Coating of snacks with fat, herbs and spices

A snack is generally a cereal-based ready-to-eat treat, mostly savoury, to grab and eat on the go. Although simple in principle, the process delivers its best when finely adjusted.

Updated Aug 08, 2021 - 10 min Read


Core products

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, expansion in hot oil or air). The resulting bulk density is very low : 0.05.



The liquid coating is prepared with:

  • Vegetable oil
  • Oil-soluble flavours
  • Dry seasonings (spice mix) optionally
  • A dry seasoning can be further applied:
  • Salt
  • A spices and herbs mix


How does it work?

The coating sequences is fairly simple and run as follows


Consistent dosing of the snacks



Liquid dosing and dispersion, often air-assisted, + 5 – 30%



Powder dosing, +1 – 10%.


Coating system


The snacks result from the cooking, expansion and drying of a cereal mix. It is carried out by single or twin-screw extruder in one single step. Alternatively, snacks can be precooked and dried like pasta and later on expanded in hot oil or hot air.

Coating relies on the 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.

The liquid ingredients are best dispersed by dedicated spraying systems.

The powder can be dispersed with a vibratory tray or blown and air borne. In the latter case, an electrostatic gun can be used to charge the particles and force the powder ingredient onto the snack bed.


After coating, the product need a short setting time for the oil to absorb and is then ready for packaging.

Coating system

The operation is continuous, mainly in line with the forming tube. It generally occurs in a rotary tumbler whose length and diameter are calculated to accommodate the product flow. Baffles inside enhance the tumbling action.

Rotation speed and tumbler tilt angle are adjusted to achieve the required friction and residence time.

The oil or slurry and powder application devices are specifically designed because the ingredients have particular rheological properties.


How do you measure your success?

Key quality features

The product is one of the most universal treat appreciated


Crunchiness through controlled expansion and drying


Mate or glossy, light or heavy coating, soft or spicy, use of visuals


No smearing of the package. No oxidation.


Key quality parameters

One of the most universal application


Flavour selection can be relative basic or a sophisticated to follow trends


Machine design, volume, accessories : tumbler length, diameter and baffles design


Mechanical energy used for mixing and dispersion: tumbler tilt angle, tumbler rotation speed.