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Doughnut with icing sugar
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Coating of fried doughnut with an icing sugar blend
The doughnut are best liked when dusted on with icing sugar. A challenge to do it at high capacity, evenly and in a clean way.


The doughnut is a flour based dough, formed, fried and cooled.


The coating ingredient may consist in :
  • a light fat spray on top to all a better adhesion if the remaining fat from the frying phase is not enough,
  • finely ground sugar, icing sugar or more often a powder mix, made of icing sugar, starch, fat and flavour.


The coating sequences run as follows:
  1. automatic transfer from the upstream forming and frying line line,
  2. spraying of fat (optionally),
  3. dusting on with the powder mix,
  4. removing and recycling of the excess.
  5. /ol> With the adequate variations, the same coating principle also applies to the following product:
    • batter-enrobed product further coated with crumbs
    • candies covered first with tempered chocolate then with particles.

    Coating system

    The coating principle relies on the application of the ingredients through dribbling over the articles or tumbling in a powder bed.
    The operation occurs usually in an enrober , powder applicator , which can be either topical dusting conveyor, a tumbler or a screw .
    Typically, the doughnuts are deposited on a conveyor whose upper surface is already covered with the sugar mix. While the doughnuts are mover forward by the conveyor, the overhead trough delivers a curtain of mix. The doughnuts are totally covered with sugar mix. The excess is shaken off by means of a rotating came or similar device. The excess is recovered to be recycled. During recycling, the sugar mix may be sifted to remove agglomerates, thus preserving its initial functional quality.
    It is usually a continuous operation in an industrial line. It can also be fulfilled in a tumbler saturated with the sugar mix or a screw conveyor large enough to accommodate the different donut sizes. Speed is adjusted to achieve the required residence time. The design of the equipment allows for easy changeover, cleaning and sanitizing.
    Ingredient application
    The finer the sugar mix, the better it adheres to the doughnut surface. Large particles can only be added if the doughnut is previously coated with a liquid layer of syrup or chocolate.
    The wide range of liquid and particle types result in multiple combinations, some receiving specific names such as Tempura.

    Key features

    Specifications need to be given to select the proper enrobing system:
    • product: throughput, doughnut shape and size, surface texture,
    • sugar mix : type, percentage added (pick up), flow behaviour.
    The equipment will be described by its main characteristics:
    • coating machine: length, width, volume, diameter, belt mesh, depending on the type of enrober used,
    • sugar dosing : screw, bucket, conveyor type and capacity.
    Quality and performance can be adjusted fine tuning the following variable parameters:
    • coating machine: motor speed,
    • sugar dosing : rotation speed.
Product - Donut dusted with icing sugar
Diagram - Doughnut coating process
Machinery - Typical doughnut coating system
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