Say Cheese

  The cow later became the major source of milk for other regions. Europe, the United States and the Oceanic countries have developed into the main producers of cheese from cows' milk. Milk from almost any mammal can be fermented into cheese, but these can differ greatly in taste, texture, appearance and cost.

  Some basic principles of cheesemaking outlined in a book by Columnella, a Roman, in 100 B.C., represent the same ones used today:

• Heat the cheese milk to a warm temperature.
• Add animal or plant rennet to the milk.
• Remove free whey and press with weights.
• Place fresh cheese in a cool area and salt surfaces.
• Periodically brush and work cheese surface.
• Allow cheese to ripen.

  Don't let the simplicity fool you. A complex set of factors and reactions dictates the variety of cheese produced, as well as the functional characteristics that will result. "Variables, such as moisture, pH, salt, culture selection and manufacturing protocols work together in an interactive fashion to influence functionality," Sommer says.

  One might commonly think of a fermented food as something on the order of wine or beer, but the manufacture of natural cheese involves the controlled fermentation of milk. Natural cheese is a general classification for cheese that is made directly from milk. Fermentation is the process leading to the anaerobic breakdown of carbohydrates. Milk fermentations cause the breakdown of lactose to lactic acid through mechanisms initiated by lactococci and lactobacilli bacteria. About 10 lbs. of milk are needed to yield 1 lb. of cheese.

Buttermilk, sour cream and yogurt also result from the controlled fermentation of milk, but the finished product depends on the character and intensity of the reactions involved.

  Cheese is described as the fresh or matured product obtained by draining the whey, or serum portion of the original milk, after coagulation of casein, the primary milk protein. Casein is coagulated by acid produced through the addition of specific microorganisms and/or by coagulating enzymes. This results in curd formation.

Until 1990, calf rennet (containing the enzyme chymosin) was the preferred coagulant in the United States. Most coagulant used today is a microbial fermentation-derived chymosin. Microbial chymosin makes high-quality, high-yield cheeses and can be kosher. (Kosher calf rennet is expensive and difficult to find.) The kosher status is not as important in the cheese as it is for the whey. Many customers require a kosher whey ingredient for their food application.

  In fresh, unripened cheese, like cottage cheese or cream cheese, the curd can be used immediately. Ripened cheeses involve the addition of select strains of bacteria, mold, yeast, or a combination of these that change the cheese's flavor and texture as it ages. A cheese is ripened by placing it in a temperature-controlled room at a selected optimum relative humidity for two to 48 months. Natural cheese is a "living" system, thus its functional and physical properties change over time. Cheese ripening gives microorganisms and enzymes in the cheese curd an opportunity to hydrolyze fat, protein, lactose and other compounds. These reactions produce a softer, pliable body and a more aromatic flavor as the unpliable, insoluble protein changes to soluble nitrogenous forms and the neutral fat splits partially into free fatty acids and glycerol.

  It is important for the cheese manufacturer, as well as the food product developer, to understand how a cheese will perform in a finished product based on its age and storage conditions. Typically younger cheeses, as little as 10 days old, are used for shredding purposes because the longer you age a cheese the more costly it is as an ingredient.

  Categories often used for cheeses which describe the amount of aging are mild, medium, and aged. Typically a mild cheese is aged less than three months, a medium three to six months, and an aged cheese more than nine months. However, an aged Cheddar is not the same as a sharp Cheddar. A sharp Cheddar simply describes a higher level of acidity (or lactic acid) that has developed in the cheese. This is directly related to the original lactose content of the cheese. A sharp cheese does not have to be aged a specific length of time.

  All ages of cheese can be grated. The shreddability of a cheese is related mainly to the moisture content of the cheese. The meltability of a cheese is related to the solubility of calcium in the cheese and the level of proteolysis. A young cheese will not melt as well as an aged cheese because of the lower level of proteolysis and greater amount of protein interactions occurring. This will give the melted surface a greater amount of shred definition and less flowability.

• the ingredients used (including the kind and quality of optional ingredients, such as color);
• the composition (the maximum moisture content and the minimum percentage of fat in the cheese solids or in the total mass of the cheese);
• the requirements concerning pasteurization of the milk or an alternate minimum ripening period;
• production procedures; and
• any special requirements peculiar to a variety or class of cheese.

  Currently, standards of identity restrict adding any ingredients to the cheese milk other than condensed skim milk or nonfat dry milk. If the cost of these ingredients is favorable, they can be added to fortify or raise the protein level of the milk, and increase the yield of the cheese. Adding these ingredients also will affect the body and heat-induced browning of the cheese, due to excess lactose present in the cheese milk.

  Potential changes in the CFR, as early as June 1999, might make it acceptable to add "any milk-derived ingredient" to the cheese milk. This change in regulations will have a large impact on cheese manufacturers because it will include ingredients such as whey proteins, milk-derived flavors and casein, to name a few. These additional ingredients will present new opportunities to modify the functionality of natural cheese, as well as widen its applications.

  Like many other food products, it is to the cheesemaker's advantage to retain as much water as possible without compromising cheese quality. Milkfat content is another cheese component that the cheese manufacturer might play with depending on the consumer and economic trends driving the price of milkfat. If milkfat is inexpensive, manufacturers will want to retain as much as possible in the cheese. But if it's expensive, they'll want to retain the minimum amount and sell off the rest as butter.

  Cheeses not governed by a standard of identity have FDA standards for classes of cheese designated by consistency. Many of these cheeses are available in reduced-fat, low-fat, light and nonfat varieties. Their composition requirements follow the Nutrition Labeling and Education Act guidelines (21 CFR 130.10) for the specific fat reduction claimed. Cheeses may be classified by country of origin, general appearance (size, shape, color), flavor and aroma, microbiological characteristics, source of milk, and chemical analysis. Classification by manufacturing process and consistency are two of the most common methods. The most common cheeses used as ingredients (listed in order of volume usage) are: Cheddar, mozzarella, process cheese, and process cheese food and spreads. Further down the list in terms of volume are cream cheese, ricotta, Swiss, provolone, Muenster and Parmesan.

  Starter cultures produce lactic acid as their major contribution to a fermentation, but flavor compounds also result. The flavor develops from diacetyl, acetaldehyde, free volatile acids, carbonyls, free amino acids, amines and other related compounds. "The addition of nontraditional types of bacteria to Cheddar cheese can give some flavor differentiation between Cheddar manufacturers," says Mike Neu, market manager, cheese ingredients, Chr. Hansen, Inc., Milwaukee. Some nontraditional types include Lactobacillus helviticus (L. helviticus), nonstarter-type or adjunct cultures. "Adjunct cultures can contain L. helviticus, L.caseii, and mutant lactis-type cultures," says Neu. Genetic engineering of lactic starter cultures has been researched to improve strains and develop new characteristics in traditional strains. "Natural genetic engineering" has been practiced in the cheese industry for years, involving the careful isolation and selection of lactic acid bacteria from nature for specific properties, such as fast lactic acid production and phage resistance.

  Traditional mozzarella is produced from whole or partly skimmed milk to which starter or organic acids are added, followed by a milk coagulant like rennet extract. The curd is cut without cooking and the whey is drained. No flavoring compounds are added. The matted curd is then formed into blocks and left in open areas to drain. Exposure of the drained curd to warm temperatures permits acid ripening to pH 5.2 using starters. The curd is heated in hot water, stretched or mixed, and molded into proper forms and salted, once the critical pH and acidity is achieved.

  Low moisture part-skim (LMPS) mozzarella finds more application than traditional mozzarella on pizza because of its better slicing qualities. LMPS has a moisture content of 45% to 52%, with a fat content on a dry basis of greater than 30% and less than 45%, as compared with 52% to 60% moisture and 45% fat on a dry basis in mozzarella. It is a pasta filata cheese, meaning that the curd is mechanically heated, stretched, and molded under hot water. This heat treatment inactivates residual milk coagulant and reduces starter populations while decreasing the potential for casein hydrolysis in the cheese during refrigeration. "Streptococcus salivarius subsp. (subspecies) thermophilus and Lactobacillus delbrueckii subsp. bulgaricus are cultures typically used for mozzarella-type cheeses," says Neu.

  A functionality important for mozzarella, shreddability is largely affected by the moisture of the cheese, which, in turn, determines the hardness or softness of the cheese. The higher the moisture, the more difficult it is to shred. Mozzarella's unique attributes of melt and stretch are related to its pH and the heat treatment it receives as the curd is mixed. "Color and blister development in mozzarella is often a function of culture selection, sugar utilization, and manufacturing protocols that promote removal of sugars," Sommer says.

  The addition of milk solids also contributes to the body of the cheese as well as increases browning of the surface. "This functional change in the cheese is positive for some customers and negative for others. Some customers prefer their cheese to remain very white, while others consider this to be a defect and prefer considerable browning of the surface on their pizzas," Sommer says.

  Blistering is one attribute that is hard to quantify due to the fact that air bubbles also form within the cheese. It sometimes is difficult to differentiate between a bubble and a blister.

  Melting qualities are related to the ability of the cheese to melt to a uniform, homogenous and smooth consistency without becoming watery and releasing oil. Greater meltability is associated with a higher moisture in nonfat elements and lower cheese pH. As cheese ages, more proteolysis occurs. This also increases meltability.

  This might change in the near future. A patent-pending technology recently developed by researchers at the Wisconsin Center for Dairy Research involves the manufacture of a pizza cheese that mimics the compositional and functional characteristics of pasta-filata-style mozzarella cheese. It is these characteristics that make the new cheese a functional food ingredient. "When comparing pizza cheese to LMPS mozzarella, pizza cheese has 50% less oiling off, and a white, opaque color that does not brown during baking," says Carol Chen, cheese applications coordinator, Wisconsin Center for Dairy Research (CDR), Madison, WI.

  Development of this cheese focused on adjusting cheese composition and limiting proteolysis. The new technology uses a stirred, washed, direct-salt cheese manufacturing protocol that produces a relatively high-moisture (47%), reduced-fat (22.9%) cheese with a final pH of 5.2. "Because no mixer-molder or brine system is used, manufacturers of stirred curd cheeses, such as Cheddar, Colby, Muenster or brick can produce a cheese for pizza," says Chen.

  Retention of stretch in mozzarella is related to the inactivation of residual milk coagulant as the curd goes through the mixer. Since this new pizza-cheese-manufacturing technique does not use a mixer, the procedure must limit proteolysis so the cheese retains its stretch. "During mixing, the heat and mixing action permit the fat to coalesce and water to pool around the protein strands in LMPS mozzarella," Chen says. "The fat globules do not coalesce, and they remain smaller within the cheese matrix in the absence of mixing and heating with the pizza cheese process." The reduced fat globule size and increased number reflect more light, yielding an extremely white appearance. The pizza cheese also contains smaller pockets of water, which, when baked on a pizza, don't produce enough steam to make a blister. The lack of browning of the cheese is due to the lack of residual sugars, which relates back to the starter culture used and the modified manufacturing procedure.

  If an upscale image is important for your pizza, other cheese varieties, such as Cheddar, Parmesan, Romano and Asiago, can add new flavors and textures to the topping. Parmesan, Romano and Asiago all have very hard, granular textures and similar melting properties, but different flavor profiles. All three have the flavor components of sweetness, lipase flavors and nuttiness. On one end of the scale, Asiago tends to be the sweetest, with the least amount of nuttiness and lipase flavors, while Romano is at the other end with the least amount of sweetness, and the greatest amount of nutty and lipase flavor notes. Parmesan fits in the middle of scale. To round out the flavor combination of the other cheeses, Cheddar could be added to this grated blend for its color and mild flavor. Once the product developer is aware of these differences in organoleptic qualities, the appropriate cheese blend can be achieved.

  A controlled-melt cheese is a new category of natural cheese in the United States. Controlled-melt cheese doesn't have a standard of identity, though it is a natural cheese manufactured with typical cheesemaking ingredients. Based on a patented technology developed by researchers at California Polytechnic State University (Cal Poly), San Luis Obispo, CA, a controlled-melt cheese has been developed with an average composition of 48% to 52% moisture, 19% to 20% fat, 21% to 22% protein, and 1.5% to 2.0% salt, and a pH of 5.1 to 5.3. It is a direct-set cheese and therefore doesn't require the addition of bacterial cultures. "The process parameters allow for a high retention of the whey proteins from the milk, in combination with a calcium and protein matrix which results in a cheese that melts, but does not flow," says Dan Best, president, Best Vantage, Inc., Northbrook, IL. The company has been in negotiation with a limited number of cheese manufacturers to license the technology on Cal Poly's behalf.

  The controlled-melt cheese can be designed to be more like Cheddar or mozzarella, depending on the application. "This cheese technology is perfectly suited to food applications like mozzarella sticks where problems such as 'blow-out' or holes developing in the sticks upon deep-frying - caused by cheese flowing out through the batter - are common," Best says.

  Other potential applications might be calzone-type products or sliced toppings for hot sandwiches. Experiments also have been conducted with the dual extrusion of the cheese inside bread sticks. Typical natural cheeses will disappear into the bread matrix or leak out and leave a gap in the crumb. Controlled melt cheeses alleviate this problem. "Not only are there functional benefits to the end user," Best says, "but economic benefits as well."

  Americans know Cheddar for its pleasing, clean, walnut flavor and waxy body, which breaks down smoothly and contains a minimum number of air holes. "For Cheddar-type cheese, flavor remains the most significant attribute that customers look at," Sommer says, "followed by body, texture and shreddability issues."

  Cheddar manufacture starts with a chymosin-coagulated milk curd to initiate fermentation. Bacterial cultures are added to the milk before the coagulant. "Lactococcus lactis subsp. lactis and cremoris are most commonly used for Cheddar cheese," Neu explains. "They are referred to as homofermentative-type cultures, because they produce acid as their only byproduct." Peak acidity is almost achieved at salting after which lactic acid fermentation decreases sharply. The curd is formed by rennet and the curd is cut and cooked in the whey to 38(C. The whey is removed and the curd cubes, now absorbing more lactic acid, mat together into a cohesive mass and are cut into distinct blocks.

  Piling and repiling of the curd blocks over time is called cheddaring. Cheddaring, besides repressing gas-forming coliforms, controls curd moisture and provides the necessary time for increasing lactic acid to strip some of the bound calcium from the curd and help give it the plastic properties in the finished cheese. Cheddaring also helps provide a sufficient substrate for enzyme action in the cheese, leading to proper flavor and texture development.

  The rate at which excess lactic acid is produced in the vat critically affects the cheese quality. A very rapid rate is not desirable because the high acid dissolves too much of the insoluble calcium phosphate into the whey. Calcium phosphate serves as an important buffer for maintaining satisfactory pH after salting. If the pH drops to 4.8 after pressing, the cheese will develop an intense acid flavor and weak, pasty texture.

  Cheese moisture control is influenced by the milk composition based on its fat-to-casein ratio. An acceptable cheese milk has a fat level of 3.2% and a casein concentration of 2.2%, providing an optimum fat-to-casein ratio of 1.0:0.68. Good cheese can be made at higher fat levels, but the casein concentration must increase proportionally.

Standardizing the milk by adding nonfat dry milk or separating out some fat enables this to happen. A higher-moisture cheese also is obtained by cutting the curd with wider wire knives so the curd is cooked less; the curd blocks are turned less often during cheddaring; they are piled higher; and the rate of salt addition is reduced. The type of packaging and mode of ripening also influence the final moisture of ripened cheese. Cheddar is ripened for four to 12 months.

  Recently, there is increased interest in reducing aging time and accelerating flavor development of sharp Cheddar cheese. Adding an adjunct-type culture would achieve the desired flavor development in a shorter time.

  Another means of reducing the fat in both natural and process cheese varieties is through the use of fat mimetics. Starches are one category of ingredients that have been successfully formulated into reduced-fat and fat-free cheeses. "Physically modified cornstarch functions well in both fat-free and reduced-fat natural and process cheese products," says Jim Podolske, director dairy applications and technical service, Opta Food Ingredients, Bedford, MA. "These cheeses benefit from the water-absorbing capabilities of the starch to provide for the textural attributes, such as sliceability and meltability."

  A manufacturer attempting to make a fat-free mozzarella will have to cook and extrude at a higher temperature due to difficulty in getting a cheese to go through a mixer/molder at typical temperatures of 120(F. "Typically, these ingredients are added to the milk before pasteurization and no further changes in the normal make procedure of the cheese are required," Podolske explains. If less fat is desired in an application, these cheeses can be used as an ingredient with some added benefits like improved meltability and freeze/thaw stability. "When using, for example, an 8%-fat Cheddar in a sauce application," Podolske says, "the reduced-fat cheese containing physically modified cornstarch melts and incorporates into the sauce without the typical fat separation seen in full-fat natural cheeses."

  Flavor attributes are another concern of reduced-fat cheeses. Bitterness can occur in reduced-fat Cheddar cheeses. The fat-content reduction and the moisture increase alter the culture growth, leading to flavor defects. New commercial starters with slower acid production and controlled proteinase activity alleviate these problems. "Generally, slow acid-producing cultures with the addition of adjunct cultures are the best for reduced-fat Cheddar cheeses," Neu says. "Fast cultures replicate so fast they don't build up enough cell mass, so when cultures finally die and release their enzymes, you may not have enough enzymes to overcome some of the bitterness effects during cheese ripening."

  The food product that we recognize as pasteurized process cheese was developed in 1911 in Switzerland. It was developed to improve the keeping quality and stability of natural cheese. Process cheesemaking is very sophisticated and complex. The industry itself is characterized by patent protection and trade secrets. Process cheese is manufactured by selecting specific natural cheeses, in combination with various types and amounts of emulsifiers, heat treatments and stirring actions, to achieve the desired type of emulsion. The addition of other ingredients, such as color, salt and emulsifiers, provide further modifications to the cheese product's appearance, texture and flavor.

  "Many manufacturers need a specific form to be able to deliver the product into their process as well as a specific functionality and flavor profile," says Betty Dawson, senior research scientist, Kraft Food Ingredients, Memphis TN. Process cheese is easily tailored to fit the physical properties, plus the color and flavor intensity required for food-processing application needs.

  "The characteristics of the source cheese and emulsifier system used are strongly related to the finished functionality of process cheese," Dawson explains. Phosphate and citrate salts are typically used as emulsifiers. Emulsifiers play a multifunctional role in process cheese by:

• regulating pH for optimum body, texture and control of spoilage;
• dissolving protein for integration of fat, protein and water into a uniform, smooth mass;
• reducing the size of the paracasein molecule through peptidization, which creates the desired texture;
• binding to calcium to achieve a smooth texture and improved flowability of the product; and
• improving the emulsifying characteristics of casein through the replacement of colloidal calcium with sodium.

  An excess amount of polyphosphates will produce a texture that is too firm and doesn't slice smoothly. A sandy texture with visible white crystals can be caused by excess phosphate emulsifier, undissolved emulsifier, free tyrosine crystals, or excess lactose. Optimum pH for most process cheese ranges from 5.4 to 5.8. In process cheese requiring greater spreadability, pH 6.2 is preferred. The desired melt quality of a process cheese might vary from one application to another. "For instance, a microwavable, cheese-filled product would require a cheese with more melt restrictions, so the cheese doesn't leak out of the product," says Dawson, stating that if a sauce is being made, a cheese that melts quickly and easily is desirable. "Melt characteristics are changed through both formulation and processing parameters."

  Like natural cheese, process cheese and its related products, process cheese food, cheese spread and cold pack are regulated as to their composition. Pasteurized process cheese must contain no more than 1% additional moisture and no less than the legal limits imposed on the natural cheese from which it is made (21 CFR 133). All these process cheese products are allowed to contain added fruits, vegetables, meats or spices, in which case the moisture can be 1% higher and the fat can be 1% lower. Pasteurized process cheese food must be at least 51% cheese by weight with a moisture range of 23% to 44%. It may contain other dairy products, such as cream, milk, whey or concentrated mixtures of these. Pasteurized process cheese spread is similar to cheese food, but contains 44% to 60% moisture and at least 20% fat. Cold pack must contain the same amount of moisture as the cheese used to make it, with no added water.

  Enzyme-modified cheeses, or EMCs, are flavor ingredients that blend lipases (natural food-grade enzymes) together with natural cheese to intensify the effect of cheese flavor development. Controlled addition of EMC of known flavor intensity with a blend of natural cheese greatly advanced the technology of producing process cheese products of uniform flavor. EMC was developed and used initially in 1972. It was approved as an optional ingredient for pasteurized process cheese in 1974. Prior to the development of EMC, process cheesemakers had to carefully select and blend natural cheeses of various types and ages to maintain a uniform flavor. Often, the methods of ripening natural cheeses to develop desired flavor and body were time-consuming, costly and could result in losses when undesirable flavors developed or the cheese spoiled.

  Cheese analogs or cheese substitutes are cheese-like products made with nondairy ingredients, such as corn oil. These nondairy cheeses can offer a cost savings over traditional natural cheese, but also have less flavor and less functionality in terms of melting characteristics.

  Whether deciding what functional properties are important in your cheese application, or trying to modify your cheese to meet an end user's requirements, the technology exists (and is constantly being improved) to meet the expectations of a changing market. The next time you eat a pizza or make a box of macaroni and cheese, chances are you'll think about cheese in a different way.

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