Coating concerns - key considerations in selecting and operating food coating applicators

Prepared Foods, Oct, 1996 by Steve Berne

Obtaining the proper coating system for chip, nut, cracker or extruded snack applications to ensure consistent quality requires knowledge of many product and process parameters. Type of coating, product shape and fragility, desired quantity of coating and other factors all play a part in the end-product quality.

Optimum equipment design depends on these parameters. Drum versus belt-type systems, type of infeed, shape and configuration of drum flights or flavor dispenser all make a difference. Generally speaking, applying liquid coatings such as sugar to cereal, or oil/color slurries to snacks requires a rotating tumble drum system. Exact design of the drum system depends heavily on product and coating interactions.

For fragile products, suppliers offer conical infeeds that gently introduce product into the drum. This lessens product impact and reduces product fines. Flights on the inside of the drum can be of many shapes and configurations to precisely control tumbling action. The height, spacing and contour of flights (straight vs. helical, etc.) determine the amount of product tumbling and agitation.

The higher the flights or greater the number of flights, the greater the agitation. This suits high surface area products such as nuts, popcorn or baked/extruded snacks. The helical pattern reduces drum length necessary to achieve maximum agitation and coating. Additionally, most drums are adjustable to different angles for optimizing tumbling action and product retention time. Dry coatings can also be applied with drum-type systems depending on product and coating.

Vibratory conveyors for product handling are another method of coating application. These systems facilitate single-side coating of products such as salted chips, crackers or pretzels. They generally offer quicker changeover times than drum systems due to easier accessibility.

Seasoning applicators for both drum and conveyor type systems use auger screws, belts, pneumatics or vibratory dispensing systems. Again, determining the optimum type and design depends on the applied coating and the end product.

One of the newer technologies in seasoning application involves an electrostatic spraying system. The Enhancer[R] from Spray Dynamics creates a differential charge between the applied coating and snack. The negatively charged coating magnetically seeks out every available space on the snack's surface for uniform coating and surface bonding.

AVOIDING PITFALLS

There are several perils that processors should be aware of when using coating systems. "Moisture in the seasoning is devastating to the applicator as well as to the finished product," says Bob Anderson Jr., operations manager at C.J. Vitner's Freeport, Ill., facility. "If ambient humidity gets too high, spices tend to clump, and uniformity in application suffers. Hygroscopic coatings such as cheese or other fine powders can really cause problems if they agglomerate."

Vitner's produces tortilla, corn and potato chips as well as plain and flavored popcorn. It uses Roll Salters from Heat and Control mounted over vibratory conveyors for coating application. Positioning the coating system is another critical area for the company. "To obtain the best adhesion, products should be as warm as possible, yet cool enough so not to suffer from fragility problems," notes Anderson. "For tortilla chips, which are a relatively sturdy product, we position the coating system directly after the fryer."

The other factor to bear in mind is the length of the finished product conveyor after coating. "Conveyors need to be of sufficient length to cool the product to a safe packaging temperature, but if they are too long, product breakage and spice fall-off can occur," adds Anderson. For minimizing product fines and free coating particles, many manufacturers also place screens before and after the coating system.