While some go low, others go high when developing different snacks and baked goods with extrusion technology.

“Low-pressure extrusion sees pressures ranging from 60 to 100 psi. This pressure is better for more delicate doughs,” said Nico Roesler, North American snack equipment sales manager, Reading Bakery Systems (RBS). “It doesn’t destroy the gluten structure of wheat-based doughs and reduces the risk of crystallization in these doughs.”

He said that crystallization completely changes the texture of a dough by creating a hard bite in the final product.

“This is basically the result of completely destroying the protein and gluten structure of a dough,” he observed.

Rafael Alvarenga, area sales manager, Wenger Manufacturing, pointed out that the main goal of low-pressure or shear extrusion is to continuously form and cook products with minimal mechanical energy input. A low-shear process can also be considered a “cold” extrusion method.

Pretzels, for example, can be formed in a low-shear, low-RPM forming extruder that are then baked in an oven to set their final texture. Another example involves extruded pellets that are later puffed via frying or hot air drying.

On the flipside, Roesler said, a high-pressure extruder involves blending a base ingredient like corn with water and oil. In the extrusion process, the blend is exposed to a high pressure and temperature that forces the water to evaporate and expand at the face of the extruder where the piece is cut.

Alvarenga noted that high-shear extrusion typically relies on significant mechanical energy to melt the extrudate at high pressures behind the extruder die.

“Direct-expanded corn snacks, for example, are created via high-shear extrusion and are cut as the product is formed at the die plate,” he said.  “As the product exits the extruder under high pressure, it expands and puffs when it meets low-pressure ambient conditions outside the extruder.” 

Alvarenga said both low- and high-shear extrusion involve manipulating many variables to achieve the proper texture, shape, density and color in the final product. Drying also plays a critical role in extruded snack production.

“To achieve a shelf-stable level, product must often pass through a dryer to remove moisture,” he explained. “Proper drying also sets the final product texture and color. In most applications, extrusion and drying should be considered complementary processes that need to work together efficiently.”

Roesler added the RBS low-pressure extruder uses a double-screw configuration.

“The design allows the dough to flow through the extrusion chamber with the appropriate amount of back flow around the screws,” he said.

This article is an excerpt from the March 2025 issue of Baking & Snack. To read the entire feature on Extrusion, click here.