Heat-Exchange Technologies for Effective Food Pasteurization
Heat-Exchange Technologies for Effective Food Pasteurization
The development of pasteurization as a method to destroy pathogenic bacteria in food and drink and, therefore, aid in food safety, dates back to the 19th century. However, the origins of heating (rather than cooking) food and drink for the purposes of preservation go back to China in the 12th century, where the technique was used to keep wine fresh and drinkable. Since these early beginnings, both the scientific understanding and the technical uses of pasteurization have improved as longer and more complex food chains have become the norm.
Developments in the equipment used for the primary methods of pasteurization mean that more products can be pasteurized with little or no impact on quality or taste. Yet, commonly held misconceptions may play a part in preventing food producers from using pasteurization technologies or getting the most out of them.
Pasteurization is not the same as sterilization. While this may seem obvious, the differences between the two processes are not always fully understood. It is, therefore, worthwhile to consider the differences at the outset to ensure you choose the right process for your requirements. Two common methods of food pasteurization are high temperature, short time (HTST) and low temperature, long time (LTLT).
Unlike sterilization, pasteurization does not completely eliminate micro-organisms that may be present in the foodstuffs. Pasteurization reduces the microbial load by a significant factor (for example, by 5-logs). In other words, in normal circumstances, pasteurization reduces contaminating pathogens to a level at which they do not pose a hazard.
In contrast, sterilization can be defined as any process that eliminates, removes, kills or deactivates all forms of life or biological agent present in a material or on a surface. There are, therefore, many ways to sterilize, including the use of heat, chemicals or radiation. As it relates to food and drink products, sterilization aims to have a much bigger effect on the microbial load of the product. It also is more likely to have unwanted effects on quality parameters such as taste and texture.
The exact costs of pasteurization equipment vary according to the requirements of each installation. In all applications, as with any other food processing activity, there is an initial capital cost together with ongoing costs associated with energy use, service and maintenance.
Food products recalls in the United States alone cost as much as $10 million each year, and that cost does not include the potential impact or damage to the brand. In 2017, 24 different food recalls — due to E. coli, Listeria monocytogenes and Salmonella — resulted in the destruction of some 700,000 pounds of products.
Pasteurization can be used for viscous fluids such as soup.
When these negatives are considered, the capital costs of pasteurization systems such as corrugated-tube heat exchanger systems appreciate. Some heat exchangers and pasteurization units are designed to reduce fouling and maintenance requirements to minimize ongoing operating costs. Furthermore, using systems that recover heat means that the energy costs required for pasteurization heating are kept to a minimum.
Pasteurization is a simple process: It requires that a material be held for a certain time at a certain temperature in order to kill micro-organisms. Additional complexity comes from the design factors applied to commercial pasteurization such as maintaining product output and quality.
There is no doubt that pasteurization is an additional step in the overall manufacturing process. If well designed, however, it should not slow down throughput or place additional management burdens on the plant. The use of continuous pasteurization systems means that the process is simple, and the potential for product damage or changes in quality is minimized.
Pasteurization Is Suitable for a Range of Materials
One misconception is that pasteurization only can be used with relatively simple fluids such as milk or fruit juice. With careful equipment selection, it can be used successfully with many liquid and semi-liquid materials.
Simple Newtonian fluids are the easiest to work with and often can be effectively pasteurized with a simple plate heat exchanger. Solutions exist for almost any material, however. Corrugated-tube and scraped-surface heat exchangers can deal with viscous fluids requiring gentle handling or with low rates of heat transfer. Such technologies also can be used with complex mixtures such as curd cheese, which could otherwise foul the heat exchanger.
Many plant managers in the food industry know that subjecting viscous or non-Newtonian fluids such as cooking sauces to shear stress during the manufacturing process can damage the quality and texture. This limitation prevents the use of certain designs of heat exchangers. Using a system such as a scraped-surface heat exchanger prevents fouling while maintaining relatively low pressure, so such unwanted effects can be overcome.
Pasteurization often is used with relatively simple fluids such as milk or fruit juice, but it also appropriate for many other liquid and semi-liquid materials. This pasteurization system is used in a tomato processing plant.
Energy and Maintenance Requirements
The amount of energy required for effective food pasteurization will vary considerably depending on:
- The type of pasteurization used (for example, HTST or LTLT).
- The type of material being treated.
- The type and design of heat exchanger used.
The bulk energy requirement is needed to raise the temperature of the foodstuff. Traditionally, many units have simply dumped this heat once the product has been pasteurized, resulting in a wasteful and inefficient process.
The solution is to recapture the remaining heat after pasteurization and use it again to either to reduce the amount of initial heat required or to provide heat elsewhere in the process such as heating cleaning water. This makes heat exchangers up to 70 percent more efficient than some traditional designs.
The use of corrugated tubes, together with integrated cleaning-in-process (CIP), minimizes the amount of fouling and, therefore, the amount of cleaning necessary to maintain the efficiency of pasteurization systems. The careful design of static tubes also helps to keep down production (and purchase) costs.
In conclusion, carrying out pasteurization need not be overly onerous or detrimental to the quality of the product. With the appropriate equipment choice, pasteurization does not need to have a negative effect on line or plant throughput or efficiency. A well-designed system incorporating heat regeneration and corrugated tubes should enhance the overall facility, helping to add flexibility to your business.
Food processors should consider whether adding pasteurization technology — to existing equipment or when a new line is specified — can improve or upgrade current processing capabilities. Bearing the above points in mind when talking to potential equipment suppliers can help ensure you achieve efficient, cost-effective food preservation.