Understanding aseptic filling technology

In this way, the organoleptic features of the product are kept for a pre-determined shelf life at room temperature. This target should ideally be reached at the lowest capital and operational cost. Several manufacturers of aseptic filling lines have introduced technological innovations to reduce the line complexity and the running costs. This chapter deals with the different technologies available on the market.

Aseptic technology: an integrated system, not a series of connected machines.

When evaluating the performance of an aseptic filling line, one should not only focus on container sterilization. For lines with similar log kill capabilities, consideration should be given to line complexity and operational product safety risk factors when making technology decisions. Some lines may offer high performances but less efficiency in the long run. Some features of an aseptic filling line also play an important role:

Thermal treatment on the product 

Thermal treatment must be complete and without failures because all further steps (filling, capping, etc.) take place at room temperature in a controlled environment. The thermal treatment should also take the presence of pulps and fibres into account and adjust the thermal treatment hold time according to the different heat penetration rate of pulpy products. 

Container design  

Bottle shape should not allow potential shadowed areas where sterilization could be less efficient; cap design has to guarantee a perfect seal to avoid any re-contamination of the aseptic product. 

Bottling bloc 

Besides the decontamination efficiency, an aseptic bloc should protect the working environment from particles coming from outside (insulation of working environment, management of discharge points) and feature reliable inlet-outlet interfaces for product and auxiliary fluids.

Structure of an aseptic filling line

Sterilization

Sterilization can be defined as a treatment aimed at destroying all vegetative microbic forms present in a surface or inside a foodstuff, together with almost all spores. After this treatment the remaining spores should not be in a position to germinate again.

Container sterilization

Chemical sterilization is presently the most common decontamination treatment for bottles and caps. The microbiological efficacy of a chemical agent is expressed using this general relation formula:

The role of the three parameters is different: temperature has the most effect on sterilization, followed by concentration and contact time. In the food industry the choice of sterilizing agents is somewhat limited, as some sterilizing agents such as formaldehyde cannot be used for food contact containers.

Treatment of containers

In an aseptic bottling line, container and caps must be sterilized prior to filling to avoid recontamination of sterile product. The determination of a treatment to obtain commercial sterility of a package must take into account the interaction among the different aspects of the treatment. It is possible to obtain a high log reduction by performing a strong treatment using sterilizing solution at high concentration and at high temperature for a long contact time. Nevertheless, this strong treatment will affect the total quantity of residuals of chemicals inside the bottle at the end of treatment. Moreover, a shrinkage of the PET bottle might occur. It is advisable then to use sterilization parameters that give acceptable results (for log reduction, shrinkage, and residual) by optimizing the working contact time, temperature, and concentration.

Peroxyacetic Acid (POAA or PAA)

Peroxyacetic acid (POAA), also known as peracetic acid (PAA), is a chemical compound in the organic peroxide family. It is a bright, colorless liquid with a strong oxidizing potential. It is widely employed as sterilizing agent, also at low concentrations (less than 1%). Peracetic acid is produced by continuously feeding acetic acid and hydrogen peroxide into an aqueous reaction medium containing a sulfuric acid catalyst. Peracetic acid is an ideal antimicrobial agent due to its high oxidising potential. It is broadly effective against microorganisms and is not deactivated by catalase and peroxidase, the enzymes which break down hydrogen peroxide. The Peracetic acid decay in enviromental friendly residuals (acetic acid and hydrogen peroxide) in the product but the limit is 0,5 ppm. It can be used over a wide temperature range, wide pH range, in clean-in place (CIP) processes, in hard water conditions, and is not affected by protein residues. Peracetic acid kills microorganisms by oxydation and subsequent disruption of their cell membrane, via the hydroxyl radical (OH·). As diffusion is slower than the half-life of the radical, it will react with any oxidizable compound in its vicinity. 

US EPA first registered peracetic acid as an antimicrobial in 1985 for indoor use on hard surfaces. Use sites include agricultural premises, food establishments, medical facilities, and home bathrooms. Peracetic acid is also registered for use in dairy/ cheese processing plants, on food processing equipment and in pasteurizers in breweries, wineries, and beverage plants. It is also applied for the disinfection of medical supplies, to prevent bio film formation in pulp industries, and as a water purifier and disinfectant. 

US EPA first registered peracetic acid as a sterilant in 2006 for use in food and beverage processing operations, including aseptic applications.

H2O2

Hydrogen peroxide (H₂O2) is a very pale blue liquid, which appears colorless in a diluted solution and is slightly more viscous than water. It is a weak acid. It has strong oxidizing properties and is therefore a powerful bleaching agent, but has also found use as a disinfectant, as an oxidizer, as an antiseptic, and in rocketry as a monopropellant, and in bipropellant systems. The oxidizing capacity of hydrogen peroxide is so strong that the chemical is considered a highly reactive oxygen species. This is why it is normally used in water solution, except for rocketry where it is used at high concentrations. At high concentration, hydrogen peroxide is an aggressive oxidizer and corrodes many materials, including human skin. In the presence of a reducing agent, high concentrations of H2O2 will react violently. Hydrogen peroxide should be stored in a cool, dry, well-ventilated area and away from any flammable or combustible substances. H2O2 reacts and decays with the light exposure, with metals or organic compound contacts. It is stored in HDPE or stainless still container in order to be protect by the light and by impurities or dust.

Hydrogen peroxide is generally recognized as safe (GRAS) as an antimicrobial agent, an oxidizing agent and for other purposes by the US Food and Drug Administration. It has been used as an antiseptic and anti-bacterial agent for many years due to its oxidizing effect. Hydrogen peroxide is the simplest element of the peroxides group. Its chemical formula is H2O2. Its molecule is not planar, because the two O-H bonds are at an angle of 111°. It contains peroxide ions (O2 ^2-) with a single bond (O-O)^2-. Its structural formula is H-O-O-H. Hydrogen peroxide always decomposes (disproportionate) exothermically into water and oxygen gas spontaneously:  

The rate of decomposition is dependent on the temperature and concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. 

Hydrogen peroxide is manufactured today almost exclusively by the autoxidation of 2-ethyl-9,10- dihydroxyanthracene (C₁₆H₁₄O₂ ) to 2-ethylanthraquinone (C₁₆H₁₂O₂ ) and hydrogen peroxide using oxygen from the air. This is known as the RiedlPfleiderer process. 

Hydrogen peroxide, either in pure or diluted form, can pose several risks. Hydrogen peroxide vapors can form sensitive contact explosives with hydrocarbons such as greases. Hazardous reactions ranging from ignition to explosion have been reported with alcohols, ketones, carboxylic acids (particularly acetic acid), amines and phosphorus.

• Each container is turned upside down before the treatment begins and a strong mechanical washing action is applied to its surface due to high spraying pressure and optimized nozzle design. This means easy removal of particles and high efficiency on cold spot contamination that might be present on the surface of the bottles.
• External and internal surface treatment are performed simultaneously, thus avoiding any possible cross-contamination.
• Wet PAA allows easy monitoring of the few critical process parameters (contact time, temperature, concentration, flow rate, spraying pressure) present during sterilization.
• Rinsing with sterile water is necessary to decrease the chemical residuals inside the treated packaging. Inside the final bottle the peroxide residuals has to be lower then 0,5 ppm according to FDA regulation.
• Sterilizing solution can be recovered and re-used after concentration checking. 

PAA vapour container sterilization

This system performs an injection of a small quantity of aerosol PAA in a flow of food-grade steam, which acts as a carrier and distributes the PAA on the surface of containers. At the same time, the temperature of steam activates the sterilizing solution. Wetting agents are added to the PAA to obtain an optimal coverage of the surface of the container. Containers are then rinsed with sterile water and sterile air before filling. This system has the advantage of reducing in a significant way the consumption of sterilizing agent and rinsing water. The drawback is that the sterilizing and rinsing system is fairly complex, as separate manifolds must be provided for steam and PAA, and bottle temperature must be carefully monitored to ascertain the activation of the sterilizing agent. When high sterilization levels for external surface of bottle are required, a liquid PAA spraying on the external surface of the bottle is performed, in a very similar way compared to wet PAA technology.

H2O2 CHP container sterilization

Among dry sterilization technlogies using hydrogen peroxide, the one called CHP (Condensing Hydrogen Peroxide) performs H2O2 vapour injection inside the containers. The difference in temperature between H2O2 vapour and container walls starts a condensation phase, where the sterilizing solution condensates in microdrops on the internal surface of the bottle. These microdrops are then removed by blowing hot air inside the container; thus evaporation of sterilizing solution occurs. As water contained in the H2O2 solution evaporates before hydrogen peroxide, the sterilizing agent becomes  more and more concentrated, which adds to the effectiveness of the sterilization process. 

On the other hand, long evaporation times are needed for complete evaporation of the sterilizing solution and the temperature of air is limited by the heat resistance limit of the PET bottle. Efficacy of this technology on the external surface is also limited: as some polluting particles on the external surface of bottles might be carried inside the filling area, these systems normally perform an intermediate SOP (sterilizing outside place) treatment to sterilize all external surfaces of the rinsing/ filling bloc with spraying of liquid PAA. It must be noted that these intermediate SOP cycles, that can last between 10 to 30 minutes reduce the line availability and overall efficiency. Moreover, they represent a source of sterilizing agent consumption and they add to the complexity of the line, as two different sterilizing agents must be used for container sterilization and ambient sterilization during normal line operations. H2O2 sterilization process doesn’t require water consumption in the rinsing phase.

Furthermore, H2O2 CHP does not perform any mechanical removal action on cold spot contaminations. The advantages brought about by this technology (elimination of rinsing with sterile water, reduction of sterilizing agent consumption) are counteracted by the long evaporation times required, limitation of sterilization temperatures due to PET low heat resistance, and the possible migration of H2O2 inside the PET matrix during treatment that can significantly raise the residuals of sterilizing solution in the product after filling. 

The activation could also be achieved with UV or infrared. The CHP sterilization process before the oven shows a very simple doser and no interference with the heating and the blowing process. The oven must be sterile and the sterile area is quite big, increasing costs and risks. The starting temperature of the preform is not under control and consequently neither is the amount of H2O2 condensed inside the preform. External preform treatment is not available. The CHP process in the oven shows the same characteristic as the process before the oven but with a more efficient drying process that uses the heat of the oven. On the other hand, in the oven, the preform has many contact points with the mandrel which, from a microbiological point of view, may create some problems.

Cap sterilization technology

PAA spray sterilization

Liquid PAA spray sterilization is one of the most widely used and reliable techniques for treating caps and guaranteeing the decontamination level needed by an aseptic filling system. As with PAA bottle sterilization, this process is based on the spraying of high pressure liquid PAA on all surfaces of the caps, followed by a sterile water rinsing phase to remove residual peracetic solution from the closure.

This technique has all the advantages of the bottle PAA sterilization (robustness, wide process window) and the implementation is usually very simple.

Before being fed to the capping unit, the caps are sorted and transferred through a channel towards the aseptic zone. It is during this transfer that the spraying phase is usually performed.

High pressure sprays of PAA are generated through nozzles (usually blade or cone) and directed towards the internal and external surface of the caps. The number of nozzles is designed to guarantee the correct treatment time (usually only a few seconds). The jets are usually directed in such a way that they push the caps forward to help the creation of a constant flow of caps towards the capping unit.

Accessibility to the internal part of the sterilizer and to the channels is usually very good.

The use of high pressure jets has the advantage of adding good mechanical washing that increases the efficacy of the sterilization by easily removing any possible contamination or external particles from the surface of the caps. The sterilizing solution can be recovered and re-used. To increase the efficiency of the recovery sterile compressed air blades are sometimes used on the caps before they reach the rinsing zone.

When applied on a linear transport channel, one of the possible drawbacks of this solution is that the length of the sterilizing unit is proportional to the treatment time. To have an acceptable footprint the total treatment time has to be short and the concentration and temperature of the sterilant relatively high (55-65°C - similar to PAA bottle treatment).

A lubricant material is usually added to the polymeric resins used to manufacture closures. This helps the ejection of the moulded closure from the tooling components and also eases the removal of the caps from the bottle by keeping the torque needed to open the bottle as low as possible. The most extensively used lubricant is erucamide (ESA) because of its low cost and good performance. 

Some of this lubricant is unfortunately removed when the cap is sterilized with a hot peracetic acid solution. Pressure and temperature are two factors that can increase this removal. 

In PAA spray sterilization, in which high pressure spraying is usually added to high PAA concentration and temperature, some surface removal of lubricant, that can lead to a decrease in torque removal performance, can be expected. 

Another drawback of this solution is that it usually requires a high number of nozzles which have very small orifices. Some nozzle clogging can be expected but it is difficult to monitor. The effectiveness of the sterilization has to be based on redundancy. 

PAA immersion sterilization

This sterilization technique is similar in many ways to PAA spray sterilization. It replaces the use of nozzles to distribute the sterilant on the caps surface with a liquid sterilization bath in which the caps are immersed for the required time to reach the desired killing rate. 

To keep the footprint of the machine as small as possible the caps channel inside the bath usually follows a path that optimizes the caps/space occupied ratio. A spiral path for example, is quite common. It is, of course, critical to obtain the correct distribution of the sterilant inside the caps, to ensure that no air remains trapped inside, and that the caps are inserted in the bath with the concave part directed upwards. 

After the contact time has elapsed the caps are removed from the bath and turned upside down to remove the residual PAA solution inside. They are then pushed towards the sterile water rinsing zone, to remove the last of the peracetic solution. 

The PAA inside the bath is heated and re-circulated. PAA streams can be used to push the caps through the sterilization path inside the bath. In comparison to the spraying technique, PAA immersion has some advantages. It is easier to design a long treatment time sterilizer (more compact, no need to use and clean hundreds of nozzles) this means lower PAA concentrations and temperatures can be used to achieve the same desired killing rate. This (added to the absence of high pressure jets) helps in reducing the lubricant removal problem and significantly reduces PAA consumption due to chemical decay. The absence of spraying nozzles also helps in limiting the PAA consumption share caused by liquid particles transported outside the machine by air flows.

CHP sterilization

CHP (condensing hydrogen peroxide) is a technology that has been used with success for both bottle and cap sterilization. As with the other H2O2 based sterilization systems, it is considered a “dry” sterilization because neither water nor any other liquid stream is used during the process.

A water-based H2O2 solution is vaporized and mixed with a hot air stream to generate a high concentration stream of sterilant. It is important that the concentration is high enough and that the dew point temperature of the mixture is significantly higher than the temperature of the caps that are entering the sterilization zone.

In this way, when the unsaturated vapours are dosed on the caps surface, local saturation of the mixture will occur on the closure surface and a uniformly thin layer of condensate will begin to form. The amount of condensation dosed will be correlated to the total contact time, the caps inlet temperature and to the dew point temperature value of the sterilant.

Since hydrogen peroxide has a lower vapour pressure than water, the final composition of the condensate that is obtained has a much higher concentration than the initial vaporized solution. Even at this very high concentration, liquid H2O2 on its own has a low killing efficiency.

The most important and critical phase is based on subsequent “activation” and re-evaporation, usually with a heat source, such as hot air.

During re evaporation, the residual H2O2 liquid concentration increases, creating areas with concentrated vapours that last only for a brief period. The activation phase is also critical to remove most of the condensed H2O2 and keep the residual values to a minimum.

One of the advantages of this technique is that with very short condensation and activation times (a few seconds each) a very good killing rate (6 log on reference microorganism) can be obtained. A downside is that the timing and sequence of treatments is very important. Condensation has to last the correct amount of time and has to be followed by activation to complete the sterilization treatment. During emergency stops and idle phases the sterilizing machine usually has to be emptied. During transient phases the management of treatment time can be complex.

The sterilization performance is also influenced by the inlet temperature of the caps because that affects the amount of hydrogen peroxide that will actually be deposited on the surfaces and has to be taken into account. Sometimes a pre-heating phase is used to heat the caps up to a known value before H2O2 treatment however this increases the complexity of the sterilization system. Another possible downside is related to the temperature of the caps that are coming out of the sterilizer. Activation requires a high amount of heat, so there is a risk that the caps exit the sterilizer at a high temperature with this sterilization technique. Unlike the PAA sterilization system, there is no water rinsing phase after sterilization, to work as a "natural" cooling phase. On HDPE and PP caps there is no shrinkage problem as with PET bottles, but nonetheless there is a significant change in the mechanical characteristics of the resins correlated with temperature. Although the torque usually applied to the caps to screw them to the neck of the container is kept constant, the cap’s mechanical properties change during the operation. The dynamics of the screw on the bottle will change too. The force required to open the capped container after the bottle cools down will, in fact, depend on the temperature of the closure at the time the closure torque was applied. 

As soon as the closures exit the sterilizer they begin to cool down and their temperature decreases more significantly when the filling bloc is stopped or kept in stand-by for some reason. It is important that the temperature of the caps leaving the sterilizer is kept as low as possible to achieve good repeatability of the opening torque on the final bottle.

VHP sterilization

VHP (vaporized hydrogen peroxide) is another H2O2 vapour-based dry sterilization technology. Here the decontamination effect is centred in the hydrogen peroxide vapour treatment phase. No activation phase is needed after the vapour treatment. A post-sterilization air treatment to reduce residuals is possible, but not mandatory. Any significant condensation of hydrogen peroxide has generally to be avoided on the caps and on the machine elements. To achieve that, the dew point of the H2O2 mixture has to be kept lower than the temperature of every surface of the machine and the caps. This means H2O2 concentration has to be limited. This, and the absence of activation, means that contact times are generally much longer than those required using a CHP treatment. Because of the long contact time needed, to keep the footprint of the machine as compact as possible the cap channels inside the treatment zone follow a path that optimizes the use of space, like a spiral, a helix or a drum.

Caps pre-heating is also possible to avoid condensation with higher H2O2 concentration and to shorten the total treatment time.

Some micro-condensation could be acceptable on the caps entering the sterilization environment providing the sterilization time is long enough. Any possible micro-condensation is removed before the caps leave the sterilizer and no activation/drying is needed. One advantage of this treatment is that the sterilization process is very simple and robust, it consists only of one phase and transient phases and stops can be handled very easily. Since the temperature is low, it is much easier to obtain low final cap temperature and good repeatability of the opening torque. This technique can also be easily applied to treat sterilizable sport caps. Vapours can easily reach and sterilize every zone of these complex caps and possible vapour leaks inside the internal parts of the closures are not visible and don’t leave any marks.

Pre-sterilized caps handling

In case the caps cannot be sterilized by Chemical sterilization, the standard solution is to pack these caps in airtight bags and treat them by irradiation with gamma rays. Some caps suppliers or specialized third party companies can provide this treatment and supply bags of presterilized caps directly to the bottlers. To correctly deploy presterilized caps it is necessary to:

• Put the bags in a controlled contamination area.
• Sterilize the environment and the outside surface of the bags to avoid re-contamination of caps once the bag has been opened. Treatment can be performed using PAA in liquid phase, H2O2 in vapour phase or other suitable sterilization techniques.
• Open the bags and feed the caps to the capper using a controlled contamination area for caps handling.  

Energy-based sterilization without chemicals

The sterilization activity of electro-magnetic waves has been studied for a long time. As there is no contact, energy-based sterilization is potentially residual-free. Radiation frequency is normally the most relevant parameter for process effectiveness compared with radiation intensity. The sterilization principle is the irreversible damage on nucleus DNA and RNA when radiation penetrates inside microorganisms.

The most promising energy-based technologies for beverage applications are: 

• Uv light 
• Pulsed light 
• Ionizing radiation 
• Electron beam

UV light sterilization

UV disinfection is used in air and water purification, sewage treatment, protection of food and beverages, and many other disinfection and sterilization applications. A major advantage of UV treatment is that it is considered safer and more reliable for disinfection of water than chemical alternatives, while the level of disinfection is much higher. UV treatment systems are also extremely cost efficient and require less space than alternative disinfection systems.

Ultraviolet light is one energy range of the electromagnetic spectrum, which lies between x-rays and visible light. Wavelengths of visible light range between 400 and 700 nanometers (nm). UV itself lies in the ranges of 200 nm to 390 nm. Optimal UV germicidal action occurs at 254 nm. Since natural germicidal UV light from the sun is screened out by the earth’s atmosphere, we must look to alternative means of producing UV light. This is accomplished through the conversion of electrical energy in a low-pressure electromagnetic spectrum.

UV light penetrates through the cell wall and cytoplasmic membrane of a microorganism and causes a molecular rearrangement of the microorganism’s DNA, which prevents it from reproducing. If the cell cannot reproduce, it is considered dead or ’inactivated’. UV dosage is the most critical function of UV disinfection, because the extent of inactivation is proportional to the dose applied. As individual UV lamps emit a set amount of ultra violet energy, it is important that a system be sized correctly.

For maximum UV transmission a ’hard glass’ quartz sleeve is recommended for two main reasons: it isolates the lamp from the water to offer more uniform operating temperatures and allows for higher UV output onto the surface to be treated.

Pulsed light sterilization

Pulsed light technology uses high power electricity to produce high intensity light pulses. Alternative current is stored in a condenser that feeds a xenon lamp. By feeding the lamp with a high voltage, a high power pulse can be created producing a high intensity light pulse with an average wave length of some hundreds of nanometers.

Pulsed light technology uses high power electricity to produce high intensity light pulses. Alternative current is stored in a condenser that feeds a xenon lamp. By feeding the lamp with a high voltage, a high power pulse can be created producing a high intensity light pulse with an average wave length of some hundreds of nanometers.

This technology is very efficient in killing all types of microorganisms. Nevertheless, its efficiency is directly correlated to the presence of direct surface illumination; any shadowed areas where light cannot reach the surface to be sterilized must be avoided.

The principle of disinfection is a combination of two effects: a photochemical effect which modifies DNA preventing mitosis and protein synthesis; a photothermal effect which rises the temperature inside the cells up to cell explosion.

The design of a reliable pulsed light system for containers should feature a handling system that exposes all surfaces of the containers to the light pulse during treatment. UV light or pulsed light are effective only at short distance from the emission source and are not considered to be penetrating.

Ionizing radiation Sterilization

Ionizing radiation consists of high-energy particles or waves that can detach (ionize) at least one electron from an atom or molecule. It is very effective when applied to viruses, moulds and yeasts, bacteria, and spores. Their sterilizing action is twofold:

• Direct effect: radiation breaks the vital components inside the cell nucleus (breaking DNA structure, building up new crosslinks). In this case the cell normally looses reproduction ability and/or dies. ) 
• Indirect effect: free radicals are formed which deactivate proteins and enzymes inside the cell. 

• A lfa rays: helium nuclei (2 protons, 2 neutrons) emitted by radioactive elements, easy to shield (a normal sheet of paper is enough).
• Beta rays: electrons or positrons with high kinetic energy emitted by radioactive nuclei. They can also be artificially accelerated using magnetic fields (accelerated electrons)
• Gamma rays: electromagnetic radiation at high frequency, emitted by radioactive nuclei during transitions among different energy levels. 
• X-rays: electromagnetic radiation at high frequency, emitted by radioactive nuclei during transitions among different energy levels. X-rays are also formed during the deceleration of charged particles, mainly electrons (Bremmstrahlung radiation). 

Electron beam sterilization

The main process parameter is the voltage difference between cathode (where electrons are emitted) and anode (where electrons are accelerated). Moreover it is possible to modulate the current (number of electrons flowing in the treatment area per second).

The system is very similar to the old cathodic tube television set, apart from the applied tension: in a standard TV set electrons are accelerated up to 20,000 Volts, whereas an industrial type emitter can accelerate electrons up to more than 10 million Volts. Electron beams destroy bacteria and moulds very quickly. Another advantage of this technology is that electron emissions are controlled by electrical power: it is always possible to switch the unit off, and the radiation will stop immediately.

The feasibility of this system for container sterilization depends on the cost of such machines and on the correct handling of the containers in the treatment area (management of treatment time, shadow area control, container jams management). In fact the application of low-energy electrons for the disinfection of containers of complex geometries has been limited due to their inability to efficiently penetrate the rigid walls. Most three-dimensional applications have been evaluated using higher energy processors with bulk or through-the-wall treatment. Many plants validate the electron disinfection of interior surfaces by injecting electrons through the open-mouth of the container. Direct thin-film dosimetric mapping results of both the interior and exterior dose distributions for in-line treatment have been compared with those from Monte Carlo modeling.

Monte Carlo modeling is a well-known computational method used in different field to simulate the results of experimental data.

Aseptic Filling

Aseptic filling technology aims at reaching the best performance in terms of filling speed, accuracy, flexibility and, at the same time, maintaining sterility of the product and of the containers.

Starting from these considerations, the design of an “ideal” aseptic filler should focus on the elimination of any possible recontamination issue. For this reason the filling environment has to be taken in high consideration: it must be absolutely aseptic. Immediately after the production a thorough cleaning must be carried out to physically remove any possible residual of product that, being organic, could become “food” for microorganisms, allowing their growth. It is important not to leave the filler environment “dirty” with product after the production, since once the microbiological isolator is opened the residual of product present inside, may get contaminated. 

The Cleaning and Sterilizazion phases shall be very accurate using proper chemicals and a strong mechanical action. The sterility of the Microbiological Isolator after the environmental sterilization cycle is maintained thanks to HEPA filtered air overpressure.

The filling phase can be considered as the heart of the aseptic filling system. It is during this phase that all the different parts involved in the process are merged together: the sterile product is transferred into the sterilized bottle and the bottle is capped with a sterilized cap inside an Aseptic environment (Microbiologic Isolator).

There are different kind of filling (Volumetric electronic filling, Weight filling, etc), but they have to be as much precise as possible to avoid leakage or possible splash out of product, especially in the high speed rotary machine where the centrifugal force tend to bend the filling flow.

The following table, although not dealing with the integration of the filler with the rest of the aseptic system, shows some critical design aspects for an aseptic filler and formalizes some strategies to correctly address these issues.

Volumetric electronic filling

Most fillers used with aseptic applications feature a magnetic flow meter installed on each filling head that determines the volume of product introduced in each bottle during each filling cycle. The magnetic flow meter is based on the principle of the variation induced in a magnetic field by the flow of a conductive liquid.

It is possible to calculate the effective flow when the pipe diameter is known. The advantages of this technology are the overall reliability, the dramatic simplification of the product path and the good filling accuracy. Modern magnetic flow meters use sintered electrodes without crevices and can directly control a membrane valve to start and stop the filling cycle. By deploying them it is relatively easy to design linear product path by eliminating all moving parts except for a single valve. The added bonus is the possibility to treat liquids containing pulps and fibers.  

When dealing with still liquids (the fast majority of aseptically filled products) it is not necessary to perform a contact filling; this is very important for aseptic filling, as the possible contamination of a single bottle is not transferred to all bottles filled by the same nozzle afterwards. 

Another important feature for aseptic filling is the availability of a system that can adjust the filling speed during operation. As many products are prone to foaming, especially when filled at ambient temperature inside family-size containers, it is sometimes necessary to start the filling phase slowly, then stepping up filling speed to achieve better performance. By reducing the filling speed in the last phase, it is then possible to achieve higher filling accuracy, as minimal variations in the membrane valves closing times will have less effect on the filled volume. 

The linear product path design allowed by magnetic flow meters helps with the design of effective CIP/SIP systems. Many manufacturers have introduced a closed loop design for CIP/SIP.

This normally implies the deployment of a so-called  “dummy bottle”; a device that is installed on each filling head to provide a return pipe for washing and sterilizing solution. The best systems feature automatic dummy bottle insertion and extraction to avoid any recontamination of the sterilized environment by wrong operator’s intervention. The control software of the filler plays an important role when dealing with filling accuracy. Avoiding overfilling is very important to reduce operational costs for the line; this is why some self-learning software solutions have started to appear. These systems can analyze all past filling cycles for each valve and can compute ideal timing for valve closing, as they compensate for variation in the filling parameters.

Weight filling

Weight filling technology measures the weight of containers during the filling cycle. An electronic weight cell is installed on each container handling device which determines the net weight of the product filled. When the preset weight is reached, a product intercept valve is closed and the filling phase ends. 

Some systems perform a weight control after filling and can adjust the filling valve according to any detected variation to compensate changes in environment temperature, product viscosity, and product specific weight. An advantage of weight filling is the high filling accuracy when dealing with “liquid food” products, which normally declare content expressed in grams on the bottle label. When dealing with soft drinks that declare content in ml on the bottle label, the accuracy is lessened by the conversion factor. Weight filling technology (especially the weight cells) can be more difficult to maintain over time compared to magnetic flow meter technology. High-speed bottle transfer implies vibrations, collisions, which have an effect on the overall measurement precision. Variations of filling line speed can also have an effect of filling accuracy.

Other filling technologies

Many different filling technologies have been used for aseptic applications for PET containers during the years. Although nowadays magnetic flow meter technology and weight filling offer the best aseptic performances, other filling technologies have been used in the past such as volumetric electronic probe fillers, gravity fillers, and counter pressure fillers. These technologies imply a contact between bottle and filling nozzle, and as such their use in an aseptic environment is subject to limitations (extra SOP cycles required, shorter continuous operation time between sterilization cycles and so on).

FOCUS: New filling trend: beverages with pieces

Fruit juices are commonly consumed all around the world. In some areas they are perceived just as a re-freshing beverage during the summer season and in others they are consumed throughout the entire year, especially for breakfast. 

Pulps and fibers are perceived by the customer as proof of high quality, because the product gives the impression of freshly squeezed juice. In recent years, especially in the Far East, the new trend is to have pieces in beverages, even in milk based drinks. Fruit, coconut, nut, aloe vera pieces, even berries and cereals may be included. This new trend sees beverages going beyond the original concept of drinking simply to quench thirst, they are also able to satisfy hunger. 

Beverages with pieces need to be chewed; so they are a food as well as a drink.

The beverage becomes a nourishment that provides fast and important elements such as carbohydrates, something that generates a limited, but constant glycemic curve, not just a peak typical of simple sugars. 

The new trend is taking pace, especially with the present day frenetic lifestyle, that does not allow the time to have a complete meal. Instead of having dinner, for example, people can have a flavoured milk-based beverage with oats or rice grains included. It provides sugars, carbohydrates, minerals, proteins and enough energy to get through the entire afternoon. Maybe it does not give the same satisfaction as a plate of “pasta alla Bolognese”… but it certainly takes less time. As the beverage industry is clearly going in this direction, the machinery manufacturers must be ready to meet the demand by producing machines able to fill beverages with pieces. 

Single Stream/Dual fill: Aseptic Piston Doser

The first choice and easiest way to produce such innovative products is to fill them without any particular care and autoclave them, with the container; this has the advantage that no hot fill or aseptic filling is required however it does mean that the container must be able to withstand such long and stressful treatment; this can easily be achieved using aluminium cans or glass bottles/ jars but it is not feasible when using plastic (PET, HDPE) containers. A step forward has been achieved by hot filling these products in plastic containers. This technology has spread all over the world giving a more flexible platform to work with but there are many restrictions connected with hot fill technology: the damage rate on pieces, kept at high temperatures for long periods of time before cooling can become critical and unacceptable, especially for delicate pieces such as aloe vera or orange and mandarin sacs. The risk is that the consumer is presented with a damaged product and the desired high value added beverage feeling is not attained.

Process

Whether the filling is easy or critical, it’s not possible to deal with those products if they can’t be properly thermally treated upstream. In all situations it’s very important to create a recipe that can be acceptable and appreciated by the consumer and handled not only by filling devices but also on process side upstream. The thermal treatment of pieces, sometime very big (even up to 10mm x 10mm x 10mm) can be difficult for the process machines, as the ‘core’ of the chunk is not easy to reach with the designed pasteurization or sterilization temperature. The problem is even worse when dealing with dry products, such as cereals, almonds and nuts, where the low affinity towards the water creates a difficult heat exchange. Generally these products are ’precooked’ before being thermally treated as it’s easier to transfer the heat throughout the whole piece.

The importance of the process upstream is not only a matter of treatment but also a matter of handling: the pieces, transferred by a liquid carrier, can bridge with each other and clog, thus making them hard to process with these machineries. Some changes to the designs have improved this aspect but in any case the percentage of pieces in the liquid carrier is strictly related to the particle size and characteristics; generally the maximum percentage for fruit particles (coconut, mango, apricot and strawberry) that can be processed by those systems is around 50-60%, whereas for dry pieces (oats, almonds and nuts) it is much less, around 10-15%.

The liquid carrier also plays a very important part in the process: its density should be, as far as possible, comparable to the density of the pieces involved in the treatment and that requires producers to add gums, sugar and other ingredients to achieve the target. Sometimes it’s very difficult to fine tune the density of the liquid to the chunk density and in some cases the viscosity is used to achieve a homogenous distribution. The viscosity of the liquid isn’t always a solution because the final product needs a specific texture: an orange juice with some sacs added can’t be very thick and could easily create a product with floating or depositing pieces depending on the density variation between liquid and pieces. In some situations (for example drinkable yoghurt) the viscosity of the liquid is, on the other hand, high enough (some hundreds cPoise) to allow an easy distribution of pieces in the final product.

Filling

Once the product has been processed it will be delivered to the filling station. Depending on size and characteristics of the pieces there are different systems to consider:

• Single stream filling when piece size and liquid carrier density permit a filling with a single valve, designed accordingly,
• Dual stream filling when piece size can’t be handled in a single station requesting either a double filling on same carrousel or a dual filling using two carrousels on the same machine frame.

Capping

At the end of the filling cycle the containers must be sealed before exiting the controlled environment to avoid re-contamination. As such, cappers are integrated in the microbiological isolator and specifically designed for aseptic applications. Eliminating all possible cross-contaminations is paramount when designing an aseptic capper. Standard cappers feature moving seals and lubricated moving parts that raise issues when deployed inside an aseptic environment. Strategies used to redesign a capper to comply with quality requirements for aseptic revolve around the separation between the components inside the microbiological isolator and mechanical components that require lubrication.

Four main aseptic capper design types are available on the market: 

• Separation is obtained using thermal barriers, either using steam or electrical coils. Thermal barriers are installed on each capping head and allow its up-down motion. ) 
• The mobile part of the capping head is protected by a diaphragm flange that performs the separation. An integrity control is very important to detect leakages and breakages of the diaphragms. ) 
• The entire capper is installed inside the microbiological isolator. Special materials must be used for gears that do not require lubrication for reliable operations at high speed. Nevertheless, moving gears are critical contamination areas that need a dedicated SOP system. ) 
• The capper is designed as a fixed unit, whereas bottles are raised towards the capping head by means of lifting jacks. In this case it is relatively easy to separate capping heads from the lubricated part of capper, but other critical issues are introduced: high speed bottle lifting may cause product splash-out and caps feeding to capping heads becomes quite difficult. 

Bottle handling

The importance of a very reliable bottle handling system for aseptic PET lines is increasing. Two reasons are the higher throughput of new aseptic filling lines and the progressive lightweighting of PET bottles due to PET price, environmental consciousness, and better design experience for bottle shapes. Reliable bottle handling systems have a huge impact on the overall line efficiency, especially when dealing with very light bottles at very high speeds. The best systems available today handle bottles using grippers that act above and below the bottle neck ring area. In this way bottles are firmly held at very high speeds, with no counter guides or oscillation prevention guides needed. Another important bonus of bottle neck handling systems is the dramatic reduction of bottle size changeover operations and downtime. Bottle inlet to controlled treatment/filling environment is critical as far as line efficiency is involved. The traditional technical solution use a pitching scroll, whereas nowadays pitching starwheels are widely used. Starwheels are much easier to substitute when dealing with different bottle necks and the system can be designed to allow pitching starwheel changeover without losing bloc sterility.

Ancillary process equipment

Ancillary process equipment is defined as all process units involved in the operation of an aseptic filling line to produce sterilizing solution and sterile water and sterilize all needed utilities. 

Sterilizing solution production

Sterilizing solutions used with aseptic lines are typically prepared by diluting concentrated chemical solutions available on the market. Dedicated equipment is used to perform a volumetric or weight dilution that guarantees an accurate process, which is required to obtain the preset process parameters (temperature, flow rate, concentration) and to feed the solution to the point of use. In a standard wet PAA system the same unit is used to recover the used sterilizing solution, to filter, to re-establish the preset concentration and to reuse it. Other technologies using H2O2 perform a dilution from concentrated solution, which is then fed to the point of use and vaporized next to the bottle. Recovery systems are not implemented in these disposable treatments due to low quantity used and complete exhaustion of the solution after use. The utmost care must be given to monitoring of H2O2 solution supply, as you cannot visually detect a problem in H2O2 supply inside the steam during treatment.

Sterile water production

Sterile water used on the line can be obtained by thermal treatment. Rinsing water in a PAA system can be filtered using active carbon system to take out residuals of sterilizing solution and then reutilized and reused. Alternatively, microfiltration system for sterile water production can also be used when dealing with dry sterilization technology due to lower use during production (water is needed for intermediate SOP cycles).

Utilities and fluids handling

An aseptic filling line needs different fluids during its operations: sterile compressed air, sterile nitrogen, and sterile steam. Dedicated filtration units are deployed to sterilize these fluids and guarantee sterility during production. Steam selfsterilization cycles before start of production ensure that all filters are sterile to avoid any possible crosscontamination during production start.

CIP, SIP, COP, SOP

CIP/SIP are the acronyms of “Cleaning In Place” and “Sterilizing In Place”. They represent all operations pertaining to washing and sterilization of all surfaces that come into contact with the product during production.

A standard CIP normally performs a washing step of all piping and tanks using caustic solution, followed by a water rinsing. Then an acid solution washing is performed, followed by another water rinsing. The operating software controls all critical parameters (temperature, flow rate, chemical solutions concentration and duration), to ensure the cycle is properly applied. 

CIP/SIP cycles are very important for the safety of an aseptic system. This is why during line design the utmost care must be taken to product path and all issues concerning product flow. It is imperative to control temperature and concentration of CIP solution. Moreover, turbulent flow must be ensured inside the piping to obtain a high mechanical washing action and remove all particles and product residuals. To enhance the mechanical washing action, cycles can be performed in countercurrent flow compared to normal product flow during production. 

COP/SOP are the acronyms for "Cleaning Outside Place" and "Sterilizing Outside Place". They represent all operations pertaining washing and sterilization of all external surfaces of the rinser and filler carrousels inside the microbiological isolator, as well as the sterilization of the whole controlled environment. These cycles are performed using dedicated piping and high efficiency spray balls that are positioned to reach a maximum coverage of all surfaces. Caustic washing solutions followed by water rinsing are used for COP, while liquid PAA spraying and sterile water rinsing are used for SOP. 

While PAA aseptic lines can run for up to 165 production hours between COP/SOP cycles, H2O2 based lines need intermediate SOP cycles (every 2.5 to 8 hours) with liquid PAA spraying and sterile water rinsing to prevent bioburden accumulation in the filling area coming from external bottle surfaces. 

Integration of ancillary process units

The best way to guarantee the safety of the finished aseptic product is to design all ancillary process units for the best integration. All process units should supply all fluids during the different line operations (start-up, production, sterilization) at the required parameters.

Integration is also important as far as single process units’ structure is concerned. To reduce installation times and speed up line commissioning “plugand play” units should be used; pre-assembled on skids and ready to be connected to the rest of the line. In this way shorter piping can be used, fluids consumption is reduced, and shorter installation times are required. 

Design of ancillary process units should take care of avoiding watertraps by correctly positioning all components and aiming for very short and linear piping. All pressure, temperature, flow rate sensors should be placed in the unit position where the performance is more difficult to get, to guarantee the overall unit performance. Access to maintenance components is also critical, as adequate access space and access devices, such as ladders and supports must be considered.

Critical process interfaces must be correctly handled: all valves that change position during line operation introduce a possible contamination point to the entire system. As such, steam barriers are placed on all valves dealing with sterile fluids, on all rotating manifolds, on all moving seals to guarantee safe operations for the entire line.  

Piping

Line piping is the name for all functional connections among all machines within an aseptic filling line, which involves product and fluids used during line operations. 

Best practices connected with line piping design:

• Reduction of volume: optimal process unit positioning reduces the volume of fluids needed during line operations, as well as the line overall footprint.
• Optimal placing of maintenance points: valves and seals should be easily accessible for inspection and maintenance operation.
• Integrated design: some manufacturers build up the line piping directly on site, without designing it first. This should be avoided, as by using 3D CAD systems it is possible to adapt the piping to the site features, avoiding positioning problems during line installation. It is also much easier to deal with accessibility features during the design phase rather than during field activities.

Simplification of line handling

An ideal aseptic system should feature a very small number of critical process parameters to monitor to guarantee the success of all line activities. In the evolution towards an ideal line it is crucial to reduce the number of fluids used and their way of application. For example, using the same fluid (liquid PAA) for internal and external bottle sterilization, caps sterilization, and environment sterilization during SOP means that the same critical parameters should be monitored, and these processed are easier to manage. On the other hand, some H2O2 systems use H2O2 vapour for bottle sterilization and liquid PAA for environment sterilization during intermediate SOP cycles. In this case, better line performance in terms of consumption is reached by adding complexity to the system. Using different fluids in different states means that different sets of parameters must be monitored during the different line cycles.

Radiation-based fluids sterilization

Interest is rising in the last years for alternative fluids sterilization systems using radiations. The target of such systems is the elimination of thermal treatment by direct application of energy.

The most promising solutions are:

• High pressure UV rays for water sterilization 
• Pulsed light systems for rinsing water recovery (peroxide residuals are easily knocked down by pulsed light) 
• Microwaves and electron beam based sterilization systems for line fluids 

Line automation

Line automation software has experienced a very fast development in later years. They started as simple human-machine interfaces for line management and progressively developed to become a monitoring and safety device for all sterilization, filling, capping and environment control operations.

In an aseptic line, automation software acts as a nervous system, where lots of information is continuously exchanged among all machines to guarantee the success of the whole process to obtain a very high safety for the finished product.

High-speed data networks are used to connect all PLC on the line for fast exchange of information.  The main control panel (HMI) is installed next to the filling bloc. There operators can start all line cycles, monitor line operations, obtain detailed information of most components and sensors installed all over the line, visualize line alarms and start resolution procedures, compute line efficiency and connect and exchange data with the company ERP system. 

DIN 8782 norms have become a standard to determine line operational efficiency. These norms describe a reference model to obtain an objective evaluation of the single units incorporated inside a production line. By determining the operation states of each production unit according to the different working conditions, modern line automation software can obtain a reference index. 

Traceability of all line working parameters is nowadays integrated in most automation software: all digital and analog data are saved on relational databases. The best software offers analysis tools to make sense of these data and help maintenance technicians to spot line issues based on line history for quick, focused, and therefore more effective interventions. 

The development of a container, and in particular the creation of the delicate balance between its operating functions and the expressive-communicative ones, must be the result of a technical process and an aesthetic combination, where functionality and aesthetics are inextricably linked to an ergonomic study and its use. In the recent years, designers and researchers have also faced the challenge of eco-sustainability which have made them arrive at a profound reflection on the need to design PET packaging in a much more responsible way. The research was focused on new materials, such as recycled PET and biomasses, and on new solutions to be adopted, most importantly on a design criterion known as lightweighting.

The advantages associated to lightweighting , that is to say, the reduction of the weight of the container and, consequently, the amount of raw material used, are essentially two: communicative , for a lower environmental impact, and economic , thanks to the cost saving obtained by reducing the quantity of raw material to use for the same production conditions.

In order to be effective, the lightweight design criterion must take into account all the above mentioned functions to create containers that, even if against reduced weights, have high mechanical performances, suitable for satisfying the operating functions, and a certain kind of quality, which can make it a tool of communicative effect, in accordance with the perception consumers should have about the packaging, the product and, consequently, the brand.

The limitation of lightweighting lies in the point where the economic reasons of cost saving prevail over the functions packaging must have to be effective: a de-structured container, unstable in line, which gets damaged during manufacturing, palletizing and transport, favoring the contamination of the product, or that manifests the implosion effect when used by the final consumer, is a container which lacks of its functions as an instrument, as packaging and as a communicative tool.

This weight reduction is achieved by both reducing the weight of the preform without any intervention on the design of the bottle, an operation which may lead to unsuitable containers for their multiple functions, or through the symbiotic design of an ad hoc preform and an optimized design for the preform itself. This design will lead to a lightweighted container capable of resisting, thanks to the best possible material distribution over the entire bottle body, to the external stresses incurred during production, handling or use, and to those internal ones, coming from the content itself. These features, associated with the appropriate neck finish and a good sealing performance, are even more important when the purpose of the container is to protect an aseptic product. 

The lightweighting may, alternatively, occur in a single area of the bottle through targeted operations: in the neck through the use of lightweighted neck finishes (currently also available for aseptic bottling), under the support ledge through solutions that limit the accumulation of amorphous material, and at the bottom with geometries which allow a correct material distribution, not concentrated on the injection point. Avoiding solutions that may affect the different functional characteristics related to packaging is the mission of every company which develops and industrializes PET containers.