Cow's milk, unless indicated otherwise on the label of the cheese, is used in the production of most cheeses. The quality of milk used in cheese-making is rigidly controlled. The majority of cheeses are made from heat-treated or pasteurized milk (whole, lowfat, nonfat). If unpasteurized milk is used, the cheese must be ripened for at least 60 days at a temperature of not less than 35°F to ensure safety against pathogenic organisms. Pasteurization requirements for milk used to make specific cheese varieties are indicated in Table 28 (PDF 9k) . The FDA has indicated that aged cheeses made in the United States from unpasteurized milk are as safe as cheeses made from pasteurized milk. The aging process has been shown to effectively ensure that aged cheeses are as safe and wholesome as those made from pasteurized milk.

Cow's milk used in cheese-making may also be homogenized, depending on the type of cheese being produced. In addition, milk may be filtered or clarified and specially treated for desired effects. Clarification of milk removes extraneous matter and may improve the body, texture, and flavor of cheese. The pigment carotene can be added to milk to give cheese a yellow color, or milk may be legally treated by bleaching with benzoyl peroxide to produce a cheese white in color. The label must state that the cheese has been treated with benzoyl peroxide. Permitted special treatments of milk used in cheese-making are indicated in the Code of Federal Regulations for cheese. Prior to cheese-making, milk may be standardized or adjusted to the optimal fat/casein ratio that determines the yield of cheese.

The basic processes or manufacturing steps described below are used to produce most cheeses. However, no two cheese varieties are produced by exactly the same method. The details of each of the steps are varied to give characteristics and qualities unique to each cheese. Today, most cheese production is mechanized and automated, which results in greater production efficiency and an improved product of uniform quality.

• Curd Formation. Curd formation or setting the curd results from introducing a coagulating agent (acid and/or a coagulating enzyme), adjusting the temperature, and adding salts. Most varieties of cheese are produced by enzyme coagulation or rennet. Rennet coagulates milk by precipitating casein. After the curd is formed, the enzyme is either inactivated or expelled with the whey. Acid coagulation of milk involves the addition of a culture of lactic acid-producing bacteria (starter culture) to warm milk. The specific starter culture depends on the type of cheese being produced. Cheese made by acid coagulation tends to be unripened. The temperature for coagulation of milk is carefully controlled and varies with the type of cheese being made. The combination of the temperature of coagulation, the starter culture, the coagulating enzyme, and the acid produced influences the rate of formation, the firmness, the elasticity, and other physical properties of the resulting curd and the degree of whey expulsion. According to federal definitions and standards, salts such as calcium chloride may be added to milk to accelerate enzyme coagulation and to increase curd strength, antimycotic agents (e.g., sorbic acid) may be added to prevent mold growth, and other additions or treatments may be permitted for specific purposes.
  
  
• Cutting or Breaking Curd. This process speeds whey expulsion and permits more uniform, thorough heating of the equal-sized smaller curd. Generally, the curd is cut by driving a stainless steel, horizontal-wired knife carefully through the curd, followed by linear movements of a vertical-wired knife. The curd particles are cut into various sizes depending on the variety of cheese being made.
  
  
• Cooking Curds. This process contracts the curd particles for more effective removal of whey from the curd. Cooking also influences curd texture and moisture and suppresses spoilage organisms in acid curd cheese.
  
  
• Draining or Dipping Curds. This step permanently separates the whey from the curds, coalesces the curds, and allows additional time for lactic acid production. Draining involves passing the whey through a metal strainer or sieve. In dipping, the curds are ladled out of the vat into perforated molds and the whey is slowly drained off through the activity of lactic acid bacteria and turning of the molds.
  
  
• Knitting of the Curds. This step transforms curd into the characteristic texture of the cheese desired, permits lactic acid development, and regulates moisture control. Examples of curd knitting include the cheddaring of Cheddar cheese, the preliminary packing of Swiss, brick, and blue cheese curd, and the pulling or kneading (pasta filata) of provolone and mozzarella cheese.
  
  
• Salting of Curds. Salting improves the flavor, texture, and appearance of cheese. This is accomplished by slowing lactic acid fermentation after an optimum peak has been reached, by suppressing the growth of undesirable microorganisms, and by controlling the moisture content of the final cheese by drawing whey out of the curd. The salt content of most varieties of cheese varies from about 1% in cottage and cream cheeses to about 5% in Parmesan and Roquefort cheeses.
  
  
• Pressing Curds. Pressing achieves the characteristic shape of the cheese by compacting the texture, extruding free whey from the curds, and completing the curd knitting. This step involves confining the curds for fixed periods of time to a constricted metal form or cloth bag. External weights or presses may be applied.
  
  
• Special Applications. Special applications for specific cheeses, such as creaming cottage cheese curd or incorporating characteristic microorganisms, are discussed under Kinds of Cheese and Cheese Products. For more information, refer to Kosikowski and Mistry and the Code of Federal Regulations.
  
  
• Ripening or Curing. Ripened or cured cheeses such as Cheddar are purposely exposed to a temperature- and humidity-controlled environment for a specified length of time. Beneficial bacteria and enzymes transform the fresh curd into a cheese with a specific flavor, texture, and appearance. Uncured or fresh cheeses such as cottage, cream, and Neufchatel are generally ready for immediate consumption following collection of the curd. These cheeses tend to have a bland flavor and a soft body. The rate, nature, and extent of cheese ripening are influenced by the kind and concentration of ripening agents, the temperature and humidity of the environment, the presence of salt, and the treatment of the cheese surface. The changes during ripening are selectively brought about by enzymes or microorganisms in or on the cheese curd. These enzymes are derived from beneficial microorganisms added as starters (e.g., lactic acid-producing streptococci and lactobacilli , and propionic acid-forming bacteria) and certain molds, or added coagulating and flavor-enhancing enzymes. During ripening, chemical and physical changes occur in cheese. These changes occur as a result of allowing microorganisms and enzymes in cheese curd to:
  
  • Hydrolyze protein to simpler compounds, such as proteases and peptones, and eventually more soluble lower molecular weight peptides and amino acids. The hydrolysis of protein during ripening contributes to the development of a softer, more pliable body and aromatic flavor of cheese.
  • Hydrolyze fat with the liberation of fatty acids and glycerol, which play an important role in the distinctive flavor of different cheeses.
  • Hydrolyze the carbohydrate (lactose) of cheese. Regardless of the stage at which lactic acid is formed, after about 2 weeks of ripening most of cheese's lactose is converted to other compounds, with only trace amounts of sugars such as glucose and galactose (hydrolysis products of lactose) remaining. The formation of lactic acid is necessary for correct manufacturing, flavor development, normal ripening, and good keeping qualities of cheese.

• Introduction
  
  
• Definition and Classification of Cheese
  
  
• Cheese Production
  
  
• Kinds of Cheese and Cheese Products
  
  
• Nutrient Content of Cheese
  
  
• Specific Health Benefits of Cheese