Twin-screw extruders, co-extrusion spur creativity

by Charlotte Atchley
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Reading Bakery Systems
Having multiple dies and cutting mechanisms available assists in not only product shape and size diversity but also managing changes in texture. 

Snacks are a category in which consumers are willing to experiment and be impulsive. This gives producers an open space to innovate and play with their flavors, texture, shapes and ingredients. It’s also a competitive category with only so much supermarket shelf space and consumer dollars to go around. To stand out on today’s shelves, snack manufacturers must differentiate their lines from the competition.

“Producers are competing for a demanding consumer looking for new and more interesting flavors and textures as well as products that are perceived to be healthier than many in the past had been,” said Vince Pasquini, pretzel and snack technical sales engineer, Reading Bakery Systems (RBS).

This intense competition has led snack producers to pursue clean labels, organic ingredients, healthier grains and inclusions. Pairing these ingredients with the extrusion process, they can combine different textures and appearances to create items that offer consumers something entirely new.

There are several different types of extruders and ways to use this technology to bring about multi-textured snacks or ones with interesting shapes. Twin-screw extruders and co-extrusion will most likely offer the most flexibility.

Twin screw extrusion is one way to get multiple textures in a single snack piece.

Twin-screw extrusion produces snacks by extruding a cooked mass through a small die aperture. The high-pressure, high-temperature thermal system mechanically cooks the product, causing it to expand when it comes out of the extruder through the die. While this process can result in a uniform texture, different ingredients help snack producers mix it up.

“The cooked mass is usually based on a grain or vegetable flour but can easily be made into multi-textured products by adding small pieces of soaked grain that can pass through the die without blocking it,” said Keith Graham, marketing manager, Baker Perkins. These can include ancient grains such as quinoa, spelt or buckwheat, which also will garner a producer that multi-grain claim.

“These ingredients are aligned with current market trends for snacks that combine positive nutrition with interesting tastes and distinctive textures,” Mr. Graham continued.

Co-extrusion offers the most straightforward answer to creating multiple textures in one snack. This method makes snacks with a center filling encased in a cereal outer shell.

Extruded Snack Chip
The snack's characteristics are impacted by the extruder technology used.

“The ability to control three key aspects of the process — texture, filling and shape — creates the ability to develop a wide variety of added-value snacks,” Mr. Graham said. “Fruit paste fillings tick the healthy box; sweet and savory creams, cheese and chocolate praline are also popular.”

Snack producers can also choose between two different co-extrusion approaches. They can use one extruder with a co-extrusion die plate, pumping material into the end of the die to create two different textures, said Michael Shaw, sales account manager, snacks/cereals, Bühler.

“There is some limitation, though, on creating the different variation of textures,” he said. “There’s a range of difference between the inner and outer shell that would be allowable.”

The second strategy is to use two twin-screw extruders and combine them at the exit.

“That would allow you to create significantly different raw materials,” Mr. Shaw explained.

When approaching which method to pursue, snack producers must know what they’re looking for. They must consider a softer or harder bite, something that dissolves quickly in the mouth or a snack that’s crunchier. Deciding which extruder technology to employ and the parameters to set will have an impact on end-product characteristics. Snack producers must determine the appropriate screw speed and profile configuration, die design, and whether to inject water or other liquids or even release steam.

“These parameters affect longitudinal and radial expansion in the finished product, cell structure and porosity: number of cells, size of cells and density,” Mr. Shaw said. “This can create a difference in finished product attributes such as a softer, quick-dissolving texture for babies and toddlers to a hard, crunchier bite for adults.”

The best way to see how these technologies and parameters will affect the finished snack is to test the formulation on the equipment itself.

“Snack manufacturers have their expertise on their product and what they are looking for, and our technologists have expertise in working with different raw materials and obtaining different textures,” Mr. Shaw said. “They meet in the middle to get the right product.”

RBS also offers snack producers the ability to conduct extensive tests on its equipment at its Science & Innovation Center.

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