The snack category is one bursting with new products. This popularity and growth inspire manufacturers to constantly turn out new products to entice consumers. Trends like indulgence and better-for-you (BFY) are at the center of much of this growth as consumers turn to snacks to satiate a variety of needs: emotional rewards, meal replacement and exposure to new flavors.
It’s important to note, however, that when it comes to BFY snacks, the definition of healthy includes a plethora of attributes. Reduced sugar as well as sodium and calorie control are still relevant, but the definition has expanded. Value-added snacks that pack extra protein and fiber exist in the space next to snacks with clean ingredient lists. Gluten-free and keto-friendly have become mainstream claims. All of these formulations add complexity not just in the R&D lab, but also on the production floor. From snack forming to seasoning, ingredients like pulses, protein and fiber bring new challenges to processing puffs, pretzels and other extruded snacks.
“The push for better-for-you snacks has increased the amount of dough that needs to be processed slightly differently, but it can perform just as well in extruders with some adjustments,” said Nico Roesler, North American pretzel and snack equipment sales manager, Reading Bakery Systems (RBS). “At our technical center, we’ve worked with customers that use gluten-free formulations that feature many new and innovative starches and proteins. These doughs all behave differently based on their protein structures, but with various modifications and pre-feed systems, these better-for-you doughs can process similar to a typical wheat-based dough.”
All it takes is understanding the dough’s performance needs and adapting the equipment, from extrusion to seasoning, to meet those requirements consistently.
BFY snacks come in a variety of forms made with many different ingredients, all of which impact extrusion. When increasing protein levels, snack manufacturers often rely on starches, protein powders, soy flours, chickpeas and even whey proteins.
“Nowadays, starch-based snacks are often enriched with fibers and proteins,” said Christian Hüttner, process engineer, food extrusion, Coperion GmbH. “This can have a major impact on the expansion characteristics, such as size and shape porosity, in the manufacturing process. If raw materials with high-moisture content like slurries from fresh fruits or vegetables or raw materials with high-fat content are used, it is a challenge to introduce enough mechanical and thermal energy into the extrusion process.”
Mike Shaw, sales account manager, snacks/cereals, Bühler Inc., noted that while healthy ingredients may require some changes to the equipment, most can easily run on twin-screw extruders.
“Some high-protein ingredients with fine granulation may require consideration for direct feeding to the extruder infeed to guarantee consistent flow,” he said. “The addition of protein and fiber can also hinder expansion in the end product, so the screw configuration must be tailored to the type of protein and quantity in the formulation.”
Both high-protein and high-fiber snacks will have an impact on texture, a direct result of the changes to the product expansion profile as the dough is pushed and cooked through high-pressure extrusion. These products also often require more mechanical energy to achieve the desired mouthfeel, explained José Coelho, president, Clextral USA.
“The more fiber and protein we add, the lower the rate of product expansion; the product bite tends to be harder and the product surface rougher,” he said. “This is not necessarily a negative consequence, depending on the product desired.”
Flexibility and parameter control are critical to addressing most of these challenges. Clextral’s Evolum+ platform provides a greater range of mechanical energy and screw speeds during processing.
“This lets us increase the mechanical energy to modify the internal product texture,” Mr. Coelho said. “When we process at higher speeds, we can obtain finer internal texture and lower density in the snacks.”
The process section of Coperion’s ZSK Food Extruder contains several barrels in which the co-rotating screws operate.
“The closely intermeshing screws with their tight self-wiping profile eliminate stagnant zones over the whole length of the process section,” Mr. Hüttner explained.
Coperion’s extruder also combines high-free screw volume, screw speeds up to 1,800 min-1 and a specific torque of 11.3 Nm/cm3. This combination allows the extruder to be configured for every application, especially high-feed intake of those raw materials that have a low bulk density, often those that have a BFY health halo.
Sticky doughs can get stuck inside the extruder and prevent product from flowing evenly. In those situations, Paul W. Hill, national bakery sales manager, Handtmann Canada, recommended feed systems that are designed to reduce friction and feature short paths.
“Material selection for the feed system is also part of the reduced friction design process, and specialized coatings can also be used to reduce the coefficient of friction,” he said. “Water-jacketed temperature control has also been very helpful in managing things like the product flow of fudge on extruded baked products without valve-free depositing systems, for instance.”
When it comes to low-pressure extruded snacks, Mr. Roesler said much of the challenge BFY doughs pose can be addressed with simple modifications.
“Gluten-free doughs, for example, are missing the elasticity and strength of wheat-based snacks, so the dough doesn’t fill the extruder chamber as easily,” he said.
This can cause gaps as the dough isn’t pulled evenly into the extruder. Those gaps impact the even pressure necessary throughout the extruder and can cause inaccurate, inconsistent piece weights. A pre-feed system attached to the front of the extruder forces the gluten-free doughs into the extruder evenly, avoiding these issues.
“Without a pre-feed system, the dough will sit on top of the screws inside the extruder and won’t get pulled in,” Mr. Roesler explained. “That creates bridging, or air pockets. The pre-feed system mechanically forces it into the chamber and eliminates the bridging.”
He did recommend snack manufacturers stick to fine flours, however, that create a homogenous dough. Low-pressure extrusion does not lend itself well to inclusions, which can get stuck and damage the extrusion nozzles in addition to affecting cuttability and piece weight. In the instance of using inclusions for low-pressure extruded snacks, Mr. Roesler said RBS will often recommend snack manufacturers use them as toppings instead, adding them after extrusion and before baking.
This article is an excerpt from the August 2023 issue of Baking & Snack. To read the entire feature on Snack Processing, click here.