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.
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.
The liquid coating is prepared with:
- Sugar, beet or cane, molasse
- Other sweet sugar solution : fruit juice, honey, caramel , malt
- Fats : oil, chocolate
- Solids : cocoa powder
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:
- Vitamins (solutions)
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
10 -30 %
110 – 120 °C
20 – 25 min
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.
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.
Syrup application drum
How do you measure your success?
Key quality features
A sweet taste is not the sole criterium
Many factors affect homogeneity. A minimal amount is necessary. Conversely, sugar reduction imposes lower percantages.
The final aspect is achieved after drying, either mate or shiny
The ceral core must retain its original shape throughout handling, coating and drying
Key quality parameters
The long and complex process uses multiple parameters.
Both cereal and syrup temperature are important. The higher the better to reduce the viscosity and ease the dispersion
Design and operation
System length, diameter and agitation design, spray manifold length and nozzle number. System rotation speed.
Although not a coating factor, it affects the final aspect depending on the temperature / time relation.