Equipment Catching Up with Theory

Numerous processing innovations were displayed at the 2005 IFT Annual Meeting + Food Expo^®, including commercial offerings of relatively new processes such as high pressure and ohmic heating, as well as old reliables such as extrusion, retorting, and drying.

Commercialization is catching up with theory, as researchers continue discussing new processes while manufacturers offer off-the-shelf equipment to apply novel technologies. Extruders, dryers, and retorts likewise are still fruitful platforms for improvements. Here are some brief descriptions of some of the offerings at Food Expo:

• High Pressure. It is rare that major pieces of process equipment are displayed at the IFT Food Expo, but this year, directly across from IFT’s own booth, a fully operational high hydrostatic pressure unit was installed by NC Hyperbaric, Burgos, Spain. Reportedly it cost about $18,000 just to unload and install the machine, which has already been sold to a firm in New Zealand. Interest in purchasing similar units was said to be high.

The machine uses a horizontal chamber within a laminated steel yoke. The ends are sealed by an automatic plug backed by a heavy plate. Packages of food are placed in carriers which are automatically loaded from one end, pushing the previous charge out the discharge end. Circulating water is pressurized, and the pressure is held for the required time. Water is caught through a strainer and recirculated. Temperature of the water is controlled, since heat and high pressure work together to reduce microbial load. Most high-pressure-treated foods are refrigerated, since the process does not appear to reduce spores or inactivate enzymes.

• Ohmic Heating. Raztek Corp., Sunnyvale, Calif., displayed its electroheating equipment for rapid heating and cooling of foods. The heating is achieved by passing an electric current through the flowing food, which therefore must have some electric conductivity. The system uses cast ceramic tubes with special graphite electrodes at each end. In a typical system there are six tubes with an internal diameter of about one inch. The tubes are quite stout, probably because of the way they are manufactured. The graphite electrodes have precisely machined openings through which the fluid flows.

Commercial applications include liquid egg products, orange juice, and other fruit juices, all products which are sensitive to thermal damage. Electroheating is quite fast and uniform and relatively easy to control by regulating the voltage applied.

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Raztek’s rapid cooling system uses an intermediate fluid, such as water, under vacuum to transfer heat from a hot fluid flowing through a coil to the same fluid at a lower temperature or to another cool fluid. In the vacuum chamber, the hot coil causes the intermediate fluid to boil and then condense on the cool coil. Condensed fluid drops back into the pool in which the hot coil is submerged. The system relies on the high heat transfer rates of boiling and condensing in the absence of non-condensable gases. Non-condensable gases, if present, form a stagnant film around heat transfer surfaces which insulates them and reduces heat transfer rates.

Raztek commercializes inventions made by David Reznik, an Israeli-born food engineer.

• Steam Pasteurization for Dry Products. Steamlab.Systems GmbH, Hamburg, Germany, displayed its system for pasteurizing delicate materials by combining steam and vacuum to avoid overheating and to remove moisture from the steam. Large chambers are used in which bins, trays or bagged products are loaded. A few cycles of vacuum and heating are then followed by a specific period under steam and then by a drying cycle. The process is intended as an alternative to irradiation or chemical disinfection of spices, nuts, cereals, teas, and dried fruits.

After treatment, products are removed to a clean room to avoid recontamination. Some may require screening or sieving before final packaging.

• Ultrasonics. Applications of ultrasonics were discussed in several technical papers during the technical program, and equipment for various applications was displayed by Sonics & Materials, Inc., Newtown, Conn. Ultrasoncics can be used for cutting, atomizing, and emulsification. Variables include frequency, probe shape, power level, and whether a liquid is flowing or in a container. For flowing liquids with viscosity of up to about 4,000 cP, ultrasonics can disperse and homogenize. Cutting with ultrasonics is especially appropriate for brittle, fragile, or sticky products.

• Small-Scale Equipment. Both Armfield, Ringwood Hants, United Kingdom, and Microthermics, Raleigh, N.C., make carefully designed and built miniature processing systems useful for education, small-volume runs, and, in some cases, scale-up. Microthermics tends to specialize in ultra-high-temperature (UHT) and high-temperature/short-time (HTST) pasteurization and sterilization processes, while Armfield makes a wide range of process equipment, such as margarine and ice cream units, edible oils processors, and spray dryers.

One of Armfield’s latest designs is the FT94X, a larger-volume UHT/HTST unit which can process 50–100 L/hr, compared to 10–20 L/hr for the company’s other models. Heating is by steam in concentric-tube or plate heat exchangers.

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• Mixers. Amixon , a division of AZO, Inc., Memphis, Tenn., was one of several companies identified helpfully as new Food Expo exhibitors by distinctive signs. Amixon offers a range of stainless-steel vessels of various volumes that typically have a helical agitator and may have heating, cooling, and vacuum capabilities. Applications are in foods, pharmaceuticals, cosmetics, foods, fine chemicals, plastics, and ceramics. Parent company AZO is best known for powder dispensing and conveying systems frequently found in bakeries.

• Microencapsulation. Harper International, Lancaster, N.Y., is commercializing a process to make very uniform microspheres developed by Brace GmbH in Germany. Microspheres can be made from suspensions, solutions, or melts which are passed through a vibrating nozzle to form perfectly spherical drops. The drops are solidified by drying, chemical reaction, or cooling, as appropriate.

Food applications include encapsulation of liquid ingredients, such as flavors, vitamins, or other ingredients. Variables include formulation of the feed liquid, frequency of vibration nozzle diameter, and solidification conditions. Harper provides complete systems of various capacities and assists customers to develop new applications.

• Extrusion. Wenger Manufacturing, Inc., Sabetha, Kans., is a traditional supplier of single and twin-screw extruders for the pet food, cereal and snack food industries. Some new developments include a back-pressure valve which enables control of specific mechanical energy and pressure. Without a valve, these parameters are controlled by flow rate and die design. Specific mechanical energy is an important scale-up parameter and contributes to product bulk density, cell structure of expanded products, shape definition, and starch gelatinization.

The conical co-rotating twin-screw extruder improves compression, compared to a conventional extruder, and thus permits a shorter and more rigid screw design. This reduces wear and also makes the machine more responsive to changes in flow rate or feed properties.

The External Density Chamber helps control product expansion by using compressed air instead of expanding directly into the atmosphere. The chamber releases expanded product through an airlock.

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Finally, Wenger’s retention time control system adjusts the time material is held in a pre-conditioning cylinder by adjusting a metering device at the discharge of the pre-conditioner. Pre-conditioning is a common step in cereal extrusion in which dry feed is moistened and partially cooked before entering the twin- or single-screw extruder. The pre-conditioner typically has a transport screw but no valve or meter. With on-line control of feed to the extruder from the pre-conditioner, there is less waste at startup and shutdown and more stable operation of the system.

A very different form of extrusion is offered by Kobird Co., Ltd., Fukui, Japan. Its machines are co-extruders, formers, and encrusters in which various doughs, and other materials are wrapped around various fillings. Shapes can be adjusted, and products may be subsequently fried, baked, or used as made.

• Integrated Filter Dryer. GEA, a division of Niro, Inc., Columbia, Md., and Hudson, Wis., displayed a new type of spray dryer in which the air filters are within the dryer chamber rather than in a separate cyclone vessel. The result is a more compact unit, reduced noise, and easier cleaning.

• Ozone. Novazone, Livermore, Calif., continues to focus applications of its ozone generators on three markets: bottled water, storage environments, and sanitation. Ozone is the preferred agent for disinfection of water because it leaves no residual taste. Ozone dissolved in wash water extends the shelf life of many fresh agricultural products. Ozone in process water is commonly used in poultry processing. Gaseous ozone in cold storage rooms helps to control mold, fungi, and bacteria.

• Automatic Retort Control. Dixie Canner Co., Athens, Ga., has long supplied small batch retorts to universities, pilot plants, and community canneries. The traditional equipment was simple and manually operated. Now the company offers an automatic control system with a touch screen and five operating modes: steam cook, steam cook with pressure cool (for glass and flexible containers), water cook, water cook and cool with air over-pressure, and manual mode, using the touch screen to open and close valves. The system is based on a programmable logic controller (PLC) and is offered complete with a retort.

by J. Peter Clark,
Contributing Editor, Consultant to the Process Industries, Oak Park, Ill. 
[email protected]