What the processor works so hard to achieve in the smokehouse can often be adversely affected by improper cooling of the product after cooking. Critical factors such as product quality, consistency, and cost of manufacture are directly related to the proper cooling of product just as they are to the proper processing of product in the smokehouse. The following discussion concerns itself with the importance of "Post- Smokehouse Processing" through cooling technology. Product Cooling Proper cooling of processed meat products is a matter of necessity in today's market. Proper cooling is needed to preserve the product in most cases. A majority of meat products depend upon cooling to prevent spoilage. Government regulations to a large extent dictate the safe temperatures to which product must be cooled, and often prescribe the amount of time in which a particular product must reach the chilled temperature. Product taste and quality can be affected by the efficiency of product cooling. After cooking, processed meats which depend upon cooling for preservation will fare better if cooled promptly, rapidly, and uniformly. Cooling also plays a role in the profitability of processed meats. Product quality, in terms of taste, shelf life, texture, and appearance, can be influenced by the cooling process. Overall product yield, yield uniformity, and slicing yield can also be affected by the manner in which product is cooled. Inefficiently cooled product may result in higher percentages of rework. And finally, operating costs are affected by the efficiency (or inefficiency), with which products are cooled. Clearly, product cooling should be considered important to the processor's profitability. Cooling Methods and Theory The proper cooling of processed meat products is directly influenced by two factors: the physical characteristics of the product, and the method of heat transfer. For these reasons, both cooling methods and cooling theory are important in understanding and evaluating the cooling of meat products. Cooling theory is used to develop cooling methods. At the same time, new cooling methods generate increased knowledge of cooling theory and product characteristics during the cooling process. Cooling Methods Four methods of cooling processed meat products are illustrated in this discussion
 These methods each have advantages, disadvantages, and limitations with respect to chilling of particular processed meats. A more detailed comparison of air chilling and liquid chilling methods appears later in this discussion. Cooling Theory Cooling technology is greatly affected by underlying cooling theory. A general knowledge of the basic principles of heat transfer, thermal properties of processed meat products, and temperature relationships between product and cooling medium is beneficial. An understanding of these principles will provide a better opportunity to evaluate the efficiency and effectiveness of a cooling system and compare alternate methods of cooling. Principles of Heat Transfer Two basic modes of heat transfer, conduction and convection, occur during the cooling of meat products.
Thermal Properties A number of thermal properties of processed meats are of specific interest in establishing a basic understanding of cooling theory. They are listed as follows:
Temperature Differential I n establishing effective product cooling parameters, the temperature difference between the product surface and the product core will determine the cooling rate. Just as a high surface-to-core temperature difference results in a faster heating rate, the same relationship exists for product cooling. This is important in achieving rapid chilling rates and in developing a proper cooling system design. Factors limiting the cooling rate, however, will be the thermal conductivity of a product and the feasible or practical refrigeration temperatures that can be used.A basic knowledge of cooling theory will allow a better understanding of product cooling and how the product is affected by different cooling methods. Experimental testing is still important, and should be relied upon to establish the basis for cooling system design. Air Versus Liquid Chilling Air and liquid chilling are the two primary methods of cooling processed meat products in use today. Each method is often promoted as superior to the other by both manufacturers and processors alike. In reality, methods, air and liquid, have advantages and disadvantages. Depending upon specific circumstances, one method may indeed be better suited than the other. It is important to consider the type of products being chilled, the particular cooling criteria demanded by a product, and limitations which might be imposed by the facility or by environmental or other regulations. This discussion presents a comparison of air and liquid cooling methods. Heat Transfer Coefficient: When evaluating cooling methods, efficiency is of significant importance. The measure of a cooling system's efficiency is expressed in terms of a heat transfer coefficient. It is often called a "U" factor. The heat transfer coefficient expresses the heat removal efficiency as Btu per hour-foot °F. It is actually a measurement of a system's capability to remove heat via convection. As noted previously, convection is the mode by which heat is transferred from the product surface to the cooling medium. The heat transfer coefficient of a cooling system is affected by two primary factors, the type of convective heat transfer and the cooling medium. Convection is classified as either "free" or "forced" convection. The cooling medium, for purposes of this discussion, refers to either air or liquid. Free convection is a mode of heat transfer in which the product heat is transferred to a non-moving cooling medium. Forced convection, on the other hand, is a mode of heat transfer in which the cooling medium is agitated or fan-driven. Of primary interest is the fact that forced convection creates a higher heat transfer coefficient than free convection because of the movement of the medium. Further, a liquid cooling medium has a significantly higher coefficient than air. Table 2 illustrates these comparisons.
Air Chilling Conventional Air Chilling. Product cooling utilizing air is by far the most common cooling method used in the meat processing industry. It has a long history of use and remains the most common method of cooling meat products despite the inefficiencies inherent in large holding coolers and many blast coolers. As a cooling method, conventional air chilling is typically applied by means of forced convection. Some strengths and weaknesses of conventional air chilling are listed as follows:
High Performance Air Blast Chilling. A significant improvement in chilling efficiency using air can be achieved using the more recently developed technology of "high performance air blast chilling." This technology effectively utilizes "moving front" air handling methods similar to those successfully used in modern food processing ovens. Results show dramatic improvements are achievable when compared to conventional holding and blast cooler performance. Some strengths and weaknesses of high performance air blast chilling are listed as follows:
Liquid Chilling The use of liquid as a method of cooling processed meats takes various forms in the meat processing industry. Water is the most common form of liquid chilling, whether used as an initial shower in the smokehouse after cooking, or in tanks for immersion chilling. Water has obvious limitations imposed by its freezing point, and is unacceptable as a recirculated cooling medium. The most prevalent forms of liquid chilling found in the industry are sodium chloride (salt) brine and propylene glycol solutions. Each of these liquid cooling mediums are widely used and accepted, and achieve the most rapid cooling of the methods compared. Some strengths and weaknesses of liquid chilling are listed as follows:
Brine vs. Glycol: When comparing brine and glycol as liquid cooling mediums, it is important to consider a number of factors. Each medium has advantages and disadvantages, as do each of the cooling mediums discussed. Further, considerations regarding the type of product being chilled will undoubtedly point to the liquid cooling medium best suited for your application.
Conclusions Cooling technology is an important aspect of "Post-Smokehouse Processing". Product quality, yields, consistency, and uniformity can be just as strongly affected by what occurs during cooling as by what happens in the smokehouse. For this reason, the cooling of processed meats requires careful attention:
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