A Wonderful World for Aseptic Packaging
In the beginning was the notion that aseptic packaging was for low-acid liquid food products in paperboard composite bricks that had a maximum size of 1 L and were difficult to open without an implement. I hope that these misconceptions derived from origins of some 30 years ago have been dispelled. I dream that students and practitioners alike appreciate the broad range of food products and packages embraced by the term “aseptic packaging.” And thus we can move forward to include more of our food supply in this category to achieve preservation with good-to-excellent quality.
Today, aseptic packaging encompasses large multi-thousand-gallon containers of orange juice or tomato paste; tubes of chocolate pudding; gable-top cartons of liquid egg; ounces of fruit beverage in squeeze bottles; beer in polyester barrier bottles; apple juice in gallon polyester bottles; and flavored milk in multi-layer barrier plastic bottles. And when you stretch the definition to its present outer limits, pasta in barrier plastic, rice in plastic trays, ice cream mix in spouted pouches; and coffee lightener in tiny polystyrene cups. And there are more—too many more to recite in this brief exposition.
Rather than extol the merits and successes of aseptic packaging or even to extend its reach here, I will address some of the issues still to be conquered before aseptic processing and packaging can achieve greater success.
The term aseptic packaging originally meant microbiological sterilization of product and package independently and assembly under sterile conditions to achieve ambient-temperature shelf stability. Today, we have gone far beyond to apply the principles to achieve extended shelf life (ESL), which usually means extended refrigerated shelf life. But the notion of sterility with aseptic processing and packaging does not mean that the contained product is forever stable, but rather that it is microbiologically stable if sterilized. The contained product is still subject to biochemical deterioration during distribution, especially ambient-temperature distribution. And, additionally, with long-term ambient-temperature distribution, the product is subject to flavor scalping by interaction with the package material.
One observation that could be made is that aseptic—and its baby brother, ultra-clean, to achieve extended refrigerated shelf life—is now in bottles and jars and analogous packaging that was contemplated but not accomplished in the past. One might say that the shape of aseptic packaging to come is different—no longer just bricks and cups and pouches, but a kaleidoscope of cylinders, cones, wasp-waist, etc.—you name it, and you can probably have it—in any consumer size, even in institutional and industrial sizes. But beware the shelf-life issues beyond the microbiological.
The Tetra Pak Entries
So what is afoot in aseptic packaging? In the realm of the classical composite paperboard, Tetra Pak, the pioneer, launched the Prisma™ Pak for high- and low-acid products several years ago with some market success. Instead of the brick shape, further scores were introduced into the longitudinal sides, and a sort of six-sided carton materialized. Nothing to it, you say? Score lines in paperboard crack and may permit air to transmit. Thus, six score lines add to the potential for air ingress that can adversely alter the biochemical shelf life.
And then there is the Tetra Pak square package with screw cap. Start with the premise of square instead of the conventional rectangular solid. Problems with stacking have always existed with cubes, but they may be attractive to many. The screw cap is a totally different issue. Such reclosure devices have been the paperboard liquid packaging industry’s answer to the barrier plastic bottle’s inherent ability for reclosure and repeated opening to access contents. The usual method is to cut a hole in the structure and insert a preinjection-molded fitment. Good thinking—and, of course, expensive—but how do you ensure a hermetic fit?
Tetra Pak’s answer to the screw cap is the Direct Injection Molding Concept (DIMC), in which the necks of the closures are molded directly into orifices in the flat composite paperboard as the web is advanced into the filling machine. After filling, the screw top is affixed to the neck in the finished package. Or, for those who prefer a less expensive opening, there is the FlexiCap, also injection molded directly into the opening in the web. The alert might note that the square shape with its direct-injection-molded closure is not for aseptic packaging but rather for chilled, but how long is ESL? The square shape may also be fitted with Tetra Pak’s StreamCap, a reclosable screw-on/-off device for 300-mL aseptically packaged cartons.
And then there is Tetra Top®, not exactly new (1985), but certainly somehow more visible than during its formative years. Also not aseptic, but rather ESL by virtue of hydrogen peroxide plus ultraviolet radiation, Tetra Top is an all-plastic top on a round-corner, square composite paperboard carton. The plastic top, with its own easy-open/reclosure, is—and read this carefully—direct-injection-molded onto the tops of the side walls of the carton while on its mandrel. After the formation of the plastic top, the carton is filled from the other end and ultrasonically or induction sealed, depending on whether or not the package material contains aluminum foil.
Recognizing the drivers toward all-plastic packaging, Tetra Pak is another entrant in the aseptic and ESL derbies, of which there are many. For example, the company now offers a “through-the-wall” high-density-polyethylene (HDPE) or polyester bottle supply to the filler which can be ESL. In this technology, the bottles are extrusion- or stretch-blow-molded and fed directly to the filler infeed. In its heralded Food and Drug Administration–approved installation at Jasper Products, Joplin, Mo., the technology is extended into aseptic packaging of barrier multilayer ethylene vinyl alcohol/HDPE bottles for low-acid flavored milks. Evidently the bottles are coextrusion blown, leading to sterile interiors attributable to the temperature of extrusion. The sealed bottles are fed into a sterile area of the filler, where the necks are removed and discarded. The bottles are immediately filled. The presence of the barrier layer permits nonrefrigerated distribution of the product, although the shelf-life kinetics discussed in our April 2003 Packaging column suggests limitations on the sensory quality. Safety is, of course, not an issue.
Tetra Pak boasts of a host of aseptic fillers for plastic bottles, largely polyester. Like their more than one dozen competitors, most of the systems consist of multi-chamber rotary fillers. One or more unit operations occur in each chamber: bottle sterilization, sterile-water rinsing, bottle filling, capping. Sterilization of the system equipment is effected by application of the controversial peracetic acid, still not accepted for low-acid systems in the United States. Bottle sterilization is achieved with a spray mist of the same chemical followed by sterile-water rinse. And sterility is maintained with overpressure of sterile air. Saying it recognizes the relative biochemical fragility of microbiologically sterile beverage products, Tetra Pak has introduced liquid nitrogen into the headspace of the bottles after filling. This inert gas helps to retard some of the potential oxidative changes and also stiffens the bottle by adding gas pressure to the interior. Our question might be, which came first—the need for rigid bottles, or the desire for better sensory quality of fruit- and tea-based beverages? Obviously, a simplified description cannot communicate the total engineering of a system that can operate at up to 600 bottles/min with, by definition, total reliability.
Tetra Pak has a number of competitors in this area:
• SIG Combibloc. Long a direct competitor of Tetra Pak in the brick/block-shaped aseptic carton field, SIG Combibloc has produced a system using preformed, knocked-down composite paperboard blanks, as contrasted to Tetra Pak’s roll stock infeed. The company claims that its system, appropriately dubbed Combishape, can produce aseptic cartons of any shape—oval, moon, triangular, quadrangular, pentagonal, or octagonal. Shades of Tetra Pak’s Prisma Pak: a new race is on to dazzle the consumer with visual effects that complement the functionality, without compromising the sterility or the biochemical stability (by multiplying the scores).
• Stork. Paralleling the Tetra Pak entry of aseptic bottling of low-acid dairy beverages has been the installation of Stork’s systems at Dairy Farmers of America and Morningstar Foods. Both are now reported to be FDA-accepted low-acid installations. The former consists of a tubular sterilization system for the product, followed by aseptic filling into coextrusion-blow-molded barrier plastic bottles on a four-lane machine. Although the bottle interiors are sterile after molding in the on-premises molder, the necks are removed and discarded, and the bottles are treated with hydrogen peroxide.
• Shibuya International. This Japanese supplier of aseptic packaging systems has worked with Mott’s to advance that company’s progress for its lines of high-acid fruit beverages from hot-fill glass to hot-fill polyester to aseptic plastic bottle packaging in clean room to Shibuya’s system. In this system, the sterile bottles are maintained in sterile condition in a sterile environment from fabrication through filling and closure. Injection-molded polyester preforms are blown into bottles on Sidel/Remy equipment and fed into the Shibuya component, a multichamber rotary machine that is presterilized. Bottles are sterilized to a 5D level with misted hydrogen peroxide at 300°C, followed by hot air and sterile-water rinses. At Mott’s, the system produces 220 1-gal bottles/min, a truly remarkable output. But the system supplier claims even-higher outputs—up to 900 500-mL bottles/min—for coffee, tea and milk in Japan.
A Vibrant Force
We can conclude from this superficial overview that aseptic packaging is not only alive and well but a vibrant force that has entered mainstream beverage processing and packaging. By moving from paperboard composites into plastic bottles and demonstrating that microbiological stability could be achieved and maintained within the bottles, the engineers and technologists demonstrated the machinery system effectiveness. The persistent use of hydrogen peroxide for low-acid installations and even for high-acid installations is somewhat surprising. Many have thought that by now someone would have developed a better sterilant, especially after so much research has been invested, but apparently the tried and true remains the best. And there is still the mystery of peracetic acid.
And the application of near-aseptic systems to deliver ESL products has opened up a whole new category of products that were never before possible. Chilled distribution, however imperfect, remains a means to deliver better-quality product to consumers. After all, isn’t that what we food scientists and technologists are in business for?
And so the beverage packaging world is in transition from cans and glass into barrier plastic bottles produced on a relatively small range of well-engineered aseptic machines to deliver sterile or ultra-clean products. The next great leap will be to maintain the biochemical sensory qualities throughout distribution and really excite the target consumers. But isn’t that the business of food scientists and technologists, or am I being redundant?
by AARON L. BRODY
President and CEO, Packaging/Brody, Inc.