Mozzarella and Pasta Filata Cheese

As a recently as a generation ago, Mozzarella was still considered a mostly ethnic cheese, used primarily as an ingredient in Italian cui-sine.The popularity of this cheese—it is now equal to that of Cheddar cheese among American consumers (Figure 5-3), is due to one product: pizza. Of the more than 1.2 billion Kg (2.7 billion pounds) of Mozzarella and related cheeses consumed each year, about 70% is used by the food service industry as an ingredient on pizza. And while Cheddar production has grown by about 60% since 1980, over that same period, Mozzarella production has increased by 400%. In fact, in the last twenty years, many cheese factories that once made Cheddar converted their operation to Mozzarella manufacturing. And despite the apparent differences in flavor and appearance between Cheddar and Mozzarella cheese, both share several common manufacturing steps.

In the United States, all Mozzarella cheese is made from pasteurized milk. In large part, this is because Mozzarella is considered a fresh cheese that is essentially never ripened.Thus, legal requirements dictate that the milk be pasteurized. Although some Mozzarella cheese is made from whole milk, most is made from reduced fat or partially skimmed milk. Special considerations for the manufacture of reduced fat Mozzarella and other low- or reduced fat cheeses will be described later. Although almost all Mozzarella cheese made in the United States comes from cow's milk, it is worth noting that some traditional Italian Mozzarella is made from the milk of water buffaloes.

After the milk is pasteurized and standardized, a thermophilic culture is added. Although the organisms used for Mozzarella, Streptococcus thermophilus and Lactobacillus helveti-cus, are the same as those used for Swiss cheese, the specific strains and ratios are likely quite different. Strain selection for Mozzarella cheese is based, like all cultures, on the desired properties of the particular cheese.This is especially true for Mozzarella cheese, where the strains may have a profound effect on the properties of the finished cheese (Box 5-5).

Box 5-5. The Science of Making Pizza

Given that the U.S. pizza industry is a $32 billion industry, that 350 slices of pizza are eaten every second of every day, and that Mozzarella and pizza-type cheeses are the main ingredients on a pizza, it is not surprising that Mozzarella producers are under considerable pressure to produce a cheese with the functional properties desired by the pizza manufacturer.

Of course, pizza restaurants are the main users of Mozzarella, with several companies dominating the industry (Dominos, Pizza Hut, Godfathers, and Papa Johns). When considering the cheese, each pizzeria seems to have their own particular preference. Some pizza chains desire cheese that stretches a particular distance when a slice is moved from plate to mouth. Others want a cheese that remains white and resists browning even when the pizza is baked quickly at extremely high temperatures.Thus, Mozzarella production is now often customized to the exact needs of the customer, such that even before the vat is filled with milk, the manufacturer is ready to produce a cheese meeting not only compositional requirements, but functional specifications as well.

Because of these considerations, there is now much interest in understanding and predicting how a given cheese will perform during pizza manufacture and how manufacturing conditions can be manipulated to produce a cheese that has specific functional properties (Kindstedt, 1993). Unlike most other cheeses, Mozzarella, at least when used on pizza, is prized less for its flavor and more for its physical and functional attributes. Mozzarella, after all is a bland, slightly acidic cheese, with no aged cheese flavor. However, it has a unusual ability to stretch, retain fat, melt evenly, and provide a chewy mouth feel.These properties, however, are not necessarily automatic, and are influenced by the culture, the coagulant, the manufacturing conditions, and post-manufacturing handling and storage. Ultimately, these factors affect pH, loss of calcium, proteolysis, and the overall composition of the finished cheese.

The metabolic activities of the thermophilic starter culture bacteria have a major impact on the finished product. After the curds are cooked and the whey is drained, the curds are either Cheddared or dry stirred. During this time, Streptococcus thermophilus and Lactobacillus hel-veticus (or Lactobacillus delbrueckii subsp. bulgaricus) ferment lactose, producing lactic acid and causing the curd pH to decrease. However, both organisms metabolize only the glucose portion of lactose; the galactose is released back into the curd.

When the pH reaches 5.2, the curds head off to the cooker-stretcher (operating at 85°C), which heats the curd to a temperature near 60°C.This process inactivates enzymes (although some residual chymosin might remain) and the starter culture (or at least reduces the cell concentration several fold).Thus, there is essentially no opportunity left for this galactose (and any remaining lactose) to ferment. Instead, it will remain intact and be present in the finished cheese.

Box 5—5. The Science of Making Pizza (Continued)

When the cheese is exposed to high baking temperatures (which dry the cheese surface and reduce the water activity), these reducing sugars react with amino acids, via the non-enzymatic Maillard reaction, to from brown pigments.Although moderate browning may be desirable, excessive browning or blistering is undesirable. Because most pizza manufacturers prefer white, nonbrowning cheese, steps must be taken to reduce the galactose concentration in the cheese.This can be done either mechanically, by simply washing the curds, or biologically, by using cultures that can ferment galactose.The latter may consist of mesophilic Lactococcus lactis subsp. lactis that have no problem fermenting galactose, but their use requires other changes in the manufacturing process (i.e., lower cooking temperature). Selected galactose-fermenting strains of S. ther-mophilus and L. helveticus can also be used, and although such cultures are available from starter culture suppliers, their availability appears limited (Mukherjee and Hutkins, 1994). Plus, even galactose-fermenting strains do not ferment galactose as long as lactose is still available. It is also technically possible to engineer such strains, but this strategy has not yet been adopted.

The culture, and specifically, the proteolytic activity of L. helveticus, also affects other important properties.The ability of Mozzarella cheese to stretch is largely a function of protein structure. If, however, the culture is proteolytic (or residual coagulant activity is present in the curd after cooking), protein hydrolysis will occur, and the shortened casein strands will lose their ability to stretch.This may or may not be a good thing, depending on the preference of the pizza manufacturer (Dave et al., 2003).

If a short, non-stretching cheese is desired, then greater proteolysis may be encouraged. However, manipulating any one variable to affect a given property will likely affect some other prop-erty.As noted previously, extensive proteolysis makes the cheese "soft" and "gummy," and less amenable to shredding. In addition, it is the protein network that traps fat in Mozzarella. During baking, the fat melts and liquefies, but is retained by the protein matrix. If proteolysis has occurred and the protein network is disrupted, the fat is no longer contained and leaks out. On a pizza, the fat forms unsightly pools of melted oil, a defect known as oiling-off. Finally, since pro-teolysis increases the free amino acid concentration, the more proteolytic the culture (or the coagulant), the greater the rate of the Maillard reaction and the potential for browning problems.

Ordinarily, the amount of time between manufacture of Mozzarella and its use on a pizza is only a few weeks.Thus, proteolysis in Mozzarella is nowhere near as extensive as in an aged cheese. Still, even moderate proteolysis can affect cheese functionality. Many Mozzarella producers, therefore, freeze the cheese within a few days of manufacture, giving it just enough aging time to develop appropriate properties. Some manufacturers have even developed processes in which the cheese is frozen within hours of manufacture.

Manufacturing variables have also been modified to affect other functional properties. For example, most Mozzarella is eventually used in a shredded or diced form, so producing a cheese that is easy to shred, without gumming up the equipment, is important. These modifications have led some to question whether the cheese produced is actually Mozzarella, as defined by the standards of identity. Nonetheless, it seems likely that the demand for Mozzarella (or Mozzarella-type) cheese with particular functional characteristics, combined with significant economic pressures, will continue to be a driving force for innovative research within the Mozzarella and starter culture industries.

References

Mukherjee, K.K., and R.W. Hutkins. 1994. Isolation of galactose fermenting thermophilic cultures and their use in the manufacture of low-browning Mozzarella cheese. J. Dairy Sci. 77:2839-2849. Dave, R.I., D.J. McMahon, C.J. Oberg, and J.R. Broadbent. 2003. Influence of coagulant level on proteolysis and functionality of mozzarella cheeses made using direct acidification. J. Dairy Sci. 86:114-126. Kindstedt, P.S. 1993. Effect of manufacturing factors, composition, and proteolysis on the functional characteristics of mozzarella cheese. Crit. Rev. Food Sci. Nutr. 33:167-187.

After rennet addition, coagulation, and cutting, the curd-whey mixture is pumped into draining tables, where the curds are gently stirred and then cooked to 56°C.The whey is drained and the curds are either allowed to mat, as far Cheddar, or are dry-stirred (as for stirred-curd Cheddar). Frequently, the curds will be washed after draining to reduce lactose levels. Mozzarella is a brine-salted cheese; however, salt may also be added directly to the curds prior to the cooking-stretching step to minimize the lengthy brine-salting time ordinarily required.

The fermentation of lactose in Mozzarella is similar to that which occurs in Swiss cheese. In both fermentations, galactose appears in the curd as a result of the inability of S. ther-mophilus to efficiently metabolize both of the monosaccharide moieties of lactose. In Swiss cheese, there is plenty of time for the companion strain (i.e., L. helveticus) to eventually ferment the galactose and remaining lactose. However, the situation is quite different for Mozzarella. This is because when the pH during Cheddaring or dry-stirring reaches 5.2, the curds are moved to a cooker-stretcher device that exposes the curds to temperatures as high as 85 °C. Although the curd temperature may not reach such a high temperature (usually the curd is about 54°C to 57°C), this treatment is still sufficient to inactivate many of the starter culture bacteria present in the cheese. Thus, any galactose or lactose still in the curd at the cooking-stretching step will likely remain in the cheese for the duration of its manufacture and storage. The consequences of this are discussed in Box 5-5.

In addition to its effect on the culture and residual enzymes, the cooking-stretching step also has an important impact on the physical properties of the cheese. Prior to this step, Mozzarella curds are not that much different than other rennet set curds. However, the cheese exiting the cooking-stretching machines has properties unlike any other cheese. The cooking-stretching machines use augers to knead, stretch, and convey the curds in an upward manner (about a 30° incline), all the while exposing the curds to a hot water-steam mixture at 85°C to 90°C. In the United States and Italy, almost all Mozzarella is stretched in high through-put continuous cooker-stretcher devices. Only a relatively few very small manufacturers rely on traditional techniques—man-ually kneading the curd in hot water, an arduous and time-consuming task.

Although what actually happens to the casein matrix during this step is not clearly understood, it appears that the casein network becomes linearized, giving the fibrous property characteristic of Mozzarella cheese and desired by most consumers. It is critical that the cooking-stretching step occurs when the curd pH reaches 5.2, otherwise the cheese will be short-textured and will stretch poorly. Finally, the molten, plastic, and fluid curds are then dropped into a hopper and filled into molds of varying loaf sizes and shapes. The cheese sets up quickly in the molds and is then dropped into a cold salt brine. After brining (about sixteen hours, but much less if dry salt had been added to the curd), the cheese is dried and packaged. In Italy and in small U.S. factories that employ traditional manufacturing practices, Mozzarella can be formed into small round shapes, which are then packaged in water or dilute brines.

Mozzarella cheese, as noted above, is not aged; however, even within just a few days or weeks, important functional properties can change. One of the first changes that occurs is the equilibration of calcium, that which exists as part of the casein complex and that in the form of calcium phosphate. Importantly, the loss of calcium from the casein complex improves the melting and stretching properties of the cheese.

The other main change in the functional properties of Mozzarella is due to protein hydrolysis. Proteolysis can occur as a result of residual proteinases released by the lactic starter culture, as well as by residual coagulant (which appears to be the main source of proteinase activity). Although flavor changes due to protein hydrolysis are usually minor, texture properties can be significant. As the long casein strands are hydrolyzed, the cheese stretches less. Also, the hydrolyzed casein is less able to hold or contain the fat.The latter may result in a defect known as "oiling off" that is readily apparent when the cheese is used in pizza and other cooked products. Also, since most Mozzarella cheese is marketed in a shredded form, excessive proteoly-sis makes the cheese less shreddable. For these reasons, fresh Mozzarella is best used within two to three weeks. Alternatively, the cheese can be frozen shortly after manufacture or after shredding (the preferred form for most of the large pizza manufacturers), and although this will prevent proteolysis, freezing is not without its own set of effects.

Mozzarella is but one of several so-called pasta filata (Italian for stretched curd) types of cheese. Another well-known variety is Pro-volone cheese.This cheese is made essentially as for Mozzarella except that a lipase preparation is added to the milk to promote lipid hydrolysis and release of free fatty acids. Lipases are either fungal-derived or are from animal tissues. A slightly rancid but pleasant flavor, described as piquant, develops during a short aging period. Provolone is often shaped into pear-shaped balls (prova is Italian for ball), and is frequently smoked.

Brew Your Own Beer

Brew Your Own Beer

Discover How To Become Your Own Brew Master, With Brew Your Own Beer. It takes more than a recipe to make a great beer. Just using the right ingredients doesn't mean your beer will taste like it was meant to. Most of the time it’s the way a beer is made and served that makes it either an exceptional beer or one that gets dumped into the nearest flower pot.

Get My Free Ebook


Responses

  • Mirren
    Is mozzarella cheese fermented?
    6 years ago
  • OLGA
    Is mozarella cheese fermented?
    4 months ago

Post a comment