- Cheese making is a way to preserve excess milk, and today about 90% of the milk produced in Wisconsin is used for cheese production.
- In 2014, the U.S. produced 11.45 billion pounds of cheese— including 4.9 billion pounds of Italian-type cheeses and 4.5 billion pounds of American-type cheeses. Mozzarella and cheddar are the most popular cheeses among Americans.
- Given the large volume of cheese produced, the incidence of foodborne illness is small, however, there have been several recent multistate outbreaks—three due to Listeria monocytogenes and one due to Escherichia coli O157:H7. In 2013, farmstead cheese products made in the U.S. were linked to a Listeriosis outbreak involving six hospitalized cases and one death. Earlier in 2010, cheese contaminated with E. coli O157:H7 resulted in 38 illnesses and 15 hospitalizations.
- L. monocytogenes has been the most common cause of foodborne illness from cheese in recent years. E. coli, Salmonella spp., and Campylobacter jejuni are also potential sources of foodborne illness from cheese. These pathogens cause gastrointestinal illness and in serious cases can lead to hemolytic-uremic syndrome, premature labor, miscarriage, and death.
Cheese is a dairy product made from pressed milk curds. The main components of cheese are water, milk fat, and milk proteins, predominantly casein. There are over 300 varieties of cheese produced in the U.S., most of which are made from cows’ milk. There are also varieties made from the milk of sheep, goats, and domestic water buffalo. The popularity of frozen meals containing cheese, such as pizza, as well as specialty, artisanal, and farmstead cheeses, contribute a tremendous proportion of the demand in the dairy and cheese industries. Specialty cheeses are regarded as having high quality and are unique in some way, whether it is the processing method used or the presence of a distinct flavor. Artisan or artisanal cheeses are made in small batches, almost entirely by hand, and with as little mechanization as possible. Farmstead cheese is a type of artisanal cheese that is produced on the farm from milk obtained from the farmer’s animals only.
Cheese can be ripened (aged) by bacteria or mold or left unripened (fresh), such as cream cheese and cottage cheese. Cheese is categorized by its degree of hardness, and legal standards dictate the maximum moisture limits and minimum milk fat levels for those categories, which include:
- Soft (e.g. Brie, ricotta, and feta);
- Semi-soft (e.g. blue, mozzarella, and provolone);
- Hard (e.g. cheddar, Gouda, and Swiss); and
- Very hard (e.g. Parmesan and Romano).
Wisconsin is the leading cheese-producing state, making 25% of U.S. cheese. California, Idaho, New York, and New Mexico are other top cheese-producing states. In 2012, per capita cheese consumption in the U.S. was 34 pounds.
From 1998 to 2011, cheese was implicated as the vehicle in 90 foodborne illness outbreaks, with 38 associated with cheese made from unpasteurized milk. Unpasteurized queso fresco has frequently been associated with Salmonella (10 outbreaks), pasteurized queso fresco or other Mexican-style cheese with Listeria (6 outbreaks). These types of cheese products, sometimes called bathtub cheese, are often produced or sold illegally.
A 2010 multi-state outbreak of E. coli O157:NM occurred in Sally Jackson’s goat, sheep and cow cheeses. Also, a 2014 multi-state Listeriosis outbreak traced to cheese products made in Delaware resulted in eight confirmed illnesses, seven hospitalizations, and one death. An investigation by the U.S. Food and Drug Administration (FDA) found the cheese processing room and several pieces of equipment in the facility to be contaminated with the same strain of Listeria implicated in the outbreak. In 2012, imported ricotta salata cheese sickened 22, hospitalized 20, and killed four due to contamination with Listeria. The outbreak investigation was complex and revealed many avenues of potential contamination. The cheese, originally imported from Italy, was cut and repackaged at various retail locations, extending the risk of contamination to other cheeses via unclean cutting boards, cutting wires, and utensils.
Commercial Cheese Making
The general flow of production is: pasteurization > pump the milk to the vat > inoculate the vat with starter culture > coagulate the milk > cut the curd > cook the curd (depending on the cheese) > drain the curd >>>
After arriving at the cheese-making facility, milk is tested for purity and quality and the fat content is adjusted depending on the type of cheese being produced. Partially skim milk or whole milk may be used; whole milk yields a creamier cheese.
Standardization includes determining the ratio of protein to fat in the milk or standardizing the solids, then weighing the milk; it takes about 10 pounds of milk to produce one pound of cheese. Various technologies including ultrafiltration are common in large cheese operations to ensure milk is cleared of debris and spores that could survive pasteurization. A specially designed centrifuge, called a Bactofuge, is often used to separate bacterial spores, which have a higher density than the milk. Unless raw milk cheese is being produced, pasteurization is carried out at this point in the process.
Coagulation is the process of denaturing the milk proteins to form a gel network which facilitates the separation of milk solids (curds) from liquid (whey) but coagulation itself does not separate curds and whey. Every step afterward is done with this task in mind, including steps in the fermentation process Bacterial cultures are added to the milk before coagulation and after pasteurization and determine the flavor and texture of the final cheese product. Streptococcus, Lactobacillus, and Lactococcus lactis are commonly used starter cultures, which convert the lactose in milk into lactic acid via fermentation. An enzyme called rennet is added, which will coagulate the milk protein, casein, forming a custard-like mass.
Cutting and Heating
The custard-like mass is cut into curds that are heated until the ideal firmness is achieved. Large curds cooked at lower temperatures retain more moisture, have less protein bonding, and result in soft cheeses, like ricotta. The opposite is true for small curds, which are cooked at higher temperatures and yield hard cheeses, like Parmesan.
The whey (mostly water with whey proteins and some residual lactose) is drained from the milk solids, or curds to obtain the desired moisture content of the cheese.
Knitting and Pressing
Knitting refers to the transformation of individual curds into one body of cheese. The way the body of cheese is manipulated during knitting differs between types of cheese and sometimes involves flipping or kneading the body of cheese to produce the desired texture. Curds are transferred to molds and pressed to form distinct shapes.
Salt may be stirred in with the curds during knitting, applied to the surface during curing, or dissolved in brine in which the curds soak. Salt enhances flavor, reduces moisture, and plays an important role in slowing bacterial activity, which prevents over-ripening.
The proper humidity, temperature, and oxygen levels must be maintained for the cheese to age as desired; this stage is key for the development of characteristic flavor, texture, and aroma. Curing temperatures range from 35-50°F and humidity from 80-95%. The curing process can take weeks, months, or years depending on the type of cheese.
Some cheeses, such as provolone, are aged by the action of bacteria uniformly spread throughout the interior of the body of cheese; these are referred to as interior-ripened cheeses. Some cheeses are aged by a bacteria, mold, or yeast that is applied to the surface of the cheese mass; these cheeses are called surface-ripened. Washed-rind cheeses are cured in a brine that may include beer, wine, or spices. All washed rind cheeses are surface ripened cheese but not all surface ripened cheeses are washed-rind cheeses. Penicillum candidum is a white mold used to make Brie, which releases enzymes that ripen the cheese from the outside-in. Blue cheese is also ripened by mold, Penicillium, but it is distributed throughout the interior of the cheese to produce the characteristic blue veins.
Currently, there are 72 varieties of cheese and cheese products that are listed within 21 C.F.R. Part 133 of the FDA regulations. While the FDA regulation requires that most cheese and cheese products are made from pasteurized milk, there are a limited number of cheese varieties that can be made with raw milk. For these varieties, curing is required for at least 60 days at no less than 35° F. For fresh cheese varieties such as mascarpone, ricotta, feta, queso fresco, etc. the 60-day aging rule is not allowed.
Vacuum packaging or the application of an edible or inedible wax coating may be used to prevent humidity loss and bacterial contamination that could result from human handling of the final cheese product.
Artisanal Cheese Making
Artisanal cheese is a growing industry in the U.S. for several reasons. First, international travel has increased, allowing Americans to try and enjoy unique cheeses abroad—then desire them after returning home. Second, more and more Americans are interested in purchasing foods that have been minimally processed—to better know what ingredients are in their food, where it originated, and how it is made.
The process of making an artisan cheese may involve several hours of continuous cutting and stirring of curds, which is often accomplished by hand. The knowledge and skill of the cheese maker is demonstrated through successful artisan cheese making. Artisanal cheese made from milk obtained on a single farm ensures a consistent product, and is known as a farmstead cheese. Garlic, herbs, or spices may be added, producing distinct cheeses to be paired with certain wines or other foods.
The use of wooden shelves for aging cheese in the artisanal cheese industry may pose an increased risk of foodborne illness. The porous composition of wood allows bacteria to enter and colonize the inner part of the wood, and it is more difficult to clean. However, wood is an excellent medium for aging cheese because of the way it controls moisture and fosters the growth of beneficial bacteria that add distinct flavors to many artisanal cheeses.
Storage and Handling
All cheese should be stored between 35-40°F and wrapped tightly to prevent exposure to air, which can lead to molding and dehydration. Cheese should be kept in the refrigerator drawer to prevent the transfer of odors and flavors to and from other foods. Soft cheeses that have been at room temperature for more than four hours should be discarded.
In general, harder cheeses have a longer shelf life of several months compared to soft cheeses that typically last one to three weeks after being opened. Large pieces of cheese will keep longer than smaller pieces of cheese, such as shredded and sliced cheese. Cheese can also be frozen for two to six months, but freezing may alter the texture.
Undesirable molds spread through cheese via hyphae, which resemble tiny roots. Hyphae do not extend as far in hard cheeses as they do in soft varieties. Hard cheeses with little mold can be salvaged by removing the mold spot and the one-inch area surrounding it, ensuring the knife does not contact the moldy part. Soft cheeses and shredded or sliced cheese with mold should be discarded. Due to high moisture content, these soft cheeses can be contaminated well beyond the surface of the moldy area. Undesirable mold in cheese is often distinguished as being black or white with hair-like structure or colored red, pink, or orange. Desirable molds associated with cheese are generally soft, white marshmallow consistency or bluish in color. Cheese with mold spoilage should be thrown out in a sealed container and placed in a secure garbage can to protect pets and wildlife.
Individuals with weakened immune systems including pregnant women, the elderly, and patients undergoing chemotherapy are at a higher risk for contracting certain foodborne illnesses, such as Listeriosis. These high-risk individuals should avoid feta, Brie, Camembert, blue-veined cheese, and Mexican-style soft cheeses, such as queso blanco and queso fresco, unless they are pasteurized.
Pasteurization is key for ridding dairy products, including milk used to make cheese, of disease-causing pathogens. However, many cheese products made with pasteurized milk still end up being implicated in foodborne illness outbreaks due to unsanitary conditions at the processing facility or retail locations. With cheese, particularly cheese made from pasteurized milk, human handling and cross contamination in retail food service have been contributing factors for spreading foodborne pathogens.
In the United States, consumption of natural cheeses has continued to steadily increase over the years. Americans were consuming an average of 34 pounds of cheese per person in 2014—a United States record. More specifically, Italian cheese varieties such as mozzarella, parmesan, and provolone have seen the greatest increase in consumption at an average of 14 pounds per person. As the popularity of Italian and Tex-Mex foods has continued to grow in the United States, cheese consumption has subsequently increased. While the consumption of processed cheese has declined to an average of 7 pounds per person, the addition of cheese to precooked meals, frozen meals, boxed foods, etc. have contributed to the overall increased consumption. In the 2006-2007 Foodnet Atlas of Exposures, 60.9% of the survey cohort reported eating any cheese sold as or cut from solid blocks within the past 7 days. Further, 56.1% reported eating cheddar, 50.9% reported eating American (processed) cheese, and 44% reported eating Parmesan or Romano within the past 7 days.
Cheese is a tasty, versatile food that is available in a wide variety of flavors and forms from blocks to individual slices to cubes and even strings. Different types of cheese vary in terms of nutritional qualities, but all types are rich sources of calcium, protein, phosphorus, Vitamin A, and Vitamin B12.
Cheese, like all dairy products, is a good source of calcium, which many Americans lack in their diets. Calcium is important for increasing bone density and reducing the risk of osteoporosis. Osteoporosis is a debilitating disease that threatens 44 million Americans and can lead to bone fractures, decreased mobility, and poor quality of life.
Externally Reviewed by: James Musetti Affiliation: Application Technologist, Cheese-DuPont Nutrition and Health Reviewed On: 8 September 2015 Externally Reviewed by: Katie Neuser Affiliation: Wisconsin Cheese Board Reviewed On: 26 October 2015