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Seasonings and coatings have different purposes and methods for various products. The equipment and processes are unique and interesting to understand.
Dry Flavors and Seasonings
Dry flavors and seasonings such as salt, powdered cheese, and dry onion or garlic may not adhere well to some snacks, while other snacks, with a residual layer of frying fat, may pick up and retain plenty of applied powder. Shiny snack pieces such as pretzels are especially challenging because the sodium carbonate or bicarbonate bath in which they are dipped before baking seals the surface and creates the characteristic surface finish. For these and other baked pieces, it is customary to spray a light coat of oil first and then apply the powder.
There are many ways to apply oil and powders, but one common method is to use a rotating metal drum with internal lifters. One supplier is Spray Dynamics Ltd., St. Clare, Mo. (www.spraydynamics.com). Doug Hanify, Director of Technology (phone 636-629-7366), operates a small test laboratory where samples provided by a potential customer can be run through a small drum to establish operating parameters. Drums come in diameters of 28–60 in and lengths of 3–18 ft. Typically, the drums rotate at about 10 rpm and are filled so that there is a bed from about 6 o’clock to 9 o’clock as one looks into the end of the drum. Pieces are introduced at one end and exit from the other. Flow is controlled by the rate of feed, the rotation speed, and the elevation of the feed end of the drum.
It can be a challenge to measure the residence time of pieces, but one way is to spray paint some pieces, drop them into the feed, and retrieve them from the exit, measuring the time when they appear. Depending on the piece shape, weight, and flow through the drum, there is some back mixing, so there is a residence time distribution. Typically, the target is about 30 sec average when just applying oil or other liquid and 60 sec when applying both oil and solids, says Hanify.
Oil is applied through a spray bar with up to six piston nozzles whose stroke and frequency of pulsing can be adjusted. Oil or other liquid flow is tested by capturing in a cup for a short length of time. A calibration curve can be prepared for a given system and given liquid. Sometimes the oil is heated, while other times it is not. It is usually desired that the oil be relatively viscous so that it adheres to the piece. Typical oil applications are 2–20% by weight; the higher values are used for crackers.
Dry seasoning is applied with a screw feeder inserted at the exit end of the drum. It is adjusted by varying the screw speed and by blocking some of the holes in the feeder tube. Seasoning is caught on a tray for a short time period and weighed. Target dry application is 5–12% by weight. Seasonings vary widely in bulk density, so feeder tube diameter and even drive motor power must be adapted to the material. Straight salt is much more dense than dry cheese. Cheese and other seasonings may be cohesive, meaning they stick together well, which can inhibit flow from the feed hopper. It is not unusual for seasoning feed to be interrupted and some product to escape unseasoned.
It is one thing to set the flows in the anticipated ratios; it may be quite another to confirm that the desired final composition is achieved. Some pieces are so uniform that the difference in weight between uncoated and coated pieces can be measured by weighing the same number of pieces from the feed and exit streams. For other, more variable, pieces, it may be necessary to measure a tracer like salt or oil by chemical analysis.
An alternative to oil to achieve adherence is an aqueous starch solution which acts like a glue for the dry seasoning. However, this approach then requires removing the water using heated air. This could be done in a separate dryer or in a special drum with perforated walls and a plenum or second shell so that hot air can be passed through the bed. The equipment to dry the pieces adds an extra cost and additional handling if using a separate dryer would increase breakage.
There are other ways to apply oil and dry seasoning, including simply spraying the products on a flat belt as they exit an oven and sprinkling salt or seasoning from a feeder over a belt, but these only treat one side of the product. However, that is adequate in some cases.
Some products, such as ice cream bars, are coated by dipping in liquid chocolate, while others are run through a falling stream on a wire mesh belt in a process called enrobing. The focus here is on some other novel approaches.
A very wide range of products is made by coating centers with sugar or chocolate in a process called panning. Centers may include nuts, fruits such as raisins or cranberries, soft gels as in jelly beans, hard candy, chocolate lentil-shaped pellets, and, in the case of pharmaceuticals, tablets of drugs. The common feature is that the centers acquire a coating from successive applications of syrups or melted chocolate which are transformed into a solid shell by various means. The pieces polish and shape each other by tumbling together in a rotating vessel. There is a great deal of art in the specific operations, which are often done in batches and still involve manual labor and close attention.
The conversion of a liquid to a solid shell is a phase transformation that may be assisted by temperature and humidity control. In the case of chocolate, the transition is from a melt to a crystallized solid fat using cold air. In the case of shells over soft centers, a sugar syrup that also contains color and flavor is dried with dehumidified air and the addition of dry solid sugar. In the case of a sugar shell over harder centers, a sugar syrup is dried using warm air. Normally, the centers are loaded by hand, syrups and solid sugar are spread by hand, and finished pieces are unloaded by hand. One person can tend about four pans at a time in many cases.
Reducing the labor involved while achieving greater consistency is one objective of automated pans, according to John Holland, Co-president of Sollich North America, Tampa, Fla. (www.sollichna.com, phone 813-345-4710 x101). Sollich is the representative for Dumoulin equipment, including automated panning systems that load, coat, and unload pieces using conveyors and a programmed controller. Holland says that sugar coating is often about 30% of the piece final weight, while chocolate is often 50%. Batch times for chocolate are 2–3 hr. The Dumoulin equipment permits coating and polishing in the same unit, while batch systems require transfer to another pan.
Holland says that the big advantage of the Dumoulin machine is its use of a very shallow bed depth, which protects soft centers, reduces batch times, and enhances uniform coating. The equipment is more extensive than a comparable set of conventional pans and is suited to relatively large batches of 500–3,000 kg, compared to about 200 kg in a typical single pan. Holland says that automation can also be flexible, in contrast to intuition which might suggest it to be best to run the same product a long time. The Dumoulin machine has a volume of about 1,300 L, and the capacity obviously depends on the bulk density of the product.
The vessel is a perforated horizontal cylinder with a shroud or plenum around it to provide air flow, in contrast to the duct or pipe pointing into the mouth of a conventional pan. Each of the many steps in whatever process is performed is programmed and sequenced, based on the specific product. The ability to reproduce the steps exactly is one advantage of automation, says Holland. An example of one extreme is the manufacture of jawbreakers, which are 100% sugar, starting with literally a grain of sugar and building layer upon layer over a period of perhaps a week.
Panning in Action
Jeff Bogusz, R&D Manager of Ferrara Pan Candy Co., Forest Park, Ill. (www.ferrarapan.com, phone 708-405-3061), displayed the versatility and challenges of conventional panning on a recent tour of the plant. Ferrara Pan has many sets of conventional pans with diameters ranging from 32 to 60 in. Speeds are 22–28 rpm. Some pans are round, while others are tulip shaped, having a slightly straight side. Once coated, panned products are transferred to polishing pans, where a small amount of carnuba wax or confectioner’s glaze is applied to protect the outer surface.
Polishing pans have ribs on the inside surface to help mixing. The flow patterns of pieces and syrup in the different sizes and shapes vary. The pans are about 30% full by volume after coating is finished. This is as full as they can be without pieces falling out. Some operators may attempt to increase the angle of the pan to increase the weight per batch, but there is an optimum angle that ensures constant movement and constant coating in the pan. Pan loads can also be limited by the product. Lower loads are used for soft centers, which could deform under their own weight.
One indication of the art involved was illustrated when Bogusz said that the various flavors of jelly bean coatings behaved sufficiently differently that a given operator tended to specialize in one or two colors.
The company has four Moguls—starch-molding machines—to make various centers and other products, such as gummy bears, which are not coated except lightly with oil to prevent sticking together.
The possibilities for creative new products seem endless: hard or soft candy centers; fruits and nuts; hard or soft sugar coatings; sugar-free coatings; chocolate centers; chocolate coatings; and sugar coatings over chocolate coatings over a choice of centers.
by J. Peter Clark,
Consultant to the Process Industries,
Oak Park, Ill.