimics a typical processing line where chicken carcasses are suspended 30.5 cm apart. The container is 32.0 cm in diameter and 43.2 cm in depth and has a capacity to hold 34.7 liters of fluid. Two similar mass chicken carcasses are suspended by their legs and dipped into ice water, and the thickest part (breast) temperature is tracked. In fact, most food cooling processes are designed based on the worst-case scenario where the largest size is used to determine the thermal process requirement. In this case, the cooling process is evaluated by following the temperature history of the thickest part of the product, so cooling it guarantees that all the other parts are in cooled conditions. In this work, the experimental cooling rate of the suspended chicken carcasses for both cooling methods will be presented. Furthermore, this work will present models that can be used to predict the cooling process for both conditions.