Vacuum coaters for fats and liquid additives
Fat applied by spraying stays on the surface of the pellet. In a vacuum coater the pores of the product are first emptied, so the liquid enters its interior. With extruded fish feed this allows 4 to 40 % oil to be applied.
The product enters the drum, the drum is rotated into working position and a vacuum is created inside it; air leaves the pores, and in that state the product is sprayed with fats or another liquid.
When the vacuum is released in a defined way, external pressure pushes the liquid inwards and almost all pores are filled. An extrudate with a larger pore volume takes up more liquid than a denser pellet.
Several liquids can also be applied one after another: the first stays in the interior and the second encloses it, so sensitive additives are protected and an unwanted taste is masked.
Because coating is carried out after the product has been made, heat-sensitive ingredients can also be added, ones that would not survive a pass through the extruder or the press.
Coating is applied to feed for fish, shrimp, dogs and cats and, increasingly, to compound feed for poultry. Adding fat afterwards raises the energy value, so the share of expensive fat components in the formulation is reduced, and a pellet with less fat also presses better.
Weighing and dosing are handled by load cells built into the coater itself, discharge is by rotating the drum downwards, and for cleaning the drum is rotated backwards. The design is compact, so it can also be retrofitted into an existing line.