The layers of a coating system
In products such as nuggets, schnitzel, coated fish and onion rings, the coating has three layers: predust, batter and outer coating (breadcrumb or breading). Each layer has a different job. Predust binds surface moisture and provides adhesion, batter binds the layers together and forms a moisture barrier, and the outer coating gives crispness and appearance. Coating quality depends on designing these three layers together.
Predust: the basis of adhesion
Predust binds free moisture on the product surface, creating a dry surface for the batter to hold on to. It consists of starch, flour and proteins. Egg white powder coagulates during cooking and strengthens adhesion of the coating to the product. Insufficient predust is the most common cause of the coating separating from the product after frying (shelling).
Batter: viscosity and crispness
Batter viscosity determines coating thickness and pick-up. Potato starch and rice starch give a crisp, light crust; modified starches strengthen adhesion and film formation and can reduce oil uptake. In tempura-type batters, leavening gives a porous, crunchy structure. Keeping batter temperature low keeps viscosity constant.
Outer coating
Breadcrumbs, cornflakes or special breading mixes form the outer layer. Particle size determines appearance and crunch: coarse particles give a more pronounced crunch, fine particles a smoother surface. The colour of the coating depends on its sugar and protein content and on frying conditions.
Contribution of fibre and protein
Wheat fibre and cellulose fibre in the batter and outer coating can help reduce oil uptake and keep crispness for longer. In egg-free (vegan) coating systems, pea protein can be considered in place of egg protein for adhesion and film formation.
Spices and flavour
Garlic powder, onion powder, black pepper, red chili powder and thyme added to the coating define the product's flavour character. Spice particle size should match the coating mix, and the level of components prone to burning at frying temperature should be set carefully.
Common problems
Coating separation usually results from insufficient predust or excess surface moisture; softening of the coating from moisture migrating out of the product; and excessive oil uptake from low oil temperature or a porous coating structure. For frozen products, crispness after reheating in an oven or air fryer should be tested separately.
Sourcing notes
PERDIST supplies potato starch, rice starch, modified corn and wheat starch, egg white powder, wheat and cellulose fibre, pea protein and spices to coated product manufacturers.
Frequently asked questions
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