APPLICATION

Coating of Ready-To-Eat cereal with a sugar syrup

A breakfast cereal is a cereal-based ready-to-eat meal, mostly sweet, to eat with a cold or hot liquid. The coating enhances the appeal of the shape and the taste while retaining longer the crispiness.

Updated Aug 08, 2021 - 10 min Read

BASE

Core products

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.

RECIPE

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%
  • Fats : oil, chocolate, 1 – 15%
  • Solids : cocoa powder, 3 – 15%
  • Flavours, 1%

The syrup 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:

  • Groundnuts
  • Vitamins (solutions)

PROCESS

How does it work?

The cereals are introduced in the coating system, the syrup is dosed and dispersed on the cereals by a mechanical motion

Optionally, particles – nuts, seeds – can be added as the syrup is still viscous. The product is not finished until it has been properly dried to avoid mould growth.

Given the volume, it is a continuous operation that involves large equipment.

The sequences run as follows

1.

Liquid application
10 -30 %

5

2.

Particles application
3-5 %

5

3.

Drying
110 – 120 °C
20 – 25 min

PROCESS

Coating system

The operation occurs in a rotary tumbler whose length and diameter are calculated to accommodate the product flow. Baffles inside enhance the tumbling action. The coating relies on the 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.

The liquid ingredients are best dispersed by dedicated spraying systems. The 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 needs to be thoroughly dried in 2 or 3-tier driers to be ready for packaging.

PROCESS

Coating system

Syrup application drum

PRODUCT EVALUATION

How do you measure your success?

Key quality features

A sweet taste is not the sole criterium

Homogeneity

Many factors affect homogeneity. The trend toward sugar reduction challenges the manufacturer

Aspect

The final aspect is achieved after drying, either mat or shiny depending on the product

Product integrity

The ceral core retans its original shape thrpughout handling, coating and drying

Key quality parameters

The long and complex process uses multiple parameters.

Temperature

Both cereal and syrup temperature are important. The higher the better to reduce the viscosity.

Design and operation

System length, diameter and agitation design, spray manifold length and nozzle number. System rotation speed.

Drying

Although not a coating factor, it affects the final aspect depending on the temperature / time relation.