Shining Up Appearances

Shining Up Appearances

May 2000 -- Applications

By: Lisa Kobs
Contributing Editor

  There's no denying the human affinity for shiny objects. Store shelves are filled with products guaranteed to make everything from furniture and floors to cars and shoes shine like never before - and the shiny apple always gets picked first. As food processing professionals, we can often enhance food's shine - and hopefully capitalize on this attraction for all that glistens.

Bake-shop shine

  Washes are a common method of adding shine to baked goods. Washes are low-viscosity, fat- or water-based mixtures that can be applied to products before or after baking to alter color and/or texture.

  When applied before baking, washes interact chemically with the crust, delaying dehydration and allowing increased product expansion. However, if applied prebake to batters or soft doughs, the additional moisture from washes can cause collapse in the oven. Washes are best used on breads and rolls with a slightly firm, dry surface that supports the wash and delays absorption.

  Washes also help adhere sprinkled-on granules or seeds, and fat-based washes act as moisture barriers. One potential drawback, however, is that washes might cause uneven coloring and detract from product appearance.

  Degree of shine and finished crust color are predominantly determined by the ingredients in a wash. Melted butter or other fats impart a mild gloss to a baked surface, as does a dilution of corn syrup or honey applied directly after baking (application before baking may produce excessive browning). Topping a wash with a sprinkle of large sugar granules also produces a fast shine.

  For years, egg washes have been the standard method for baked goods. Glenn Froning, Ph.D., consultant for the American Egg Board, Park Ridge, IL, explains that the portion of the egg used affects color and shine: "Egg white will give a lighter, shiny surface, whereas egg yolk will give a more deep-brown surface. Whole egg falls somewhere in between."

  Added ingredients also affect shine. "Browning occurs when milk is used for dilution, due to the interaction of proteins with reducing sugars during heating," says Froning. "When using egg white strictly for a shiny surface, the source of the egg white should have the glucose removed (e.g., stabilized dried egg white) to prevent browning."

  While raw egg has connotations of food-safety issues, an egg wash is a very safe way to create eye-appealing shine when properly used. "Because these washes are added just as the product is placed in the oven, temperatures are well in excess of those needed to destroy pathogens," says Froning.

  Egg washes should be used sparingly, to prevent sticking and burning. Viscosity-modifying ingredients such as modified tapioca starch can thicken thin liquids and help provide cling. While still a low-viscosity system, built-in body helps the wash stay put and develop shine where it's wanted.

  A cornstarch-paste glaze also contributes to shine and improves the crispness of hearth-bread crust. This type of wash has traditionally been used on rye breads and to enhance the appearance of braid- and wreath-shaped loaves. A boiled cornstarch-and-water paste can be applied either in one coat before baking, or in multiple applications during the last five to 10 minutes of the bake.

  A variety of other ingredients also impart shine to bakery products. Coating snack crackers with a solution of tapioca dextrin before baking, for example, creates a very shiny, stable, clear gloss. The film-forming polymer arabinogalactan also helps develop clear, glossy films. Protein Technologies, St. Louis, has shown that a 9% solution of hydrated isolated soy protein, with added lecithin for foam reduction, can be a good pre- or postbake egg-wash replacer.

  Ingredient manufacturers have developed a variety of premade wash products to satisfy the growing need for convenience. For example, Baker's Bright, Cincinnati, manufactures an eggless liquid shine/wash based on sodium caseinate. For optimum shine, the wash is brushed or sprayed onto goods after baking, when the product temperature is still at 200°F. It can also be applied before baking.

  Caravan Products, Totowa, NJ, also manufactures a variety of shine-producing products. Their egg-free, casein-based washes can create a non-sticky shine on a variety of baked goods. Danish, pies and sweet goods receive a coating prior to baking, but breads and rolls are washed directly out of the oven. The company's dairy-free wash can be used for a pareve-certified shine using maltodextrin and algin. The company also offers a powdered ingredient that requires a two-stage boiling process to develop a light syrup prior to use. Its high sugar content makes it best suited to sweet doughs and Danish.

  Steam, or water brushing, can also develop a shiny baked-good exterior. The first seconds of baking determine whether or not a glossy crust is formed. When product enters the oven, its surface temperature rises very rapidly and vapor condenses on the surface. This forms a starch paste that gelatinizes, forms dextrins and eventually caramelizes, yielding both color and shine. Excess surface water contributes to paste-type gelatinization, while insufficient water causes crumb-type. To ensure glossiness, paste-type gelatinization must take place before there's any chance of crumb-type occurring.

  Time, temperature and humidity all play key roles in the development of gloss via steam. Maintaining sufficient water on the crust for an adequate time requires a crust temperature below the dew point of the oven atmosphere. A minimum oven temperature of 165°F must be maintained, and practical applications typically range from 10 minutes at 171°F to 15 seconds at 210°F. As the crust temperature reaches 212°F, steam has little effect, since condensation will not occur.

  Steam delays surface dehydration. Crust remains elastic for a longer period of time, reducing the potential for ragged breaks. Steam can also allow the development of greater volume, and it modifies browning reactions, yielding a better crust color.

Sugary coatings

  Cakes, doughnuts and pastries can all benefit from the addition of lustrous topical sweet glazes. Relatively high-moisture, low-viscosity products, glazes are applied as clear- to slightly-opaque films. They contribute visual appeal with a brilliant shine, as well as improve flavor and add textural contrast.

  A glaze is a two-phase system consisting of small sugar crystals dispersed in a syrup or saturated-sugar solution. Control of this sugar-water system during shelf life is critical to a quality glaze, and is achieved through the use of supplemental ingredients. A glaze with maximum gloss and long-lasting stability requires a balance between the glaze's sweeteners, humectants, water, fats and stabilizers. Any change may reduce gloss potential or cause fading during storage.

  A variety of ingredients can be manipulated to promote maximum glaze shine. Humectants, used for texture modification, have the added benefit of producing increased gloss. Invert sugar or corn syrup used at 2% to 4% improves shine. Low levels of dextrose provide a small amount of gloss. Certain stabilizers, such as carrageenan, xanthan gum and gum arabic, and some modified food starches, also increase shine level, as does a small amount, less than 1%, of vegetable oil.

  Adding high-melting-point distilled monoglycerides also increases gloss. This requires boiling the liquid syrup, which causes the monoglycerides to gel. When the gel cools below the melting point of the monoglycerides, crystals begin to form, which provide a thin film over the icing surface. Recommended usage level for this ingredient is 0.5% or less, based on the weight of powdered sugar.

  Sugar can also be related to the finished shine level. Gritty glaze, from too large a grind of sugar or the formation of large sugar crystals during temperature extremes, creates a rough surface that alters light-reflection characteristics, resulting in a duller finish. Too much granulated sugar in the syrup hinders clarity, and thus shine.

  Other ingredients that can make a glaze appear cloudy include improper stabilizers, highly emulsified shortenings and calcium carbonate, which is added as a buffer for free fatty acids picked up during frying.

  Processing also impacts shine levels. Excess aeration during mixing reduces clarity and detracts from shine, while excessive drying may lead to cracking, chipping and an irregular surface.

Putting a shine on produce

  Surface coatings applied to fresh produce reduce moisture loss and prevent shriveling and wilting, but a secondary benefit is the luster produced. Surface coatings also reduce abrasion during handling, thus reducing decay at injury sites.

  Many surface coatings are actually emulsions with added surface-active materials for stability. Emulsified surface coatings should be microemulsions with particle size of 1,000 to 2,000 angstroms to ensure stability and clarity and help impart gloss. Emulsifiers can be added, but natural waxes also have emulsification properties thanks to their long-chain alcohols and esters. Elizabeth A. Baldwin, with the USDA/ARS Citrus and Subtropical Products Laboratory, Winter Haven, FL, explains that the alignment of wax crystals creates shine: "When you rub an apple on your shirt you align the natural wax on the surface of the apple and make it shine."

  Waxes are the most common surface coatings applied to fresh produce. Waxing replaces some of the natural wax that's removed during washing and cleaning. Natural materials include carnauba wax from the Brazilian wax palm; candelilla wax, the resinous exudate of a Latin American shrub; rice-bran wax; and beeswax. Petroleum-based waxes of paraffin and polyethylene are also used. Waxing has been shown to reduce spoilage decay and it can have a preservative effect when fungicides are added.

  Lipid crystals in wax coatings are excellent moisture and gas barriers. In emulsified surface coatings, the size of the suspended globules also has an impact. While carnauba and polyethylene wax are good moisture barriers, they're more permeable to gasses than resins and other materials. When developing a wax coating, care must be taken with regard to respiration modification. Waxing modifies the internal atmosphere of the produce, resulting in a lower O₂ content and higher CO₂ content. If the oxygen level falls too low, off-flavors may develop.

  Food-grade shellac comes from a resinous secretion of the female beetle Lassifer lacca. This secretion is bleached, precipitated and dried, which results in an off-white, amorphous granular resin. Bleached shellac, also called lac-resin, maintains gloss in high-humidity conditions, doesn't get tacky or dull, and adheres to many surfaces. Shellac is typically dissolved in a solvent before applying to foods. It is slowly soluble in ethanol, insoluble in water and slightly soluble in acetone and ether.

  Corn zein, extracted from corn gluten, is also soluble only in ethanol or other solvents, although water-dispersible types have been developed. It forms a clear, hard and nearly invisible coating - and because it's hydrophobic, it is stable in high-heat and high-humidity conditions. An added benefit is its natural resistance to bacterial, and even some insect, attacks. Corn zein is kosher and GRAS.

  Food-grade polyvinyl acetate (PVA) dissolved in alcohol-water mixtures contributes high gloss and allows higher levels of water-vapor and oxygen retention than shellac and resin coatings. It also prevents fermentation during storage. PVA coatings do not whiten on contact with water condensation, as is the case with some other coatings.

  "Synergies between ingredients for creating better shine definitely exist," says Baldwin. "For example, zein protein will make a shiny coating with certain plasticizers - low-molecular-weight ingredients added to make coating more flexible - and not with others. Some companies add proteins such as soy or gelatin to deepen shine.

  "Gloss can also be lost over time due to improper storage conditions," says Baldwin. "Shellac and carnauba coatings will lose shine if the fruit goes in and out of cold storage and 'sweats' with condensed surface water that then dries, thus dulling appearance. Shellac and zein can discolor and whiten."

  New work is being done to make surface coatings more functional than ever. Agricultural Research Service scientists have developed biocontrol coatings that help maintain quality by promoting beneficial bacterial and yeast growth on fruit. The coatings are made from reformulated shellac and sucrose ester, a compound derived by combining sugar with a fatty acid. These beneficial populations compete for nutrients more efficiently than pathogens at critical early stages in the pathogen's development, in essence starving the pathogens that would otherwise cause decay.

Coating confections

  Shiny confectionery products can be divided into three categories: chocolate, hard-panned and soft-panned products. Each type requires its own method of manufacture and shine development. The panning process coats candy by rotating it in a coating material in a revolving pan. The buffing action during the pan's rotation produces the gloss. The key is to first develop the gloss, and then maintain it over the storage life of the candy.

  "Candy coatings offer many benefits besides shine," says Beth Silverwater, president of the confectionery-consulting firm Sweet Solutions, Minneapolis. "They also provide protection from cracking and splitting, and offer protection from moisture loss or pickup. No one coating may be right for all applications. Some are permeable to oxygen, some lack strength, others are brittle and may not be able to withstand temperature and humidity conditions. They can mask or enhance their candy center. Function must be thought of first when formulating, and gloss is typically a secondary benefit."

  Gloss is first developed with a polishing process, followed by glazing. "Confectioners typically use carnauba, beeswax or candelilla wax to polish hard-panned candies," says Silverwater. "They can be applied in crystalline form, or dissolved in food-grade organic solvents such as ethanol. Mineral or vegetable oils can be added to lubricate and smooth the candies' surface."

  Powdered waxes can cause white spotting on dark- or bright-colored confections if individual particles embed themselves in the crevices of the candy surface, notes Silverwater. When used alone, carnauba wax can create a gray haze on surfaces, but a blend of beeswax and carnauba wax will minimize this problem.

  Dissolving wax in organic solvents also helps alleviate spotting by preventing the particles from settling in the low spots. Care must be taken, however, to avoid applying alcohol-based dispersions to wet candy, because the surfaces will cloud. Shellac in dispersion applied to a wet surface roughens surfaces and diminishes shine. Solvent-based polishers are faster, but the evaporating solvent must be exhausted into the atmosphere. "Some manufactures have attempted to create aqueous-based polish and glaze combination products," says Silverwater, "although these require special application equipment and may also solubilize water-soluble colors in the underlying sugar-coating layers."

  A variety of prepared finishing products give heightened gloss to confections. For example, Colorcon, West Point, PA, offers a line of sealants, glazes, barriers and polishes that are custom formulated in either wax or shellac base, for use with batch and continuous operations. Specialized, premixed dispersions of confectioner's shellac that promote deep shine with only one or two applications are also available. The company's product line also contains formulas with plasticizers, yielding a more flexible film that accommodates temperature variations during processing, and a dispersion formula of waxes and shellac used to seal and polish confectionery items with one application. Yet another product, an oil- and wax-based polish, can polish soft-panned confections in one step.

  Manufacturers glaze candy to prolong its freshness and appearance, prevent color bleeding, and heighten gloss. Glazing also helps dissolve any white spots, and the moisture-barrier glaze minimizes gloss loss, as well as maintains proper sugar shell crunch and texture. Glazes are typically shellac or zein lacquers dissolved in alcohol; they may also contain plasticizing agents such as oils or waxes to increase flexibility and reduce tackiness.

  For chocolate-panned products, chocolate is applied in several layers using varying amounts of air. Coated centers should be stored overnight to allow the fats to solidify and achieve a stable beta-prime crystal form before polishing. Incorrect crystal formation leads to fat bloom, which appears as white or gray flecks. Also, if polished when soft, the coating will absorb the glazing materials, which is inefficient and expensive. It's imperative to seal nutmeats, dried fruit, chocolate and high-acid centers prior to pancoating. Otherwise, oil and acids may migrate to the surface and cause white spotting, color mottling and clouding.

  Polishing is carried out in ribbed polishing pans with a polishing material that is typically an aqueous solution of gum arabic, modified starch, maltodextrin, xanthan gum, waxes, oils, corn syrup and sucrose. Several coatings of the polishing agent are applied, and air-dried between applications.

  "If the polish is not completely dried between applications or before the glazing step," notes Silverwater, "premature dulling will occur as the moisture from the polish layers migrates and penetrates the surface over time." Also, if air temperature is too high, frictional heat caused by tumbling in the pan can cause the surface to soften. Once softened, fat can penetrate the surface and cause dulling and a patchy surface.

  After several applications of polishing solution have developed a sufficient gloss, the candy pieces are glazed either with zein or shellac. Glazing delays chocolate melting under high-temperature storage conditions.

  Hard-panned products, such as jaw breakers and sugar-coated almonds, start with a center that is panned in sugar/corn syrup blends. "Layers are panned on, then dried successively until enough layers are applied to reach the proper size," says Silverwater. "Once the last coating has been applied, the product is polished and then glazed. Hard-panned candy must be completely dry prior to polishing in order to achieve optimal shine."

  Soft-panned candies, such as jelly beans, do not require air and heat during panning. They use an adhesive solution that is applied to the centers, which are then coated with sugar. Repeating the process bulks up the layers; flavor and coating can also be added at this point. After coating, the jellies are conditioned in an air-conditioned room at approximately 50% relative humidity for about two days. "This allows the sugar-jacket coating to harden so that it can withstand the polishing process," says Silverwater.

  The candies are then coated with powdered sugar to prevent sticking during storage. "Prior to polishing, however, the candy must be finished," notes Silverwater. "This is achieved with a sucrose solution that is continually applied until all of the powdered sugar is dissolved and the surface is smooth. The last syrup applications should not be dried completely, as the small amount of residual moisture will improve the gloss, she says.

Snack shine

  A variety of snack foods such as dried fruits, nuts and baked particulates benefit from a glossy surface. "Dextrins are often used as surface coatings for snacks," says Michael Augustine, manager of food and ingredient applications, A.E. Staley Manufacturing Company, Decatur, IL. "Dextrins and maltodextrins may be used with other sugars or sweeteners to create a sweet, relatively stable glass. Shine results because they are clear and totally soluble, allowing light to penetrate the coating and also reflect off of the surface. Any crystallization or unsolubilized particles would create opacity, and not give the same appearance.

Source: "Egg Science and Technology" short course, American Egg Board, Park Ridge, IL

  "Honey and high-fructose corn syrup (HFCS) also work well to create shine," continues Augustine. "Sucrose is not as effective because it will readily crystallize and create a hazy appearance, but if the sucrose crystallization can be controlled, then it can work more effectively. The fructose in both honey and HFCS will prevent sucrose crystallization and give the desired glassy appearance. The problem, of course, is that these materials are very hygroscopic and may cause handling problems. In these types of systems, a larger starch hydrolysate product can be blended in to increase the stability of the glass."

  Grain Processing Corporation, Muscatine, IA, also provides a variety of ingredients for adding gloss to fruits, nuts and snack foods. Their modified food starches can be used for organoleptic enhancement, with the added benefits of seasoning adhesion, reduced breakage and oxygen- and moisture-barrier properties. The starch quickly dries to a clear, glossy, water-soluble coating that resists cracking and peeling. Increased sheen and faster drying times, without extra sweetness, can be achieved by adding maltodextrins to increase solids. The company also offers a coating that can be prepared with room-temperature water, without any cook-up, simplifying processing and improving performance of temperature-sensitive ingredients.

  Hydrocolloid films can also help form a deep, shiny coating. Gelatin, gellan, agar, agarose, gum arabic, xanthan gum and alginate films, at varying degrees of concentration, have all been shown to produce excellent high-gloss films. Zein and shellac are also used as a coating agent for some dried fruits and nuts.

  A topical lipid application is an easy way to make snacks shine. "Raisins and other dried fruits are commonly coated with a light coat of liquid oil to prevent desiccation and sticking, but also for a glossy appearance," says Willie Loh, national marketing manager, refined oils, Cargill, Minneapolis. "Roasted nuts are sprayed with oil for a similar effect," he continues, explaining that because fat crystals block light reflectance, oils must be used for this purpose.

  Spray oils, high-stability oils that remain liquid at room temperature, are typically used for topical applications, says Loh. "In addition to liquidity, spray oils must have very high oxidative stability. High-oleic vegetable oils, such as canola and sunflower, are good choices. These oils are inherently more stable and require no hydrogenation," he says. "Standard commodity oils, such as canola and soybean, are unsuitable for coating because they lack sufficient oxidative stability." These oils contain high levels of polyunsaturates, which oxidize rapidly, increasing oil color as well as imparting rancid flavors to the product.

  If a lipid coating is unacceptable due to the oily residue it tends to leave on the fingers, light coatings of propylene glycol, glycerin and sorbitol can also contribute shine.

  Whatever the requirements, numerous tools are available to promote shine and attract attention. With these methods and ingredients, it's always time for food products to shine.

  Lisa Kobs, M.S., is a Minneapolis-based food scientist and technical writer who focuses on new product development.

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