Method and apparatus for producing fully cooked extrudates with significantly reduced specific mechanical energy inputs

Abstract

Improved extruders and methods for the extrusion cooking of comestible products such as human foods or animal feeds are provided wherein the products may be produced with very low specific mechanical energy (SME) inputs as compared with conventional processing. The methods preferably involve introduction of very high levels of steam into the extruder barrel (12) during processing, which concomitantly reduces necessary SME inputs required to achieve desired cook and expansion levels in the products. In accordance with the invention, fully-cooked pet foods can be fabricated with SME inputs of up to about 18 kWhr / T, whereas aquatic feeds can be fabricated with SME inputs of up to about 16 kWhr / T. In preferred forms, the extruder (10) includes specially configured, intermeshed extrusion screws (18, 20) and a plurality of obliquely oriented steam inlets (48, 50), and an upstream, dual-shaft preconditioner (90) is used having individual variable frequency drives (98, 100) which allow infinite variablility in the speed and rotational direction of the preconditioner shafts (94, 96).

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention is broadly concerned with improved extruders and methods for extrusion processing of comestible products with very low specific mechanical energy (SME) inputs as compared with conventional methods. More particularly, the invention is concerned with extruders having specially configured screws designed to permit addition of very high quantities of steam, so that the amount of SME required to for complete cooking is maritally reduced. The resultant feeds have very high cook values and expansion characteristics.[0003]2. Description of the Prior Art[0004]Extrusion processing of comestible products such as human foods and animal feeds has long been practiced and is a highly developed art. In general terms, food extruders of the single or twin screw variety are employed, having elongated, tubular barrels with inputs adjacent one end thereof and restricted orifice dies at the outlet thereof, and one or tw...

AI Technical Summary

Benefits of technology

The solution significantly reduces SME inputs, lowering equipment costs and energy consumption, enabling the production of fully cooked and expanded products with improved cook values and expansion characteristics, while maintaining product quality and reducing wear on extruder components.

Problems solved by technology

Conventional extrusion systems are limited in the amount of steam which can be injected into the extruder barrel, typically no more than about 5% by weight.

Consequently, the extrusion equipment must have a more robust and therefore construction than would otherwise be necessary, the extent of extruder component wear is higher than desirable, and utility costs are increased.

Skilled artisans understand that a ratio of 1.3 is too small, in that the screw(s) lack free volume, creates excessive shear inputs and consumes too much power.

Similarly, a ratio above 1.8 is deemed too large, in that the screw has too much free volume and which will prevent barrel fill and the ability to achieve a desired cook value.

Any significant axial gap or clearance between the adjacent flighting sections is considered to be detrimental in that it could create dead zones of accumulated product, and also would decrease the extent of product mixing within the extruder barrel.

However, these types of extruders will be deficient in that cook values will be unacceptably low and significant expansion cannot be achieved.

Alternately, an aggressive extruder design can be used, which will assure adequate cook and expansion of products, but this will inevitably result in high shear and SME inputs with resultant higher costs.

Images