Pasteurization and Aseptic Processing
Pasteurization and Aseptic Processing
Grade "A" Pasteurized Milk Ordinance
By: U.S. Food and Drug Administration
Source: "Item 16p. Pasteurization and Aseptic Processing." in U.S. Food and Drug Administration. Grade "A" Pasteurized Milk Ordinance, 2001 Revision. pages 62-63. Available online at: 〈http://www.cfsan.fda.gov/∼acrobat/pmo01.pdf〉 (accessed January 25, 2006).
About the Author: The U.S. Food and Drug Administration is a federal agency responsible for ensuring the safety and regulation of food, drugs, cosmetics, medical devices, animal feed, and radiation-emitting products such as cell phones, lasers, and microwave ovens.
Pasteurization is the term for a process where milk is heated to reduce the numbers of microorganisms (bacteria, molds, and yeast) that would otherwise spoil the milk and possibly pose a health threat to those drinking the milk or eating the milk product. The temperature used is not, however, harsh enough to alter the taste or appearance of the milk.
Pasteurization does not necessarily kill all the microbes in the milk. However, the numbers of organisms become so few that they pose no threat to milk quality or health, assuming the product is used by a certain date (the expiration date).
Pasteurization accomplishes two goals. First, the milk is rendered safe from microbial contamination. Second, because the pasteurized milk is packaged in clean containers and kept away from contact with air (which also contains microorganisms that could re-contaminate the milk), the milk will stay fresher for a longer period of time. This allows milk to be transported greater distances to the supermarket shelf, and to be sold for a longer period of time.
The temperature and time conditions used in pasteurization were determined following experiments that utilized a variety of microorganisms. Of particular concern is Coxiella burnettii, a type of bacteria that is resident in some barnyard animals, and so can be transmitted to milk, and which is resistant to the protein-coagulation activity of heat. By selecting conditions of temperature and time that kill this bacterium, other, less heat-tolerant microbes will also be killed or greatly reduced in number.
Pasteurization is accomplished in one of two ways; the batch method or the continuous method. In the batch method, milk is added to a vat that is surrounded by a jacket of water or steam. The milk is heated to the desired temperature for the determined time and then either cooled down or transferred to another container for cooling. This process is used more for milk products such as ice cream than for liquid milk.
Far more commonly, liquid milk is pasteurized using the continuous flow method, in which the milk is pumped past heated stainless steel plates into a tank where it cools and finally into another tank where the milk is packaged into jugs or cartons. Because the process involves the continuous flow of milk, a greater volume can be pasteurized in a given time than in the batch method.
The continuous method has been modified such that the milk is exposed to a higher temperature at a greater flow rate. This process—known as high-temperature, short-time pasteurization (HTST)—allows even greater quantities of milk to be treated in a given time without compromising quality of the final product.
With proper technique, high-temperature, short-time pasteurization reduces the number of microorganisms by 0.00001 times the original number. A final form of pasteurization is called ultra-high temperature (UHT) method involves heating the product at 138 degrees Celsius (280.4 degrees Fahrenheit) for a minimum of only two seconds.
Ensuring the safety and quality of milk is one of the U.S. Public Health Service's oldest activities, as it first enacted standards for pasteurization in 1924. Then called the Standard Milk Ordinance, numerous revisions have been made under the auspice of the Food and Drug Administration.
ITEM 16P. PASTEURIZATION AND ASEPTIC PROCESSING
Pasteurization shall be performed as defined in Section 1, Definition X of this Ordinance. Aseptic processing shall be performed in accordance with 21 CFR 113, 21 CFR 108 and the Administrative Procedures of Item 16p., C, D, and E of this Section.
PUBLIC HEALTH REASON
Health officials unanimously agree upon the public health value of pasteurization. Long experience conclusively shows its value in the prevention of disease that may be transmitted through milk. Pasteurization is the only practical, commercial measure, which, if properly applied to all milk, will destroy all milkborne disease organisms. Examination of lactating animals and milk handlers, while desirable and of great value, can be done only at intervals and; therefore, it is possible for pathogenic bacteria to enter the milk for varying periods before the disease condition is discovered. Disease bacteria may also enter milk accidentally from other sources, such as flies, contaminated water, utensils, etc. It has been demonstrated that the time-temperature combinations specified by this Ordinance, if applied to every particle of milk, will devitalize all milkborne pathogens. Compilations of outbreaks of milkborne disease by the PHS/FDA, over many years, indicate that the risk of contracting disease from raw milk is approximately fifty (50) times as great as from milk that has been "pasteurized."
A note of caution is in order. Although pasteurization destroys the organisms, it does not destroy the toxins that may be formed in milk when certain staphylococci are present, as from udder infections, and when the milk is not properly refrigerated before pasteurization. Such toxins may cause severe illness. Aseptic processing has also been conclusively demonstrated to be effective in preventing outbreaks from milkborne pathogens.
Numerous studies and observations clearly prove that the food value of milk is not significantly impaired by pasteurization.
The pasteurization portion of this Item is deemed to be satisfied when:
1. Every particle of milk or milk product is heated in properly designed and operated equipment to one of the temperatures specified in the following table and held continuously at or above that temperature for at least the time specified:
Pasteurization Temperature vs. Time
63°C (145°F) ∗ 30 minutes
72°C (161°F) ∗15 seconds
89°C (191°F) 1.0 second
90°C (194°F) 0.5 seconds
94°C (201°F) 0.1 seconds
96°C (204°F) 0.05 seconds
100°C (212°F) 0.01 seconds
∗If the fat content of the milk product is 10 percent (10%) or more, or if it contains added sweeteners, the specified temperature shall be increased by 3°C (5°F).
Provided, that eggnog shall be heated to at least the following temperature and time specifications:
69°C (155°F) 30 minutes
80°C (175°F) 25 seconds
83°C (180°F) 15 seconds
Provided further, that nothing shall be construed as barring any other pasteurization process, which has been recognized by FDA to be equally efficient and which is approved by the Regulatory Agency.
2. The design and operation of pasteurization equipment and all appurtenances thereto shall comply with the applicable specifications and operational procedures of Subitems (A), (B), (D) and (E).
Pasteurization protects consumers from the health hazards that would otherwise result from the consumption of raw milk. Milk is an abundant source of nutrients for bacteria and other microorganisms. Thus, if not handled properly, milk can become contaminated. Without pasteurization, milk could not be transported long distances to market, or be held on the supermarket shelves for very long. Pasteurization, therefore, has made possible the current conventional selling of milk and other dairy products. Pasteurization also can ensure the quality and safety of other products, including fruit juices, cider, honey, and beer.
The process of pasteurization was named after its discoverer, Louis Pasteur. In addition to pasteurization, Louis Pasteur made a number of other discoveries in the nineteenth century concerning microorganisms that fundamentally changed the world. In one series of investigations, Pasteur demonstrated absolutely that the growth occurring in a liquid food source was due to the presence of microorganisms, and not to the spontaneous appearance of life (a theory called spontaneous generation). Pasteur ingeniously designed a flask with a long neck that bent downward and then upward. Sterile growth medium in the flask did not become cloudy with growth, even when left exposed to the air, since the microbes that entered the neck settled out in the lower portion of the S-shaped neck. But, when the neck was broken to eliminate the curved portion, growth quickly developed in the medium.
This line of experimentation peaked Pasteur's interest in fermentation, the microbial alteration of a nutrient source that occurs under certain environmental conditions. His studies led to the demonstration that wine and milk could be heated to kill spoilage bacteria and mold. In particular, his work with wine was hailed, as spoilage of grapes was a significant problem in the French winemaking industry. The process was later called pasteurization in his honor.
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Shearer, J. K., K. C. Bachman, and J. Boosinge. University of Florida, Institute of Food and Agricultural Sciences. "The Production of Quality Milk" 〈http://edis.ifas.ufl.edu/DS112〉 (accessed January 22, 2006).