Pursuing the Perfect Melt

November 2003

Pursuing the Perfect Melt

By Sharon GerdesContributing Editor

Stretchy and stringy, soft and flowing, or firm and barely moving, the application dictates the required characteristics a cheese ingredient needs. While most cheeses show intrinsic melt properties, a little scientific push in the right direction can help achieve the perfect melt. And while a natural cheese’s melt properties are somewhat predetermined by the type, a process cheese, with modification, can have a wide range of melt profiles.

Cheesemakers can modify the melt properties of natural and processed cheese. Manufacturers of processed cheeses can select from a variety of ingredients, and adjust their levels to create a wide range of melt characteristics. And university researchers have developed numerous methods to help measure the melt, flow, stretch and even chew characteristics of cheese.

More cheese, pleaseCheese is one of the United States’ favorite comfort foods. The 2002 edition of the International Dairy Foods Association’s Cheese Facts notes that, per capita, Americans eat approximately 5 lbs. of natural cheese and 8 lbs. of process cheese annually. Data from Chicago-based Information Resources Inc. indicate that dollar sales for natural cheese rose 6.1% during the 52-week period ending April 20, 2003.

Natural cheeses are made directly from milk. According to legend, the first cheese was created accidentally by a traveler who carried milk in a pouch made from the dried stomach of a sheep. The hot sun and enzymes in the lining of the stomach turned the milk into curds of cheese and liquid whey.

Cheesemaking has evolved to include a wide variety of natural cheeses, including Cheddar, mozzarella and Swiss, and Hispanic types. The finished natural cheese is a product of ripening agents — added strains of bacteria, mold and yeasts. It is a living system, and its functional and physical properties change over time. Some natural cheeses are consumed shortly after production, while others are aged. This aging process affects flavor, texture and melt properties as enzymes in the cheese continue to work, making the cheese drier and more suitable for certain applications. For instance, fresh mozzarella can be aged slightly to provide superior melt characteristics in fried-cheese appetizers.

Blending natural cheeses with other ingredients produces another group, process cheeses. According to “A Century of Kraft® Cheese Ingredients for Success,” 2003, by Kraft Food Ingredients Corporation, Memphis, TN, their story began 100 years ago in Chicago, where James L. Kraft began selling cheese from a rented wagon. Around 1912, he started experimenting with the pasteurizing and blending of cheese. Through his labors, Kraft produced a new product known as pasteurized process cheese, or simply, process cheese. In contrast to natural cheeses that change in flavor and texture with age, process cheeses are more consistent over time.

Sizing up the jobThe food and foodservice industries are increasingly using both natural and process cheeses in applications where melt properties are important, such as main dishes, side dishes and fried-cheese appetizers. Many of these cheese ingredients are baked, fried, microwaved or even retorted at various stages before consumption. All these have particular requirements for melt properties.

“Process cheese can be formulated to the desired melt properties by varying the emulsifiers, pH and process conditions,” notes Kristi Jankowski, group director for Sargento Cheese, Plymouth, WI. “Food manufacturers can also select the appropriate natural cheese for their application by understanding how the type of cheese and age of cheese affect melt properties.”

For example, “Mozzarella cheese is available with varying degrees of meltdown and flow, and also with various appearances upon melting,” notes Bob Boynton, senior vice president, marketing and sales, Leprino Foods Company, Denver. In some applications, the customer might want the mozzarella to melt but not flow out too much, so that upon eating, the consumer sees a distinguishable piece of cheese (especially in an enrobed application). In some pizza applications, the customer might want a very light cheese appearance (small blisters with light coverage, or no blisters at all), or, alternatively, a pizza with heavy, dark blister coverage.

Cheese flavors from south of the border are nudging into market position. According to the USDA’s National Agricultural Statistical Service, Hispanic-cheese production rose 52% from 1996 to 2001. Queso fresco, or “fresh cheese,” applies to many different sweet and savory foods, plus frozen dishes. The cheese softens but does not melt. “Our customers are seeking very authentic profiles, in addition to functionality, such as melt restriction,” notes Steve Williams, associate director of R&D, Flavors and Cheese, Kraft. For example, customers might demand a strong jalapeño-Cheddar profile with an authentic Mexican flavor.

In a microwavable sandwich, the cheese should flow, not blow, out of the crust. An ideal fried appetizer might have a soft texture, but still be easily consumed as finger food. In a hot dog, the customer might expect to see distinct pieces of soft melted cheese. Each application requires careful selection of cheese with the right melt properties.

Williams explains that the best way for a product-development team to select the proper cheese for a given application is to have extensive dialogue with its supplier. The real key to cheese selection is how a specific cheese ingredient performs in the intended application, and many food manufacturers will have their own internal cheese tests and specifications.

Factors such as moisture and fat content, storage conditions, packaging and cook time all require evaluation. Generally, a supplier will send several different cheese samples and allow the product-development team to select the one that performs best in its specific application. Williams adds that Kraft has an R&D group with expertise in process-cheese development that works with food manufacturers to develop custom melt cheeses for specific applications.

To further assist product developers in choosing the right cheese for their application, Dairy Management Inc.™ (DMI), Rosemont, IL, offers an online referral service featuring 39 different cheese ingredients, and is adding several new categories, such as processed-cheese products and organic cheese. The industry group also offers a cheese lexicon to assist in selecting the ideal cheese ingredient for an application. Once the end user defines what it wants, DMI’s application staff can help the cheese manufacturer to develop it.

Any way you slice itBoth natural and process cheeses are available in multiple forms to meet almost any application need. Both types of cheese can be sliced, diced or shredded to a variety of sizes and shapes, including chips and cubes. The converting of high-melt cheeses into dices or shreds gives the customer an opportunity to deliver visual particulate that will add an upscale appeal to almost any application, notes Williams.

Another option for many applications is pumpable cheese. “Pumpable restricted-melt cheese sauce is somewhat soft and pliable at refrigerated temperatures,” Williams notes. “This ingredient, which may be pumped or deposited into the application, maintains integrity in the end product. This versatile cheese ingredient can be very efficient and is widely used in extruded pocket-type sandwiches or products where cheese is deposited on top, such as entrées.”

Kraft has developed a variety of sauces within this application category. Even though these products are designed to be melt-restricted, they contribute a rich, velvety mouthfeel with creamy cheese notes to soups and sauces. They are also cost-effective, providing an excellent method of delivering flavor and mouthfeel in an extremely competitive environment, notes Williams.

How slow does it flow?Once you choose a cheese, you must measure its meltability. There is no uniform terminology to determine cheese melt. “Each company typically has its own internal tests to define melt restriction,” notes Williams. However, he says a good starting point is a simple 2-in. melt test. This test involves placing a 2-in. cube of cheese into an oven at a specified temperature for a specified time, depending on the application. This cube is then carefully measured to quantify the melting properties of the cheese.

The Schreiber melt test has long been considered the industry standard, and is widely used by both cheese manufacturers and end users. The test involves placing a 0.5-cm- (3/16-in.-) high plug of cheese in a glass petri dish, heating it in an oven at 232°C (450°F) for 5 minutes, and then cooling it for 30 minutes. The results are read over a concentric-numbered, target-type graph.

Analyzing process-cheese melt may require more-sophisticated testing methods. “Experimental variables, such as type and level of emulsifying salt, manufacturing parameters and natural-cheese characteristics, influence the quality of process cheese,” says Lloyd Metzger, Ph.D., Department of Food Science and Nutrition, University of Minnesota, Twin Cities, Minneapolis. However, the Rapid Visco Analyser (RVA) from Newport Scientific, Warriewood, Australia, a device that measures the viscous properties of cooked foods, can provide an ideal way to accurately analyze process-cheese melt.

Metzger and his research team developed a method to measure the melted viscosity of process cheese, as well as the changes in viscosity during heating and cooling. “Using the RVA to produce a 30-gram batch allowed us to systematically investigate the experimental variables rapidly and inexpensively,” he notes. The researcher believes the size of the RVA will allow dairy-product manufacturers to assess experimental variables in product development and full-scale manufacture.

Various suppliers may have slightly different descriptions, but in general, the industry uses the following terms to describe cheese melt characterisitics, notes Michael Ritchie, director of key accounts at Thiel Cheese & Ingredients in Hilbert, WI. A score of 0.0 to 0.5 on the Schreiber scale is considered “no-melt.” Cheeses with a score of 0.5 to 3.5 are “restricted-melt” or “high-melt.” Applications include chicken cordon bleu and convenience-store sandwiches. “Restricted-melt cheeses are showing good growth in the sandwich-manufacturing operations; the reason being, restricted-melt cheese doesn’t migrate with the other components such as bread, meat, etc., like standard-melt cheese does, therefore retaining its identity as a slice of cheese,” he explains.

Those with a score of 3.5 to 5.5 are “standard-melt,” or “regular-melt.” This category is used on the all-American cheeseburger and in the grilled cheese sandwich.

The final category, cheese with a score above 5.5, is described as “easy-melt.” It is ideal for macaroni and cheese, cheese dips and cheese sauces. It is also showing tremendous growth in the Mexican category for application in dips and sauces, as well as for fillers and toppings in burritos, tacos and enchiladas.

Boynton notes: “In the last few years, growth in special-melt cheese types has been both in so-called ‘reduced-melt’ for frozen-food applications — though we think ‘reduced-flow’ is a more accurate descriptor for what the customer actually wants the cheese to do — and cheese that does not blister highly, but still melts completely in an impingement oven. In the past few years, cheese that melts as desired under microwave cook conditions has been increasingly requested.” Leprino offers cheeses with a wide variety of melt properties for many applications and cook conditions; the unique properties are achieved via special manufacturing processes and conditions, as well as ingredients.

Care for a chew?These traditional measuring techniques are somewhat one-dimensional in that they only measure the distance a disc of cheese spreads (modified tube, Schreiber) or decreases in height (Arnott) upon heating, giving just one side of the cheese-melt story. “These traditional methods may be a good tool for QA purposes, as they are easier to perform,” notes Carol Chen, a researcher at the University of Wisconsin, Madison, Center for Dairy Research (WCDR). “However, their interpretation is limited as it describes melt using one value, and the melting of cheese is a dynamic process.” This makes a test like the modified squeeze flow much more useful in research and product development.

Chen and her collaborator, Kasiviswanath Muthukumarappan, assistant professor, Minnesota-South Dakota Dairy Foods Research Center, South Dakota State University (SDSU), Brookings, have been using the modified squeeze flow method, which provides a “melt profile,” to study the relationship between cheese meltability and functionality of melted cheese. Their work provides a technical basis for controlling melted-cheese surface and textural characteristics.

Cheese melts in several phases. Chen explains: “When cheese is initially placed into an oven, the cheese temperature rises quickly, but cheese shape does not change. As the cheese reaches a critical temperature called the ‘softening temperature,’ it begins to flow. At this point, the cheese not only continues to rise in temperature, it is also changing shape. The cheese will decrease in height and will fuse together into one semisolid mass. Flow rate can be measured by calculating the slope of the best-fit line in a cheese-height vs. time plot. Next, the melt profile reaches a third critical point called the ‘complete melt point.’ After this point, there are only minimal changes in cheese height, and the cheese temperature slowly approaches the temperature of the oven.”

The researchers measured the melted-cheese textural attributes, “chewiness” and “hardness,” in Cheddar, mozzarella, colby, Monterey Jack and non-pasta-filata mozzarella cheeses, using quantitative sensory analysis and trained panelists. Chewiness was defined as the time required to masticate a sample to a pending state of swallowing. Panelists used a scale from 0 to 15 to evaluate the chewiness of melted cheese, with 1 equaling chew characteristics similar to pound cake, which almost falls apart in the mouth, and 15 describing a chew that would be similar to chewing gum. The desired chewiness may vary, depending on the application, but most end users desire something in the 4 to 7 range, with a 7 similar in chewiness to a Fig Newton.

Hardness is slightly different, and relates to the force required to bite through a cheese sample with molars. Chen’s research revealed that the melt-profile curve attributes of softening temperature and flow rate correlate well to melted-cheese chewiness and hardness.

Process-cheese solutionsChen’s research project also provided insights into melting mechanisms. One theory is that as cheese gets warmer, fat becomes more liquid and leaks out, causing the cheese to melt. An alternate explanation is that, as proteins shift and unwind, the free oil is released. The research supports the latter theory, which has important implications in designing cheeses for special-melt applications. It dispels the theory that low-fat cheese inherently has worse melt characteristics than regular cheese.

Controlling melted-cheese surface and textural characteristics can be accomplished by modifying proteins. It is especially important to control the degree of proteolysis in the cheese (the degree milk proteins are broken down), the pH of the cheese (during manufacturing and final pH) and the density of the protein (ratios of protein to moisture or protein to fat).

Manufacturing process cheese requires heating at high temperatures, which separates the cheese into a fat and serum phase. Emulsifying salts must be added to shift the pH, solubilize proteins, sequester calcium ions, and produce a smooth, homogeneous mass. Various citrates, phosphates and polyphosphates help form stable emulsions. Careful selection of the appropriate blends of emulsifying salts produces a process cheese with the desired characteristics of firmness, spreadability and smoothness.

Alginates can help modify the melt characteristics of a variety of process-cheese products. Some alginate blends have been formulated to provide structure while giving a range of melting rates, from fast-melt to no-melt. “Some alginate products can also improve melted stretch of process cheeses,” notes Jennifer Heyer, technical specialist at International Specialty Products Inc. (ISP), Wayne, NJ. “Although the interactions between proteins, phosphates, alginates and calcium are very complex, selecting the right combination of alginates and phosphates for each application is critical,” she explains.

Many parameters differentiate alginate products, including weed source, molecular weight, calcium content, particle size and morphology, and algin type (sodium, potassium or propylene glycol alginates). Several properties differentiate the phosphates, such as pH shift, solubility, ion exchange and calcium binding.

The phosphates and citrates used as emulsifying salts in process-cheese systems can sufficiently control calcium-alginate interaction, so it is not necessary to add other sequestrants. Heyer adds that it is important to select emulsifying salts that provide the desired functionality, as phosphates also affect melting characteristics and can enhance the melt profile of the finished product.

Alginates can be used to modify melt in process-cheese spread loaves and slices, process pizza cheese or Mexican-style cheese with stretch, or imitation cheeses.

ISP has developed a new line of alginate/phosphate blends that, in addition to modifying melt characteristics, can improve texture, provide structure, increase firmness and reduce stickiness in process-cheese products. The company has dedicated technical resources specifically to process-cheese applications, and has built technical alliances with other specialty suppliers to the process-cheese industry to customize ingredient solutions in several application areas.

Beating the heatSliced and diced cheeses often use flow agents. A joint research project between WCDR and SDSU evaluated the effect of flow agents on cheese melt functionality. This research compared shredded mozzarella and Cheddar incorporating microcrystalline cellulose, potato starch or no flow agents. Overall, the use of a flow agent decreased meltability and free-oil release, and increased skinning (formation of a hard surface) of shredded cheese when melted. The melted texture of cheese with potato starch as a flow agent was more tender than that containing microcrystalline cellulose. Chen notes that, depending on the application, this might or might not be a desirable characteristic.

“Ingredient interactions are critical for process-cheese quality; however, less is understood about how mechanical and thermal treatments affect final processed-cheese functionality,” notes Chris Daubert, a researcher at North Carolina State University, Raleigh. His group recently studied the effects of thermal history (heating) and shear history (mixing) on process-cheese functionality. Their objective was to determine how a balance between thermal and mechanical energy might affect final cheese melt. He hopes that his research will assist major process-cheese manufacturers to predict optimal mixer times and temperatures.

Other thermal effects contribute to the design of a cheese formulation — in particular, excess browning. Even this variable, however, can be tamed. “Hexose oxidase (HOX) is an enzyme that, under the presence of oxygen, oxidizes several sugars to an acid plus hydrogen peroxide,” notes Lars Petersen, scientific director of Danisco Foods, New Century, KS. For example, lactose oxidizes to lactobionic acid. When added to shredded mozzarella cheese, HOX minimizes excessive browning caused by the presence of galactose and lactose. In essence, it reduces the Maillard reaction. HOX can treat cheese that browns too much to enalbe it fulfill pizza manufacturers’ specifications.

Processors can add HOX to the shred by blending it with an anticaking agent, or by dissolving it in water and spraying it on. A flush of modified atmosphere may not be needed, as HOX will consume oxygen in the package, reducing it to the ppm level.

The future of meltThe methods and technologies behind formulating cheese melt have enabled food product designers to inch closer to meeting consumers’ expectations. Because these expectations constantly evolve, however, the dairy industry’s work is never done, and research is ongoing. “In recent years, dairy-farmer dollars have helped to fund a number of projects relating to cheese-melt properties at various dairy research centers and affiliated universities,” notes Amy Skovsende, director, technology marketing, DMI. The cheese project work for 2003 continues with extensive investigation of manufacturing technologies and process methodologies affecting the functionality, performance and flavor characteristics of cheese.

Despite the assistance of science, for now, creating a cheese with the perfect melt is still very much an art. But by communicating the desired properties and goals with their cheese-ingredient suppliers, product developers can reap big rewards and satisfying stringy, stretchy or silky results.

Sharon Gerdes writes and consults for various food-industry clients, with emphasis in dairy products, baked goods and nutrition specialty items. Gerdes holds a bachelor’s degree in food science and nutrition from Kansas State University, Manhattan.

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