Fine-Tuning Cheese Performance
By Kimberlee J. Burrington
Contributing Editor
Cheese technology basics
In basic terms, cheese making is a concentration process. But it is far more than just a means to remove water from milk and concentrate the casein and fat. The skilled hands of cheese-makers bring a tremendous diversity in how cheeses taste, melt, stretch, shred and slice, or whether they are hard, soft, brittle or crumbly. It is the cheese-making process, mainly acid development by the added starter culture and the activity of added or native enzymes, as well as microorganisms, that create these characteristics.
Cheese making begins by the coagulation of the casein, the main protein in milk. Most varieties of cheese use rennet to clot the milk, but some cheeses use heat and acid (ricotta) or just acid (cottage cheese). Water, or serum, and fat are trapped in the developing mesh or network of casein. After the coagulum, or curd, is formed, it is cut into small pieces and the casein network tighten and pushes the serum out to form the whey. Heating and acid development by the starter bacteria greatly facilitate this process. After cheese-makers remove the whey, they eventually salt, then press, the curds into compact forms and age the product for a specific period of time to develop specific flavor and body characteristics. Cheese making, or curd manipulation, is a relatively simple process.
However, it involves very complex and precise manipulations of the casein molecules in order for a cheese to have the desired physical or functional properties demanded by the consumer, especially those who wish to use the cheese in baking. “Whether a cheese softens, flows or even stretches when heated, or has a rough mouth-feel, is brittle, or even if it is white or translucent after baking, it is all about controlling casein chemistry (the interactions of casein molecules),” says Mark Johnson, Ph.D., senior researcher, Wisconsin Center for Dairy Research, Madison.
The degree to which casein molecules are physically separated (the fat and moisture content of cheese) or prevented from interacting (through casein chemistry) determine the desired body — the firmness and smoothness — texture, and physical properties, such as melt and stretch, of the final cheese. Casein chemistry may be manipulated by the cheese-maker through strategic control over the extent of acid development that is allowed to occur at key steps in the manufacturing process. It involves the loss of calcium from the casein and the pH of the cheese. The calcium loss from the casein increases the flow or melt of the cheese, but if the pH is allowed to drop too far the cheese will not flow when heated. Also involved is the proteolysis that occurs during the ageing process. Proteolysis, the breakdown of the casein molecules into smaller pieces called peptides, might take weeks to be sufficient to influence the melt, (e.g., it increases the melt, softens and makes the cheese less chewy and smoother). This is caused by the activity of the rennet, microorganisms and enzymes naturally present in the milk. There are many ways to modify the functionality of natural cheese through the chemistry just described. Process and product limitations are described in the standards of identity for natural cheese that can be found in Title 21 of the Code of Federal Regulations (CFR), Section 133.
Culture effects
Cultures are multifunctional ingredients in cheese. They metabolize lactose to produce energy and lactic acid, provide flavor development, contribute to cheese texture, aid milk coagulation, and provide moisture control. In general, mesophilic cultures, like Lactococci starter cultures, convert lactose to lactic acid at optimum temperatures from 86°F to 90°F. Thermophilic cultures, like Steptococcus thermophilus and Lactobacillus sp., convert lactose into lactic acid and galactose at optimum temperatures from 98.6°F to 112°F. Many thermophiles are unable to metabolize galactose, which can later create cheese defects.
Flavor development occurs by protein breakdown into peptides, amino acids, amines and ammonia. Other common flavor compounds — diacetyl, lactic acid, propionic acid and acetic acid — form during the breakdown. Texture development is a function of protein breakdown, pH and moisture. Cultures for mozzarella or provolone type cheeses consist of primarily S. thermophilis for fast acid formation. Addition of a Lactobacillus will add flavor and accelerate ripening. Lacto bacillus casei or Leuconostoc will provide buttery notes. Swiss-type cheese will use an S. thermophilus for acid production and possibly combined with a Lactococcus. Propionibacteria develop the eyes and add some flavors.
Lactobacillus helveticus provides some flavor and removes the residual sugars during pressing. Lactobacillus casei and Lactobacillus helveticus are examples of nonstarter lactic-acid bacteria (NSLABs). NSLAB are the bacteria normally present in a cheese plant and can cause the characteristic flavor fingerprint of that plant.
Manufacturers use adjunct cultures for different cheeses to produce similar characteristics. “Lactobacillus helviticus will form ethyl esters due to synthesis by lipases and esterases, which develops into a fruity flavor in Cheddar or a Parmesan cheese,” says David McCoy, Ph.D., principal scientist, Chr. Hansen, Milwaukee, WI. “Monterey Jack and feta can utilize the same acid-producing cultures, but their make procedures are different so the final cheeses are very different.” The pH at draw and the final pH of the cheese help determine some of those differences.
Adjuncts can also control bitterness in aged cheeses. Adjunct cultures can accelerate flavor development or contribute additional flavors to cheese as it ages, depending on the make procedure and adjunct type. Some cultures used as adjuncts are “attenuated” to reduce acidification while preserving flavor-development properties. Addition of selected lactose-negative or protease-negative cultures to aging cheese will increase the rate of flavor development and reduce the amount of bitter peptides.
Modified meltability
Meltability is one characteristic that has been designed into many cheese types, but the most well known is mozzarella. When a cheese like mozzarella melts, several distinct phases occur. “When cheese is first put into an oven, the cheese temperature increases, but the shape does not change,” says Carol Chen, researcher, Wisconsin Center for Dairy Research. “Once the cheese reaches a critical temperature called the softening point, it begins to flow and change shape. The cheese matrix collapses and becomes one semisolid mass. The last critical point the cheese reaches in its melt profile is the complete melt point.” After this point, height changes are minimal and cheese temperatures eventually reach the oven temperature. Cheese-melt properties are a combination of the decrease in height of the cheese and the actual cheese temperature, and are quantified as a melt-profile analysis. A melt curve has three regions of change occurring in the cheese: softening region, flow region and complete melt.
In the softening region, the cheese temperature increases, but the cheese doesn’t physically change much or flow. Softening temperature is a good indicator of melted cheese structural strength. The flow region describes the extent the cheese flows, which can predict if a cheese will melt and flow off the edge of a pizza. Cheese-flow rates relate to the ability of caseincasein interactions to relax and reform. After two to six weeks, mozzarella functionality stabilizes.
The pH of the cheese is related to meltability. “The higher the pH of the cheese, the higher the softening temperature and lower the amount of flow results,” says Chen. “Softening and flow characteristics, combined with composition and degree of proteolysis, affect the stretch, free-oil release and chewiness or hardness of melted cheese,” she says. Stretch is a characteristic of melted cheese that makes eating pizza more fun and results from casein-casein interactions that are broken and quickly reformed. A combination of a high concentration of intact casein within a narrow range of colloidal calcium phosphate provides a good stretch.
Put through the shredder
“For American cheeses, like Cheddar, firmness and fractureability are the best predictors of shreddability,” says Chen. “Firmness and adhesiveness are the best predictors for mozzarella and pizza cheese.” Shreddability typically improves as firmness increases and adhesiveness decreases. Mozzarella tends to be less firm and more adhesive than American cheeses. It is typically shredded after a minimum of one week of aging. Colder cheese temperatures at shredding means that the cheese is firmer, which helps shreddability. A colder cheese temperature does not mean the cheese is less adhesive, though. Shred appearance is also important and has characteristics that can be quantified. Shred size and shred-size distribution — measured as the percentage of long shreds — in a sample are quantifiable attributes that contribute to consumer acceptance of a pizza.
Shred appearance and melt are not necessarily related; good shreddability does not necessarily mean good meltability. “Generally, we find that consumers prefer finer (fancy) shreds on fruit and green salads and thicker shreds on heartier salads, such as pasta and potato, as well as baked dishes, such as lasagnas, pizzas or enchiladas,” says Barbara Gannon, vice president, communications, Sargento Foods Inc., Plymouth, WI. “Fine shreds are also ideal for quick-melt applications, such as microwave usage and cheese toppings that will be added after the food is heated so that the hot food will melt the cheese without additional cooking.” Furthermore, “applications for cold use, such as slices and shreds, use natural cheese and those that require a melt with stretch also tend to gravitate toward natural cheese,” she says.
Dialing-up browning
Browning is typically a desirable property for baked cheese. “The browning of cheeses like mozzarella during baking is due to the Maillard reaction, a heat-induced reaction between sugars and protein,” says Chen. The intensity of the browning depends on the lactose and galactose content of the cheese and the ability of the free-amino groups to remain hydrated during baking. However, excessive browning creates a problem for cheeses like mozzarella, pizza cheese or Parmesan.
The desire for less browning in pizza cheese is often driven by pizzerias that use impinger ovens. Impingers expose the cheese to very high temperatures (550°F) for six minutes or more, which stresses the cheese and creates a much greater degree of browning than would occur in a conventional home oven. “In the case of mozzarella or pizza cheese, browning comes from the splitting of the lactose into glucose and galactose by thermophilic cultures,” says Dean Sommer, cheese applications specialist, Wisconsin Center for Dairy Research. “The cultures will continue to metabolize the glucose, but they won’t metabolize the galactose as readily. Galactose, being a more-powerful reducing sugar, will accentuate the browning of the cheese during baking.” Typically, cheese-makers will fortify the cheesemilk with non-fat dried milk (NFDM) or condensed skim to increase the solids and overall protein in the milk to increase yield.
These ingredients used for fortification also contain a substantial amount of lactose, which in turn increases the galactose levels in the cheese and even greater browning issues. Often, cheese-makers try to use shorter make times, like three to four hours “in an effort to reduce production time and cost, but shorter make times will lead to a less-complete fermentation of lactose, so the overall concentrations of lactose in the cheese will be higher, and greater browning will still occur,” says Sommer.
Many solutions help to decrease browning in pizza cheese. Technologies to reduce lactose, such as using ultrafiltered milk for fortification instead of NFDM or condensed skim, are a good start. Ultra-filtered milk has much less lactose, but does have the proteins that the cheese-makers want. Longer make times, like five to six hours, “will allow for a more-complete fermentation of the lactose and reduce browning,” adds Sommer. Washing the curd will help remove residual galactose, which will decrease browning. Selecting a culture that provides a more complete fermentation will also help reduce browning. Any one of these modifications will reduce browning, but when used in combination, greater decreases in browning might occur.
Parmesan browning is a negative attribute for the dry Parmesan in the shaker can, as well as for Parmesan table cheese when it is baked. Block Parmesan cheese has about 36% moisture while “dry Parmesan is typically about 18% moisture and, when it is exposed to warm temperatures, over time, it gradually browns or becomes darker in color in the container,” says Sommer. Not only is the color less appealing, but sweet, and caramel flavors will also develop, which are not typical Parmesan flavors that a consumer expects.
The causes of browning in Parmesan are similar to pizza cheese. Usually, the root of the problem is incomplete fermentation of lactose. Parmesan will sometimes have uneven browning when it is shredded or grated as a topping. “The cause of the uneven browning is due to the varying levels of lactose breakdown and metabolism on the inside of cheese wheel, versus the rind or the outside of the wheel,” says Sommer. Parmesan is brined after it is formed. The brine is kept cold so, when the cheese wheel sits in the brine, the outside of the cheese gets colder faster than the inside. The cold temperatures will reduce the fermentation occurring toward the outside of the wheel. The salt, as it penetrates the cheese, causes a loss of moisture, which further inhibits the fermentation process. Brining Parmesan immediately after the wheel is formed will exaggerate this variation in browning throughout the cheese. The solutions for reducing browning in pizza cheese can also be applied to Parmesan.
Process-cheese technology
Controlling cheese functionality is the cornerstone of process-cheese technology. Process cheese represents a range of products with specific standards and allowable ingredients that are listed in 21 CFR, Sections 133.169 to 133.180 (available online at www.access.gpo.gov/nara/cfr/waisidx/21cfr133_99.html) under the main categories of pasteurized process cheese, pasteurized process cheese food and pasteurized process cheese spread. “Process cheese represented breakthrough technology in 1915 when J. L. Kraft successfully marketed his American- Cheddar process-cheese tins,” says Jim Wild, senior business manager, Kraft Food Ingredients, Memphis, TN. “Innovation continues a century later as KFIC offers food processors a line of specialty process cheeses developed to deliver flavor and functionality at an economically advantaged price point compared to standard of identity process cheeses.” Furthermore, “flexibility in formulation allows for unique product features in the specialty line ranging from melt restriction to high-impact bases,” he says. Though some of us cheese lovers prefer the taste and texture of natural cheese, there are reasons for selecting a processed cheese over a natural cheese in a food application. “In general, processing conditions and storage can have a greater impact on natural cheeses than process cheeses,” says Jill Norcross, associate principle scientist, Kraft Food Ingredients. “The flavor and body of natural cheese continues to develop with age. Processors who can’t consume natural cheese within a short timeframe will face inconsistencies in their finished products,” she adds. Formulating with natural cheese can offer some functional challenges. “Natural cheeses do not lend themselves readily to smooth, silky sauces and fillings,” she continues, “Emulsification and/or processing expertise must be applied to natural cheese to prevent oiling-off in these applications. Process cheeses contain significant amounts of natural cheese, but the resultant textural characteristics are quite different from natural cheese.”
“Process cheese is homogeneous, provides a more-uniform melt, and has improved keeping quality throughout the recommended shelf life,” she notes.
Like the chemistry of natural cheese, the chemistry of process cheese is quite complex. Fortunately for formulators, certain companies have invested a lot into the chemistry and formulation of process-cheese products. A food formulator only has to provide some knowledge of the application, process and desired cheese functionality in order to get a process-cheese ingredient that works for them. “There continue to be opportunities for developers to learn advantages of using process cheese as an ingredient,” says Wild. “Some of the key advantages include: increased functionality, multiple cheese varieties, consistent flavor and texture over an extended shelf life.”
Many factors contribute to the overall functionality of process-cheese formulations. “Key to the formulation approach is the emulsifying salt selection,” says Gannon. With various emulsifiers, the scientist can formulate a product that has a high degree of melt, or one that is melt-restrictive. “Generally, higher-melt formulations use sodium phosphate and/or sodium citrate emulsifiers, whereas melt-restricted formulations use hexa-metaphosphate or pyrophosphates. Firmness is impacted by the amount of solids, hydrocolloid selection, fat content, and other components. Flavor delivery can be modified based on dairy-component selection, cheese type and/or age and additional flavoring agents,” she adds. Standards of identity for process cheese allows for greater flexibility than natural cheese, and hence the ability to further-modify formulas to meet consumers’ needs. “High-flavored process cheeses used at low levels are more desirable in systems that sustain thermal abuse,” says Norcross. “Additionally, combinations of KFIC’s specialty process cheeses and highly flavored cheese powders create unique solutions for customers,” she adds.
“With lower-cheese formulations, such as dips, enzyme-modified cheeses (EMCs) are frequently used to boost cheese-flavor impact, and is an excellent way to boost overall cheese flavor while controlling costs,” says Gannon.
“Flavor improvements in process cheese have come from development of EMCs with stronger and more-intense flavors with a balance of proteolytic and lipolytic character. Better delivery systems like EMC powders with different release mechanisms, such as encapsulation, have also provided flavor improvements to process-cheese products. Other developments in blends of flavor compounds and enzyme-modified dairy ingredients have also made improvements,” says Nachi Adaikalavan, director of marketing, dairy flavors and process cheese industry, Chr. Hansen. Adding these flavor systems at different stages of the manufacture can also change the impact of the flavor. Before, flavors were always added in the cooker with all the other ingredients, but the high cook temperatures often destroyed much of the flavor. Now, adding flavors inline can minimize heat damage and flavor loss.
“Acceptance of process-cheese products has been most successful through educational and promotional programs that highlight value and convenience,” says Wild.
Future developments
The future of cheese looks promising. “We expect growth in the natural cheese category to be driven by continued interest in ethnic and specialty cheeses, as a reflection of consumers’ broader experiences and demographics,” says Mary Taylor, business manager, Kraft Food Ingredients. “In response to these interests, KFIC recently introduced a natural Italian cheese blend of Asiago, Parmesan and Romano.” Flavorful, high-impact artisan cheese blends help manufacturers “achieve productivity goals without sacrificing quality and taste,” she adds.
“Growth in process cheese will continue as more developers become aware of its versatility, increased cost stability, consistency, efficiencies in handling and extended shelf life as compared to natural cheese,” says Wild. Food formulators can look forward to formulating with better-tasting and highly functional cheeses in years to come.
