Food Canning in the 21st Century

With apologies to Abraham Lincoln:

Nine score and nine years ago, give or take a few, our (IFT) father Nicholas Appert brought forth on this planet a new food preservation technology. Conceived with erroneous theory absent of peer review and dedicated to the proposition that all Napoleon’s troops would eat on the road to and from Russia, tenured confectioner Appert empirically created thermal processing of closed containers.

Now we are at a crossroads to determine if Appert and his invention can survive and grow as we approach the 200th anniversary of his revolutionary thinking. Can this people, who now consume frozen, dry, and refrigerated home meal replacements, long endure with the range of ambient-temperature shelf-stable foods emanating from our canners? Will IFT’s Chicago section, originator of our highest award, named for our founding father, continue to fund and deliver the bronze medal bearing his likeness to our best and brightest?

We contend that this technology, which has graced our shelves for so many decades, fed so many with safe food, and provided dining pleasure, shall not perish from this Earth.

Despite the cannibalization from so many other food technologies, canning will enjoy a rebirth whose glimmerings we are today witnessing. Plastic will indeed grow and intrude into canning, but the result remains thermal preservation in rigid containers, direct descendants of the work of Ball, Martin, Stumbo, Clifcorn, and Pflug, the successors of Appert.

• Low-Acid Foods. Crucial to predictive analysis is the technical and regulatory distinction between low and high acid, the dividing line being pH 4.6. Above this invisible fence, foods generally require heating well above 212ºF to ensure that anaerobic pathogens do not grow. This temperature range usually dictates heating under pressure subsequent to filling and sealing in hermetic packages.

With regard to thermal sterilization equipment, engineering for traditional cylindrical metal cans containing low-acid foods has led to elevated-pressure vessels carefully controlled with respect to heat transfer and internal product flow. These include still, rotating, spinning, hydrostatic with and without agitation, and a host of other types of equipment, all intended to decrease total thermal input to achieve commercial sterility while minimizing overcooking of the contents. Now have come methods for heating, filling, and holding hot while still open, heating further and later closing, the notion being that less total energy is required to achieve the sterilization.

Metal Cans. Today, metal cans are not necessarily cylindrical, and containers of other materials are hardly uncommon: the old-timer, glass, is still around, and plastic entered about 20 years ago in the form of truncated cones or “buckets.” How can anyone overlook flexible plastic lamination pouches in pillow and standup structures, plastic trays and cups, and those forms that defy description, such as metal bodies with plastic closures? And plastic has now graduated to a variety of shapes for low-acid/post-fill “cans” that are more like bottles. All are “cans” within the traditional definition of container for post-fill thermally processed low-acid foods.

Shapes for metal cans offered for low-acid foods include flat rectangles, tall and thin, squat, pot, pot-bellied, wasp-waist, parallelopiped, twisted, embossed, faceted, multi-ringed, and who knows how many others? Bodies may be three- or two-piece, fabricated from steel or aluminum, with protruding or flush end seams, preprinted or bright. Closures may be double seamed, with or without full panel, tear-drop easy open, heat-sealed flexible peelable on a double seam, or directly adhered.

The thermodynamics for post-fill thermal processing for this broad matrix are increasingly complex. And the engineer must determine the temperature patterns within each under a variety of post-fill protocols to maximize input to achieve sterility while minimizing cooking and avoiding damage to the “cans” and closures within the heating chamber.

To compound the complexity is the entry of Pressure Pack, presterilization in pressurized chambers prior to closing, the successor to Flash-18 but in a robotically controlled environment.

Indeed, the options for thermal post-fill processing for low-acid foods have expanded enormously in recent years, and not necessarily to accommodate the myriad of structures that have been introduced to maintain and increase the market position of canned foods. Matching the “can” to the heat-transfer vehicle represents a major challenge.

Plastic Cans. And then there is the array of multi-layer plastic “cans” with limited temperature and physical resistance which do not quite fit all the thermodynamic engineering developed for metal or even glass. Most are known as “buckets,” but many have moved away from this difficult-to-process shape to “more-difficult-to-process” shapes.

In the beginning were cylinders with seamed metal ends, a transition of metal into plastic—with eventual recognition that metal-to-plastic seams are fragile under elevated temperature, that wide-mouth, full-panel, easy-open aluminum ends can fracture if pressures are not tightly controlled, and that the plastic would soften as temperatures approached their glass transition. Translation of the new requirements to commercial practice was difficult because most of the challenges were not recognized before implementation.

Eventually, equipment was married to barrier plastic cans of most shapes, and a new product niche, the microwavable can, settled comfortably into consumer consciousness. This can is now expanding its reach into liquids for consumption from the can—almost unheard of before the development of the plastic can.

Today, the “bucket” is available in an all-barrier plastic version (Hormel Kids’ Kitchen) incorporating oxygen scavengers to stem the passage of oxygen in the friction-sealed closure—a winner of the 2001 DuPont award for achievement in packaging.

Retort Pouches. Flexible pouches were heralded during the 1960s through the 1980s as the next new food technology and consumer package of choice. After decades of extraordinarily meticulous development, the most that could be said during the 1990s was that the retort pouch had found a home in military rations. Despite numerous forays into consumer and military markets, the retort pouch’s cousin—retort multilayer plastic trays with peelable flexible closures—were limited to a few prepared foods from Hormel.

And then came the daring thrust of Mars, Inc.’s European operations: aluminum and then barrier plastic retort trays for super-premium cat food. How better to differentiate the very best of food for felines than to offer the “lightly heated” product in gold-colored square squat cans with easy-peel flexible closures? Because aluminum in body foil gages dented too readily in distribution, multilayer barrier plastic trays were ultimately substituted, despite their challenges of temperature resistance in retorts. By using heat sealing and, in this instance, peelable instead of the fusion seals used in previous incarnations, delivery of reliable hermetic seals was a challenge, requiring slowing of outputs and almost 100% monitoring and quarantine to ensure sterility.

Mars’ success with retort trays for pet foods in Europe led to a new iteration of retort flexible pouches for related pet foods in the United States. Being bold, and needing a shelf presence, the retort pouches added a new dimension to challenge the technologists: a standup feature, which added an extra set of heat seals with which to contend. This was followed by other pet food manufacturers introducing retort pouches, thus fostering the first successful commercial retort pouch packaging of low-acid foods, even though some might dispute the notion that pet foods are food and others might question the definition of “success.”

The next visible action was by Heinz Inc.’s Starkist tuna, which, with much fanfare, introduced tuna in retort pouches in 2000. This time, a mainstream food had been promoted from traditional cylindrical metal cans into, what was for consumers, a totally new concept in ambient-temperature food packaging—and probably a totally new product, since the “fresher” product obviously received significantly less heat to achieve commercial sterility. Starkist leapt into several pouch sizes and expanded the category by offering the pouches in kits for easy lunch preparation. Not to be outdistanced, competitor Bumblebee offered its clones of retort pouches of tuna and related species.

Now that retort pouches of low-acid solid foods appear to have attained some commercial acceptance and recognition of superior quality and more convenient packaging, the expectation is that other heat-sterilized foods will appear in pouches, creating a new segment within the canned foods category. Because of the evident ability to produce foods with less heat damage, we should expect a revisit to multilayer barrier retort trays for lowacid particulate wet foods. And Tetra Pak has introduced a composite paperboard carton capable of retorting—another direction for “canned” foods.

Aseptic Packaging. Sterilization of low acid foods has been the target of development by aseptic packaging interests. Born in cans, aseptic packaging has largely focused on fluid foods such as puddings, dairy mixes, soups, and now liquid nutritional drinks. Recently, a consortium of organizations combined to develop a comprehensive system to aseptically package particulate-containing potato soup. Although the package happened to be a traditional can, nothing in the results, which were accepted by regulatory authorities, precluded employing any sterilizable and sealable package to deliver ambient-temperature shelf-stable low-acid wet foods. Technologists did not have an easy time quantifying the thermal input into irregular particles in dynamic flow, but using electronic tools, measurements were made to sterilize the product with minimum damage.

The development of aseptic packaging of particulates is intriguing because many of the highly publicized thermal processes of recent vintage—ohmic heating, microwave sterilization—require aseptic packaging. Sterile transfer of cooled particulate foods is not nearly as reliable as it is for liquid foods or even foods containing tiny particulates, such as some European soups in composite paperboard cartons.

Another innovation from Europe is aseptic packaging of heat-sensitive dairy liquids in tall, thin aluminum cans with internal counterpressure provided by sterile nitrogen. Another interesting device is induction heat sterilization of the can ends, a radical departure from traditional superheated steam.

The new saga of canned low-acid foods is just beginning, considering the array of materials, structures, shapes, and equipment alternatives available or possible. Just objectively evaluating the possible combinations would represent a major project for food companies wanting to optimize their offerings of “canned” foods.

• High-Acid Foods. Because of the relatively lower thermal input required to sterilize high-acid fruit and tomato-based foods, this category has been enjoying an exciting ride into a new era of packaging. The hot-filled glass juice bottle is almost a relic in the face of the relentless surge of heat-set polyester bottles—believe it or not, only 15 years old. Led by Ocean Spray’s Ray Bourque and his colleagues and suppliers Monsanto, Yoshino, and White Cap, polyester bottles were engineered to resist 180ºF sterilization temperatures and collapse from internal vacuum.

Originally a substitute for the 64-oz and then for the traditional 46-oz cylindrical steel can, the polyester bottle has expanded up to 128 oz and down to 20 oz by optimizing structure, with control of the product temperature before and after filling. Following the juice successes has been the translation of a series of hot-filled high-acid products such as jams, jellies, and pasta sauces from metal cans and glass jars into polyester packages.

Baby Foods. Except for young mothers, how many technologists have noticed high-acid baby juices in reclosable extrusion-blow-molded multilayer barrier plastic jars? These glass bottle substitutes are side-by-side with aseptically packaged fruit purees in multilayer plastic tubs aseptically packaged with peelable flexible heat seals on Hassia equipment. Both plastic packages are reported to be preferred by purchasers, belying earlier mythology that customers insist on glass jars.

Fruit Slices and Dices. These products are now in multilayer barrier plastic cups with peelable flexible-heat-sealed closures. These lunchbox/bag packages are purported to be more consumer friendly than small metal cans with full-panel easy-open cans, and so a new “canned food” segment has emerged.

Soups. Not to be left behind in the home meal replacement market, Campbell Soup Co., one of the pioneers in convenience packaging, has performed a dramatic development with one of its anchor products. In addition to enhancing the value of soup to its mainstream consumers by graphically depicting its products on labels, the company has added full-panel easy-open ends to its single-strength soups in metal cans—an engineering feat, considering the relative fragility of scores.

But the greatest technological hurdle has been single-strength tomato soup in polyester bottles. With this low-acid product, transfer into post-fill-heated polyester would be not possible because of the low melting point of polyester. Furthermore, polyester, desired because of its glass-like transparency, does not have nearly enough oxygen barrier to economically deliver traditional shelf life.

Reducing pH to convert tomato soup into a high-acid food was resisted because tomato soup is the core of Campbell’s product mix. Formulation refinements provided flavor at low pH that is accepted by consumers. High acid permits hot filling within the temperature parameters of polyester, provided that the structure is engineered to permit collapse upon vacuum formation. By increasing the gage of the polyester, shelf life was extended beyond that of “economic” polyester. Traditional Campbell’s soups in cans have biochemical shelf lives well in excess of one year, an objective not possible today with conventional polyester. Once again, compromise was reached by truncating the expiration date of the polyester-packaged product to nine months, a distribution datum that apparently disturbed neither retailers nor consumers.

If canning is defined narrowly as post-fill thermal sterilization in cylindrical metal cans and glass jars, the static status of canning in the U.S.—30 billion cans annually—is understandable. The small increases in canned food consumption attributable to shaped and embossed cans do not represent distinguishable advantages from a consumer-perceivable product quality perspective. Enhancements derived from two- vs three-piece, or even welded side seam replacing solder, are not visible to consumers.

If, however, canning is thermal processing to deliver ambient-temperature shelf-stable wet foods, then we add the ten billion aseptic bricks and blocks, billions of hot-filled polyester bottles, several hundred million plastic buckets, and, now, millions of retort pouches of tuna and baby food jars and cups. A whole new dimension of “canned” foods is evident.

Not nearly as easy to achieve as traditional retort processing of cans, thermal sterilization in plastic pots, bottles, and tubs represents major technological achievements. The superior flavor, color, and mouthfeel qualities of food contents from these new processes and packages are recognizable by consumers, who have been purchasing them in unprecedented numbers. By integrating product technology with thermodynamics, packaging technology, and distribution, entirely new dimensions of retailer and consumer satisfaction have been generated. The new products represent a quality, safety, and convenience level never before experienced, thus rendering the prospects extremely bright for the future of “canned” foods.

PRODUCTS & LITERATURE
Plastic Containers for Foodservice use keep food protected and tightly sealed while remaining fully visible. Made from PETE, a clear, crack-resistant plastic, the Crystal Seal™ containers keep foods in while the leak-resistant seal keeps air out. The containers are available in 12 sizes, are stackable, and can also double as a serving dish. For more information, contact Placon Corp., 6096 McKee Rd., Madison, WI 53719-5114 (phone 800-541-1535, fax 608-271-3162, www.placon.com).

Zippered Resealable Package for Sargento shredded cheese makes opening and closing packages easier, faster, and more secure than resealable packages that must be pressed to close. The Hefty® Slide-Rite® Advanced Closure System, manufactured by Pactiv Corp., recently won two awards the World Packaging Organization’s 2001 WorldStar Packaging Award in the retail food category and the Institute of Packaging Professionals’ Ameristar Award for packaging excellence. The closure system is available on all sizes and varieties of Sargento cheese except 3-oz and 2-lb bags. For more information, contact Pactiv Corp., 1900 W. Field Ct., Lake Forest, IL 60045 (phone 888-828-2850 or 847-482-2704, www.pactiv.com) or Sargento Foods Inc., 1 Persnickety Pl., Plymouth, WI 53073-3547 (phone 800-558-5802, fax 920-893-8399).

Seal Inspection System, the TGC inline gas analyzer provides 100% monitoring of every package to determine oxygen or oxygen and carbon dioxide content in modified-atmosphere packaging of foods. The gas analyzer easily integrates with automated form/fill/seal, tray-packaging, and flow-wrapping machinery to provide a fast, nondestructive gas measurement at the point where the sealing jaws create the package seal, without delaying or impeding packaging line output. For more information, contact PBI-Dansensor America Inc., 139 Harristown Rd., Glen Rock, NJ 07452 (phone 201-251-6490).

Pouch Machine, the WP-12, produces three-sided pouches for products such as yogurt, applesauce, pudding, and frozen desserts. The machine produces 0.1- to 3.0-fl-oz pouches at up to 320/min, utilizing a single roll of laminated plastic material. The vertical form/fill/seal machine is said to be ideal for small-volume marketers of liquid or viscous snack and novelty products and for processors wishing to do test marketing of products in tubular-shaped, three-sided pouches. A volumetric piston filler assures fill accuracy for hot-filled, ambient-temperature, or high-temperature, short-time products. For more information, contact Winpak, Inc., 998 S. Sierra Way, San Bernardino, CA 92408 (phone 800-804-4224 or 909-885-0715, fax 909-381-1934, www.winpak.com).

Push-Pull Cap for sport beverage bottles features an induction liner and overcap. The 38-mm closure, being used for Just Juice fruit juices marketed in New Zealand, comes in various colors. Tilt-top, twist-top, and hinged closures are also available. For more information, contact Creative Packaging Corp., 700 Corporate Grove Dr., Buffalo Grove, IL 600898 (phone 847-808-7200, fax 847-215-0351, www.creativepkg.com).

Wax Marking and Coding of packages is accomplished by the WaxJet® Model 6100 Wax Printing System. It provides high-resolution, small character printing without the use of solvent-based inks. The nontoxic wax eliminates the mess and smearing of inks, adheres to many substrates, immediately dries on many substrates, and is light fast and water fast. The printing systems can print up to five lines of high-resolution alphanumeric text, graphics, and logos within a ½-in image area. For more information, contact Norwood Marking Systems, 2538 Wisconsin Ave., Downers Grove, IL 60515 (phone 800-626-3464 or 630-968-0646, fax 630-968-7672, www.itw-norwood.com).

by AARON L. BRODY
Contributing Editor
President and CEO, Packaging/Brody, Inc.
Duluth, Ga.