Filled food is ubiquitous across the globe: empanadas, pastries, spring rolls and a variety of dumplings from Italy to China and every country in between.
“If you look at the different cultures from around the world, you will see many filled products in each of them,” said John Giacoio, vice-president of sales, Rheon USA.
These traditional filled foods supplied the original need for nutrition and sustenance on-the-go, and their persistent place in global diets speaks to their popularity. As snack technology evolved to create co-extruded filled snacks, it only makes sense that people around the world would also gravitate toward these products. Filled snacks deliver satiety, indulgence and an experience; consumers not only enjoy the surprise of the filling inside but also the different textures being experienced all at once.
The most obvious challenge of working with filled snacks is balancing at least two very different materials — the filling and the dough shell — in one piece of equipment. When working with multiple fillings in one product, this challenge can become even trickier. The greatest pitfall in balancing it all is preventing the filling from leaking into the dough or even outside of the shell. While low-moisture fillings often work best to prevent this situation, co-extruders might have to work with a range of viscosities.
To produce an intact final product that consumers will not only accept but also enjoy, the equipment must preserve the integrity of the filling and the outer shell, both of which have very different needs. Controls and technology can help bakers and snack makers achieve this balance. Clextral uses a combination of precision extruder control and independent local control for the filling equipment to respond to the divergent demands of shell and filling.
For the dough, Clextral’s Evolum extruders feature independent heating and cooling circuits in each modular barrel segment. These circuits are controlled by the company’s proprietary Advanced Thermal Control (ATC), which continuously monitors and adjusts to changes in production parameters.
“We design the screw configuration to provide the correct cooking-to-resting ratios for the dough, and inside the twin-screw extruder barrel, the self-cleaning screw action ensures complete mixing of the ingredients and transformation of the starch,” explained Gilles Maller, vice-president, sales and international, Clextral.
Clextral also uses a precisely controlled system to protect the filling integrity with local control on the filling platform that is integrated with the plant supervision system. After ingredients are metered and mixed in the stainless-steel filling tank, strict temperature control and a recirculation loop maintain the filling’s optimum viscosity before being extruded into the shell.
Choosing the proper equipment configuration is also critical in preserving dough and filling integrity. Handtmann tailors its co-extrusion systems to the manufacturers’ product, combining different machine specifications to optimize dough and filling handling.
“We can offer a dough filler to handle an airy, soft dough that will maintain the structure during the co-extrusion process in combination with a filler that will handle stiff and dry or viscous fillings,” said Cesar Zelaya, bakery sales and technology manager, Handtmann.
When tailoring co-extrusion equipment to the dough and filling, it’s important to approach them separately, as their needs are so different, said John McIsaac, vice-president, strategic business development, Reiser.
“We work to make sure the dough is fully developed as it is formed around the inner filling,” he said. “This involves both work on the Vemag machinery and the coextrusion process.”
Reiser’s bakery specialists collaborate closely with the baker or snack manufacturer to develop the appropriate equipment setup before optimizing the process to create the desired dough volume and crumb.
“Each customer is after certain attributes that make their product unique to them,” Mr. McIsaac said. “We certainly have the equipment and technology, but more importantly, we have the people and expertise to work with our producer customers. Our bakery specialists first learn about the customer’s product and the process. We then match the equipment to the process.”
When approaching the filling, Reiser’s bakery specialists start with the finished product and work backward with the intention of maintaining the filling’s final quality.
“The filling is often made up of larger chunks and inclusions,” Mr. McIsaac explained. “The Vemag’s gentle infeed and double-screw portioning technology are geared toward gentle handling with precise portioning and positioning of the filling within the outer shell.”
Gentle co-extrusion is key to maintaining the integrity of the entire product, and it’s something suppliers have had to adapt the equipment to for the baking and snack industries.
“When most people think of an extruder, they think of a machine that may have a feed rate as high as 20 to 1,” Mr. Giacoio said. “This means for every product that is pushed out of the machine, 20 times that volume of product was pushed toward the exit of the machine. This compacts the material and destroys any particulates, which is great if you’re making hamburger patties, but it’s not for making delicate products.”
Rheon USA’s co-extruders have a feed ratio as low as 1.5 to 1. The company designed them to enable bakers and snack manufacturers to create filled products that appear handmade, even though they were created in a commercial setting. To further support delicate products, Rheon’s machines have the shortest and most direct path possible for product to flow through.
“We eliminated hard twists and turns,” Mr. Giacoio said. “This reduces the friction that is created, and as a result, the temperature of the materials is not increased, and particulates are not damaged.”
Friction isn’t only damaging to particulates but also can harm the outer dough and fillings without particulates. Reading Bakery Systems (RBS) designed a wirecut head to co-extrude fig bars, breakfast bars and cookies.
“The feed rolls are designed to softly push the dough through the die and filler block to form the product,” said Sam Pallottini, director of cookie, cracker and pet food machinery sales, RBS. “The design hinges around the filler block and die to create enough back pressure to form the cookie while not imparting any work into either the outer dough or inner filling.”
In RBS’s low-pressure co-extrusion system for snacks, plastic extrusion augers gently advance and pressurize the dough into a compression head assembly for equalization of dough pressure before the dough jacket is formed.
“Overworking the dough during the extrusion process results in loss of elasticity and extensibility of the dough, further resulting in product blow-outs during the baking process,” said John Eshelman, director, pretzel and snack machinery sales, RBS.
Minipan also has pursued friction reduction with the dough in its co-extruders. The company has focused on two main changes to the head of its machines: increasing efficiency through bigger diameter rollers while improving their grip to the dough.
“Better grip equals less friction, which avoids generating inconsistent temperature pockets,” said Franco Fusari, commercial director and co-founder, Minipan.
This article is an excerpt from the May 2019 issue of Baking & Snack. To read the entire feature on coextrusion, click here.