Whether it’s the carrot of new-product opportunities or the stick of regulatory and customer demands, North American bakers are investing in production systems that deliver both greater flexibility and increased productivity.
Coextruded snacks and cereals typify the kinds of products that once were considered exotic and now are gaining a growing audience. An example is Lion cereal from Nestle. A whole-grain, vitamin-fortified, premium product, Lion has a core of caramel paste surrounded by a crisp wafer enrobed in milk chocolate. Produced in a plant in France and distributed throughout Europe, North America and elsewhere, Lion is made possible by twin-screw extruders that output a continuous rope that is then enrobed, cut and crimped into bite-sized dimensions.
Twin-screw technology dates to the mid-20th Century and is used extensively in plastics and other industries, but cost and complexity relegated it to incidental use in food production until more recent years. Cost remains a barrier, and single-screw extruders still dominate in snacks and other foods, but the machines’ versatility and consistency in producing complex products at high volumes are prompting many food companies to give the technology serious consideration.
The diversity of interest in twin-screw extrusion is illustrated in the mix of corporate executives, entrepreneurs, operations and R&D personnel who attend Clextrol USA’s annual Extrusion Discovery Course at its Tampa, Fla., pilot plant each year (this year’s program runs April 10-12).
“The fear factor has disappeared,” says Gilles Maller, vice president-sales and international (www.clextral.com). “People are more and more comfortable with the technology.” Many are considering replacing multiple single-screw machines with one twin-screw extruder that can produce a more diverse range of products, including super-premium and indulgent foods.
Clextral modified its earliest extruders for food applications in the 1970s. The latest are the Evolum series, machines with 30-40 percent higher capacities than the previous generation. They also reflect the higher sanitary standards now applied to food manufacturing, as well as the latest technical advances.
“The need for hygienic design has become more intense in the past 5-6 years,” says Maller. Stainless steel construction and component accessibility for cleaning and sanitizing were integral to the redesign. “It wasn’t a barrier before, but if we did not have a hygienic design today, that would be a big barrier,” he notes.
The re-engineered extruder incorporates advanced thermal controls that help enhance the consistency, structure and mouthfeel of products. High sheer is a distinguishing characteristic of extrusion, along with pressure and heat. Maintaining consistency is critical in creating light, finely textured products.
PID loops typically are used to monitor and adjust temperature in the barrel. The new machines rely on sensors and software that factors in temperatures in the zones, each with its own heating and cooling system, to understand the overall impact.
Heat transfer is optimized “not area by area, but what is happening everywhere,” Maller explains. Less fluctuation from setpoint is provided; whereas variations of 2-3°C occurred before, deviations of plus or minus 1°C is the new norm.
Machine intelligence also is enhanced, with the extruder “learning” how best to balance pressure, heat and sheer for each recipe, based on prior outcomes.
Improvements in materials of construction for the barrel and screws are part of what Clextral calls Total Preventive Maintenance. Machine wear leads to gaps between the screws and barrel over time. The metallurgy in the new machines helps hold tolerances for more than 20,000 hours of run time, five times longer than the prior generation of extruders.
Total Preventive Maintenance also guides operators through daily routines that free maintenance technicians for more value-added activities. And relieving skilled technicians of mundane tasks that take time from more value-added projects and contribute to on-the-job drudgery is a priority.