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 â€“ 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 â€“ snacks like General Mills’ Bugles â€“ 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.
|NOTE TO R&D
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 imitations
Extruded 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 â€“ 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.”