Extrusion systems for aqua feed and pet food: Single- or twin-screw?

By Diego Clivio, Clivio Solutions, Argentina

The extrusion process is a thermo-mechanical process that consists of forcing a product to pass through one or more holes of a specific size under pressure and temperature thanks to the Archimedes screw concept (also known as "endless screw").

The extrusion processes in the processing of extruded pet food and aquaculture aim to cook a mixture of raw materials and ingredients, giving it the form of croquette (pellet/kibble) that facilitates its subsequent handling.
 

The most important processes that take place inside an extruder is the gelatinisation of starches and texturisation of proteins. Both processes help aid in greater digestibility, as well as to form a structure and texture that hosts other ingredients, minerals and fats in a stable and uniform way.

For a good gelatinisation of starches and texturisation of proteins, moisture is needed (which is added in the form of liquid water and steam in pre-conditioning and/or extrusion). Suitable temperatures are also needed, which can be provided through the addition of steam, as well as being produced by the mechanical work and friction produced by the screws. Mechanical energy is also needed, granted by the shearing action of the screws.

Today, there are two technological forms of extrusion, single-screw (SSE) and twin-screw (TSE). In this article we will talk about the features, advantages and disadvantages of each of these technologies.

Read more, HERE.

The Aquaculturists

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