Aseptic packaging: Thinking inside the box


Aseptic packaging benefits manufacturers, consumers, and the environment—and changes perceptions about food safety.

By Sarah Fister Gale

In many ways, aseptic packaging for beverage products changes the way food processors think about food safety. Using a completely different approach to sterilization, aseptic processing eliminates bacteria in less time and more completely than conventional methods, resulting in commercially sterile products that better retain their appearance, texture, taste and vitamin content. It allows dairy manufacturers to create shelf-stable drinks that don't have a cooked flavor and, because these "drink boxes" preserve their contents without refrigeration, don't require refrigerated trucks and warehouses, retail freezers and coolers for shipping and storage.

Aseptic is a major advance in packaging technology that has been embraced in Europe, Asia and South America for decades. Because of uneven milk production, difficulties in shipping cold products, and limited cold storage in these markets, aseptic packages offer a convenience that has made them instantly popular in these regions.

However, aseptic drink packaging has been slow to gain popularity in the United States. American consumers, used to the idea that juice and dairy products have shorter shelf lives and must be kept cold to remain safe, have been skeptical of boxed beverages sold on store shelves instead of in refrigerator cases. They have made assumptions about preservatives being used to prevent bacteria growth and have had no driving need to incorporate the foreign-looking packages into their shopping habits. Because the U.S. market has such a well-established logistical cold chain for production, distribution, and sales, there has been little need for an alternative way to buy and store their frequently used beverages.

Figure 1. Aseptic containers come in many shapes and sizes. Courtesy of Tetra Pak.
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Over the past five years, however, American consumers have warmed to the idea of shelf-stable drink cartons. Their attitudes began to change with the introduction of the juice box. The convenience and spill-proof design of these child-friendly drinks broke down the barriers for American shoppers, luring busy parents with their ease of use and handy storage options. Once juice boxes established themselves as a familiar staple in American homes, consumers became aware of the convenience of aseptic products and began to reshape their perceptions about how a drink container should look. They let go of their belief that cold storage is the only option and saw value in bulk purchases of previously delicate brands (see Figure 1).

Dairy beverages especially grabbed the interest of marketers and consumers looking for ways to extend the longevity of popular flavored milks, protein drinks and smoothies. These low-acid dairy foods, which have an equilibrium pH above 4.6, offer rich growth opportunities for aerobic and anaerobic bacteria, making aseptic a natural fit in these categories.

As consumers began to recognize the efficiency and practicality of aseptic packaging for dairy, it blazed the trail for other products that consumers would prefer to use in more lightweight convenient packaging options. Today, manufacturers are investing in aseptic packaging for a range of products, including soups, stews, and wine, as well as soy and dairy products.

The Great Wall of Chili

As they opened to the option of aseptic packaging, manufacturers began to see the advantages for themselves, the consumers, and the environment. Because of the way the product and package are sterilized, they maintain their quality, taste and color better than traditional packages, and require no refrigeration during transport, marketing and storage. They produce less waste during the manufacturing process, use less energy to produce and ship, and offer a more appealing visual marketing tool, notes Colleen Zammer, a food and beverage technology consultant at TIAX, a collaborative research and development company in Cambridge, Mass. She points to the recent introduction of Hormel Chili in a Tetra Retort carton from Tetra Pak USA, a manufacturer of aseptic equipment and packaging materials (Vernon Hills, Ill.) that offers more than 150 different aseptic paperboard containers that can be matched with 10 types of openings and closures. "The flat aseptic packages offer better graphics opportunities," she says. "You can build a wall of chili on a shelf with square cartons. You can't do that with cans."

Market researchers predict that by the year 2015, 30 percent of the food in the United States will be aseptically processed, and major players in the food production industry join the aseptic ranks every day. Companies like Gerber Products (Parsippany, NJ), Dean Foods (Franklin Park, Ill.), Horizon Organic (Longmont, Colo.), Hain Celestial Group (Melville, NY), and Minute Maid (Houston, Texas) have made significant investments in aseptic processing machinery, as have contract packagers like Jasper Products (Joplin, Mo.) and Steuben Foods (Elma, NY).

Aseptic processing is especially popular with the organic food sector, which benefits from the fact that products can be made shelf-stable without the addition of preservatives that may compromise their organic certification. They also don't require costly refrigeration space in stores, notes Jennifer Rubinstein, product manager for the non-dairy beverages division of Hain Celestial Group, a natural products and snack food company whose brands include WestSoy soy milk and Rice Dream products. Rubinstein believes that the aseptic package is a natural fit for organic processors and natural foods consumers. "The cost of entry for a shelf-stable product is much less expensive, and aseptic is better for the environment," she says. "It uses less energy and material and it's more efficient." Hain Celestial, like many smaller product manufacturers, outsources it's packaging to a contractor to avoid the cost of launching and operating an aseptic packaging facility in house.

Beyond it's retail appeal, aseptic cartons are attractive to the foodservice industry because they require no refrigeration until opened and the square containers take up less shelf space than round cans. Unlike cans, aseptic products do not need to be transferred to another storage container and, because no can opener is required, there are no exposed sharp edges, making the aseptic carton a safer choice in kitchens.

What's in a carton?

Figure 2. Aseptic cartons are comprised of several layers. Courtesy of Tetra Pak.
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The U.S. Food and Drug Administration (FDA) defines aseptic processing and packaging as the filling of pre-sterilized containers with a commercially sterilized cooled product, followed by aseptic hermetical sealing with a pre-sterilized closure in an atmosphere free of microorganisms. The packaging is comprised of layers of paper, plastic polymers, and aluminum in a 70:24:6 percent ratio (see Figure 2). The paper provides stiffness, strength and shape; the polyethylene plastic forms the seal on the innermost layer to make the package liquid-tight while providing a protective coating on the exterior to keep the package dry; and the aluminum forms a barrier against light and oxygen, eliminating the need for refrigeration and preventing spoilage without using chemical preservatives. The three major players in the U.S. aseptic packaging market are SIG Combibloc (Columbus, Ohio), Tetra Pak, and International Paper (Stamford, Conn.). Outside the U.S., major aseptic equipment suppliers include Krones (Germany), Shibuya Kogyo (Japan), Procomac and SIG Simonazzi (Italy), and Stork Food and Dairy Systems, a unit of the Stork Group (Netherlands).

Environmentally correct

Aseptic packaging is a good choice for the environment because it has a low packaging to product ratio–aseptic packages are typically 96 percent product and only 4 percent packaging material by weight–and they are tremendously energy efficient, says Jeff Kellar, vice president of strategic business development for Tetra Pak USA (see Figure 3). "Drink boxes save energy at every stage of their lifecycle." They crush down to a size 50 percent smaller than comparatively-sized steel cans, and they create a lighter volume of waste. Unlike plastic, the carton paper comes from a renewable resource, he notes. These containers also require less energy to produce, ship and recycle. The cartons are shipped to the production facility on a flat paper roll, allowing manufacturers to ship larger quantities of material without the wasted space that comes from shipping preformed packages, such as glass bottles or plastic jugs (see Figure 4). This, in turn, lowers freight costs and energy absorption. "One standard semi-trailer truck can transport 1.5 million empty drink boxes versus only 150,000 glass bottles."

Figure 3. Compare the amount of space required by aseptic cartons to the amount of space required by traditional packaging. Courtesy of Tetra Pak.
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When aseptic packages are recycled, the paper is reclaimed through a recycling process called hydrapulping. The hydrapulper, which operates much like a large household blender, is filled with water and cartons. Motion from large rotor blades on the bottom of the vat creates the friction that separates the paper fibers away from the layers of polyethylene and aluminum foil. Because neither glue nor adhesive is used to bond the aseptic package materials together, water and the churning motion of the hydrapulper's rotor blades easily break down the paperboard into its original pulp within 30 to 40 minutes. When the hydrapulper is drained, filters allow the paper pulp to pass through while the polyethylene and foil are screened off. The pulp can be fed directly into a papermaking machine, or dehydrated, pressed and shipped to a paper mill. Because the ink is separated off with the plastic, no de-inking process is required. This recycled pulp can be used to make paper towels, tissues, and writing paper. "From start to finish it's a very efficient packaging option," Kellar says.

Steam injection protects taste, consistency

Perhaps the most intriguing feature of the aseptic package is the unique way in which it is processed and sterilized, says Clair Hicks, professor of food science at the University of Kentucky in Lexington and a member of The Institute of Food Technologists (IFT). "It's a whole different mindset," he says.

Figure 4. Cartons begin as a flat paper roll. Courtesy of Tetra Pak.
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With traditional shelf-stable containers, such as cans or glass bottles, the packages are filled with ambient product and then sterilized, usually through a retort process that requires the container to be placed in a hot water bath and brought slowly up to a high temperature.

The retort process can take 20 to 60 minutes, depending on the product and the size and material of the container, Hicks says. It is also inconsistent, requiring some areas of the container to reach higher temperatures to ensure that the cold spot–usually three-fourths of the way down and in the middle of the container–reaches the minimum temperature needed to kill all harmful bacteria.

"That slow heating process has a significant impact on quality and taste," Hicks says. "When you leave a product at such high heat for a long time it loses it's texture and has a cooked flavor." It also cooks out many of the vitamins and minerals of the original formula requiring either additional vitamin fortification or resulting in a less healthy product.

For dairy products, such as milk or cream, the beverages can't be brought to such high temperatures because it alters the quality and texture of the proteins. Instead, these products are pasteurized, not sterilized. The pasteurization process kills the bacteria, but the product still requires refrigeration to prevent the growth of spores that remain in the liquid and can affect the taste and texture of the product under ambient temperatures. The result is a product that requires refrigeration and should not be consumed after six weeks, even under the most hygienic circumstances.

Aseptic packaging solves these problems using a form, fill and seal packaging process that kills more bacteria in a shorter time, and can be used on dairy products. Unlike traditional packages that are sterilized after they are filled, the aseptic package is sterilized separately from the food product, says Mark Tagatz, vice president of operations at SunOpta, a natural and organic foods manufacturer (Ontario, Canada).

At SunOpta, batches of product are mixed in large tanks and then pumped through a processor for sterilization. The liquid enters a pre-heat stage, where it is brought from roughly 40ºF to 160ºF. Then it is pumped into a multiverter agitation vessel with a steam injection system that instantly brings the liquid from 160ºF to 290ºF, and holds it at that temperature for nine seconds to sterilize it.

This process is tailored to place the least amount of thermal stress on the product while increasing bacteriological safety. "With steam injection, every particle of liquid is brought to the correct temperature at the same time," Tagatz says. The product is then pumped into a vacuum chamber which rapidly pulls the temperature back down to 160ºF. It is then sent into an aseptic surge tank with sterile filters where it maintains its sterility even as product is pumped in and out. "At that point it's commercially sterile," he says. "We've destroyed all the organisms that could cause injury or commercial loss."

For the soy products that SunOpta packages in it's aseptic plant, this flash sterilization process is critical. "You can't get the same flavor profile in a longer heating process," Tagatz says. "This most closely matches a refrigerated alternative, but it can be stored on a shelf for 12 to 18 months."

Contained equipment eliminates need for cleanroom

While the liquid is being sterilized in the enclosed steam injection system, the aseptic carton is sterilized in a separate machine. A roller feeds a sheet of packaging through a closed system where it is sterilized by way of a hot hydrogen peroxide bath. The paper is then pressed clean and hot-air dried, ensuring that the amount of hydrogen peroxide residue conforms to the FDA requirement of less than 0.1 ppm (see Figure 5).

Figure 5. An example of an aseptic packaging line. Courtesy of Tetra Pak.
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Within an enclosed sterile environment, the processing equipment builds the paper into brick-shaped containers in a range of sizes up to a half gallon. It is then sent into a sterile encased filler cabinet where product is pumped into the containers and sealed without any oxygen in the headspace, ensuring continued sterility and allowing for a shelf-stable product that remains viable for several months without the use of chemical preservatives or refrigeration.

Both the steam injection system and the enclosed packaging system are cleaned and sterilized with steam. Aseptic HEPA air filters and constant positive pressure eliminate the risk of outside air contaminating the cabinets, allowing the systems to remain continuously sterile.

Aseptic bottles gain momentum

Demand for aseptic packaging choices for U.S. products has clung stubbornly to child-focused products, largely because adult consumers are not completely comfortable drinking beverages from a box. But that may change with the growing interest in new aseptic plastic bottles and cups, notes Zammer. In late 2002, the FDA approved Tetra Pak's LFA-20 filler for high-density polyethylene (HDPE) bottles, paving the way for plastic bottles that have the same longevity as their aseptic carton cousins.

The LFA-20's small internal aseptic chamber is equipped with fully-integrated cleaning in place (CIP) equipment and filling nozzles which do not contact the package at any stage. It also features a bottle transport mechanism that handles bottles by the neck for size flexibility and quick change-overs without resterilization. Unlike fillers for paperboard composite packages, the HDPE and PET bottle fillers use hydrogen peroxide gas to achieve package sterilization. Because they are not required to withstand the heat of a retort or hot fill process, the plastic bottles are lighter, requiring up to 30 percent less material and eliminating the need for vacuum panels that cause bottles to have a crinkly feel.

Tetra Pak Plastic Packaging offers two options for aseptic plastic bottles. One method involves coating the inside of blown bottles with a clear glass-like layer of silicon oxide (SiOX). The SiOX coating is applied in a vacuum chamber by a machine capable of treating containers up to 2 liters in volume, without shape limitations, at a rate of up to 18,000 bottles per hour. The other process involves the over-injection of the barrier material on PET preforms. This system consists of two rotating cavities: one for the injection of the preform, the other for the subsequent injection of the barrier material. The resulting preforms are compatible with all stretch blow-molding systems.

This technology ensures that the consistency of the coating, through online control, can be changed to suit the customer's specific requirements. And, unlike co-injection, it offers even distribution of the barrier over the entire surface.

A double strategy has also been followed in the design of the aseptic bottle filling systems, aimed at satisfying consumer demand for resealable packs as well as requests from the industry for more flexible package design options that keep material and energy costs down.

The bottles are either blow-molded on site, or shipped post-production and sterilized with hydrogen peroxide steam. HDPE packages, suitable for a range of products from milk and juices to water, can be blown aseptically, with oxygen and light barriers to increase the shelf life of the product. Rotary blow-molding machines are used where the manufacturer demands high volume production of a single bottle. However, shuttle blow-molders are more suitable for flexibility in bottle shape and size.

Because the chamber is completely contained and sterile, the molding does not require a cleanroom. It does require, however, a separate line of equipment and significant additional space.

The plastic bottles and cups are innovative, but they've been slower to catch on, Zammer admits, largely because of the initial start-up investment, which can cost several million dollars for the filler system. "So, many companies haven't yet invested in the aseptic technology and it's quite a capital investment."

However, on a large enough scale, the savings in plastic costs for packaging can offset start-up costs in a relatively short amount of time. Consumer preference for bottles over cartons, which for certain products can have a huge impact on market share, is also a factor. For example, according to AC Nielsen scantrack data, when Nesquik launched its line of flavored milk drinks in 10 ounce aseptic bottles, sales increased 111 percent, while at the same time increasing the category of 16 ounce bottles of flavored milk by 43 percent.

Similarly, Gerber recently replaced its glass jars with aseptic resealable plastic cups for 15 Second Foods and 10 First Fruits and Vegetables, recognizing the growing demand for convenience, safety, and ease of use. Gerber now packages up to 285 million aseptic plastic cups a year. A low-acid form fill and seal system from Hassia TAS sterilizes injection-molded cups with 150°C steam, then seals them with a foil lid and tops them with a plastic overcap.

Although the aseptic process results in less degradation of vitamins and other nutrients than retort, it is the convenience of plastic cups over glass jars that Gerber is promoting. The resealable cup offers desirable features such as a lightweight design for parents toting multiple jars in diaper bags and no risk of broken glass around children.

Other drink manufacturers choose aseptic bottles to meet the desire for a more adult-looking package. They see the benefit of aseptic bottles over cartons for certain product lines, such as high protein drinks and smoothies. For example, Morningstar Foods, a Dean Foods unit in Mount Crawford, Va., will use aseptic bottles for milk drinks branded by Hershey Foods and for Folgers brand latte drinks for Procter & Gamble.

"Eventually, plastics are going to open up the market like never before," Zammer says, "because no matter how good the product is, adults just don't want to drink out of a box."

The benefits of aseptic packaging seem clear: once an aseptic packaging plant is operational, production costs are similar to retort and pasteurization lines, and shipping and store shelf costs are significantly lower. That said, it does require a major up-front investment to launch an aseptic packaging line, causing manufacturers to look long and hard at the pros and cons of making the switch. Unless there is demand for a shelf-stable alternative in their product category, it is unlikely that manufacturers will abandon an existing line for an aseptic one. In the end, the choice to embrace aseptic for any product, whether in a carton, cup or bottle, relies on consumer demand, Kellar says. "Aseptic is the right choice if it improves your costs, wins market share, or offers a solution."