Pasteurization

Introduction
History
Purpose
Foods used for Pasteurization
Steps in Pasteurization
Process Flow Diagram Pasteurization Milk
Milk Pasteurization
Methods of Pasteurization
Advantages
Disadvantages

1. FOOD PRESERVATION BY PASTEURIZATION BY ASSIT. PROF. Dr. P . BERCIYAL GOLDA

2. CONTENTS Introduction History Purpose Foods used for Pasteurization Steps in Pasteurization Process Flow Diagram Pasteurization Milk Milk Pasteurization Methods of Pasteurization Advantages Disadvantages

3. INTRODUCTION

4. Steps of Pasteurization 1. Milk chilling Chilling is not a pasteurization process but it is a necessary step when dealing with large volumes of milk. Milk leaves the cow’s udder at temperatures above the ambient, which encourages rapid bacterial multiplication that speeds up spoilage. However, reducing the temperatures to between 2° C to 5° C arrests bacterial growth and metabolism. This provides a head start at keeping the quality before proper pasteurization commences.

5. 2. Pre-heating (regeneration) and Standardization Stage After bulking, the chilled milk is heated to about 40°C to facilitate easy separation of butterfat during standardization. The system uses regenerative heating, i.e., it uses the heat of the already pasteurized milk to heat up the incoming chilled milk. The chilled milk, in a counter current flow, cools down the pasteurized milk. The purpose of standardization is to obtain a product with uniform content of butter fat

6. 3. Clarification stage Clarification is essential for removing all foreign matter from the product. Large solid particles are removed by straining the milk through tubular metallic filters. A centrifugal clarifier (not the one used for standardization) is used to remove all soil and sediments from milk. The filters, usually fitted in parallel twins permits continuous processing as one can be cleaned while the other is running. Clean the filters regularly (between 2 to 10 operational hours depending on the level dirt) to avoid growth of bacteria.

7. 4. Standardization stage It is important to standardize milk fat to ensure that you end up with a product of consistent quality in the market. Different consumers prefer different products. There are customers who will consume skim milk only while there are those who will take low fat milk. There are those who will take standardized milk while there are those who prefer high fat milk. Standardization is necessary to ensure that all the customers are catered for. Again, it is during the process of standardization that you get to separate the butterfat that is used for making cream and other fat based products such as butter and ghee.

8. 5. Homogenization stage Homogenization is a physical process of breaking down the the milk fat globules into tiny droplets to discourage cream separation. Tiny droplets of fat do not rise in a milk column since reducing their sizes also increases their density in the milk. A milk homogenizer working at between 100 to 170 bars splits all the fat globules into very tiny droplets that increases the level of integration of the fat in the milk. As a result, the milk fat remains uniformly distributed in the milk.

9. 6. Heating section Utilizes heat from steam to raise the temperatures of the milk from about 60°C to the required 72°C that is effective to kill the Clostridium botulinum  spores. The steam exchanges heat with the milk across the PHE plates in a counter current motion. At the end if this section, there is a temperature sensor, which controls the flow diversion valve. Any milk that does not attain the required temperature is diverted back to the heating section until it attains the required temperatures .

10. 7. Holding section After heating, milk flows into the holding tubes whose lengths have been calibrated with the milk flow rate to ensure that milk takes at least 16 seconds in the tubes. All the milk must maintain the required pasteurization temperatures at the end of the tubes. In case of a breach, a sensor will trigger the flow diversion valve to take the milk back to the heating section to bring the milk to the required temperature. Once the milk has attained the required temperatures at the end of the holding tubes, milk flows back to the regeneration section to heat the incoming chilled milk while in itself being cooled down to about 30°C.

11. 8. Cooling/chilling section After regenerative cooling of pasteurized milk, it moves to the cooling section of the PHE where chilled water/PHE coolant lowers the temperature of pasteurized milk to 4°C. The chilled milk is then pumped to the packaging machines for aseptic packaging and subsequent storage in the cold room.

12. Milk pasteurization Milk pasteurization  is the process of heating milk (or milk product) to a predetermined temperature for a specified period without re-contamination during the entire process. The predetermined temperature usually depends on the heat resistance of spoilage microorganism that the pasteurization program is targeting to destroy

13. Vat pasteurization, also known as batch pasteurization or the holding method, heats every particle of milk or cream in properly designed and operated equipment, at 145°F (63°C) for 30 minutes*. If the fat content of the milk product is 10 percent or greater, or a total solids of 18% or greater, or if it contains added sweeteners, the specified temperature shall be increased by 5°F (3°C). Vat pasteurization helps destroy all disease-producing bacteria, as well as 90-99 percent of all other bacteria that may affect product quality. Because of this, pasteurization is the most important function of a milk plant. In vat pasteurization, it is necessary to heat the milk product to 145°F in the vat. The presence of both butter granules and cream plug are possible in milk and cream. Agitation is necessary to achieve the proper consistency and texture as well as rapid, even heating. Incorrect agitation will cause churning.

14. Operating a Vat Pasteurizer Finding the right balance of heating and agitation is important to efficiently operate vat pasteurization equipment. If the heating temperatures are too low, the milk product temperature will not raise quick enough. If heating temperatures are too high, the milk product may “cook on” the heating surface. The speed of heating is affected by the ability of your agitator to keep the product moving to, and away from, the heating surface. However, simply speeding up your agitator will not necessarily give you the desired result. Agitators are designed for certain speeds and highly efficient agitators may require high heating water temperatures. Failure to balance the heating surface with your agitation type and speed can result in improper pasteurization.

15. During the holding period, the vat must remain closed to prevent cooling from occurring during pasteurization. Proper vat pasteurization equipment should have an airspace heater to keep the air above the product at or above 145°F. Airspace heaters also ensure the pasteurization of milk droplets that are splashed on the sides of the vat and condensate on the inside of the vat cover. The bottom and sides of the vat must be insulated or jacketed to maintain proper temperatures during the holding period.

16. High-Temperature Short-Time (HTST) Pasteurization HTST pasteurization uses stainless steel heat exchange plates where product flows on one side while the heating media flows on the opposite side to raise milk temperatures to at least 161° F (72° C) for at least 15 seconds*, followed by rapid cooling. This was first developed by A.P.V. Co. in the United Kingdom in 1922. It is the modern method of pasteurizing milk and is invariably used where large volumes of milk are handled. The HTST pasteurizer gives a continuous flow of milk which is heated to 72°C for 15s and then promptly cooled to 5°C or below. Flash pasteurization, also called "high-temperature short-time" processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, kosher wine, and some dairy products such as milk.

17. Why is HTST Pasteurization the Preferred Method? High temperature short time pasteurization is a continuous process that efficiently and effectively destroys microorganisms in milk products. An HTST pasteurization system is a modular unit that includes a  plate-and-frame heat exchanger ,  stainless steel balance tank ,  pumps ,  holding tube, valves piping  and controls.  Vat pasteurization , or the holding method, is the oldest method for pasteurizing food products. However, over the years HTST has gained favor in the food industry for multiple reasons: Large equipment capacity allows large volumes at one time Continuous process allows for bottling to begin when pasteurization begins Highly energy efficient Minimal chance of damage to milk product Fully utilized regeneration Equipment is easy to clean and sterilize Thermophiles are less troublesome

18. Low-temperature long-time (LTLT)/Batch pasteurization Milk is heated, held and cooled in the inner vessel. The space between vessel and the outer casing forms a jacket, through which the heating or cooling medium is circulated. To heat the milk, hot water or low-pressure steam is circulated through the jacket and milk is continuously agitated for rapid and uniform heating. The heating process could be manually or automatically controlled. The milk is heated to a minimum of 62.7°C and held at this temperature for minimum 30 min. It is then cooled as rapidly as possible to 4°C. A cooling medium is circulated in the jacket for chilling the milk, but more often the heated milk is discharged to a surface cooler where a film of milk flows down the corrugated metal plates or series of interlocked tubes. A cooling medium such as brine or chilled water is circulated on the other side of the plates or through the tubes.

19. This is a completely closed pasteurization method. The product is never exposed even for a fraction of a second during the entire process. It involves heating milk or cream to between 135°C to 150°C for one to two seconds, then chilling it immediately and aseptically packaging it in a hermetic (air-tight) container for storage.

20. Despite the risk of Millard browning, UHT pasteurization remains the most popular milk preservation method for safe and stable milk. (UHT) pasteurization involves heating milk or cream to 138°to 150° C (280° to 302° F) for one or two seconds. Packaged in sterile, hermetically sealed containers, UHT milk may be stored without refrigeration for months. Ultra high temperature pasteurization, sometimes referred to as HST pasteurization or ultra-pasteurization, is a process in which milk or other dairy products are heated to 280 degrees Fahrenheit for a brief time—just two seconds—and then quickly cooled back down.

21. ULTRA STEAM IRRADIATION

22. Advantages 1. Capacity to heat treat milk quickly and adequately, while maintaining rigid quality control over both the raw and finished product 2. Less floor space required 3. Lower initial cost 4. Milk packaging can start as soon as milk is pasteurized 5. Easily cleaned and sanitized (system adapts itself to CIP) 6. Lower operating cost (due to regeneration system) 7. Reduced milk losses 8. Development of thermophiles is not a problem 9. Automatic precision controls ensure proper pasteurization.

23. Disadvantages 1. The system is not well-adapted to handling small quantities of liquid milk products 2. Gaskets require constant attention for possible damage and lack of sanitation 3. Complete drainage is not possible (without losses exceeding those from the holder system) 4. Margin of safety in product sanitary control are so narrow that automatic control precision instruments are required in its operation 5. Lethal effect on high- thermoduric bacteria in raw milk is not as great as compared to LTLT system 6. Accumulation of milk-stone in the heating section.