Packaging materials play an important role in food processing. Organizations spend a great deal of time identifying the right packaging for their products and processes. From bottling to food packaging, end users want to ensure they are operating efficiently in order to provide consumers with a quality product. Even when choosing the right packaging for the product and process, issues can still arise. One of the problems that can occur is the bacteria that reside within packaging materials.
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Manufacturers take the necessary steps of sanitizing produce or introducing various wash methods to clean food products. While these are helpful measures, bacteria can be hidden and grow in the packaging materials, causing harm in many ways. Some examples of bacteria found in packaging include E. coli and Salmonella. Failing to remove bacteria can reduce a product’s shelf life, causing unnecessary waste. Also, bacteria can produce harmful side effects on consumer health, and even death, if not removed entirely from the packaging process. In order to minimize any issues with the end product, manufacturers use sterilization to remove harmful pathogens from the process.
Hot Air Sterilization Processes
Sterilization end users rely on different methods to ensure that harmful bacteria are eliminated from equipment and packaging. Sterilization, which can be used on metal, glass, or porcelain, can have cycle times lasting up to 30 minutes. One of the methods utilized in the sterilization process is hot air, which achieves precise temperature regulation and safe process control. Not only can end users achieve a repetitive process, but it is also environmentally friendly and nontoxic. Two examples of hot air implementation would be static and forced hot air.
With static air, end users introduce hot air from a location near the bottom of a tunnel or an enclosure and let the heat dissipate toward the top. An example of static hot air implementation would be a hot air oven or autoclave for pasteurizing glass jars and tin cans. While this method does provide a level of sterilization, it is not an effective solution for a couple of reasons. The first is that the temperature profile will not be uniform, meaning that certain surfaces will receive more heat than others. The second reason is that it will require a longer dwell time for the heat cycle, which may have a significant impact on product quality. This means that packaging companies will not be able to get the necessary throughput required to meet manufacturing demands.
With forced air, hot air is introduced by a compressed air source or blower system. An example of forced hot air implementation would be dry sterilization for beverage filling processes. This is a preferred method for a majority of the end users for a couple of reasons. With forced air, you get better temperature uniformity within the process, which allows the heat to be evenly distributed over the product. Forced air also decreases the necessary dwell time in the process, which can reduce manufacturing process time.
Hot Air Sterilization Benefits
In industrial beverage filling systems, hydrogen peroxide (H2O2) is used in combination with hot air. First the containers are pre-heated using air heaters to get the surface temperature of the container to approximately 140 degrees Fahrenheit. In the next step, H2O2 is evaporated at around 392 degrees Fahrenheit. To ensure the vapor doesn’t cool down while flowing to the nozzle, double-walled tubes are used. These tubes are heated from the outside to avoid the cooling down of the vapor. To heat the tubes, hot air is blown into them. This hot air is typically generated by electric air heaters due to the precise temperature control those heaters offer. Nowadays, many companies are using hot air recycling systems, such as the Leister RBR blower and DF-R air heater combination, to help improve the efficiency of dry aseptic decontamination systems.
This vapor is sprayed into the containers and settles at the inner surfaces of the container. Important for this method is a full coverage without any blind spots to be able to kill all spoiling organisms inside the container. In bottle decontamination systems the surfaces above the neck ring are exposed to the vapour as well.
This process is necessary to ensure complete sterilization of all surfaces that will be in contact with the product. After approximately 4 seconds, the H2O2 residuals are dried out with hot air to ensure a maximum residual level of less than 0.5 ppm H2O2. This so-called “dry sterilization” offers some advantages: Dry aseptic is cost efficient, has a small footprint in the aseptic filling machine, generates zero waste, and doesn’t need sterile water rinsing.
To assess such systems, sterility tests are performed at every new installation using H2O2, peracetic acid, or steam in accordance to various equipment testing standards. To make sure the sterilization process is efficient, test germs like Bacillus atrophaeus and Bacillus subtilis SA 22 are used. For steam, the test germ is Geobacillus stearothermophilus NCA 1518. All surfaces of the packaging material in contact with product will be exposed to the test germs. The contaminated packaging material is then exposed to the sterilization systems of a filling machine using H2O2, peracetic acid, or steam. After the decontamination is completed, the log reduction rate has to be at least 10-5 for aseptic systems.
Even though there are many dry sterilization systems in use today, there are alternative sterilization solutions that can be implemented with hot air. While the beverage carton industry is dominated by dry sterilization systems, the majority of aseptic bottle filling systems in the market utilize peracetic acid (wet aseptic) to sterilise the inside and outside of the bottle.
Steam sterilization is mainly used for bottling applications that involve glass packaging. One side effect of this sterilization method is the moisture generated on the surface of the bottle. Not removing this residual moisture can lead to issues with coding, labeling, and bacteria growth. In order to remove this moisture, manufacturers locate hot air products and high-volume blowers on bottling lines before coding and labeling in order to achieve a dry surface on the outside of the bottle; it can also be used to dry the inside of the bottles as well. This method is referred to as a hot air knife.
With the hot air knife process, bottlers mount high pressure blowers and air heaters directly on the manufacturing line. In order to concentrate the airflow to the surface of the bottle, a special type of nozzle is utilized to direct airflow. This nozzle blows a curtain of air, which provides a level of evaporation as the bottles run down the line. Since the high-pressure blower and air heater can be regulated from a control system, this allows for a repeatable process that provides a clean, dry bottle, and can be documented for validation purposes.
The use of air heaters and blowers for the sterilization process provides many benefits for the end user. The air heaters and blowers can be integrated into sterilization equipment with ease by simply sending a signal to obtain the desired output temperature. This allows for repeatability for the end user that can help remove pathogens, improve product quality, and minimize waste. The repeatability also assists in the validation process of the sterilization system. With these added benefits incorporated into the process, manufacturers can have confidence in knowing that they have removed harmful bacteria from their end products.
For food packaging processes, it is essential to take the necessary precautions to ensure that packaging has been thoroughly sterilized. Whether a bottling application or food packaging process, hot air can be used as the driver for the sterilization process to deliver a quality product that is consumer friendly. The end result is a product that is produced in an efficient manner that is safe for consumption.
Sanders is a product specialist, with Leister Technologies, LLC, a partner member of the Control System Integrators Association (CSIA). Contact him at Jason.Sanders@leister.com.