Technology Update: Shape of things to Come

March 1, 2002
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From pasta to plastics, tools used in other industries are coming on stream in snack food production

General Mills’ first new salty snack in 35 years exemplifies the textural improvements possible with pellets made from twin-screw extruders.
For those who see a half-empty glass, the snack food category is what soft drinks would be like without Pepsi: one big company and everyone else. In that kind of environment, innovation takes a back seat to cost reduction.

For those who see a glass that is half full, the category is being reinvigorated with new products made possible by improved processes and better controls, many of which represent technology transfers from other industries. Snacks are a mature market, they concede, but that's all the more reason for process improvements that create consumer excitement.

As proof, optimists can point to Wahoos! Following a late fall launch in Wahoo, Neb., General Mills rolled the lattice-textured puffed snack item into the national market early this year. Wahoos mark the Minneapolis cereal manufacturers' first new salty snack since Bugles were introduced more than 35 years ago. And although both items exemplify pellet-based snacks, the textural differences demonstrate how extrusion technology has advanced in the last three decades.

Both are corn-based products, but the textures are very dissimilar. Twin-screw extrusion was in its infancy when Bugles were created, and Bugles have a "texture and composition that result in a crunchy taste," General Mills publicist Kelley Walhof explains. Wahoos, on the other hand, exhibit "a unique melt-away taste and light texture," Walhof says. High-barrier metallized film is used to package these fried snacks, with attention-grabbing colors on the reverse-printed bags. Those colors are keyed to Wahoos' three flavors: blue for Seasoned Original, bright pink for Nacho Fiesta and deep red for Backyard BBQ.

These are examples of extruded pellets that are fried, toasted or otherwise thermally treated to make them pop in exotic shapes. Frito-Lay rolled out Doritos 3-Ds four years ago and recently introduced a potato-flake version under the Ruffles brand. The low moisture content of pellets make them stable for storage so that final processing can be done months later and at remote locations. In the case of Rudolph Foods' Bacon Snaps pork rinds, people pop the pellets in their microwave. Manufacturers in Europe and Asia are developing supplier relationships with North American processors who would then do the popping.

Refinements in drier technology for pasta production are turning up in snack processing. Technicians (top) execute a screw changeover on an extruder. Photos courtesy of Clextral Inc.
The technology behind pellets represents a merger of traditional extrusion cooking and pasta processes. Refinements in the extruder barrel and cooling of the extruder head are critical to control the dough's rheological properties. The dough can be cut by fancy-shaped die inserts; formed into sheets that are laminated with cutting and pinching machines to create a hollow pillow that will form a three dimensional snack; or punched with holes and cut into a desired shape in a high-speed synchronous process that results in highly-gelatinized, perforated pellets. Drying techniques used in pasta production complete the process.

"You can get very sophisticated shapes, and the texture is finer and crispier than with single-screw extrusion," says Gilles Maller, head of Tampa, Fla.-based Clextral Inc. In the 1950s, Clextral transplanted co-rotating twin-screw extrusion technology used in the chemical industry to the food industry. "You apply a lot of pressure, heat and sheer to your product," Maller explains, "which gives you a very light product" when the plasticized material is food.

Snack pellet extrusion systems also are produced by Italy's Pavan SpA, which also manufactures pasta machinery. Pavan applies multi-stage drying processes to create three-dimensional pellets. Product passes through a shaker pre-dryer, moves to a belt pre-dryer and then to a belt final dryer. Alternatively, Clextral adapted a Rotante dryer used for short pasta for snack pellet drying. Afrem International designed the dryer.

Unlike the multi-layer belt design of most pasta dryers, the Rotante unit is a rotary dryer that provides uniform, gentle drying of pellets that are moved forward by means of a screw that gently shakes them. "Sizewise, it doesn't change much from a belt dryer," Maller says of the unit, with the typical dryer measuring 20 feet long and 20 feet high. But there is a tendency for pellets to fall from belt to belt in a conventional dryer, he says, and the rotating tubes within a cylinder in the Rotante dryer resolves that problem. "All the motors and other parts are outside the process area," he adds, helping to maintain product integrity.

Singles vs. twins

Although twin-screw extruders have been around for years, snack manufacturers have been slow to embrace the technology because of the machines' high capital cost and maintenance needs, according to Mian N. Riaz, head of the extrusion technology program at Texas A&M's Food Protein R&D Center in College Station. Twin-screw's versatility appeals to processors of pasta, textured vegetable protein and oily foods, such as enrobed meat and seafood products, Riaz says, but improvements in single-screw units have given snack companies an acceptable alternative. But three-dimensional snacks, multi-colored pellets and exotic shapes are beyond single-screw's capabilities, he adds, and twin-screw extruders can output those products and also handle powdery materials and other ingredients that make new products possible.

Supercritical fluid extrusion is another technology that has migrated to the food industry, this time from work with plastic polymers. Food scientists and engineers in South Korea have used the process to produce Yukwa, a puffed rice snack. However, the process remains experimental and very costly, Riaz notes.

Carbon dioxide is the supercritical fluid in this process. The gas is injected into the dough, increasing the density and texture and making possible high-sheer extrusion. The process opens the door to dairy-based ingredients, raising the possibility of salty snacks that can be positioned as healthy foods. The process has been applied to cereal production in tests, as well, with milk being substituted for water in the formulation. Nutritional value was enhanced, and the food exhibited a different texture and appearance. The hope was that the cereal would be less absorptive, possibly putting an end to the age-old problem of soggy cereal.

Much of the domestic work in carbon dioxide extrusion has been conducted by Syed Rizvi a researcher at Cornell University's Northeast Dairy Foods Research Center in Ithaca, N.Y. Recognizing the technology's potential to open up extrusion processing to dairy ingredients, Dairy Management Inc. helped fund Rizvi's work in 1998, and development was progressing on commercial-grade equipment with Wenger Manufacturing Inc. in Kansas City. To date, carbon dioxide extrusion remains experimental.

Whether they choose single-screw, twin-screw or carbon dioxide extrusion, manufacturers can jump-start mature snack brands with new flavors. Spicy coatings are particularly hot, and habanero seasonings are being applied liberally by processors big and small. Electrostatic seasoning systems that create a charge to evenly and completely coat dry ingredients "are getting more attention in Europe, and the big volume producers here are using the technology," Texas A&M's Riaz says. The process also means less waste, and the cost savings can be significant for a costly seasoning. But small and mid-sized manufacturers still regard electrostatic coating as somewhat high tech, he adds, and the training and high-voltage required has stalled wider adoption of this technology.

The technology has been used for decades in paint applications. Snack processors didn't begin applying it until the 1990s. Besides better product coverage and cleaner equipment, electrostatic systems result in savings of 5 percent or more on seasonings, one vendor estimates. His firm's system runs on 100,000 volts, though the amperage is only 0.25 amps.

Process control tools

Equipment to improve coatings and create snacks with new textures is well and good. Unfortunately, commercial processes tend to grind to a halt because variances in the dough to be extruded are not well understood and controlled. "Starch, moisture and protein can look the same under near-infrared analysis from one batch to the next," notes technician Jeff Herbster of J. Herbster Inc., Basehor, Kan. "Then, all of a sudden, one batch runs differently, it's sticking, and people always blame the equipment. But the problem is usually formula related."

Protein content and ash have been the traditional specifications for wheat flour and corn meal, notes cereal chemist Lloyd Rooney of Texas A&M, but variables such as water absorption rate may have a greater bearing on how the dough performs when it is extruded. Food scientists are just beginning to appreciate those control variables, and Rooney is excited about the off-line quality assurance tools that are becoming available to measure those variables.

Rooney and Riaz conduct a snack-food short course at the university the week before the Snaxpo trade show each year (the next course runs March 9-14, 2003). Some of the control devices detailed this year were the Rapid Viscosity Analyzer from Foss North America, III Sigma's AquaDens unit for automated moisture and bulk density measurement and the Phase Transition Analyzer (PTA) from Wenger. The latter calculates both the glass and melt temperature of a batter.

The technology behind PTA originated in the synthetic polymer industry as a tool for graphing changes in glass and melt transition points as temperature and moisture change. Glass is the point at which ingredients change from a brittle crystalline state to a soft, rubbery composition. A number of analyzers are suitable for that analysis. The melt temperature is the point where flow occurs, and gauging melt has been problematic. PTA is a closed-chamber capillary rheometer that uses pressure, temperature, time and moisture to determine these two interrelated set points.

PTA was developed by engineers at Wenger and is being brought to market by Herbster's firm. Compared to analyzers limited to glass measurement, PTA uses a relatively large sample size, says Herbster.

"Some products have a processing window the size of a bus, and you can run the dough through the extruder and come up very close in the finished product," Herbster acknowledges. "On the other hand, there are products that have a processing window the size of a dime." For those, PTA can be a valuable QA tool.

A pet food manufacturer is applying the device, and Herbster sees great potential in snacks and other foods. "We've just started to scratch the surface of where this can be used," he notes.

In contrast to PTA's pressurized chamber, RVA relies on an atmospheric cook to determine at what point starch gelatinization occurs. "It's more than a measure of moisture, fat and protein," explains Dick Metzger, RVA product manager at Foss North America, Eden Prairie, Minn. "By measuring viscosity over time, it determines the functionality of how the ingredients will perform." Process time, temperature and screw speed can then be altered accordingly.

Starch gelatinization is determined with the RVA analyzer from Foss North America.
Already used extensively by cereal manufacturers and starch millers, RVA has potential as a specification tool for salty snacks, Metzger believes. It becomes one more spec when communicating with raw material suppliers, he says.

New to the snack business is AquaDens, a device based on moisture measurement technology originally developed for the plastics industry. Described as "RF technology with some modern twists" by Brian Marlow, founder and chief technology officer of Lawrence, Kan.-based III Sigma, the unit can detect molecular levels down to 25 parts per million. Though not yet in use for snack processing, similar devices have been adapted for moisture monitoring in fertilizer, wood and other materials.

"Near-infrared is wonderful for use in the laboratory where you can grind your sample, but it doesn't work as well at line for moisture measurement," explains Marlow. While AquaDense is not on-line instrumentation, users pull a sample at line for quick analysis. "People are very leery about on-line moisture systems," says Marlow. "They've been burned before." His first objective is to develop a confidence level among processors for AquaDens's performance.

The goal for PTA and, presumably, these other QA tools is to migrate eventually from the lab to the line so that operators can use them to set screw speed and other process parameters. In the meantime, knowledge transfers from other industries will likely continue to help snack manufacturers further improve their processes and controls.

Sidebar: Beef jerky: from bar food to healthy snack

Bar flies are still scratching their heads and wondering what happened, but the reinvention of beef jerky as a good-for-you snack is one of the most dramatic and successful turnabouts in food annals.

Both processing and packaging changes are helping spur annual sales growth of 25 to 30 percent in recent years, though shifting consumer perceptions certainly have helped. High-protein diets play to dried meats' strength, and marketers have pumped millions into promotions ballyhooing the low-fat content of naturally cured meats. Goodmark Foods, maker of the processed meat sticks known as Slim Jims, invested $10 million last year to advertise its upscale Pemmican natural-style beef jerky. Similar spending is being invested in Oh Boy! Oberto since the brand's acquisition two years ago by Frito-Lay.

Bridgford Foods Corp. is the king of the category, though, thanks in large part to its pioneering distribution work in the supermarket and mass-merchandiser channels. The 1.25-oz. package was the category staple until the Anaheim, Calif.-based meat processor introduced the 4 oz. variety five years ago. Since then Bridgford has ushered in an 8 oz. variety for club stores, and it was the first to employ oxygen-absorbing sachets in the package to safeguard the flavor of the shelf-stable products.

A relatively new entrant to the jerky business, Bridgford never had produced an extruded meat snack. The company began with a naturally cured, whole-muscle cuts process executed by a network of copackers.

High-protein diets have helped spur jerky's sales growth, says Cory Robbins, Bridgford's national account manager, and the female consumer is being targeted by all the major processors. Bridgford had her in mind in formulating Tender Steak Bites, a new product set to debut this spring. "They're smaller pieces and a lot more tender," Robbins says. The product will join a lineup that includes teriyaki, hot 'n spicy, pepperoni and BBQ beef, plus turkey jerky original.

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