Compound Coatings

Abstract

It might seem that a material that looks like chocolate, smells like chocolate, and tastes like chocolate, must indeed be chocolate. Not necessarily, if it is a compound coating. Loosely, a compound coating is any material that looks, smells and even tastes like chocolate but that, for one reason or another, does not meet the legal requirements (Standard of Identity) of chocolate and so, cannot be called chocolate. That is, a compound coating contains an ingredient (or ingredients) not specified in the Standard of Identity or a permitted ingredient not at the right proportion to fit within the Standard of Identity. For example, the fat phase may be a different fat than cocoa butter, a nonnutritive sweetener may be used in the coating or the coating may contain flavors not specified for chocolate.

1 Introduction

It might seem that a material that looks like chocolate, smells like chocolate, and tastes like chocolate, must indeed be chocolate. Not necessarily, if it is a compound coating. Loosely, a compound coating is any material that looks, smells and even tastes like chocolate but that, for one reason or another, does not meet the legal requirements (Standard of Identity) of chocolate and so, cannot be called chocolate. That is, a compound coating contains an ingredient (or ingredients) not specified in the Standard of Identity (see Section 15.1) or a permitted ingredient not at the right proportion to fit within the Standard of Identity. For example, the fat phase may be a different fat than cocoa butter, a nonnutritive sweetener may be used in the coating or the coating may contain flavors not specified for chocolate.

Historically, compound or confectioners coatings came into their own during the 1950s due to a sudden spike in cocoa prices (Urbanski 2009). When the price of cocoa increased substantially, manufacturers sought options to reduce the cost of making chocolate coatings. Replacing the cocoa butter was the primary alternative since it is the highest cost ingredient in chocolate. However, at that time, very few alternatives to cocoa butter were available from fats and oils suppliers, especially with the same desirable melting properties of cocoa butter (see Section 15.8.4). At that time, hydrogenation was the primary method for treating natural fats to modify melting profiles and only a limited number of products were available. In general, compound coatings or imitation chocolates , developed a reputation of being a cheap alternative to chocolate because the fat phase did not mimic very well the melting profile of cocoa butter. Advances in fat modification technologies over the past five to six decades have vastly improved the options available for coating manufacturers so that coating quality can now rival that of chocolate.

Many names exist for chocolate-like materials that do not meet the Standard of Identity for chocolate. Products may be called “chocolate-flavored ”, “chocolatey ” or even “fudgey ”, but they cannot be called by the standardized terms for chocolate defined in the Code of Federal Regulations . Regardless of what they are called, compound coatings play an important role in the food (and confectionery) industry . Compound coatings are typically used in the same way as chocolate. They can be molded, enrobed, and panned. They can be used for candy fillings, exterior decorations, and as inclusions in other products (e.g., cookies and bars). Because the ingredients can be tailored to meet the specifications of the application, compound coatings often give food manufacturers added flexibility or allow them to do things not allowed under the chocolate Standard of Identity. For example, pastel coatings , which come in a variety of colors and flavors, provide unique benefits in numerous food applications. Yogurt-flavored compound coatings are common for panned goods and enrobed bars . Compound coatings containing fats with high melting point can be used to provide enhanced moisture and lipid barrier properties as well as in melt-resistant applications. And, in general, compound coatings can be produced for significantly less cost than chocolate, so provide significant cost savings.

Compound coatings generally have the same desirable properties as chocolate. That is, they should have a shiny surface appearance and dry touch (at room temperature). As far as possible, compound coatings should have similar texture and melting properties as chocolate. They should be easily processed to help reduce costs. Similar melting properties and flavor release during consumption are desirable. Finally, compound coatings should have a long shelf life , at least as long as chocolate. For the compound coating manufacturer, maintaining these properties at a reduced cost can be a significant challenge.

2 Formulations and Ingredients

Unlike chocolate, compound coatings can have nearly unlimited composition, as long as the finished product retains the desirable qualities as outlined in the previous section. For the most part, compound coatings are made with nearly the same ingredients as chocolate, with several major exceptions. First, the fat phase in compound coatings can be derived, in part or in full, from any fat that meets the requirements of the application. Second, different sweeteners can be employed to meet any need; for example, sugar-free coatings can be made with maltitol in place of sugar. Third, compound coatings can come in a variety of flavors and colors, whereas chocolate can have no added color and is limited in what ingredients and flavors can be added.

2.1 Ingredients

The properties of compound coatings are governed primarily by the same parameters that govern the properties of chocolates. Specifically, it must look and taste like chocolate as well as have the same physical attributes (melting profile, snap, etc.). Thus, the coating manufacturer must carefully choose fat, sweetener, emulsifier and flavors to suit the specific applications.

2.1.1 Fat

The primary difference between most compound coatings and chocolate is the source of the fat phase. In chocolate, only cocoa butter and milk fat (at some level) can be used according the US Code of Federal Regulations . Although some countries allow up to 5% of certain vegetable fats within the standards for chocolate, no such limitation on the type of fat applies for compound coatings.

In fact, any fat can be used as long as it meets the specifications (melting profile, etc.) of the application. In reality, commercial constraints often govern which fats are viable, as for example seen with the recent move away from fats that contain trans fatty acids . Historically, confectionery fats have been categorized as either lauric or nonlauric fats , based on the primary fatty acid composition. Lauric fats are those that contain a significant portion of lauric acid (C12:0), whereas nonlauric fats typically contain longer-chain fatty acids like palmitic (C16:0), stearic (C18:0) and oleic (C18:1) in addition to some polyunsaturated fats (see Table 4.1). Palm kernel and coconut oils are the primary lauric fats used in the confectionery industry, with palm kernel oil finding the majority of application in compound coatings. Palm, shea nut, cottonseed, soybean, canola, sunflower, safflower and peanut oil are all nonlauric fats that can be used in compound coatings, although most require substantial modification to achieve the functional properties needed. Lauric and nonlauric fats have different compatibility with cocoa butter, itself a nonlauric fat, and this level of compatibility often determines their use in coatings . This compatibility is related to the interactions among the specific triacylglycerols (TAG) present in each fat (see Section 4.3.2.3).

Based on their compatibility with cocoa butter , fats used in compound coating are typically characterized as either cocoa butter equivalents, replacers or substitutes (Lipp and Anklam 1998; Timms 2003). Lipp and Anklam (1998) provide detailed composition data for cocoa butter and a variety of cocoa butter alternative fats .

2.1.1.1 Cocoa Butter Equivalent (CBE)

CBEs are chemically (TAG, etc.) and physically (melting point, etc.) equivalent to cocoa butter. Because of this, CBEs can be added at any level to cocoa butter since they are completely compatible. That is, they contain the same types of TAG: SOS , POP and POS (P-palmitic; S-stearic; O-oleic). Tropical fats , such as palm, shea, ilipé, kokum, sal and mango, fit into this category. Although these fats do not have the exact same TAG composition as cocoa butter, combinations of fractions from these sources can be made that closely mimic cocoa butter.

CBEs are often further distinguished as cocoa butter extenders (CBEx) and cocoa butter improvers (CBI) . CBEx may not be compatible at all mixture levels whereas CBI usually have more high-melting TAG to help improve characteristics of soft cocoa butters.

Traditionally, CBEs have been used in chocolates, where allowed, at relatively low levels to enhance the properties of cocoa butter. In many countries, up to 5% of certain CBEs are allowed within the standard definition of chocolate. More recently, however, compound coatings with increased levels of CBE in various mixtures with cocoa butter have become common. For example, “super” compounds are now available, where all the extra fat added, over and above the cocoa butter in the chocolate mass, is comprised of a CBE. Because the melting properties of the CBE closely mimic those of cocoa butter, super compounds closely mimic real chocolate (all cocoa butter), but with certain advantages. The CBE can be tailored to the application (e.g., melting point) and are said to provide enhanced bloom stability , faster processing (crystallization) time, and cost savings. They may also be less susceptible to softening by milk fat in milk chocolate coatings. However, because they behave essentially like cocoa butter, CBE must be tempered in the same way as cocoa butter to develop a stable polymorphic crystal form.

2.1.2 Cocoa Butter Replacers (CBR)

Fats that replace a portion of the cocoa butter in a coating formulation are considered as CBR. These are typically fats with similar fatty acid chain length (C16:0, C18:0 and C18:1) as cocoa butter, but with different arrangement of the fatty acids on the TAG. For this reason, they are typically only compatible with cocoa butter up to a certain level, about 20%. Higher levels generally lead to excessive softening and bloom problems . CBR are nonlauric fats usually made through modification of palm, soybean or cottonseed oils.

In the past, these vegetable fats have been partially hydrogenated to raise the melting point to more closely mimic the melting behavior of cocoa butter. However, since formation of elaidic acid (C18:1 trans) commonly occurs during hydrogenation, partially hydrogenated vegetables fats used for nonlauric-coatings typically contained well over 40–50% trans fatty acids; it is this problem that has seen their use decline precipitously over the past decade or two. In fact, partially hydrogenated fats no longer have GRAS (generally recognized as safe) status , so they are no longer in use.

Alternatives to hydrogenated CBR are available based on mixtures of palm oil fractions, but these CBR fats often have other issues (e.g., slow crystallization) that limit their application. They are typically used for soft applications and fillings .

2.1.3 Cocoa Butter Substitutes (CBS)

Lauric fats , when hardened appropriately, find favorable application as a substitute for cocoa butter in compound coating recipes, generally as a substitute for all of the cocoa butter in the coating formulation. Typically, palm kernel oil is the most common lauric-based coating fat, modified in such a way as to better mimic the melting properties of cocoa butter. CBS may be partially hydrogenated, fractionated and/or interesterified to create fats with the desired melting profile and final melting point. Typically, fractionated palm kernel oil is now used to avoid the term hydrogenation on the label.

Lauric fats crystallize directly into a β′ polymorphic form that is stable for extended periods (up to 1 year) under ideal conditions (although palm kernel oil will eventually transform to the more stable β polymorph ). For this reason, lauric-based coatings have the advantage of not requiring tempering prior to solidification, although proper cooling conditions must be maintained to ensure rapid crystallization. Specifically, much lower cooling temperatures are required to promote rapid crystallization of CBS coatings than those typically used for cocoa butter chocolate.

Because lauric fats contain nearly 50% lauric acid (C12:0), they are not compatible with cocoa butter, even at very low levels. Coatings made with modified PKO should contain less than about 5% cocoa butter (on a fat basis), otherwise problems during manufacture and storage can arise. The eutectic softening effect that occurs when these two fats mix causes the coating to be undesirably soft and prone to rapid bloom formation . In melt-away candies, the eutectic softening between cocoa butter and CBS is utilized to give a soft texture. Also, coatings for frozen desserts are generally made with coconut oil to provide a softening effect for the low temperature application .

2.1.4 Sweetener

In compound coatings, sugar content can be over 50% of the mass of the product. As with chocolates, the important characteristics of the particulate sweetener phase include particle size and distribution, shape, surface properties and sweetness. Typical sweeteners used in coatings include sucrose, inulin, resistant dextrins and lactose along with various sugar-free sweeteners such as maltitol, lactitol, erythritol, stevia and Monk fruit extract. Note that technically, the term sugar-free chocolate is actually a misnomer in the United States because it implies chocolate, but uses an ingredient (e.g., maltitol), a sweetener not accepted in the Standard of Identity. Correct phraseology for this product would be a sugar-free coating .

As with chocolates, the particle size of sugar is important to both rheological properties of the melted coating and sensory attributes during consumption. Generally, particles less than 10 μm or so contribute a significant thickening effect on viscosity, requiring use of higher fat levels. On the other side, if particles are too large, above about 20–25 μm or so, they may be detected in the mouth and impart a coarse mouth feel. Most often, compound coatings are used for enrobing or coating a product, where smooth eating quality is less critical than for molded chocolate. As for chocolate, compound coatings that are molded generally require smaller particle size than coatings used for enrobing .

2.1.5 Cocoa Powder

The use of chocolate liquor (with ≈50% cocoa butter) is generally limited in compound coatings by issues of fat compatibility, meaning that the primary chocolate flavor of a chocolate-type coating comes from cocoa powder. However, even cocoa powder contains cocoa butter (usually 10–12%, but may be 22–24% cocoa butter) and so, even the use of cocoa powder may be limited in a compound coating. This is particularly true in coatings made with lauric fats because of the limited compatibility with cocoa butter. A reduced fat cocoa powder (≈5%) may be used in lauric-based coatings to minimize problems of softening and bloom formation .

To combat the softening effect of the cocoa butter present in the cocoa powder, lower levels of cocoa solids nonfat are often seen in coatings compared to chocolate. This will result in a lighter color coating with less chocolate flavor. A common practice is to use a cocoa processed with alkali (Dutched) to give a darker more appealing color.

In white or pastel coatings, no cocoa powder is used at all, meaning there is very little chocolate flavoring to these products. On a positive note, this results in a product that readily accepts other colors and flavors and will not mask them .

2.1.6 Dairy Based Powders

Many compound coatings contain milk and/or whey powder. Milk coatings may contain up to 10–15% milk powder, while white coatings may contain even more (15–20%). Milk powders contribute to a dairy flavor and impart an off-white or yellowish color to the coating. However, because of issues with fat compatibility (see Section 16.4.3), nonfat milk powders are most often used, particularly in lauric-based coatings. Levels of free milk fat mixing with the fat phase of a lauric coating should be less than 3% to prevent problems of softening and bloom formation . Whey powders and lactose may also be used in some compound coatings for reducing sweetness levels and economic reasons. When used, whey powders are often demineralized to remove salts that would otherwise introduce undesirable off-flavors .

2.1.7 Nucleator

In certain applications , coating manufacturers add a small amount (≈1% to 3% on the fat phase) of a high-melting nucleator to enhance solidification rates and contraction from molds. These nucleators are often fully hardened vegetable oils (i.e., cottonseed, palm or soy oil) with a melting point greater than 60 °C (140 °F). The purpose of this nucleator is to promote solidification of the coating by increasing the speed of fat crystallization while also raising the melting point. They also reduce solidification time, for example, in a cooling tunnel, enhance contraction from the mold, and enhance appearance (glossy surface). They are particularly effective in coatings where higher levels of cocoa powder introduce more cocoa butter. Certain types of high-melting point emulsifiers may have the same effect .

2.1.8 Emulsifiers

Various emulsifiers are added to compound coatings to serve a variety of purposes. Lecithin is still the primary emulsifier used in coatings and it serves the same purpose as in chocolate, to lower viscosity. In the same way as it affects chocolate viscosity (see Section 15.5.3), lecithin acts at the sugar particle-fat interface to reduce particle agglomeration in coatings. The phosphatidyl group of lecithin sits at the hydrophilic surface of the sugar particles with the lipophilic fatty acid groups extending into the fat phase. This prevents the hydrophilic surfaces of the sugar particles from sticking together and allows them to flow more easily across each other under shear forces. The result is a decrease in viscosity on about the same order of magnitude seen in chocolate. That is, addition of 0.5% lecithin results in a viscosity decrease equivalent to adding approximately 5% extra fat (Minifie 1989).

Other emulsifiers may be added to coatings to enhance solidification, improve appearance, and inhibit bloom development during storage (Weyland and Hartel 2008). Sorbitan monostearate (SMS) and mono- and diglycerides (MAG/DAG) , specifically glycerol monostearate (GMS) , may be used as nucleators to promote solidification and contraction of some lauric-based coatings. Sorbitan tristearate (STS) is widely used in compound coatings as a bloom inhibitor. The specific application and benefits of added emulsifiers vary from coating to coating, so each coating manufacturer has its own standard practices related to emulsifier usage .

2.1.9 Flavors

Since there is no Standard of Identity for coatings, there are no restrictions on flavors that can be added. In chocolates, no flavors that mimic chocolate or milk flavors can be added, whereas in coatings, any flavor can be added to enhance the sensory properties. Types of flavors that may be added include caramel, butterscotch, vanilla, yogurt, cinnamon and fruit flavors.

As might be expected, flavors for use in compound coatings should be oil-based or powdered to prevent an increase in viscosity. Flavors are also added near the end of processing to minimize flavor degradation.

A popular compound coating flavorant is peanut butter . Unlike most other coatings where a flavor is added, peanut butter coating will often use a partially defatted peanut flour to reduce the softening tendencies found when using a full fat peanut butter. Salt is also added to enhance the peanut notes. The peanut butter used may also have additional hardening fats added to help reduce the softening effects .

2.1.10 Colors

As with flavors, there are no limits on what colors can be added to compound coatings other than those imposed by the physical system itself. Typically, coloring agents like titanium dioxide are added to white coatings for the desired visual effect. As with flavorings, the colors added should be oil based or powdered dyes to prevent an increase in viscosity. Oil-based lake dyes are most often used because of their ease of incorporation. Oil-based dyes need to be mixed well to ensure they are homogeneous since separation may occur upon storage. It should also be noted that the oil carrier for dyes can become rancid upon storage and should be evaluated periodically. While powdered dyes do not have these disadvantages, care must be taken to prevent specking in the finished coating .

2.2 Coating Formulations

The diversity of compound coating formulations matches the diversity of applications for which they are used. From molded pieces intended for direct consumption to coatings for granola or nutritional bars, the applications for compound coatings vary widely, as do the requirements for their functionality. Perhaps even more so than for chocolate, control of the physical and sensory properties of coatings are critical to their success. Choices for both ingredients and processing technology must be made carefully, with all key elements, including cost, taken into account.

Table 16.1 summarizes the range of ingredients that are most commonly found in lauric-based compound coatings . Typically, total fat content in compound coatings is 30–35%, about the same as for the fat phase in chocolate. The type of fat depends on the specific application and how much cocoa butter accompanies the use of either chocolate mass or cocoa powder. Furthermore, the fat level also depends to some extent on the type of fat used. Lauric fats tend to give slightly lower viscosity than nonlauric fats at the same usage level, meaning that slightly less lauric fat can be used to target a certain viscosity.

Table 16.1 Typical formulations (in %) for lauric-based compound coatings

Powdered sweeteners (usually sucrose) makes up the bulk of the coating (40–55%), with the fat making up most of the remainder. Dairy based powder can be used at varying levels. Typically 0–5% is found in dark coatings and 10–15% in ‘milk’ coatings. Cocoa powder usage typically ranges from 5% to 10% for ‘milk’ coating and 10–18% for dark coatings. As mentioned earlier, higher levels of cocoa have a softening effect and a greater tendency for fat bloom. White coatings have a substantial amount of dairy powders (15–20%), but no cocoa powder.

Compound coatings also contain emulsifiers, flavors and may contain colors, especially in the case of pastel coatings.

3 Manufacturing

In general, compound coatings are processed through the same steps as used in chocolate (Figure 16.1), although several important differences can be noted (Urbanski 2009). First, the ingredients are mixed together, after which the particle size is reduced through a grinding process, followed by liquification of the paste and standardization prior to use. The coating manufacturer delivers the coating in either liquid or solid form depending on the needs of the end user. Solid coatings can be found in a variety of shapes and sizes, from large blocks to wafers to drops, depending on the eventual application.

Figure 16.1

Typical processing steps for compound coatings

The first steps of coating manufacture include mixing the ingredients , except perhaps for a portion of the fat, together into a homogeneous mass and reducing particle size. Particle size reduction techniques commonly used for compound coatings include dry grinding methods for powders, roll refiners for paste mixtures, and ball mills for more liquid materials. The amount of fat added to the dry powder mixture is determined by the refining method, from no fat added in dry grinding methods to all the fat being added when ball mills are used for particle size reduction.

In dry refining , the sweetener and other dry ingredients (milk powder, etc.) are blended in the appropriate portions and mixed into a homogenous powder. This powder goes through a classifier mill as described in Section 15.4.8. The powder is fed to a rotating milling disk with hammers, wedges or pins to break the particles to smaller sizes. An air classifier removes small particles while larger ones are retained in the mill until they have been reduced to the desired size. The fine-particulate powder is collected in a cyclone or bag filter, ready for mixing with the other ingredients in the coating formulation.

Another method for grinding particulates in compound coatings is the ball mill. In this case, nearly all the fat is mixed with the powders prior to particle size reduction. The slurry of particles in liquid fat is fed into the ball mill where contacts between steel balls being agitated in the mill cause breakage of the particles. Finished product is withdrawn through a sieve, which retains larger particles within the mill for further particle size reduction. Ball mills can be operated either in batch mode or continuously.

Probably the most common method of particle size reduction in coatings is the roll refiner , the same as used in chocolate processing. For coatings, the dry powders are mixed with sufficient fat to form a thick, wet paste. The paste is fed into the gap between the feed rollers where initial particle size reduction occurs. The paste is sequentially passed through smaller and smaller gaps between the rollers until the final particle size has decreased to the desired level. As in chocolate processing, five-roll refiners are common in the coating industry. Another option available for the manufacture of compound coating is the refiner conche . See Section 15.4.8 for more details of the five-roll refiner and the refiner conche operations.

Regardless of the refining operation , the requirements for particle size reduction in coatings are the same as for chocolate. Particles must be smaller than about 20–25 μm to ensure a smooth eating characteristic, but production of too many particles smaller than 10 μm can have negative effects and require additional fat to maintain viscosity. As found with chocolate, larger particle size can be acceptable when a smooth mouth feel is not required (e.g., coated pretzels) or for economic considerations.

The product exiting the five-roll refiner is a dry paste due to the numerous small particles that have been formed. In chocolate, this refiner paste goes to a high-shear machine, the conche (see Section 15.4.9), where particle de-aggregation, liquefication, water and flavor loss occur. In coatings, only certain of these processes are important and thus, some consider conching to be unnecessary (Urbanski 2009). For one, the dry paste needs to be liquefied, or plasticized, for further use. This may be done in a conche or in large mixing tanks that provide some shearing action. The mixing also ensures de-aggregation of the small particles formed in refining. Additional fat and emulsifier are added here as well to control viscosity to meet the desired specification. Minifie (1989) also claims that cocoa flavor development is enhanced through conching of compound coatings where flavors from the cocoa powder equilibrate with the deodorized fat, whether lauric or nonlauric. Minifie (1989) also states that elevated conche temperatures of 80 °C (176 °F) are beneficial for flavor development in coatings.

Once the coating has been liquefied, it is standardized to the desired viscosity through addition of more fat and/or emulsifiers. When called for in the formulation, colors and flavors are also added in the mixer. At this point, the coating is ready for final disposition, which depends on the size of the user and the ultimate application. For large end users, liquid coating may be shipped in heated vehicles and pumped into storage tanks in the users’ facilities. More often, compound coatings are processed into wafers or drops for distribution and use. This process is similar to the belt depositing systems used for making chocolate chips, drops and wafers (see Section 15.4.11.1). After depositing, the coating pieces pass through a cooling tunnel to promote solidification. At the end of the tunnel, the solid pieces are removed from the conveyor and packaged in boxes, bags or totes.

4 Applications

Compound coatings are used in much the same way as chocolate, so the discussion on methods of forming chocolate in Section 15.4.11 applies in general to coatings as well. However, several important differences between chocolate and coating may be noted, particularly related to tempering and cooling tunnel requirements.

Tempering requirements for compound coatings depend on the fat being used. Coatings based on CBE require the same tempering as chocolate, since the fats have essentially the same TAG composition and similar polymorphism. In contrast, it is generally considered that both lauric and nonlauric fats used in coatings do not require tempering because they are not polymorphic. Having said that, both types of coatings may sometimes be pre-crystallized to either help speed processing or enhance contraction (and mold release). Lauric-based coatings in particular crystallize rapidly and give good contraction (although not quite as good as chocolate) and generally do not benefit from a tempering process unless other factors become important. For example, lauric-based coatings with higher levels of cocoa butter may benefit from tempering or seeding with hardened fat to offset the inhibition of cocoa butter on fat crystallization. Nonlauric-based coatings crystallize more slowly and contract less from the mold, such that pre-crystallization (or seeding) may often enhance operations (i.e., processing speed, contraction from the mold, etc.).

Coatings are widely used in all forms of molding. Almost any method used for chocolate can be used for compound coatings, although there are certain differences depending on the nature of the fat used in the coating. For one, contraction of a coating piece can be substantially less than for chocolate. When tempered chocolate is solidified, a high percentage of the cocoa butter crystallizes into a stable β V polymorph, giving the necessary extent of contraction, on the order of 9–10%. This contraction allows ready removal of the molded piece from the mold itself. In most cases, the molded piece simply drops out when the mold is inverted. In compound coatings, solidification is not as well controlled and this sometimes causes problems with pieces sticking to the mold. Good contraction requires that a sufficient amount of fat changes state during solidification and that a compact polymorph is formed. Some coating fats do not have the same high solid fat content as cocoa butter, meaning that less fat changes state during solidification. Other coating fats, especially lauric-based fats, crystallize directly into the β′ polymorph, which generally exhibits less contraction due to the looser molecular packing compared to the β polymorph . Either (or both) effects can lead to problems of molded coating pieces sticking to the mold and causing problems with further processing. For this reason, mold temperatures for coatings generally need to be less than used for chocolate.

Although many coatings do not exhibit problems of poor contraction, to circumvent problems in those cases when contraction is limited, a small percentage (2%) of hardened fat or high-melting emulsifiers may be added to the coating fat. These additives are typically called nucleators because they also promote more rapid crystallization, but they also enhance contraction and allow easier demolding. They work best in systems where, for one reason or another, too little fat crystallizes at once to give good contraction.

Compound coatings are also used widely for enrobing candy bars or baked items , where they may even have a decided advantage over chocolate because they do not need to be tempered. Many problems with enrobed chocolate pieces stem from maintaining a constant state of good temper in the chocolate as it forms the curtain through which centers must pass to get enrobed. Coatings generally solidify quickly and directly into the desired polymorph and are thus, relatively easy to use in enrobing operations. In an enrober, melted coatings are simply brought to a few degrees above their melting point prior to forming the curtain. The enrobed pieces then go into a cooling tunnel for solidification .

Cooling tunnel conditions , whether for molded or enrobed pieces, are different for coatings than for chocolate, and cooling conditions are particularly critical for nonhydrogenated coatings. This is again related to the different requirements for fat solidification, particularly the need for maintaining the tempered state in chocolate. If a chocolate piece is cooled too quickly, unstable polymorphs can form at the coldest points near the surface. These unstable polymorphs lead to surface dulling and bloom formation . For this reason, the entrance stages of a cooling tunnel for chocolate need to be relatively warm, say about 15–17 °C (59–62 °F) with minimal air velocity. In contrast, low entrance temperatures with vigorous air movement are used in cooling tunnels for compound coatings to help promote rapid solidification. In particular, nonhydrogenated PKO-based coatings must be cooled rapidly to promote proper crystal formation. Typical temperatures for the different zones of a cooling tunnel for compound coatings are given in Table 16.2. For both lauric and nonlauric-based compound coatings , initial cooling tunnel temperatures are significantly lower than those used for chocolate (see Section 15.4.12). Inlet temperatures between 5 and 8 °C (41 and 46 °F) are common for compound coatings, depending on fat type, as compared to 15–17 °C (59–62 °F) for chocolate. Temperatures in the center of the cooling tunnel can also be cooler for compound coatings since the issue of unstable polymorphism is not a concern. Outlet temperatures for cooling tunnels are again governed by dew point temperatures, with temperatures of 12.8–15.5 °C (55–60 °F) usually being sufficient to prevent moisture condensation as the piece exits the tunnel above the dew point and enters room air. Dwell times for compound coating pieces in a cooling tunnel vary with the nature of the coating, but are typically shorter (about half) than those for chocolates due to the quicker setting.

Table 16.2 Typical cooling tunnel temperatures for compound coatings

5 Compound Coating Characteristics

In the sense that compound coatings are intended to replace chocolate in many applications, the characteristics desired of compound coatings are generally the same as those desired in chocolate. Some exceptions include applications where coatings can be tailored to actually enhance an application. For example, a compound coating with high melting point may be used in a high-temperature environment or applied to the bottom of a fondant-filled cherry cordial to help prevent leaking.

In particular, the phase behavior and melting properties of the fats used in compound coatings are key elements to successful application. Through careful control of the fat behavior, compound coatings with specific attributes can be made to fulfill specific product needs.

5.1 Melting Profile and Fat Modification

Although compound coatings can be tailored for specific applications, in general, the melting properties of the fat in compound coating should match those of cocoa butter (see Figure 15.17) as closely as possible. Specifically, the solid fat content (SFC) at room temperature should be high to give the desired hardness and snap. It should melt quickly over a narrow range of temperatures and be completely melted at mouth temperature. As seen before in Chapter 4 (see Figure 4.15), natural fats like palm kernel and coconut oils, palm oil and butter do not meet each of these specifications, which means that some method of fat modification is required if they are to be used to replace or substitute for cocoa butter. The three methods that are used for processing confectionery fats to improve melting profiles include hydrogenation, fractionation and interesterification. In Chapter 4 (Section 4.5), these technologies were described in detail. In this section, the application of each of these modification technologies for producing fats for compound coatings will be discussed.

5.1.1 Hydrogenation

As discussed in Section 4.5.2.1, hydrogenation is the process of saturating unsaturated fatty acids by adding hydrogen to the carbon double bonds. Polyunsaturated fatty acids (i.e., linoleic, linolenic) are converted to monounsaturated fatty acids (oleic and elaidic) and eventually to the fully saturated fatty acid (stearic). Complete hydrogenation of vegetable oils results in essentially all fatty acids being fully saturated; typically, stearic and palmitic acids dominate the TAG composition , with no trans fatty acids.

Depending on the fat being hydrogenated and the hydrogenation conditions, different final products can be obtained, many of which find utility in compound coatings. In the past, nonlauric fats were partially hydrogenated under conditions that gave a substantial trans fatty acid composition to take advantage of the plastic fat properties of elaidic acid (C18:1 trans). Thus, vegetable oils (soy, cottonseed, etc.) could be partially hydrogenated to give cocoa butter replacers (CBR) for use in compound coatings. Due to concerns regarding the safety of fats containing trans fatty acids and changes in regulations, use of this type of CBR has been virtually eliminated.

Full hydrogenation of lauric fats , palm kernel oil (PKO) in particular, can be used in compound coatings to substitute for the majority of cocoa butter. Because of the limited long-chain unsaturated fatty acid composition in PKO, very little (if any) trans fatty acids are produced during complete hydrogenation (to Iodine Values less than 4). Thus, completely hydrogenated, or hardened, PKO (HPKO) products have good functional utility in compound coatings. However, the high lauric acid content in HPKO means it is not compatible with cocoa butter. They must be used as substitutes for cocoa butter (CBS), replacing the majority of cocoa butter in the finished product. Also, even though these fats do not have significant levels of trans fatty acids, the negative consumer perception of hydrogenation limits their use. Further, complete hydrogenation of PKO raises the melting point temperature above the temperature in the mouth, as seen in Figure 16.2 by the significant SFC value (10%) about 35 °C.

Figure 16.2

Solid fat content (SFC) curves for palm kernel oil (PKO), fully hydrogenated PKO (HPKO), and interesterified HPKO (HEPKO) (Data courtesy of Fuji Vegetable Oil, Inc.)

5.1.2 Fractionation

Fats with modified properties can be produced by separating specific TAGs of a natural fat based on differences in melting point or solubility in a solvent (see Section 4.5.2.2). The technologies generally used for fractionation of confectionery fats include dry fractionation and solvent fractionation.

The dry fractionation process involves cooling the molten fat under controlled conditions to crystal a high-melting portion and then separating the crystals from the liquid oil by filtration. The solid material remaining on the filter has higher melting point, with the entire melting profile having higher SFC . This is shown schematically in Figure 16.3, where higher fractionation temperatures are seen to produce stearin fractions with increasing SFC and final melting point. Fractionated palm kernel products, often called palm kernel stearins (PKS) , can be made with a range of melting points for use in compound coatings. As seen in Figure 16.4, PKS can be produced that closely mimic the melting profile of cocoa butter .

Figure 16.3

Schematic depiction of effects of increasing fractionation temperature on melting properties of a vegetable fat (lower solid line). Upper solid line represents cocoa butter

Figure 16.4

Solid fat content (SFC) of palm kernel oil (PKO), fractionated palm kernel oil/stearin (PKS ), and hydrogenated PKS (HPKS) (Data courtesy of Fuji Vegetable Oil, Inc.)

5.1.3 Interesterification

Chemical or enzymatic rearrangement/randomization (see Section 4.5.2.3) of a fat or mixtures of fats can be used to produce confectionery fats with desired melting attributes. A wide range of modified products can be produced based on the nature of the rearrangement (chemical/enzymatic) and the source fat(s). For confectionery fats, chemical interesterification is used almost exclusively. Much of the work on interesterification of confectionery fats is proprietary information, held closely by the fats and oils manufacturers .

5.1.4 Combined Methods

To most closely mimic the melting profile of cocoa butter , it is common to use more than one modification technology together. A combination of methods has been increasingly used since the virtual elimination of fats containing trans fatty acids . For example, HPKO may be softened to some extent by using interesterification, as seen in Figure 16.2. Specifically, the waxy mouthfeel of HPKO can be reduced through interesterification.

Interesterification might also be used on fractionated PKO , although the advantages are generally limited. Interesterification of PKS actually reduces the SFC over the range from 10 to 25 °C without significantly changing the final melting point.

5.2 Phase Behavior

By their nature, compound coatings generally contain mixtures of at least two natural fats – cocoa butter and CBE, CBS or CBR. Since the interactions between fats found in coatings play such an important role, it is necessary to understand the phase behavior when the two fats are mixed. Section 4.3 covers some of the more fundamental aspects of phase behavior and phase diagrams of lipid mixtures, but specific aspects of importance to compound coatings will be covered here.

Of primary importance in compound coatings are the mixtures between cocoa butter and the coating fat , whether CBE, CBR or CBS. As noted in Section 16.2.1, each of these fats has different mixing properties , or compatibility, with cocoa butter. Timms (2003) defined extent of compatibility between two fats based on three properties: (1) thermal properties such as melting point, solid fat content, and heat of melting; (2) molecular size and shape , meaning the type of fatty acids and their arrangement on the TAG; and (3) polymorphic behavior . Two fats that are similar in all three properties exhibit greater compatibility; greater differences in any or all categories indicate greater incompatibility.

By design, CBE have very similar molecular composition as cocoa butter and thus, are considered to be fully compatible with cocoa butter at all addition levels. Based on the isosolid diagram approach covered in Section 4.3.2.3.1, cocoa butter and CBE exhibit an isosolid diagram with essentially flat lines (see Figure 4.13a). The exact mixing behavior between cocoa butter and a CBE depends on the specific TAG composition of the CBE. Bigalli (1988) states that CBE containing higher ratios of SOP and SOS to SOP exhibit perfect compatibility with cocoa butter, whereas those containing higher levels of POP are softer and exhibit a slight eutectic mixing pattern with cocoa butter .

CBR , the nonlauric-based confectionery fats, contain triacylglycerols (TAG) with the same chain length as cocoa butter and are typically considered to mix sufficiently well with cocoa butter up to a level of about 15–20% on a fat basis. Bigalli (1988) presents isosolids diagrams for a trans-containing CBR made by hydrogenation and fractionation of a seed oil (soy, palm olein, cottonseed, or rapeseed; source not specified by Bigalli 1988). In this example, addition levels of about 10–15% of CBR to cocoa butter caused little overall change in SFC at almost any temperature (there was a slight decrease in SFC at 21.1 °C). Beyond this level, however, there was a steep drop in SFC at 21.1 and 26.7 °C (70 and 80 °F). This is eutectic fat mixing behavior (as seen schematically in Figure 4.13b) and this sharp drop in SFC is what causes significant softening of the fat blend. The addition of up to 20% cocoa butter to CBR causes only a relatively small (8–10%) decrease in SFC at 21.1, 26.7 and 33.3 °C (70, 80 and 90 °F) with no change in SFC seen at 10 °C (50 °F). It is this behavior that leads people to say CBR is compatible with cocoa butter at up to 20% cocoa butter addition levels. Note that the softest eutectic mixture occurred at a ratio of about 80:20 cocoa butter to CBR. For this mixture level, the eutectic softening effect could be used to advantage to make a melt-away candy center, for example .

CBS made from lauric fats are considered to be even less compatible with cocoa butter than CBR, with addition levels of only 5% cocoa butter on a fat basis to CBS considered to give excessive softening and lead to rapid bloom formation . Figure 16.5, the isosolids diagram for a mixture of a fractionated palm kernel oil and cocoa butter (from Ivory Coast), clearly shows the eutectic softening effect between these two fats. Although the primary eutectic , or the softest mixture, occurs at about a 50:50 blend, there is significant softening that takes place even with less than 10% addition of the cocoa butter to the CBS. In addition to this softening, cocoa butter addition in a CBS-based compound coating causes rapid bloom to occur. For these reasons, it is generally considered unacceptable to have more than 5–6% of cocoa butter in a compound coating on a fat phase basis. This often limits the amount of cocoa powder that can be added to a coating .

Figure 16.5

Isosolids diagram for a mixture of cocoa butter (ICCB) with a cocoa butter substitute (fractionated palm kernel oil, FPKO) (From Williams 1996)

Milk fat does not mix well in particular with lauric fats and even a few percent of milk fat in the fat phase can cause problems. Although milk fat and palm kernel oil do not exhibit a clear eutectic (Williams et al. 1997), there apparently is enough mismatch between the triacylglycerols (TAG) of each that just a few percent milk fat in PKO causes significant softening and leads to rapid bloom formation (Ransom-Painter et al. 1997). Figure 16.6 shows the isosolid diagram between anhydrous milk fat (AMF) and a lauric coating (fractionated and hydrogenated PKO ). At low levels of addition (<10%) of AMF to this lauric coating fat, there is a significant softening at low temperatures (high SFC levels) even though there is little effect on melting point (lower SFC levels). Addition of AMF to lauric-based coatings also leads to rapid bloom onset. For these reasons, milk fat is rarely found in a lauric-based compound coating. When milk powder is added, it is usually skim milk powder to avoid negative interactions between fats.

Figure 16.6

Isosolids diagram of a mixture of milk fat (SAMF) with a cocoa butter substitute (fractionated palm kernel oil, FPKO) (From Williams 1996)

5.3 Viscosity and Flow Properties

As a high particulate phase volume material, the rheological properties of compound coatings are generally quite similar to those of chocolate, and influenced in the same way by various factors (see Section 15.5.3). Numerous parameters, including moisture, fat content, particle size, number and shape, and emulsifier content and composition, can have significant effects of compound coating rheology .

It is interesting to note that even the composition of the fat can influence viscosity. It is well known that lauric-based coatings typically require less fat to reach a certain viscosity, all else being equal, than nonlauric coatings. That is, inherent properties of the fat, particularly the type and amount of polar lipid impurities present, also influence viscosity.

As with chocolates, compound coatings are made to whatever viscosity specification is needed for the application. The final standardization procedures of adding fat and emulsifier are designed to meet those specifications.

6 Shelf Life

Well made compound coatings can last to about a year under proper storage conditions, typically thought to be cool temperatures and low (≤50%) relative humidity. However, even under ideal storage conditions, compound coatings can lose quality. Plus, some question whether cool storage temperatures are always the best – there is some evidence that storage of certain types of coatings at cool temperatures actually promotes bloom.

6.1 Sugar Bloom

The same issues that apply for moisture and chocolate (see Section 15.6.1) apply for compound coatings. When moisture contacts the surface of a compound coating, the sugar from within is drawn into the moisture, leaving a mound of whitish sugar crystals when the moisture subsequently dries off. Moisture may be a problem from condensation in humid air or may occur as direct contact (drop of water onto exposed product surface).

Preventing sugar bloom in compound coatings involves eliminating any potential contact with moisture. For example, product exiting the end of a cooling tunnel should have a temperature above the dew point of the air so moisture condensation does not occur. Product that is chilled or even frozen should be well sealed to prevent ingress of moisture through the package and onto the surface. Temperature tempering by moving the product from frozen to refrigerated to ambient temperatures while still tightly packaged can greatly reduce the risk of condensation and subsequent sugar bloom.

6.2 Storage Bloom

Some people say that the mechanism for bloom in compound coatings is different from that in chocolate. This comment is usually based on the slight differences in appearance and some interesting differences in conditions that promote bloom in coatings. In particular, some argue that bloom is exacerbated in compound coating when held at 18 °C, rather than at elevated temperatures.

Smith et al. (2004) studied the nature of fat bloom in compound coatings over the temperature range from 15 to 25 °C to help understand why low temperature storage can actually promote bloom in some cases. At 15 and 20 °C, fat bloom scraped from the surface of the coatings was found to contain TAG from both cocoa butter and palm kernel stearin . At 25 °C, bloom was primarily from the palm kernel stearin, with no evidence of cocoa butter TAG. This result was explained based on the phase diagram of the two fats, where a phase separation of cocoa butter was observed if the sample was stored below a certain temperature (see Timms 2003 for more details of this concept).

Often, sorbitan tristearate is added to compound coatings specifically to prevent storage bloom formation. It has proven successful at reducing the rate of bloom formation in both lauric and nonlauric coatings (Laustsen 1991). The exact mechanism for this inhibition is unknown, although it has been hypothesized either to be related to its effect on increasing the density of the fat crystalline structure or to inhibition of the polymorphic transition (Timms 2003).

6.3 Moisture Uptake

It should be noted, that as with chocolate, coatings can pick up moisture during storage, even when held under ideal conditions (cool temperature and <50% RH). Because of the higher surface area, coatings deposited in drops, wafers and buttons will exhibit a much larger increase in viscosity upon storage when compared to coating deposited in blocks. As well, there is a much larger increase in viscosity seen with white coatings when compared to dark chocolate over storage time presumably because of the higher sugar and milk powder content .

6.4 Rancidity

Oxidative rancidity (see Section 4.2.3.1) is the result of breakdown of fats from the action of oxygen. It is influenced by the chain length of the fatty acids on the TAG as well as the degree of unsaturation . Photooxidation (see Section 4.2.3.2) may also be a concern in some cases. For example, exposure of white coatings to light can lead to oxidative rancidity, with production of off-flavors.

Lauric-based coatings when in contact with moisture and enzymes are particularly prone to hydrolytic rancidity (see Section 4.2.3.2). Here, the enzymes cleave the fatty acids from the TAG, even under the low water-content environment in coatings. The release of soapy flavors as a result of hydrolytic rancidity is more of a problem in lauric coatings than nonlaurics because the threshold detection level of lauric acid is much lower (700 ppm) than that of stearic acid (15,000 ppm) .

6.5 Off-Flavors

Just as with chocolate, the fat phase of compound coatings is susceptible to picking up various flavors and aromas from the environment. Storage of compound coatings in the vicinity of odorous things like skunks, mint, cleaning compounds and fruity candies leads to rapid transfer of those aroma compounds into the coating, especially if packaging is inadequate to protect against diffusion of these molecules. Transport containers and trailers are often a source of off-flavors and should be inspected for cleanliness and off-odors to reduce this risk. Storage in the refrigerator or freezer is especially problematic due to the abundance of other flavors that can be absorbed by the coating. Proper packaging is needed to reduce off-flavor pick up during long-term storage .