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Bakery - Glaze
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Doughnut with icing sugar
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Pet food coating
Snack coating
Vegetable casing extrusion
Snack coating
A snack is generally a cereal-based ready-to-eat treat, mostly savoury, to grab and eat on the go and eat. Although simple in principle, the process delivers its best when finely adjusted.


The core is made of a pre-cooked and expanded cereal mix (corn, wheat, rice, potato...). Expansion is either direct (high pressure short time extrusion) or indirect (low pressure extrusion, drying, epansion in hot oil or air). The resulting bulk density is very low : 0.05.


The liquid coating is prepared with:
  • vegetable oil,
  • oil-solublle flavours,
  • dry seasonings (spice mix) optionally.
A dry seasoning can be further applied:
  • salt ,
  • a spice and herbs mix.


The coating sequences run as follows:
  1. consistent dosing of the snacks,
  2. liquid dosing and dispersion, often air-assisted, + 5 - 30%,
  3. powder dosing, +1 - 10%.

Coating system

The operation occurs in a rotary tumbler whose length and diameter are calculated to accomodate the product flow. Baffles inside enhance the tumbling action.
The coating relies on dispersion of the liquid and powder ingredients first, then on the mechanical friction caused by tumbling.
Liquid and powder ingredients can be added separately. One option is to mix finely ground spice powder into the oil and carry out just one application. This 'slurry' needs to be constantly agitated until it is applied.
Ingredient dispersion can be enhanced by blowing air. Liquid ingredient are best dispersed by dedicated spraying systems.
Powder can be dispersed with a vibratory tray or blown and air borne. Inn the latter case, an electrostatic gun is used to charge the particles and force the powder ingredient onto the snack bed.
It is a continuous operation. Rotation speed and tumbler tilt angle are adjusted to achieve the required friction and residence time.
After coating, the product need a short setting time for the oil to absorb and is then ready for packaging.

Key parameters

Summary :
  • tumbler length,, diameter and baffles design,
  • product rate, liquid and powder relative rates,
  • tumbler tilt angle,
  • tumbler rotation speed.

Key features

Snack manufacture and coating is a rather simple operation :
  • comparatively low machine and ingredient cost,
  • easy to run operation with high volume,
  • wide range of shapes and flavours.
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Coated snack product.
Application diagram
Coating tumbler. Courtesy of Spray Dynamics.
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