Aseptic Filling—The Process And The Benefits
Monday, April 2nd, 2018
In comparison to hot-fill technology, cold aseptic filling provides the required shelf life without adversely affecting the quality of the product, says Alessandro Bellò, vice president of Blowing-Filling & Packaging, GEA.
Aseptic filling technology has created a major shift for beverage producers in recent years. In the past, shelf life was achieved through hot-fill technology that, in effect, sterilised the bottle with the hot liquid as part of the filling process. Effective it may have been, however, there were limitations in terms of product quality and the design of the plastic bottle was limited by their ability to withstand the heat applied during filling without distortion. Cold aseptic filling, by comparison, provides the required shelf life without adversely affecting the quality of the product, uses less plastic and gives much greater flexibility in bottle design.
An Integrated System
Aseptic is a multi-disciplinary approach and an aseptic bottling line is much more than a series of interconnected machines. It is an integrated system, the performance and efficiency of which are influenced by different aspects: an efficient sterilisation process; a correct thermal treatment of the product which takes into account the different heat penetration rate of pulpy products; the container design that has to look good while avoiding any ‘hidden’ areas where sterilisation could be less efficient; and a bottling and capping area that operates within a microbiological zone that excludes contamination from outside. A successful aseptic bottling line must address all these aspects of the process.
Sterilisation aims to destroy all vegetative microbic forms, rendering them incapable of germination. Absolute sterility is impossible to achieve as the destruction of microorganisms follows a logarithmic path. Hardly any technology can obtain absolute sterility with any certainty and this would not represent an optimal solution in any aspect. For this reason, industrial food manufacturers practice so called ’commercial sterility’, a compromise between the advantages of a suitable shelf life obtained and the disadvantage of higher costs for the extensive sterilisation process. The effectiveness of sterilisation is influenced by three basic factors: temperature, chemical concentration levels and contact time. Of these, temperature has the most effect on sterilisation followed by concentration and contact time.
It is important for processors to get the balance right as an extended contact time reduces productivity. High concentration of chemicals is expensive and potentially creates an environmental problem, while high temperature wastes energy and can cause shrinkage of the bottle. The compromise is to find the optimum level between these elements—this is defined as ‘The Working Field’. In an aseptic bottling line, both the container and the caps must be sterilised prior to filling to avoid recontamination of the sterile product.
There are four accepted and commercially available sterilisation techniques for high-speed rotary aseptic filling lines that can be applied to both PET and HDPE bottles as well as plastic caps, each one with different characteristics:
- Wet PAA-based technology sprays liquid Peroxyacetic Acid at high pressure and relatively low temperature. Light PET bottles can withstand Wet PAA treatment without significant shrinkage. This simple and robust system can also be applied in a similar way to flat caps, which are immersed in a liquid PAA sterilisation bath to distribute the sterilant on the cap surfaces and reach the desired killing rate. Rinsing with sterile water removes the last residuals of the PAA solution.
- Vapour PAA treatment uses small quantities of PAA in food-grade steam. This uses very small amounts of chemical but is more complicated as the temperature of the bottle must be closely monitored to ascertain the activation of the sterilising agent. Further, it may not be sufficiently effective when high sterilisation levels are required.
- H2O2 CHP container sterilisation uses a Hydrogen Peroxide vapour that condenses when it is injected into the bottle, causing micro drops to form on the internal walls. These are removed with hot air. H2O2 CHP treatment that is also used for foil sterilisation.
- H2O2 VHP (Vapourised Hydrogen Peroxide) is a dry sterilisation technique using H2O2 The bottles are heated before treatment to prevent the steam from condensing on the internal surfaces, minimising residue values. This technique can be easily applied to treat sterilisable flat and sport caps.
To reduce the effect of heat on the bottles, some systems operate by sterilising the preform before blowing in a sterile environment, thereby minimising the amount of chemical required and preventing shrinkage. CHP and VHP processes are preferred for preform decontamination in aseptic lines. The CHP sterilisation process takes place before the oven: this implies an increase in costs and risks related to preventing the potential preform re-contamination inside the oven, the impossibility of getting the starting temperature of the preform under control and, consequently, the amount of H2O2 condensed inside the preform. The VHP treatment on preforms takes place after the oven: the oven heats the preform to around 100 deg C and is then treated with H2O2 vapour at 80-90 deg C. Once sterilised, the preform is blown in a sterile environment and then filled.
Aseptic filling technology aims to achieve the best filling speed, accuracy and flexibility while maintaining the sterility of the product and containers throughout the process. Avoiding recontamination is key. The filling environment must be aseptic: the whole area must be thoroughly cleaned and sterilised before starting production using proper chemicals and a strong mechanical action and, immediately after production, any possible product residue must be removed to avoid the risk of microorganism growth. Once clean, the sterility of the microbiological isolator is maintained by HEPA filtered air at overpressure.
Containers can be filled by volume or by weight. Both have proven advantages for fillers and have outclassed other formerly-used filling technologies which require contact between bottle and filling nozzle. Volumetric filling uses a magnetic flow meter fitted to each filling head to accurately control the flow of the liquid. The flow meters can directly control the membrane valves to start and stop the filling cycle. Most aseptic products are still liquids so they can be bottled without the filling head touching the bottle. However, some products are subject to foaming, so it is necessary to carefully control the flow rate, and, if necessary, varying it during the filling of each bottle to achieve the required accuracy.
Filling by weight is usually reserved for liquid foods that have their contents declared in grams on the packaging. It can also be used as a second check to take account of variations caused by temperature and product viscosity. Filling by weight can, however, be more difficult to control in high-speed operations as vibration and collisions within the system can affect measurements.
Capping And Sealing
In an aseptic bottling line, the capper is integrated within the microbiological isolator. When designing the capper, it is essential to eliminate the opportunity for cross-contamination. This requires the isolation of moving parts that require lubrication from the aseptic area within the isolator. There are four main methods of achieving this:
- Separation is achieved using a heat barrier from steam or electric coils attached to each capping head.
- The mobile part of the capping head is protected by a diaphragm flange that performs the separation. It is very important to detect any leaks or breakages within the diaphragm.
- The entire capper is installed within the isolator. Materials that do not require lubrication must be used; the moving gears and critical contamination areas need a dedicated sterilisation system.
- The capper is designed as a fixed unit with the bottles raised to the capping heads with lifting jacks. The feeding of the caps can be difficult with this method and care must be taken to avoid splash-out.
The major types of closure devices commonly used for sealing PET bottles for aseptic beverages are: pre-threaded plastic caps, lip seal and liner seal. There are also several tamper-evident systems on the market designed to alert the consumer to the possibility that the seal has been compromised and the quality of the product detrimentally affected.
Welded foil seals are mandatory on HDPE bottles where the natural pliability of the material makes it difficult to guarantee an airtight, robust seal by using a screw cap alone. Foils are also used on PET bottles when the cap design cannot ensure a perfect seal with the neck of the bottle or when the brand owner wants to deliver premium product awareness. Consumers recognise that the foil closure provides maximum product safety in a higher value product. This compensates for the slightly more complicated opening of the container. It is important, therefore, for any aseptic bottling system to be sufficiently flexible to accommodate all variations in capping technology, providing the manufacturer with the ability to select the closure option most suitable for the application, while ensuring the sterility of the process.
How To Make Aseptic Technology Fit
Aseptic technology today is the best production system for the beverage industry, but the investment required to install an aseptic technology system is high. The cost/benefit analysis for aseptic bottling is based upon three factors: the volume of production, the product quality required and the bottle design.
- Volume: Aseptic lines are designed to run 24 hours a day and ensure a high level of efficiency. High output allows the costs to be amortised over higher production runs. However, using aseptic technology for smaller volumes might still make sense if the quality level required by the market is sufficiently high.
- Product quality: At a basic level, aseptic technology provides a very consistent output with the minimum use of chemicals or additives. However, the maximum benefit is obtained in applications where high product quality is critical as it preserves the individual characteristic of the raw materials maintaining their taste, colour and nutritional content.
- Bottle design: Filling at room temperature allows for much greater flexibility in bottle design. If producers wish to have complex designs or change designs frequently, then aseptic technology is a distinct advantage.
There are other considerations. If companies are considering expanding production in the foreseeable future, the installation of an aseptic line will provide futureproofing for the line, thus allowing it to expand to meet the developing needs of the business. Aseptic technology may also allow for the consolidation of production into larger, more efficient plants as the longer shelf life means that the product will not deteriorate during storage and transportation.
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