Coatings or enrobings are fat-based mixtures that are solid at ordinary room temperatures but melt in the mouth. They are typified by chocolate preparations such as milk chocolate, and are always applied after baking and usually after cooling the product to room temperature. They do not react chemically with the crust, frequently require elaborate tempering processes, and are always opaque. In many cases, they are used to completely cover the product, and then they considerably inhibit moisture exchange between the contents and the atmosphere.
Bakery products that have been enrobed include individual cakes, which may be round, rectangular, or finger-shaped (plain or with cream" fillings), doughnuts, Swiss rolls, petit fours, pretzels, and many types of cookies. Some of the advantages resulting from enrobing are

-Improve­ment of appearance,
-Enhancement of flavor,
-Improvement of shelf life by preventing moist re loss transfer,
-Shielding sticky surfaces, and
-Increasing structural strength.

The principal ingredients in a coating are sugar and fat. The proportion of fat to nonfat solids, the melting point of the fat, and the particle size of the nonfat solids are major determinants of texture. The fat must have a melting point above the highest temperature expected to be encountered by the product during storage, distribution, and display for sale. It must, however, quickly melt in the mouth when the food is consumed. Cocoa butter is an ideal fat from the eating texture standpoint, although it has its storage weaknesses, and is quite expensive.
Sucrose is, by far, the most common carbohydrate ingredient in enrobing preparations, but corn syrup solids and dextrose are sometimes used. Rarely, lactose may be made a part of the carbohydrate mixture if the goal is to greatly reduce sweetness. The sugar must be finely powdered, with all of the particles preferably below: 40 microns in their largest dimension. . Chocolate or imitation chocolate coatings as well as pastel-colored coatings of similar characteristics are used to enrobe many kinds of bakery products. They are probably most common on cookies and snack foods of the Swiss roll type. The coating may be a true chocolate (semi sweet, sweet, or milk chocolate) or it may be a compound coating resembling chocolate in appearance. True chocolate coatings have the best texture and (almost always) the best flavor, but they are relatively expensive and are often replaced by compound coatings. Chocolate coatings, when described as such on the label or otherwise implied to be pure chocolate, are covered by federal definitions - and standards of identity. These regulations specify with considerable exactitude the types and amounts of ingredients that must be used in coatings identified by any of the standard names. Both the chocolate and the cocoa used in coatings will normally be of the so-called "natural" variety, that is, will not be alkalized or dutched.
Many chocolate-colored or -flavored coatings used to enrobe bakery foods do not meet the federal requirements for chocolate. Some manufac­turers feel that the standards result in coatings that are too strong in flavor to be compatible with certain fillings. Also, the requirement for a large proportion of cocoa butter causes the coating to be too expensive for popularly priced lines. Cheaper, less highly flavored coatings are prepared by using cocoa as the flavoring ingredient and some other fat besides cocoa butter. If properly formulated and processed, these types of coatings can have very good organoleptic properties.
Compound coatings, sometimes called confectioners' coatings, are basically white, but they may be colored to resemble chocolate, or given any other color for which a suitable food dye is available. Even the best compound coatings tend to have a somewhat waxy texture. On the other hand, they seldom develop fat bloom or sugar bloom. These coatings were formerly made from the so-called hard butters based on imported lauric oils such as palm kernel and coconut, but development of methods for fractionating and modifying other fats have resulted in specialized ingredients that are more satisfactory than the natural oils.
Most of the natural fats used for compound coatings are not compatible with cocoa butter and when a mixture of, say, a coconut oil fraction was used in combination with chocolate, the coated piece almost always bloomed in a short time. The newer modified fats can be used, with certain limitations, in combination with real chocolate to make superior type coatings which have a rather wide range of melting points.
Although the lower cost of a compound coating is a powerful motive for using it, there are some other advantages that can be more important in specific situations. They can be made softer than chocolate coatings, making them easier to cut and less messy to bite in cold weather. They can also be made harder, so that they do not soften -in summer temperatures. Compound coatings are not as sensitive to tempering and setting conditions as chocolate coatings. In addition to fat and sugar, coatings will contain flavor, color, and emulsifiers. Vanillin is a very common flavor in both pastel coatings and chocolate. Colors are usually lakes or non-certified colorants. Lecithin is usually added to control viscosity. Its principal function is to offset the traces of moisture, which tend to greatly increase viscosity of the melted coating and thus make the enrobing operation very difficult. Moisture in the, finished coating should be around 0.5% and never above 1.0%.
Most commercial coatings now being offered have good shelf life provided the initial flavor is satisfactory. Contact of the material with copper lines or vessels is very undesirable, since the slightest traces of this element greatly accelerate oxidative reactions and the development of rancidity.
The amount of coating applied to a cake or cookie should be adjusted to give optimum eating quality in the finished piece. Thin coatings do not provide adequate protection against moisture transfer and are easily broken. The exact percentage needed for best results will be related to the size and shape of the enrobed part, i.e., smaller or irregular pieces take a higher percentage of coating than do larger or smoother or more uniform base cakes.
The thickness of the coating that will adhere to a given piece is related to the viscosity of the coating. This is controlled in practice by varying the percentage of fat in the coating or, occasionally, by temperature manipulations. Temperature can be adjusted only within a narrow range in the case of pure chocolate coatings, but the enrober temperature of some hard butter coatings can be adjusted more freely.
Coatings made with chocolate liquor and with mixtures of this ingre­dient and other fats require careful handling during application if fat bloom and dull surfaces are to be avoided. The tempering procedure recommended "for chocolate must be strictly followed. This requires that the composition be fully melted by bringing it to 11°F; it is then cooled with constant stirring until it develops a mushy consistency. This can be expected to occur in the range 80° to 85°F, and typically at 84°F. At this point, "seed" or crystal­lization nuclei of the preferred form of fat crystals have been formed. The coating is then brought back up to 88° to 90°F to melt unstable crystal forms. At this point, the coating should have a viscosity suitable for proper application in the enrober and subsequent cooling should result in the formation of only stable fat crystals. Continuous and automatically controlled equipment is available for tempering chocolate coatings'. Various additives have been proposed for delaying or preventing the appearance offat bloom in tempered or untempered chocolate. It is very desirable to have the temperature of the baked products in the range of 68° to 72°F when they pass through the enrober. The excess chocolate is blown off or shaken off. Coverage, or the thickness of the coating layer, is related to such factors as the baked product's temperature and the geometry of its surface, the viscosity and temperature of the coating, and the vigor and duration of the shaking and blowing process.
The enrobed pieces pass into a tunnel through which chilled air is blowing. Radiation coolers are also being used in some, plants. After the pieces emerge from the far end of the tunnel, they should be stored at 72°F for at least 48 hours. During this period, various fractions of the fat continue to solidify and the relatively low temperature prevents remelting due to release of heat of crystallization. Under unfavorable conditions, a thin layer of relatively low melting fat may migrate to the surface and cause a dull appearance or even a white "frost," the so-called fat bloom that has been mentioned previously.