Thread: Pasteurization
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Old Monday, May 14, 2012
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Default Pasteurization

The process of pasteurization was named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk.
The heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process.
There are two distinct purposes for the process of milk pasteurization:
1. Public Health Aspect - to make milk and milk products safe for human consumption by destroying all bacteria that may be harmful to health (pathogens)
2. Keeping Quality Aspect - to improve the keeping quality of milk and milk products. Pasteurization can destroy some undesirable enzymes and many spoilage bacteria. Shelf life can be 7, 10, 14 or up to 16 days.
The extent of microorganism inactivation depends on the combination of temperature and holding time. Minimum temperature and time requirements for milk pasteurization are based on thermal death time studies for the most heat resistant pathogen found in milk, Coxelliae burnettii. Thermal lethality determinations require the applications of microbiology to appropriate processing determinations. An overview can be found here.
To ensure destruction of all pathogenic microorganisms, time and temperature combinations of the pasteurization process are highly regulated:
Ontario Pasteurization Regulations
63 C for not less than 30 min.,
72 C for not less than 16 sec.,
or equivalent destruction of pathogens and the enzyme phosphatase as permitted by Ontario Provincial Government authorities. Milk is deemed pasteurized if it tests negative for alkaline phosphatase.
Frozen dairy dessert mix (ice cream or ice milk, egg nog):
at least 69 C for not less than 30 min;
at least 80 C for not less than 25 sec;
other time temperature combinations must be approved (e.g. 83 C/16 sec).
Milk based products-
with 10% mf or higher, or added sugar (cream, chocolate milk, etc)
66 C/30 min, 75 C/16 sec
Methods of Pasteurization
There are two basic methods, batch or continuous.
Batch method
The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water, steam or heating coils of water or steam.

In the vat the milk is heated and held throughout the holding period while being agitated. The milk may be cooled in the vat or removed hot after the holding time is completed for every particle. As a modification, the milk may be partially heated in tubular or plate heater before entering the vat. This method has very little use for milk but some use for milk by-products (e.g. creams, chocolate) and special batches. The vat is used extensivly in the ice cream industry for mix quality reasons other than microbial reasons.
Continuous Method
Continuous process method has several advantages over the vat method, the most important being time and energy saving. For most continuous processing, a high temperature short time (HTST) pasteurizer is used. The heat treatment is accomplished using a plate heat exchanger. This piece of equipment consists of a stack of corrugated stainless steel plates clamped together in a frame. There are several flow patterns that can be used. Gaskets are used to define the boundaries of the channels and to prevent leakage. The heating medium can be vacuum steam or hot water.

Effectiveness of pasteurization
Milk pasteurization has been scientifically proven to be at least 90% effective in eliminating harmful bacteria in milk. While some few pathogens are heat resistant, modern equipment is readily able to test and identify bacteria in milk being processed. Pasteurization is the only effective means of eliminating 90% or more of harmful organisms in milk.
Non pasteurized, raw milk, according to the Centers for Disease Control (CDC), was responsible for 86 reported food poisoning outbreaks between 1998 and 2008, resulting in 1,676 illnesses, 191 hospitalizations, and two deaths. Improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food borne disease outbreak.
Diseases pasteurization can prevent include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever.
it also kills the harmful bacteria Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli among others.
Side-effects of pasteurization
Fans of raw milk (meaning milk that has not been pasteurized or homogenized) credit it with having more beneficial bacteria and enzymes than its processed counterpart. Though raw milk cannot be preservedfor a long time, its benefits may exceed its disadvantages. Raw milk does contain antimicrobial properties, which are destroyed with the heat of pasteurization, along with many of the vitamins within the milk itself. Raw milk consumption has also been shown to positively influence the immune system's resistance to the development of asthma, hay fever, and atopic sensitization, although the mechanism is not entirely understood.
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