HEAT TRANSFER
RISING TO THE FOOD CHALLENGE
Heat exchanger solutions for five challenging foodstuffs, by Matt Hale, Global Key Account Director, HRS Heat Exchangers
T
hermal treatments, such as pasteurisation, heating and cooling, feature in the manufacture of multiple food and drink products. Many of these treatments use heat exchangers, but manufacturers must take into consideration various factors when choosing the right heat exchanger for their process, not least the physical
properties of the product itself. In this article we look at five of the most challenging foodstuffs in terms of thermal processing, and the heat exchanger solutions to help manufacturers handle them correctly.
1. Highly viscous materials Highly viscous foods,
including nut butters and other fat-based products, can be almost solid at low temperatures. This creates a number of challenges, one of which is physically moving the material through the heat exchanger. Other considerations include preventing the product from fouling the surface of the heat exchanger (which reduces thermal efficiency) and ensuring an even temperature throughout.
Nut butter requires a heavy duty rotating scraped surface heat exchanger (SSHE). The HRS RHD Series was specifically designed for such tough material. Combining the proven rotary scraper rod action of our standard R Series heat exchanger with a larger motor and bigger scraping rods, together with extra mounting supports, the RHD Series is equipped to handle even the toughest foodstuffs. 2. Products containing pieces The challenge when dealing with pieces of product is ensuring the mixture moves through the process at a constant speed (to ensure the correct temperatures are
38 NOVEMBER 2024 | PROCESS & CONTROL
maintained for the required time) without damaging the physical integrity of the product. This type of product can contain anything from small, diced vegetables to large fruit pieces. Many manufacturers also process a range of products using the same equipment, so processing lines need to be flexible – capable of working with both hard and soft products across a range of sizes. For this type of product, the Unicus Series of reciprocal SSHE is perfect. The separately controlled hydraulic scrapers are available in a range of designs and are fully controllable so a variety of products can be moved gently but effectively through the heat exchanger. 3. Thermally challenging products Some ingredients, such as eggs or chocolate, are very sensitive to temperature and must be processed at precise
temperatures to avoid damaging the product. Liquid egg, for example, is extremely delicate and the white and yolk are distinct components with different compositions and behaviours. When mixed, they interact mutually: egg white is denatured at 58°C while yolk is denatured at 65°C.
Because of this, pasteurising liquid egg can have a number of unwanted effects, including gel formation and softening of the yolk, irreversible denaturation of the proteins, or changes to the appearance. Choosing the right pasteurisation regime and equipment is therefore vital to minimise and prevent unwanted effects. Depending on the required handling, corrugated tube heat exchangers or SSHEs (like the HRS Unicus Series) are ideal for processing liquid eggs and other egg-based products.
Likewise, tempering chocolate is extremely
difficult. Without strict temperature control, the crystals formed are of different sizes and the resulting chocolate will ‘bloom,’ having a matt appearance and waxy texture. Without tempering, it is impossible to achieve chocolate’s characteristic ‘snap’ and glossy finish. The HRS R Series has been successfully used to commercially temper chocolate. The system uses three R Series
rotary scraped surface heat exchangers in series: the first raises the temperature by 19°C; the second cools it back down by 2°C; and the final heat exchanger raises it again, allowing the chocolate to be transported and worked elsewhere.
4. Delicate products
Many sauces, and some dairy products such as thick cream, need to be handled delicately in order to avoid splitting or shearing, while careful temperature control is required to avoid the creation of undesirable flavours, such as a burnt taste.
Heat exchangers used in the production of sauces and dressings must also work with high viscosity fluids and preserve any particles in the food without breaking them. Once again, the solution is a gentle yet thermally efficient reciprocating SSHE, such as the HRS Unicus Series. This quickly raises or lowers the product temperature while keeping pressure and physical agitation low to avoid damaging the product. 5. Very dense materials
Globally, there is increasing interest in using heat exchangers to process mechanically deboned meat (MDM), meat slurry and viscera components. One advantage is that heat exchangers have the potential to generate products with better quality, at lower cost and with less waste and lower energy consumption than via traditional methods. Many of these products have high fouling potential (which limits heat transfer), but also need delicate handling to preserve their integrity. In addition, their thick nature means that it can be difficult to achieve the required temperature all the way through the material. The HRS RHD Series has been employed commercially to keep meat viscera and similar materials below a specified temperature of 4°C. Modifications for this project included adapting the internal scraper configuration to achieve the necessary performance and implementing a heavy-duty gearbox to withstand the higher torques required to keep the product moving. Some heat exchanger developers will not offer solutions for certain food products because they are so challenging in terms of physical and thermal handling. However, HRS Heat Exchangers has spent the last forty years developing heat exchangers and processing systems, which are installed worldwide to handle these most difficult products.
HRS Heat Exchangers
www.hrs-heatexchangers.com
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