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Extruding new opportunities

Nov. 16, 2004
New ways of shaping, forming, squeezing and puffing foods – cooking
them along the way – are coming out of today’s extruders.
By Mike Pehanich, Plant Operations Editor

They’re not just for pet foods and kid snacks anymore. Today’s extruders have opened the door to a global array of new food products – including new nutrition-packed varieties.

More than two generations have passed since the birth of the twin-screw extruder. During this period, U.S. consumers have taken gradually to extruded foods. The most conspicuous examples of the technology – snacks like General Mills’ Bugles – have enjoyed some marketplace success. But they have been, by and large, the flyweights of the food pyramid. When it comes to nutrition, we just haven’t taken them too seriously.

But time, circumstance and imagination have changed the reality if not the perception. Today, food makers around the world are discovering new ways of shaping, forming, squeezing and puffing foods not only for fun and flavor but to create healthful substance as well. Today’s extruders are producing crispy flat bread, baby food, pet food, high fiber products, candies, puffed snacks, pellet snacks, ready-to-eat breakfast cereals in puffed and flaked forms, meat analogues, pasta, cheese snacks and instant drinks and soups.


Starch content plays a major role in the type of product an extruder can produce. Rice, potato and tapioca expand well when fried. Rice yields a crunchy texture. With a lower starch content than the others, corn expands less. The resulting product has a harder texture and crunchier bite.

Wheat, oat, barley and other high-fiber grains also expand less. They are the central ingredients in healthful snacks and cereals. Expect a heavy and crunchy cereal with these grainy ingredients.

Where have all these variants come from? How is it that a pet- and snack-food technology has suddenly spilled nutrition into the processing stream?

An extruder works by taking a blend of raw ingredients in one end and subjecting it to high heat and pressure in a cylinder. As the mix passes through the extruder cooker, it is shaped and fully or partially cooked. It takes its final shape as it is forced through a die at the exit end.

Twin screw extruders welcome nearly all forms of foods and ingredients. They can handle a wide variety of granules and products with a wide range of moisture, fat, and carbohydrate content.

Their adaptability is well suited to a processing era that demands flexibility to control both capital and operations costs. Twin screw extruders permit precise control of process parameters and can perform multiple functions at once.

They are reliable machines that yield consistent product repeatedly. Furthermore, products vary little from lab to production line, making scale-up a relatively simple process.

Meaty imitationsExtruded protein extenders and meat analogues have sparked global interest. They offer alternative high-quality main-course protein foods from vegetable sources. Today processors can simulate nearly any type of fish, poultry or meat flesh in a highly palatable and easy-to-use form.Texturized vegetable proteins have found their way into thousands of formulations. Soy protein, always valued for its versatility, has become a preferred protein source offering an assortment of nutritional advantages.“Alternative protein sources are becoming critically important,” says Doug Baldwin, director of sales and marketing at Wenger Manufacturing Inc. (www.wenger.com), the Kansas City, Mo.-based manufacturer of extruders. “The food industry looks to extruders to process soy or other oil seeds into texturized protein.”

Texturized vegetable protein (TVP) is the preferred protein material for the majority of today’s meat analogues because, in the hands of an able processor, it can duplicate true meat fiber.

“A high-moisture meat analogue material doesn’t require drying,” says Baldwin. “It comes off the processing line with 70 percent moisture. You can get product that resembles a chicken breast fillet right off the extruder.”

Archer Daniels Midland (www.admworld.com), Decatur, Ill., commercialized its high-moisture meat analogue this past year. Marketed as Nutrisoy Next, it is available in a ready-to-use form.

“The previous generation of TVP, ADM’s texturized defatted soy flour, used a single screw extruder to yield a product with low moisture content – less than 35 percent,” explains Cheryl Borders, manager of soy foods applications for ADM. “Our new products range in moisture content from 50 to 80 percent, varying with preferred texture.”

The new generation of meat analogues offers convenience and quality advantages. Available in strips, nuggets, cubes and shreds, they can be used in hot or cold entrees and retort applications. The products are more receptive to flavors than previous generations of analogues. Though they can mimic beef or pork in flavor or texture, poultry has been the principal target.

“While you can add flavor to low-moisture extruded meat analogues, the product loses a lot of flavor when it leaves the extruder due to the pressure drop,” says Borders. “There’s less pressure drop with high-moisture product. As product exits the extruder and enters the cooling die, the temperature change increases the viscosity, which also helps in developing the desired texture.”

The technology for such products, including use of the cooling die, has been available for a quarter of a century. “But really, it’s not so much the improvement in twin screw extruders as much as the time becoming ripe for this type of analogue,” says Borders. “Seventy-four percent of consumers perceive soy as healthy today. Now they are accepting soy foods and looking for new options.”

The products are used by foodservice outlets or used by other food processors in entrée or component meals. They can be breaded and battered like their natural counterparts. They save the user the additional processing step of rehydration, unlike previous textured vegetable products. “The product is also fully cooked as it exits the cooling die,” says Borders. “That’s adds a convenience for the user.”

Two screws better than one

Twin-screw extruders have displaced their single screw counterparts in most food operations. Single-screw extruders have been relegated largely to animal feed manufacture in recent years, though some use in human food products continues.

Pre-conditioning the raw material mix for extruded product dates back to the 1950s. “But learning how to utilize pre-conditioning has really advanced in recent years,” explains Baldwin.

Extruder size is generally given in terms of a length-to-diameter (LD) ratio; that is, the length of the overall barrel to the screw diameter. “We have been able to reduce the length of the extruder barrel and thus reduce hardware requirements,” says Baldwin.

“We also work more with thermal energy than mechanical energy,” Baldwin continues. That’s a plus with energy consumption an ongoing issue in the plant. “It’s more economical to process with thermal energy than with mechanical energy. If you can do more with steam during pre-conditioning, you can do more cooking with less horsepower.”

Clextral Inc. (www.clextralgroup.com), Tampa, Fla., was the first to adapt the twin-screw extrusion concept to food applications. The equipment maker’s emphasis today is on the modular concept, simplifying changeover and removal of screws, barrels and dies. New designs allow screw elements to slide onto splined shafts. They also are more hygienic and operate at higher speeds. These practical design improvements also have made the twin-screw extruder more welcome on the processing floor.

“Our twin-screw extruders today allow quick change of screws and easy cleaning capability,” notes Laurent Garcia, sales manager of Clextral. “With hydraulic opening, you can access the screws within five minutes for maintenance and quick changeover. You also get a good view of what is happening in the machine. You can see where the starch is gelatinized.”

Better temperature control and auto-mation capabilities not only have improved product quality and consistency, they also add to the flexibility and versatility of today’s machines. “You can adapt an extruder platform to new applications. Keep in place your main equipment and add auxiliary equipment for new products,” says Garcia.

Twin-screw extrusion offers an infinite range of possibilities, inviting innovation in mixtures of fillings and colors and a wide variety of tastes and textures.

“We were the first to develop flat crisp bread, coextruded with a sugar filling inside,” notes Garcia. “You can add chocolate, marmalade and other fruit-taste fillings.”

Snacks and RTE cereals may be the most conspicuous areas of extrusion application, but Garcia likes the possibilities opened in the nutrition area, particularly for low-carb products and texturized proteins.

Snack power

The extruder’s adaptability to such a wide range of raw materials has opened a large window of opportunity in snacks. Snack pellets have had more significant impact in the marketplace in Asia and the Mideast than they have in the U.S.

Economics explain part of their popularity. Pellet products begin with blended ingredients that emerge from a cooking extruder as a dense pellet. Their moisture content is reduced.

Shelf-stable pellets are passed to the processor, who prepares the final product by “puffing” it with hot oil, microwave heat, hot air or other method. In some markets, the final preparation is left to the consumer.

What’s the next likely trend in extruded products?
Extruded snacks with reduced carbohydrate content are a no-brainer and already in the product mix. Extruded soy proteins will likely spread into more simulations of meat-based products.Frito-Lay, the snack giant from Plano, Texas, owns a gold mine in its Cheetos line of extruded snacks. The company has developed its own proprietary extrusion technology, company sources say. Latest is an extruder that produces a spiral Cheeto.The company’s most recent addition to the line is Baked Cheetos, a snack that qualifies as a healthier option with the package display of the PepsiCo Smart Spot, a marketing item Pepsico is adding to the packaging of all its “healthier” products.The current quality of today's meat analogues offers tremendous opportunity to spread good nutrition in good-tasting forms to developing nations. But the current generation of high-quality analogues carries a cost that may relegate the products to the realm of higher ticket value-added products for some time. Still, the promise of solving human hunger continues to make extrusion technology a potential savior as well as a profit maker.So sophisticated has extrusion technology become that its targets today are analogues nearly indistinguishable from the real McCoy.“We have done work on extruded cereal flakes and have seen interesting development in that area,” says Doug Baldwin of Wenger Manufacturing Inc., a Kansas City, Mo., manufacturer of extruders. “Processors are trying to develop an extruded flake to match the appearance, quality and texture of a processed flake.”Add that to a chicken breast not even the Colonel could tell from the original, and we have seen how far extruder technology has come.

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