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Ready-To-Eat cereal coating
 
dfd

Product

A breakfast cereal is a cereal-based ready-to-eat meal, mostly sweet, to eat with a cold or hot liquid.

Base

The core is made of a pre-cooked, flaked or expanded cereal mix (corn, wheat, rice, oat, rye...). Expansion is either direct (high pressure short time extrusion) or indirect (low pressure extrusion, drying, expansion in hot air). The resulting bulk density range is : 0.05 – 0.3.

Ingredients

The liquid coating is prepared with:
  • water, 20 – 40%
  • beet or cane sugar, 60 – 80%
  • other sweet sugar solution : fruit juice, honey, caramel , malt, 5 – 10%
  • fat : oil, chocolate, 1 – 15%
  • solid : cocoa powder, 3 – 15%
  • flavour, 1%li> The ssyrup is prepared in a mixing and cooking vat. Heat is required to dissolve the sugar and prevent crystallization. The higher the temperature, the lower the viscosity. The typical solid content ranges from 50% to 75% to easily spread on the cereal. A higher concentration allows to reduce the further drying time but requires advanced cooking, application and tumbling systems.
Further ingredients can be applied separately:
  • ground nuts ,
  • vitamins (solutions).

Process

The coating sequences run as follows:
  1. consistent dosing of the cereals,
  2. liquid dosing and dispersion, often air-assisted, + 5 - 50%,
  3. solid 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 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 powder into the syrup (cocoa, cinnamon) 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.
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 to be thoroughly dried (120°C – 20 minutes, typically) to be ready for packaging.

Key parameters

Summary :
  • cereal temperature
  • syrup temperature tumbler length, diameter and baffles design,
  • spray manifold length and nozzle number,
  • product rate, liquid and powder relative rates,
  • tumbler tilt angle,
  • tumbler rotation speed.

Key features

Cereal manufacture and coating is a rather complex operation :
  • comparatively high machine and ingredient cost,
  • low to high volume operation, from 100 – 3 000 kg/h ,requiring large capital investment
  • wide range of shapes and flavours.
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Cereal coating process diagram
 
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