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Thermal Processing for Food Sterilization and Preservation
C H A P T E R
20 Thermal Processing for Food Sterilization and Preservation Arthur A. Teixeira University of Florida, Gainesville, FL, United States O U T L I N E 20.1 Introduction
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20.2 Retort Systems 20.2.1 Batch Retorts 20.2.2 Continuous Retort Systems
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20.3 Automated Materials Handling Systems
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20.4 Aseptic Process Equipment Systems
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20.5 Low-Acid Canned Food Regulations
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References
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20.1 INTRODUCTION Thermal processing of shelf-stable foods, normally thought of as canned foods, has been one of the most widely used methods of food preservation during the 20th century, and has contributed significantly to the nutritional well-being of much of the world’s population. Thermal processing consists of heating food containers in pressurized retorts (steam autoclaves or “pressure cookers”) at specified temperatures for prescribed lengths of time. These process times are calculated on the basis of achieving sufficient bacterial inactivation in each container to assure food safety to the consuming public, and to ensure that the probability of spoilage will be less than some minimum. Associated with each thermal process is always some degradation of heat-sensitive vitamins and other quality factors that is undesirable. Because of these quality and safety factors, great care is taken in the calculation of these process times and in the control of time and temperature during
Handbook of Farm, Dairy and Food Machinery Engineering DOI: https://doi.org/10.1016/B978-0-12-814803-7.00020-8
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© 2019 Elsevier Inc. All rights reserved.
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processing to avoid either under- or overprocessing. This chapter will describe the food process machinery systems used in the food industry to accomplish sterilization both incontainer (retort systems) and out-of-container (aseptic systems), along with a summary of the Food and Drug Administration (FDA)/USDA low-acid canned food (LACF) regulations that apply to the operation of these equipment and machinery systems.
20.2 RETORT SYSTEMS This section describes briefly some of the commercial retort equipment systems used in the food canning industry to accomplish thermal processes efficiently on a production scale. Just as with most industrial processing operations, both batch and continuous systems are available. As the name implies, batch systems are made up of individual batch retorts that operate intermittently. Scheduling of the retorts is skillfully staggered so that workers move from retort to retort, manually unloading and reloading each retort as its scheduled process cycle comes to an end. In continuous systems, cans are automatically fed into and out of retort systems that operate continuously over one or more working shifts.
20.2.1 Batch Retorts The vertical still cook batch retort shown schematically in Fig. 20.1, together with its horizontal counterpart in Fig. 20.2, are perhaps the grandfathers of all batch retorts. Hardly any food science pilot plant or laboratory is complete without one. The units shown in Fig. 20.2 are of historical vintage, but many still operate today in various parts of the world. A typical production vertical unit will measure 42 in. in diameter by 8 or 9 ft. in height. Cans are loaded in crates that are handled by chain hoist for lifting and lowering into vertical retorts, or into wheeled carts that roll on rails into horizontal retorts. Most retorts are designed to hold either three or four crates or carts, with a total capacity of more than 1000 No. 2 cans per batch, or 400 No. 10 cans. Although the basic design of these retorts has changed little since the turn of the century, they are still quite popular and can be found operating in many food canneries today. Part of the reason for this continued popularity is the simplicity of their design and operation and their versatility to accommodate virtually all can sizes and shapes. Although the unloading and reloading operations are labor intensive, a well-managed cook room can operate with surprising efficiency. The cook room is the room or area within a food canning plant in which the retorts are located. Some cook rooms are known to have more than 100 vertical still cook retorts operating at full production. Although each retort is a batch cook operation, the cook room as a whole operates as a continuous production “system” in that filled and sealed unsterilized cans enter the cook room continuously from the filling line operations, and fully processed sterilized cans leave the cook room continuously. Within the cook room itself, teams of factory workers move from retort to retort to carry out loading and unloading operations, while retort operators are responsible for a given number or “bank” of retorts. These operators carefully monitor the operation of each retort to make sure that the scheduled process is delivered for each batch.
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FIGURE 20.1 Schematic diagram of vertical still-cook retort showing basic controls and piping. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
In general, all operations are the same for horizontal retorts as vertical retorts, except that crates are usually moved into and out of horizontal retorts on trolley tracks instead of chain hoists. For convection-heating products that benefit from mechanical agitation during processing, agitating batch retorts are available. A modern-day horizontal batch retort is shown in Fig. 20.3, with a battery of several such retorts making up a large cook room operation shown in Fig. 20.4. Batch retorts designed for flexible or semirigid retortable packaging systems require overriding air pressure to protect packages from bursting during processing. These operate with water spray, water cascade, or steam air mixtures with overriding air pressure, and are capable of delivering end-over-end agitation when desired (Fig. 20.5).
20.2.2 Continuous Retort Systems Continuous retort operations require some means by which filled, sealed containers are automatically and continuously moved from atmospheric conditions into a pressurized steam environment, held or conveyed through that environment for the specified process time, and then returned to atmospheric conditions for further downstream handling operations. The best-known commercially available systems that accomplish these
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FIGURE 20.2 Historical vertical (top) and horizontal (bottom) still-cook retorts (vintage 1900 40).
FIGURE 20.3 Modern-day horizontal batch retort. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA. HANDBOOK OF FARM, DAIRY AND FOOD MACHINERY ENGINEERING
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FIGURE 20.4
Batch retort system in large cook room operation. Source: Photo courtesy: JBT Food Tech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.5 Rotating batch retorts with end-over-end rotation and overriding air pressure for flexible and semirigid retortable packages. Source: Courtesy Allpax, a ProMach Product Brand. Covington, LA.
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requirements are the crateless retort, the continuous rotary cooker, and the hydrostatic sterilizer. Two other systems, which operate on different principles but accomplish this same purpose for special products, are the Flash “18” system and the Steriflamme system. 20.2.2.1 Crateless Retorts A crateless retort system is, in a sense, an automatic cook room in that the system is made up of a series of individual retorts, each operating in a batch mode, with loading, unloading, and process scheduling operations all carried out automatically without the use of crates. An individual crateless retort is illustrated schematically in Fig. 20.6, and as it appears on the factory floor in Fig. 20.7. When ready to load, the top hatch opens automatically, and cans fed from an incoming conveyor literally “fall” into the retort, which is filled with hot water to cushion the fall. Once fully charged, the hatch is closed and steam entering from the top displaces the cushion water out the bottom. When the cushion water has been fully displaced, all valves are closed and processing begins. At the end of the process time, the retort is refilled with warm water and the bottom hatch, which lies beneath the water level in the discharge cooling canal, is opened to let the cans fall gently onto the moving discharge conveyor in the cooling canal. After all cans are discharged, the bottom hatch is reclosed and the retort is ready to begin a new cycle. This sequence of operations is shown schematically in Fig. 20.8. A commercial system of crateless retorts would consist of several such retorts in a row sharing a common infeed and discharge conveyor system to achieve continuous operation of any design capacity. 20.2.2.2 Continuous Rotary Cookers The continuous rotary pressure sterilizer or “cooker” is a horizontal rotating retort through which the cans are conveyed while they rotate about their own axis through a spiral path and rotating reel mechanism as illustrated in the cutaway view in Fig. 20.9 and the schematic diagram in Fig. 20.10. Residence time through the sterilizer is controlled by the rotating speed of the reel, which can be adjusted to achieve the required process time. This, in turn, sets the line speed for the entire system. Cans are transferred from an incoming can conveyor through a synchronized feeding device to a rotary transfer valve, which indexes the cans into the sterilizer while preventing the escape of steam and loss of pressure. Once cans have entered the sterilizer, they travel in the annular space between the reel and the shell. They are held between splines on the reel and a helical or spiral track welded to the shell. In this way the cans are carried by the reel around the inner circumference of the shell, imparting a rotation about their own axes, while the spiral track in the shell directs the cans forward along the length of the sterilizer by one can length for each revolution of the reel. At the end of the sterilizer, cans are ejected from the reel into another rotary valve and into the next shell for either additional cooking or cooling. Most common systems require at least three shells in series to accomplish controlled cooling through both a pressure cool shell and an atmospheric cool shell following the cooker or sterilizer. For cold-fill products that require controlled preheating, as many as five shells may be required to deliver an atmospheric preheat, pressure preheat, pressure
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FIGURE 20.6
Schematic diagram of crateless retort illustrating basic principle of charge and discharge through cushion of water.
cook, pressure cool, and atmospheric cool. By the nature of its design and principle of operation, a continuous rotary sterilizer system is manufactured to accommodate a specific can size and cannot easily be adapted to other sizes. For this reason it is not uncommon to see several systems (filling lines) in operation in one food canning plant, each system dedicated to a different can size.
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FIGURE 20.7
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Exterior schematic of crateless retort showing details of mechanical operations.
20.2.2.3 Hydrostatic Sterilizers These systems are so named because steam pressure is controlled hydrostatically by the height of a leg of water. Because of the height of water leg required, these sterilizers are usually installed outdoors adjacent to a canning plant. They are self-contained structures with the external appearance of a rectangular tower, as shown in Fig. 20.11. They are basically made up of four chambers: a hydrostatic “bring-up” leg, a sterilizing steam dome, a hydrostatic “bring-down” leg, and a cooling section.
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Vapor Colchon de agua hasta WCC
Inundacion de agua hasta WCC
Etapa 1
Vapor
Condensado hasta WCC
Etapa 2
Etapa 3
Vapor Agua hasta WCC
Condensado hasta WCC
Aire
Agua de refrigeracion
Etapa 4
Etapa 5
Etapa 6
FIGURE 20.8 Schematic of sequence of operations in crateless retort system (in Spanish). From Rees, J.A.G., Bettison, J., 1991. Processing and Packaging Heat Preserved Foods, Springer, US, Reproduced with permission of SNCSC.
The principle of operation for a hydrostatic sterilizer can be explained with reference to the schematic flow diagrams in Figs. 20.12 and 20.13. Containers are conveyed through the sterilizer on carriers connected to a continuous chain link mechanism that provides positive line speed control and thus residence-time control to achieve specified process time in the steam dome. Carriers are loaded automatically from incoming can conveyors and travel to the top of the sterilizer, where they enter the bring-up water leg. They travel downward through this leg as they encounter progressively warmer water. As they enter the bottom of the steam dome, the water temperature will be in equilibrium with steam temperature at the water seal interface. In the steam dome, the cans are exposed to the specified process or “retort” temperature controlled by the hydrostatic pressure for the prescribed process time controlled by the carrier line speed. When cans exit the steam dome, they again pass through the water seal interface at the bottom and travel upward through the bring-down leg as they encounter progressively warmer water until they exit at the top. Cans are then sprayed with cooling water as the carriers travel down the outside of the sterilizer on their return to the discharge conveyor station. Pressure and temperature profiles that are experienced by the water and steam in the various chambers, as well as by the cans themselves in a typical hydrostatic sterilizer system, are shown in Fig. 20.14.
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FIGURE 20.9 Cutaway view of three-shell continuous rotary cooker. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.10
Schematic describing helical path of can movement through a continuous rotary cooker shell. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
20.2.2.4 Flash “18” The Flash “18” process is unique in that the product is brought to sterilizing temperature prior to filling through steam injection heating, and then pumped while at sterilizing temperature to a “hot fill” operation carried out under pressure to accomplish
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FIGURE 20.11 External view of full-scale industrial hydrostatic retort. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
sterility at the product can wall interface. Conventional filling equipment and steamflow can sealers are housed in a pressurized room or “tank” maintained at 18 psi pressure above atmosphere, as shown in Fig. 20.15. Hot product enters the tank at a sterilizing temperature of 265 F. It then flash cools to 255 F (the boiling point at 18 psi pressure). The filled and sealed cans are then processed through a continuous horizontal retort to accomplish a controlled hold time at 255 F to sterilize the inside can surfaces and deliver the required process time before final cooling and exit through pressure seal valves. This system is used primarily for large institutional size cans that would otherwise require such long retort processes that the resulting product quality would be unacceptable. 20.2.2.5 Steriflamme System The Steriflamme process is shown in Fig. 20.16. After closing under a high vacuum, cans are first preheated in steam and then further heated by rotating rapidly over direct contact with flames from a gas burner. After a necessary holding time to ensure sterilization, the cans are cooled by means of a water spray, as shown in the schematic diagram of the process in Fig. 20.16. A high vacuum is important to prevent distortion of can seams, as the cans themselves become their own retort pressure vessels when heated by the gas flames. The process is often used for canned vegetables such as corn, peas, carrots, and mushrooms when minimum brine content is required.
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FIGURE 20.12 Schematic illustration of hydrostatic retort showing basic principle of operation. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
20.3 AUTOMATED MATERIALS HANDLING SYSTEMS The preponderance of thermally processed shelf-stable foods in the marketplace today continues to be processed in batch retorts that must be repeatedly loaded and unloaded between each process cycle throughout the workday. In years past this was performed by teams of workers with the help of chain hoists and rail carts as they moved from retort to retort around the cook room floor, while retort operators kept vigilance as time keepers, temperature monitors, and record keepers. Recent innovations in retort control and materials handling systems have essentially revolutionized traditional cook room operations. Today’s modern retorts such as those shown in Fig. 20.17 are equipped with sophisticated computerized electronic control systems that can be remotely monitored from a control room by a single operator who may be responsible for an entire battery of retorts (Fig. 20.18). These control systems are capable of operating each retort through its entire process cycle, while controlling and recording temperatures and pressures, as well as monitoring process conditions at all critical control points. At the end of each process cycle, a complete set of batch records is provided for compliance with record keeping requirements of the FDA LACF regulations. The introduction of automation and robotics for materials handling operations on the cook room floor has perhaps had the greatest impact in reducing the cost to manufacture thermally processed products. An automated batch retort system in a modern cook room today consists of a battery of retorts laid out in a row on the cook room floor to accommodate automated loading and unloading (Fig. 20.19). Both track-guided and trackless systems are available for this purpose. In track-guided systems, a rail cart transfers crates or
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20.3 AUTOMATED MATERIALS HANDLING SYSTEMS
Preheater zone
Air cooling section
Inlet water temperature 180ºF–190ºF
Can feed Can discharge
Hydrostatic head
Spray cooling leg
Bring down leg (in water)
Steam chamber temperature 240ºF–265ºF
Bring up leg (in water)
Feed le g
Outlet water temperature 190ºF–200ºF
FIGURE 20.13 Machine schematic of hydrostatic retort showing details of mechanical operations. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
Leg temp. 225ºF–245ºF Water Seal Temperature 230ºF–260ºF
Leg temp. 225ºF–245ºF
Cooling water bath
baskets of product from loading stations to the retorts, and from the retorts to the unloading stations automatically on a rail track. The track allows the cart to move in a transverse direction along the cook room floor until it is aligned with the target retort (Fig. 20.20). Once the cart is aligned with the retort, the loaded baskets or crates automatically transfer from the cart into the retort for loading operations, or from the retort onto the cart for unloading operations. Trackless systems work in much the same way, except that rails and rail carts are replaced by automated guided vehicles (AGV) that move about the cook room floor controlled by electronic guidance systems (Fig. 20.21). These systems offer the advantage of keeping the cook room floor free of rails or tracks that could impede safe movement of
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External pressure
30 Pressure, psi
Spraying
Pressure inside the can
0
Preheat
Sterilizing
Cooling
Drying
Time
FIGURE 20.14 Pressure and temperature profiles during thermal processing in a typical hydrostatic retort sterilizer system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
Can valve to transfer cans to inside Typical food preparation
Sterilized product to filler
Can conveyor to filler
Steam injectors Stuffer
Cans to labeling and case packing machine ray r sp ate ld w
Cans from storage
Entrance lock Closer Filler
Hold’ tunn.
Deaerator Cooling tunnel
Co
Entrance lock
Can
ler coo
tor va Air to ele n new process RM Ca
Can valve to transfer cans outside
FIGURE 20.15 Schematic diagram of Flash “18” system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
workers on the floor. A close-up view of AGVs approaching or returning from retorts awaiting loading or unloading is shown in Fig. 20.22, and an AGV having just loaded or about to unload a retort is shown in Fig. 20.23.
20.4 ASEPTIC PROCESS EQUIPMENT SYSTEMS Recent regulatory approval for the use of chemical sterilants such as hydrogen peroxide to sterilize the surfaces of various paper, plastic, and laminated packaging materials has opened the door to a wide array of commercially available aseptic filling systems to produce shelf-stable liquid foods in a variety of gable-topped, brick-packed, and other novel package configurations. Filling machines designed for these packaging systems are usually based on the use of form fill seal operations. In these machines, the packaging material is fed from either precut blanks or directly from roll stock, passed through a chemical sterilant bath or spray treatment, formed into the final package shape while being filled with cool sterile product from the product sterilizing system, and then sealed and discharged, all within a controlled aseptic environment (Fig. 20.24).
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20.4 ASEPTIC PROCESS EQUIPMENT SYSTEMS
Drum filler
Elevator can position 30° Angle preheater
Checkweigher
Liquid or brine filler
Can clincher Vertical exhaust Can seamer
Take away conveyors
Steriflamme
Steriflamme feed
Steam heater
Gas flames
Holding section Gas flames
Can load
Water sprays
Can discharge
FIGURE 20.16 Schematic diagram of Steriflamme system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc. Schematic diagram of Steriflamme system sequence of operations within Steriflamme. With courtesy from Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD.
Another important commercial application of aseptic processing technology is in the storage and handling of large bulk quantities of sterilized food ingredients, such as tomato paste, fruit purees, and other liquid food concentrates that need to be purchased by food processors, or institutional end users for use as ingredients in further processed prepared foods. The containers for such applications can range in size from the classic 55-gallon steel drum to railroad tank cars or stationary silo storage tanks. Specially designed aseptic
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FIGURE 20.17 Modern day retorts on cook room floor in a large food canning facility. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.18 Computerized electronic control systems to remotely monitor retort operations by a single operator responsible for an entire battery of retorts. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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FIGURE 20.19 Modern cook room showing battery of retorts arranged for automated loading and unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
transfer valves and related handling systems make it possible to transfer sterile product from one such container to another without compromising sterility. A schematic flow diagram of a typical aseptic processing system for 55-gallon steel drums is shown in Fig. 20.25, with a cutaway view of a typical aseptic drum-filling station in Fig. 20.26. A system such as this is capable of filling 15 drums/h, with each drum containing nearly 500 lb of product (Rice, 1987; Wagner, 1982).
20.5 LOW-ACID CANNED FOOD REGULATIONS Food engineers involved with thermal processing operations should be familiar with all federal regulations applicable to sterilization of low-acid canned foods. The specific provisions for regulating the LACF industry are contained in Title 2, Part 113 of the US Code of Federal Regulations entitled “Thermally Processed Low-Acid Foods Packaged in Hermetically Sealed Containers.” These regulations are also published in detail in The Almanac of the Canning, Freezing, Preserving Industries (Judge, 2012), and were summarized earlier by Teixeira et al. (2007). The purpose of this concluding section is to acquaint the food engineer with the scope of compliance activities required to initiate and sustain commercial food canning operations under these regulations. In the broadest sense, these regulations direct the attention of LACF processors to four operational levels: 1. Adequacy of equipment and procedures to perform safe processing operations. 2. Adequacy of record keeping to prove safe operations.
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FIGURE 20.20
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Track-guided automated batch retort system. Source: Courtesy Allpax, a ProMach Product Brand.
Covington, LA.
FIGURE 20.21 Trackless system layout for automated guided vehicles. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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FIGURE 20.22 Automated guided vehicles in the process of approaching or returning from retorts awaiting loading or unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.23
Automated guided vehicle in process of retort loading/unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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Drying rollers Roller Hydrogen peroxide sterilizing bath Plastic sealing strip applicator
Sterile milk inl
Roller
Code dater
Side-seam seal
Internal heater for sterilizing container interior Milk-level cont Milk outlet tube Carton top sealed
Packing material
Finished carton
FIGURE 20.24 Schematic illustration of form fill seal aseptic filling machine with packaging material fed from roll stock. Source: Courtesy: Tetra-Pak.
3. Justification of the adequacy of time-and-temperature processes used. 4. Qualifications of supervisory staff responsible for thermal processing and container closure operations. The requirements of the regulation can be further broken down into 11 specific compliance activities, as described below. 1. Plant registration: This compliance activity requires that every plant producing low-acid canned foods and selling these foods in the United States be registered with the FDA. This is accomplished by the submission of necessary forms (FD 2541), which require such information as • Name of company. • Place of business.
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FIGURE 20.25
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Schematic diagram of aseptic drum filling operation (Rice, 1987; Wagner, 1982).
FIGURE 20.26 Schematic illustration with cutaway view of dual chamber aseptic drum filling operation. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
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• Location of plant. • Processing method: type of equipment used. • List of food products processed. Although most processors normally provide this type of information regularly for their trade associations and for various business accounting purposes, technical and administrative personnel need to exercise care in such matters as choosing appropriate definitions for the type of equipment and processing method they use, and in defining each “product” for the list of products required. If a plant has to close for reasons other than seasonal operations or labor disputes, the regulation requires notification to the FDA within 90 days of closing. 2. Process filing: This compliance activity requires all processors to file Form 2541a for each product with the FDA within 60 days of plant registration and prior to packing any new product or adopting any change in process for an existing product. The type of information required on each form may include: • Name of product and container size. • Processing method used and type of retort. • Minimum initial product temperature (IT). • Time and temperature of processing. • Process lethality or equivalent scientific evidence of process adequacy. • Critical factors affecting heat penetration. • Authoritative source used and date of establishment of the process. One form containing all of this information is required for each product in each size container for all product container size combinations processed in any given plant. 3. Personnel training: This compliance activity requires that supervisors of operators of retort processing systems and container closure inspectors must have attended a school approved by the FDA and have satisfactorily completed the prescribed course of instruction. These “Better Process Control and Container Closure” schools are sponsored jointly on a regular basis by the FDA and the National Food Processors Association. They are held in conjunction with the food science departments at a number of colleges and universities across the country to bring them within reasonable proximity to most canned food processors. The curriculum is presented in a short-course format over 4.5 days, including examinations of the material presented and the awarding of certificates of completion. 4. Equipment and procedures: This compliance activity requires all processors to make certain that equipment related to the thermal processing operations is maintained in compliance with established specifications. For still cook retort operations, these requirements relate to such items as • Mercury and glass thermometers. • Temperature recorders or recorder-controllers. • Steam pressure controllers and gauges. • Steam inlet size, headers, and location in retort. • Steam spreaders and bleeders. • Crates (baskets), crate supports, and separators. • Vents, size and location, venting times and temperature.
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6.
7.
8.
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• Water-level indicators. • Level indication for retort headspace in pressure cooking. • Air supply to pneumatic controllers. Product preparation: This compliance activity requires each processor to have documented policies and procedures for this product preparation, production, and sanitation, delineating proper procedures to be followed in such areas as • Raw material testing and certification, including proper storage and inventory control. • Blanching and cooling operations. • Filling operations, including frequent monitoring of critical factors such as IT, fill weight, headspace, product density, viscosity, and pH. • Exhausting of headspace air prior to closing by heat, vacuum, steam injection, hot brine, and so on. • All areas of plant, equipment, and material-handling sanitation. This compliance activity forces all processors to review thoroughly existing quality control and sanitation policies and procedures, or develop appropriate policies and procedures where none have previously existed. Establishing scheduled processes: This compliance activity requires all processors to document and file the following information in support of establishing the scheduled process for any new product or product-process change that is to be filed with the FDA: • The source of qualified expert knowledge used in establishing the scheduled process. • The heat penetration tests, microbial death time data, and thermal process calculations used to establish the scheduled process. • Specification of all critical control factors affecting the scheduled process. • Verification of the scheduled process through inoculated packs, or incubation of product samples from initial production runs. Thermal process operations: This compliance activity specifies minimum requirements that processors have to meet with respect to operations that take place in the retort room or cook room, where the filled and sealed cans or jars are sterilized under pressure in steam or water air override retorts. Some of these requirements include • Posting of scheduled processes. • Use of heat-sensitive indicators. • Review of data on all critical control factors to make certain that they fall within specifications for the scheduled process prior to sterilization. • Calibration of thermometers, recorders, controllers, and timing devices. • Control of retort operations to assure compliance with specified venting procedures and time temperature conditions for the established thermal process. • Use of a fail-safe traffic control pattern to make certain that no unprocessed product can be mistaken for processed product, or vice versa. Process deviations: This compliance activity specifies what processors have to do in the event of a process deviation, such as drop in temperature caused by a sudden loss of steam pressure or a reduced cook time caused by a faulty timer, which would suggest that the product received a process less than the scheduled process. In the event of such a process deviation, the regulation specifies that the processor must
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either (1) reprocess the product according to the established scheduled process and retain all records of such event, or (2) put the product on “hold” and have the “deviate” process evaluated for its public health significance by a recognized processing authority with qualified expert knowledge. Such a processing authority may “clear” the deviation if it is judged to pose no significant risk to public health. Again, records containing documentation in support of such an evaluation have to be retained on file. As most canned food products cannot tolerate a second exposure to the heat sterilization process without serious degradation in physical quality, processors generally prefer to put products on hold while process deviations are evaluated. Large processors clear deviations quickly with appropriate documentation. Other processors may rely on outside services provided by trade associations, can manufacturers, or consultants. 9. Container closure and coding: This compliance activity specifies the inspection and testing required to assure that all containers are properly closed and coded prior to sterilization. Some of the activities specified include • Visual inspection of can top seams (or glass jar closures), at a minimum frequency of once every 30 min, with documentation for records retention. • Complete seam teardown with measurement of critical dimensions taken under optic magnification (or coldwater vacuum tests for glass jars) at a minimum frequency of once every 4 h, along with documentation for records retention. • Periodic testing of cooling water to check concentration of residual chlorine. • Proper code on each container for • Identity of product. • Where packed (plant). • When packed (date). • Who packed (shift or line). • Use of proper postprocessing can handling systems to minimize damage to can seams or closures prior to labeling and case packing. 10. Records and storage: This compliance activity requires all processors to prepare, review, and retain all records from each product packed for at least 1 full year or packing season at the processing plant itself, followed by retention of these records for at least 2 years at some other location, so that all records will be readily available for inspection over a minimum period of three full years from the date the product was packed. The records themselves include all documents and recordings of data, test results, inspections, critical control factors, and so on, required by all of the individual compliance activities described previously. This means that on a continuing basis, essentially all processors must have procedures in place at each plant to • Review all records for completeness. • Collate and arrange records in an organized file for each product “batch code.” • Store the records in sequence with a systematic file system for future retrieval. 11. Recall planning: This final compliance activity requires that all processors have on hand a plan for recalling any product through primary distribution, plus a plan for each distributor to use in recalling the product from further distribution channels downstream. Some processors have adopted the practice of conducting “drills” to test the effectiveness of their recall plans. Such drills are not specifically required by the regulation, but are strongly advised as part of this compliance activity.
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References Judge, E.E., 2012. The Almanac of the Canning, Freezing, Preserving Industries. Edward E. Judge and Sons, Westminster, MD (Published annually). Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc, Baltimore, MD. Rees, J.A.G., Bettison, J., 1991. Processing and Packaging Heat Preserved Foods, Springer, US. Rice, J., 1987. International trends in food packaging. Food Process. 48 (10), 86 91. Teixeira, A.A., Heldman, D.R., Lund, D.B., 2007. Thermal processing of canned foods. In: Heldman, D.R., Lund, D.B. (Eds.), Food Engineering Handbook. CRC Press, Taylor and Francis Group, Boca Raton, FL, pp. 592 659. Wagner, J.N., 1982. Aseptic drum processing. Food Eng. 54 (1), 120 121.
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20 Thermal Processing for Food Sterilization and Preservation Arthur A. Teixeira University of Florida, Gainesville, FL, United States O U T L I N E 20.1 Introduction
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20.1 INTRODUCTION Thermal processing of shelf-stable foods, normally thought of as canned foods, has been one of the most widely used methods of food preservation during the 20th century, and has contributed significantly to the nutritional well-being of much of the world’s population. Thermal processing consists of heating food containers in pressurized retorts (steam autoclaves or “pressure cookers”) at specified temperatures for prescribed lengths of time. These process times are calculated on the basis of achieving sufficient bacterial inactivation in each container to assure food safety to the consuming public, and to ensure that the probability of spoilage will be less than some minimum. Associated with each thermal process is always some degradation of heat-sensitive vitamins and other quality factors that is undesirable. Because of these quality and safety factors, great care is taken in the calculation of these process times and in the control of time and temperature during
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processing to avoid either under- or overprocessing. This chapter will describe the food process machinery systems used in the food industry to accomplish sterilization both incontainer (retort systems) and out-of-container (aseptic systems), along with a summary of the Food and Drug Administration (FDA)/USDA low-acid canned food (LACF) regulations that apply to the operation of these equipment and machinery systems.
20.2 RETORT SYSTEMS This section describes briefly some of the commercial retort equipment systems used in the food canning industry to accomplish thermal processes efficiently on a production scale. Just as with most industrial processing operations, both batch and continuous systems are available. As the name implies, batch systems are made up of individual batch retorts that operate intermittently. Scheduling of the retorts is skillfully staggered so that workers move from retort to retort, manually unloading and reloading each retort as its scheduled process cycle comes to an end. In continuous systems, cans are automatically fed into and out of retort systems that operate continuously over one or more working shifts.
20.2.1 Batch Retorts The vertical still cook batch retort shown schematically in Fig. 20.1, together with its horizontal counterpart in Fig. 20.2, are perhaps the grandfathers of all batch retorts. Hardly any food science pilot plant or laboratory is complete without one. The units shown in Fig. 20.2 are of historical vintage, but many still operate today in various parts of the world. A typical production vertical unit will measure 42 in. in diameter by 8 or 9 ft. in height. Cans are loaded in crates that are handled by chain hoist for lifting and lowering into vertical retorts, or into wheeled carts that roll on rails into horizontal retorts. Most retorts are designed to hold either three or four crates or carts, with a total capacity of more than 1000 No. 2 cans per batch, or 400 No. 10 cans. Although the basic design of these retorts has changed little since the turn of the century, they are still quite popular and can be found operating in many food canneries today. Part of the reason for this continued popularity is the simplicity of their design and operation and their versatility to accommodate virtually all can sizes and shapes. Although the unloading and reloading operations are labor intensive, a well-managed cook room can operate with surprising efficiency. The cook room is the room or area within a food canning plant in which the retorts are located. Some cook rooms are known to have more than 100 vertical still cook retorts operating at full production. Although each retort is a batch cook operation, the cook room as a whole operates as a continuous production “system” in that filled and sealed unsterilized cans enter the cook room continuously from the filling line operations, and fully processed sterilized cans leave the cook room continuously. Within the cook room itself, teams of factory workers move from retort to retort to carry out loading and unloading operations, while retort operators are responsible for a given number or “bank” of retorts. These operators carefully monitor the operation of each retort to make sure that the scheduled process is delivered for each batch.
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FIGURE 20.1 Schematic diagram of vertical still-cook retort showing basic controls and piping. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
In general, all operations are the same for horizontal retorts as vertical retorts, except that crates are usually moved into and out of horizontal retorts on trolley tracks instead of chain hoists. For convection-heating products that benefit from mechanical agitation during processing, agitating batch retorts are available. A modern-day horizontal batch retort is shown in Fig. 20.3, with a battery of several such retorts making up a large cook room operation shown in Fig. 20.4. Batch retorts designed for flexible or semirigid retortable packaging systems require overriding air pressure to protect packages from bursting during processing. These operate with water spray, water cascade, or steam air mixtures with overriding air pressure, and are capable of delivering end-over-end agitation when desired (Fig. 20.5).
20.2.2 Continuous Retort Systems Continuous retort operations require some means by which filled, sealed containers are automatically and continuously moved from atmospheric conditions into a pressurized steam environment, held or conveyed through that environment for the specified process time, and then returned to atmospheric conditions for further downstream handling operations. The best-known commercially available systems that accomplish these
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FIGURE 20.2 Historical vertical (top) and horizontal (bottom) still-cook retorts (vintage 1900 40).
FIGURE 20.3 Modern-day horizontal batch retort. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA. HANDBOOK OF FARM, DAIRY AND FOOD MACHINERY ENGINEERING
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FIGURE 20.4
Batch retort system in large cook room operation. Source: Photo courtesy: JBT Food Tech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.5 Rotating batch retorts with end-over-end rotation and overriding air pressure for flexible and semirigid retortable packages. Source: Courtesy Allpax, a ProMach Product Brand. Covington, LA.
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requirements are the crateless retort, the continuous rotary cooker, and the hydrostatic sterilizer. Two other systems, which operate on different principles but accomplish this same purpose for special products, are the Flash “18” system and the Steriflamme system. 20.2.2.1 Crateless Retorts A crateless retort system is, in a sense, an automatic cook room in that the system is made up of a series of individual retorts, each operating in a batch mode, with loading, unloading, and process scheduling operations all carried out automatically without the use of crates. An individual crateless retort is illustrated schematically in Fig. 20.6, and as it appears on the factory floor in Fig. 20.7. When ready to load, the top hatch opens automatically, and cans fed from an incoming conveyor literally “fall” into the retort, which is filled with hot water to cushion the fall. Once fully charged, the hatch is closed and steam entering from the top displaces the cushion water out the bottom. When the cushion water has been fully displaced, all valves are closed and processing begins. At the end of the process time, the retort is refilled with warm water and the bottom hatch, which lies beneath the water level in the discharge cooling canal, is opened to let the cans fall gently onto the moving discharge conveyor in the cooling canal. After all cans are discharged, the bottom hatch is reclosed and the retort is ready to begin a new cycle. This sequence of operations is shown schematically in Fig. 20.8. A commercial system of crateless retorts would consist of several such retorts in a row sharing a common infeed and discharge conveyor system to achieve continuous operation of any design capacity. 20.2.2.2 Continuous Rotary Cookers The continuous rotary pressure sterilizer or “cooker” is a horizontal rotating retort through which the cans are conveyed while they rotate about their own axis through a spiral path and rotating reel mechanism as illustrated in the cutaway view in Fig. 20.9 and the schematic diagram in Fig. 20.10. Residence time through the sterilizer is controlled by the rotating speed of the reel, which can be adjusted to achieve the required process time. This, in turn, sets the line speed for the entire system. Cans are transferred from an incoming can conveyor through a synchronized feeding device to a rotary transfer valve, which indexes the cans into the sterilizer while preventing the escape of steam and loss of pressure. Once cans have entered the sterilizer, they travel in the annular space between the reel and the shell. They are held between splines on the reel and a helical or spiral track welded to the shell. In this way the cans are carried by the reel around the inner circumference of the shell, imparting a rotation about their own axes, while the spiral track in the shell directs the cans forward along the length of the sterilizer by one can length for each revolution of the reel. At the end of the sterilizer, cans are ejected from the reel into another rotary valve and into the next shell for either additional cooking or cooling. Most common systems require at least three shells in series to accomplish controlled cooling through both a pressure cool shell and an atmospheric cool shell following the cooker or sterilizer. For cold-fill products that require controlled preheating, as many as five shells may be required to deliver an atmospheric preheat, pressure preheat, pressure
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FIGURE 20.6
Schematic diagram of crateless retort illustrating basic principle of charge and discharge through cushion of water.
cook, pressure cool, and atmospheric cool. By the nature of its design and principle of operation, a continuous rotary sterilizer system is manufactured to accommodate a specific can size and cannot easily be adapted to other sizes. For this reason it is not uncommon to see several systems (filling lines) in operation in one food canning plant, each system dedicated to a different can size.
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FIGURE 20.7
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Exterior schematic of crateless retort showing details of mechanical operations.
20.2.2.3 Hydrostatic Sterilizers These systems are so named because steam pressure is controlled hydrostatically by the height of a leg of water. Because of the height of water leg required, these sterilizers are usually installed outdoors adjacent to a canning plant. They are self-contained structures with the external appearance of a rectangular tower, as shown in Fig. 20.11. They are basically made up of four chambers: a hydrostatic “bring-up” leg, a sterilizing steam dome, a hydrostatic “bring-down” leg, and a cooling section.
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Vapor Colchon de agua hasta WCC
Inundacion de agua hasta WCC
Etapa 1
Vapor
Condensado hasta WCC
Etapa 2
Etapa 3
Vapor Agua hasta WCC
Condensado hasta WCC
Aire
Agua de refrigeracion
Etapa 4
Etapa 5
Etapa 6
FIGURE 20.8 Schematic of sequence of operations in crateless retort system (in Spanish). From Rees, J.A.G., Bettison, J., 1991. Processing and Packaging Heat Preserved Foods, Springer, US, Reproduced with permission of SNCSC.
The principle of operation for a hydrostatic sterilizer can be explained with reference to the schematic flow diagrams in Figs. 20.12 and 20.13. Containers are conveyed through the sterilizer on carriers connected to a continuous chain link mechanism that provides positive line speed control and thus residence-time control to achieve specified process time in the steam dome. Carriers are loaded automatically from incoming can conveyors and travel to the top of the sterilizer, where they enter the bring-up water leg. They travel downward through this leg as they encounter progressively warmer water. As they enter the bottom of the steam dome, the water temperature will be in equilibrium with steam temperature at the water seal interface. In the steam dome, the cans are exposed to the specified process or “retort” temperature controlled by the hydrostatic pressure for the prescribed process time controlled by the carrier line speed. When cans exit the steam dome, they again pass through the water seal interface at the bottom and travel upward through the bring-down leg as they encounter progressively warmer water until they exit at the top. Cans are then sprayed with cooling water as the carriers travel down the outside of the sterilizer on their return to the discharge conveyor station. Pressure and temperature profiles that are experienced by the water and steam in the various chambers, as well as by the cans themselves in a typical hydrostatic sterilizer system, are shown in Fig. 20.14.
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FIGURE 20.9 Cutaway view of three-shell continuous rotary cooker. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.10
Schematic describing helical path of can movement through a continuous rotary cooker shell. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
20.2.2.4 Flash “18” The Flash “18” process is unique in that the product is brought to sterilizing temperature prior to filling through steam injection heating, and then pumped while at sterilizing temperature to a “hot fill” operation carried out under pressure to accomplish
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FIGURE 20.11 External view of full-scale industrial hydrostatic retort. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
sterility at the product can wall interface. Conventional filling equipment and steamflow can sealers are housed in a pressurized room or “tank” maintained at 18 psi pressure above atmosphere, as shown in Fig. 20.15. Hot product enters the tank at a sterilizing temperature of 265 F. It then flash cools to 255 F (the boiling point at 18 psi pressure). The filled and sealed cans are then processed through a continuous horizontal retort to accomplish a controlled hold time at 255 F to sterilize the inside can surfaces and deliver the required process time before final cooling and exit through pressure seal valves. This system is used primarily for large institutional size cans that would otherwise require such long retort processes that the resulting product quality would be unacceptable. 20.2.2.5 Steriflamme System The Steriflamme process is shown in Fig. 20.16. After closing under a high vacuum, cans are first preheated in steam and then further heated by rotating rapidly over direct contact with flames from a gas burner. After a necessary holding time to ensure sterilization, the cans are cooled by means of a water spray, as shown in the schematic diagram of the process in Fig. 20.16. A high vacuum is important to prevent distortion of can seams, as the cans themselves become their own retort pressure vessels when heated by the gas flames. The process is often used for canned vegetables such as corn, peas, carrots, and mushrooms when minimum brine content is required.
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FIGURE 20.12 Schematic illustration of hydrostatic retort showing basic principle of operation. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
20.3 AUTOMATED MATERIALS HANDLING SYSTEMS The preponderance of thermally processed shelf-stable foods in the marketplace today continues to be processed in batch retorts that must be repeatedly loaded and unloaded between each process cycle throughout the workday. In years past this was performed by teams of workers with the help of chain hoists and rail carts as they moved from retort to retort around the cook room floor, while retort operators kept vigilance as time keepers, temperature monitors, and record keepers. Recent innovations in retort control and materials handling systems have essentially revolutionized traditional cook room operations. Today’s modern retorts such as those shown in Fig. 20.17 are equipped with sophisticated computerized electronic control systems that can be remotely monitored from a control room by a single operator who may be responsible for an entire battery of retorts (Fig. 20.18). These control systems are capable of operating each retort through its entire process cycle, while controlling and recording temperatures and pressures, as well as monitoring process conditions at all critical control points. At the end of each process cycle, a complete set of batch records is provided for compliance with record keeping requirements of the FDA LACF regulations. The introduction of automation and robotics for materials handling operations on the cook room floor has perhaps had the greatest impact in reducing the cost to manufacture thermally processed products. An automated batch retort system in a modern cook room today consists of a battery of retorts laid out in a row on the cook room floor to accommodate automated loading and unloading (Fig. 20.19). Both track-guided and trackless systems are available for this purpose. In track-guided systems, a rail cart transfers crates or
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Preheater zone
Air cooling section
Inlet water temperature 180ºF–190ºF
Can feed Can discharge
Hydrostatic head
Spray cooling leg
Bring down leg (in water)
Steam chamber temperature 240ºF–265ºF
Bring up leg (in water)
Feed le g
Outlet water temperature 190ºF–200ºF
FIGURE 20.13 Machine schematic of hydrostatic retort showing details of mechanical operations. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
Leg temp. 225ºF–245ºF Water Seal Temperature 230ºF–260ºF
Leg temp. 225ºF–245ºF
Cooling water bath
baskets of product from loading stations to the retorts, and from the retorts to the unloading stations automatically on a rail track. The track allows the cart to move in a transverse direction along the cook room floor until it is aligned with the target retort (Fig. 20.20). Once the cart is aligned with the retort, the loaded baskets or crates automatically transfer from the cart into the retort for loading operations, or from the retort onto the cart for unloading operations. Trackless systems work in much the same way, except that rails and rail carts are replaced by automated guided vehicles (AGV) that move about the cook room floor controlled by electronic guidance systems (Fig. 20.21). These systems offer the advantage of keeping the cook room floor free of rails or tracks that could impede safe movement of
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External pressure
30 Pressure, psi
Spraying
Pressure inside the can
0
Preheat
Sterilizing
Cooling
Drying
Time
FIGURE 20.14 Pressure and temperature profiles during thermal processing in a typical hydrostatic retort sterilizer system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
Can valve to transfer cans to inside Typical food preparation
Sterilized product to filler
Can conveyor to filler
Steam injectors Stuffer
Cans to labeling and case packing machine ray r sp ate ld w
Cans from storage
Entrance lock Closer Filler
Hold’ tunn.
Deaerator Cooling tunnel
Co
Entrance lock
Can
ler coo
tor va Air to ele n new process RM Ca
Can valve to transfer cans outside
FIGURE 20.15 Schematic diagram of Flash “18” system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
workers on the floor. A close-up view of AGVs approaching or returning from retorts awaiting loading or unloading is shown in Fig. 20.22, and an AGV having just loaded or about to unload a retort is shown in Fig. 20.23.
20.4 ASEPTIC PROCESS EQUIPMENT SYSTEMS Recent regulatory approval for the use of chemical sterilants such as hydrogen peroxide to sterilize the surfaces of various paper, plastic, and laminated packaging materials has opened the door to a wide array of commercially available aseptic filling systems to produce shelf-stable liquid foods in a variety of gable-topped, brick-packed, and other novel package configurations. Filling machines designed for these packaging systems are usually based on the use of form fill seal operations. In these machines, the packaging material is fed from either precut blanks or directly from roll stock, passed through a chemical sterilant bath or spray treatment, formed into the final package shape while being filled with cool sterile product from the product sterilizing system, and then sealed and discharged, all within a controlled aseptic environment (Fig. 20.24).
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Drum filler
Elevator can position 30° Angle preheater
Checkweigher
Liquid or brine filler
Can clincher Vertical exhaust Can seamer
Take away conveyors
Steriflamme
Steriflamme feed
Steam heater
Gas flames
Holding section Gas flames
Can load
Water sprays
Can discharge
FIGURE 20.16 Schematic diagram of Steriflamme system. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc. Schematic diagram of Steriflamme system sequence of operations within Steriflamme. With courtesy from Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD.
Another important commercial application of aseptic processing technology is in the storage and handling of large bulk quantities of sterilized food ingredients, such as tomato paste, fruit purees, and other liquid food concentrates that need to be purchased by food processors, or institutional end users for use as ingredients in further processed prepared foods. The containers for such applications can range in size from the classic 55-gallon steel drum to railroad tank cars or stationary silo storage tanks. Specially designed aseptic
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FIGURE 20.17 Modern day retorts on cook room floor in a large food canning facility. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.18 Computerized electronic control systems to remotely monitor retort operations by a single operator responsible for an entire battery of retorts. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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FIGURE 20.19 Modern cook room showing battery of retorts arranged for automated loading and unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
transfer valves and related handling systems make it possible to transfer sterile product from one such container to another without compromising sterility. A schematic flow diagram of a typical aseptic processing system for 55-gallon steel drums is shown in Fig. 20.25, with a cutaway view of a typical aseptic drum-filling station in Fig. 20.26. A system such as this is capable of filling 15 drums/h, with each drum containing nearly 500 lb of product (Rice, 1987; Wagner, 1982).
20.5 LOW-ACID CANNED FOOD REGULATIONS Food engineers involved with thermal processing operations should be familiar with all federal regulations applicable to sterilization of low-acid canned foods. The specific provisions for regulating the LACF industry are contained in Title 2, Part 113 of the US Code of Federal Regulations entitled “Thermally Processed Low-Acid Foods Packaged in Hermetically Sealed Containers.” These regulations are also published in detail in The Almanac of the Canning, Freezing, Preserving Industries (Judge, 2012), and were summarized earlier by Teixeira et al. (2007). The purpose of this concluding section is to acquaint the food engineer with the scope of compliance activities required to initiate and sustain commercial food canning operations under these regulations. In the broadest sense, these regulations direct the attention of LACF processors to four operational levels: 1. Adequacy of equipment and procedures to perform safe processing operations. 2. Adequacy of record keeping to prove safe operations.
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FIGURE 20.20
20. THERMAL PROCESSING FOR FOOD STERILIZATION AND PRESERVATION
Track-guided automated batch retort system. Source: Courtesy Allpax, a ProMach Product Brand.
Covington, LA.
FIGURE 20.21 Trackless system layout for automated guided vehicles. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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FIGURE 20.22 Automated guided vehicles in the process of approaching or returning from retorts awaiting loading or unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
FIGURE 20.23
Automated guided vehicle in process of retort loading/unloading. Source: Photo courtesy: JBT FoodTech, formerly FMC FoodTech, Madera, CA.
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Drying rollers Roller Hydrogen peroxide sterilizing bath Plastic sealing strip applicator
Sterile milk inl
Roller
Code dater
Side-seam seal
Internal heater for sterilizing container interior Milk-level cont Milk outlet tube Carton top sealed
Packing material
Finished carton
FIGURE 20.24 Schematic illustration of form fill seal aseptic filling machine with packaging material fed from roll stock. Source: Courtesy: Tetra-Pak.
3. Justification of the adequacy of time-and-temperature processes used. 4. Qualifications of supervisory staff responsible for thermal processing and container closure operations. The requirements of the regulation can be further broken down into 11 specific compliance activities, as described below. 1. Plant registration: This compliance activity requires that every plant producing low-acid canned foods and selling these foods in the United States be registered with the FDA. This is accomplished by the submission of necessary forms (FD 2541), which require such information as • Name of company. • Place of business.
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FIGURE 20.25
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Schematic diagram of aseptic drum filling operation (Rice, 1987; Wagner, 1982).
FIGURE 20.26 Schematic illustration with cutaway view of dual chamber aseptic drum filling operation. Source: From Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc., Baltimore, MD. Courtesy: CTI Publications, Inc.
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• Location of plant. • Processing method: type of equipment used. • List of food products processed. Although most processors normally provide this type of information regularly for their trade associations and for various business accounting purposes, technical and administrative personnel need to exercise care in such matters as choosing appropriate definitions for the type of equipment and processing method they use, and in defining each “product” for the list of products required. If a plant has to close for reasons other than seasonal operations or labor disputes, the regulation requires notification to the FDA within 90 days of closing. 2. Process filing: This compliance activity requires all processors to file Form 2541a for each product with the FDA within 60 days of plant registration and prior to packing any new product or adopting any change in process for an existing product. The type of information required on each form may include: • Name of product and container size. • Processing method used and type of retort. • Minimum initial product temperature (IT). • Time and temperature of processing. • Process lethality or equivalent scientific evidence of process adequacy. • Critical factors affecting heat penetration. • Authoritative source used and date of establishment of the process. One form containing all of this information is required for each product in each size container for all product container size combinations processed in any given plant. 3. Personnel training: This compliance activity requires that supervisors of operators of retort processing systems and container closure inspectors must have attended a school approved by the FDA and have satisfactorily completed the prescribed course of instruction. These “Better Process Control and Container Closure” schools are sponsored jointly on a regular basis by the FDA and the National Food Processors Association. They are held in conjunction with the food science departments at a number of colleges and universities across the country to bring them within reasonable proximity to most canned food processors. The curriculum is presented in a short-course format over 4.5 days, including examinations of the material presented and the awarding of certificates of completion. 4. Equipment and procedures: This compliance activity requires all processors to make certain that equipment related to the thermal processing operations is maintained in compliance with established specifications. For still cook retort operations, these requirements relate to such items as • Mercury and glass thermometers. • Temperature recorders or recorder-controllers. • Steam pressure controllers and gauges. • Steam inlet size, headers, and location in retort. • Steam spreaders and bleeders. • Crates (baskets), crate supports, and separators. • Vents, size and location, venting times and temperature.
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• Water-level indicators. • Level indication for retort headspace in pressure cooking. • Air supply to pneumatic controllers. Product preparation: This compliance activity requires each processor to have documented policies and procedures for this product preparation, production, and sanitation, delineating proper procedures to be followed in such areas as • Raw material testing and certification, including proper storage and inventory control. • Blanching and cooling operations. • Filling operations, including frequent monitoring of critical factors such as IT, fill weight, headspace, product density, viscosity, and pH. • Exhausting of headspace air prior to closing by heat, vacuum, steam injection, hot brine, and so on. • All areas of plant, equipment, and material-handling sanitation. This compliance activity forces all processors to review thoroughly existing quality control and sanitation policies and procedures, or develop appropriate policies and procedures where none have previously existed. Establishing scheduled processes: This compliance activity requires all processors to document and file the following information in support of establishing the scheduled process for any new product or product-process change that is to be filed with the FDA: • The source of qualified expert knowledge used in establishing the scheduled process. • The heat penetration tests, microbial death time data, and thermal process calculations used to establish the scheduled process. • Specification of all critical control factors affecting the scheduled process. • Verification of the scheduled process through inoculated packs, or incubation of product samples from initial production runs. Thermal process operations: This compliance activity specifies minimum requirements that processors have to meet with respect to operations that take place in the retort room or cook room, where the filled and sealed cans or jars are sterilized under pressure in steam or water air override retorts. Some of these requirements include • Posting of scheduled processes. • Use of heat-sensitive indicators. • Review of data on all critical control factors to make certain that they fall within specifications for the scheduled process prior to sterilization. • Calibration of thermometers, recorders, controllers, and timing devices. • Control of retort operations to assure compliance with specified venting procedures and time temperature conditions for the established thermal process. • Use of a fail-safe traffic control pattern to make certain that no unprocessed product can be mistaken for processed product, or vice versa. Process deviations: This compliance activity specifies what processors have to do in the event of a process deviation, such as drop in temperature caused by a sudden loss of steam pressure or a reduced cook time caused by a faulty timer, which would suggest that the product received a process less than the scheduled process. In the event of such a process deviation, the regulation specifies that the processor must
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either (1) reprocess the product according to the established scheduled process and retain all records of such event, or (2) put the product on “hold” and have the “deviate” process evaluated for its public health significance by a recognized processing authority with qualified expert knowledge. Such a processing authority may “clear” the deviation if it is judged to pose no significant risk to public health. Again, records containing documentation in support of such an evaluation have to be retained on file. As most canned food products cannot tolerate a second exposure to the heat sterilization process without serious degradation in physical quality, processors generally prefer to put products on hold while process deviations are evaluated. Large processors clear deviations quickly with appropriate documentation. Other processors may rely on outside services provided by trade associations, can manufacturers, or consultants. 9. Container closure and coding: This compliance activity specifies the inspection and testing required to assure that all containers are properly closed and coded prior to sterilization. Some of the activities specified include • Visual inspection of can top seams (or glass jar closures), at a minimum frequency of once every 30 min, with documentation for records retention. • Complete seam teardown with measurement of critical dimensions taken under optic magnification (or coldwater vacuum tests for glass jars) at a minimum frequency of once every 4 h, along with documentation for records retention. • Periodic testing of cooling water to check concentration of residual chlorine. • Proper code on each container for • Identity of product. • Where packed (plant). • When packed (date). • Who packed (shift or line). • Use of proper postprocessing can handling systems to minimize damage to can seams or closures prior to labeling and case packing. 10. Records and storage: This compliance activity requires all processors to prepare, review, and retain all records from each product packed for at least 1 full year or packing season at the processing plant itself, followed by retention of these records for at least 2 years at some other location, so that all records will be readily available for inspection over a minimum period of three full years from the date the product was packed. The records themselves include all documents and recordings of data, test results, inspections, critical control factors, and so on, required by all of the individual compliance activities described previously. This means that on a continuing basis, essentially all processors must have procedures in place at each plant to • Review all records for completeness. • Collate and arrange records in an organized file for each product “batch code.” • Store the records in sequence with a systematic file system for future retrieval. 11. Recall planning: This final compliance activity requires that all processors have on hand a plan for recalling any product through primary distribution, plus a plan for each distributor to use in recalling the product from further distribution channels downstream. Some processors have adopted the practice of conducting “drills” to test the effectiveness of their recall plans. Such drills are not specifically required by the regulation, but are strongly advised as part of this compliance activity.
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REFERENCES
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References Judge, E.E., 2012. The Almanac of the Canning, Freezing, Preserving Industries. Edward E. Judge and Sons, Westminster, MD (Published annually). Lopez, A., 1987. A Complete Course in Canning, Book 1, Basic Information on Canning, twelfth ed. CTI Publications, Inc, Baltimore, MD. Rees, J.A.G., Bettison, J., 1991. Processing and Packaging Heat Preserved Foods, Springer, US. Rice, J., 1987. International trends in food packaging. Food Process. 48 (10), 86 91. Teixeira, A.A., Heldman, D.R., Lund, D.B., 2007. Thermal processing of canned foods. In: Heldman, D.R., Lund, D.B. (Eds.), Food Engineering Handbook. CRC Press, Taylor and Francis Group, Boca Raton, FL, pp. 592 659. Wagner, J.N., 1982. Aseptic drum processing. Food Eng. 54 (1), 120 121.
HANDBOOK OF FARM, DAIRY AND FOOD MACHINERY ENGINEERING