Method and apparatus for extrusion of expanding water holding products such as foodstuff particles or feeding stuff pellets

Abstract

In the extrusion of feed-stuff pellets and relevant consumer products, the extruded products are subject to expansion as a result of the boiling of their water content when the products, after being exposed to high extrusion pressure and a correspondingly high temperature, are discharged to the atmosphere through the extrusion nozzles. Such an expansion is directly aimed at, but it is desirable to be able to control it, which is difficult by adjustment of the ordinary process parameters. With the invention it has been found that the expansion which arises can be controlled in a highly constant manner, i.e. by carrying out the extrusion into a closed chamber in which an over-pressure of a few bar is established in relation to the atmospheric pressure, and which can be regulated. The extrusion products can be continuously discharged from this chamber, or they can be discharged intermittently in portions. The over-pressure moderates the momentary development of steam in the extruded product, and the product is given time to stabilise before being discharged to atmospheric pressure, so that the subsequent further development of steam influences the structure of the product only to a minor degree.

Description

[0001] This invention relates to a method of product extrusion where the extruded product material is formed into discrete products which stabilize after extrusion of the product material.

[0002] This applies in the production of “solid” unexpanded products where it is desired to avoid expansion, and especially in the production of expanded products where the dimensions of the product are greater than the nozzle aperture(s), where it is aimed to achieve a specific dimension increase in relation to the nozzle dimension.

[0003] The problem presents itself mostly in the manufacture of expanded products where the expansion is normally aimed at in order to ensure specific characteristics, such as viscosity (fish-foods), sinking characteristics (specifically slow sinking speed of fish-foods), liquid absorption characteristics (fish-foods, pet-food, foodstuffs), constant low specific density (pet-food, snacks, breakfast products), constant crispness (fish-foods, pet-food; foodstuffs), constant ...

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