Methods of freeezing

Taskheer Zahoor
15-Arid-4317

1. Group members Name Ieman Siddiqui Safi Ullah M.Taskheer Zahoor Malik Rashid Ullah Muhammad Saqlain Shaista parveen Arid no: 15-Arid-4312 15-Arid-4316 15-Arid-4317 15-Arid-4322 15-Arid-4324 15-Arid-4325

2. Methods of food freezing

3. Contents Introduction Types/methods of food freezing Freezing in air. Indirect contact freezing. Immersion freezing. Cryogenic freezing . Conclusion

4. Introduction What is food freezing? freezing is a change in state allow preservation of taste, texture and nutritional value in foods provide a significant extended shelf life to food.

5. Advantages and disadvantages of freezing Advantages Freezing decreases the water activity. It retard the growth of micro-organisms. It controls/decrease the enzymatic activity. Disadvantages Freezing changes color , texture and flavor of food. It can cause damage to cell by ice crystallization.

6. Types/methods of food freezing There are 4 methods of food freezing. Freezing in air. Indirect contact freezing. Immersion freezing. Cryogenic freezing.

7. Freezing in air What is freezing in air? Packaged or unpackaged non fluid foods can be frozen in air at temperatures ranging from –18° to – 40 °. Have further three types. Still air sharp freezing. Blast freezing. Fluidized bed freezing.

8. Freezing in air Still air sharp freezing It consists of placing products in a very cold room, maintained at temperatures in the range of –15 °C to –29°C. Sharp freezers are cold storage rooms especially constructed to operate at and maintain low temperatures. Freezing time is generally 3-72 hours or more depending on the conditions and the size of product. No fan is use for this type of freezing.

9. Freezing in air Air Blast freezing Vigorous circulation of cold air enables freezing to proceed at a moderately rapid rate. Products are placed on trays, either loose or in packages and the trays are placed on freezing coils in a low temperature room with cold air blowing over the product . In this freezing method fan is used for air circulation. The temperature of the air is usually between –28 ° and –46° and air velocity is 15 m/s.

10. Freezing in air 3. Fluidized bed freezing Fluidized bed freezing is a modification of air-blast freezing. Solid food particles ranging in size from peas to strawberries can be fluidized by forming a bed of particles 1-5 in. Deep on a mesh belt (or mesh tray) and then forcing air upward through the bed at a rate sufficient to partially lift or suspend the particles in a manner somewhat reminiscent of a boiling liquid.

11. Freezing in air Advantages Easy and economical to build. Can accommodate a wide range of products. Economical operation. Space efficient. Superior quality due to continuous processing flow and controlled heat transfer. Easy to clean. Disadvantages Labor intensive. Occupies a large floor space. Poor heat transfer may occur resulting in poor product quality. Excessive dehydration in unpacked products. Product damage due to sticking. Labor intensive and costly to clean.

12. Indirect contact freezing What is indirect contact freezing? Indirect contact freezing, e.g. plate freezers, where packaged foods or liquids are brought into contact with metal surfaces (plate, cylinders) cooled by circulating refrigerant . For indirect contact freezers, the product is indirectly exposed to the freezing medium while in contact with the belt or plate, which is in contact with the freezing medium.

13. Indirect contact freezing

14. Types of indirect contact freezing There are 2 types of indirect contact freezing. Plate freezing a). Single plate freezing b). Double plate freezing c).Pressure plate freezing 2. Slush freezing

15. Types of indirect contact freezing Plate freezing In plate freezing layers of the packaged product are sandwiched between metal plates. The refrigerant is allowed to expand within the plates to provide temperatures of -28 F (-33 C) or below. The plates are brought closer together mechanically, so that full contact is made with the packaged product. This method can be used for meat, fish, and dairy and other products where agglomeration of the food particles is not a concern.

16. Types of indirect contact freezing There are further three types of plate freezing. Single plate freezing Double plate freezing Pressure plate freezing Automatic pressure plate freezing.

17. Types of indirect contact freezing Pressure plate freezing It is an important type of contact freezing . This consist of number of metal shelves or plates through which refrigerant is circulated. The food usually as flat packages is placed between shelves and there is provision after loading for applying pressure to squeeze the shelves into more intimate contact with the top and bottom of the packages for faster freezing.

18. Types of indirect contact freezing Pressure plate freezing All is enclosed within an insulated cabinet. Depending on refrigerant temperature, package size, degree of contact and the type of food, freezing time is 1-2 for commercial packages 4-5 cm thick.

19. Types of indirect contact freezing Automatic pressure plate freezing A recent development in frozen food processing is the portable automatic double pressure plate freezer.These have provisions for automatically loading shelves from the package line. As s shelf is loaded , it is moved into pressure contact with the preceding shelf and into an insulated zone where freezing proceeds.At the rear of freezing zone , frozen packages are discharged one shelf at a time and the empty shelves return to the loading position.

20. Types of indirect contact freezing Automatic pressure plate freezing These freezers provide for continuous operation are automatically loaded from a conveyer, frozen under pressure and automatically discharged for casing with elimination of manual labor. This is done automatically and continually. Each freezer is portable and can be move from one place to another.

21. Types of indirect contact freezing Slush freezing In case of liquid food and purees, the food is pumped through a cold wall heat exchanger and frozen to the slush condition. The votator is widely used for slush freezing. A thin strem of juice is forced at about 50 p.s.i. pressure into the space between the center shaft and the heat transfer tube.

22. Types of indirect contact freezing Slush freezing Just as rapid evaporation requires a large area of refrigerated heat transfer surface per unit of juice, so does the rotator freeze rapidly by causing a thin layer of juice to pass over a large area of refrigerated heat transfer surface. Floating scraper blades affixed to the rapidly revolving center shaft are forced outward against the heat transfer surface and automatically remove the product film which would otherwise accumulate. Ammonia is ordinarily used as a refrigerant in this equipment.

23. indirect contact freezing Advantages This method is used for both liquid and solid foods. It is relatively faster and freeze individual food particles. This method is Ideal for thin, flat foods such as steak, fish fillets or burgers . Disadvantages In flexible: used primarily for foods in packages. Limited package geometry. Labor cost is high.

24. Immersion freezing What is immersion freezing? Liquid immersion freezing (usually referred to as direct immersion freezing) is accomplished when a food product, either packaged or unpackaged, is frozen by immersion in or by spraying with a freezant that remains liquid throughout the process. Aqueous solutions of the following substances have been used as freezants : Propylene glycol, Glycerol, Sodium chloride, Mixtures of salt and sugar.

25. Immersion freezing Cooling media should be non –toxic. If sugar solution contain 62% sucrose it can decrease temperature up to -21°C. 23% NaCl solution decrease temperature up to -21°C. Glycerol is mixed with water to make a solution 67% glycerol solution can decreases temperature up to -47 °C.

26. Immersion freezing This technique, although not common, is used commercially for canned citrus juice concentrate (cans of juice are passed continuously through a chamber containing liquid freezant); for poultry especially during the initial stages of freezing ( to impart a uniform, white color to the surface); and an occasionally for fish and shrimp.

27. Immersion freezing Advantages Disadvantages

28. Cryogenic freezing What is cryogenic freezing? using low boiling point liquid gases to freeze food product is called cryogenic freezing.

29. Cryogenic freezing What is cryogenics? Cryogenics is a branch of engineering where the production of cryogen and maintenance of low temperature technologies are studied. A person who study elements that have been subjected to extremely cold temperature is called cryogenicist.

30. Cryogenic freezing Cryogenic freezing is a new method of freezing, here the food is exposed to an atmosphere below -60 ° c through direct contact with liquefied gases such as nitrogen or carbon dioxide. Due to liquid extremely low temperature (-196 ° c) and (-79 ° c) freezing is instant. Liquid nitrogen is most commonly used because of very low boiling point (-196 ° c).

31. Types of cryogenic freezers There are two main types of cryogenic freezers. The one using immersion or dipping of product into the medium. In second type medium is sprayed on the product. In both type the product is continuously transported on a belt to the other end of the freezer. Usually those cryogenic freezers using dipping method or consuming more medium but give better freezing results. While spraying method ensure lower medium usage therefore lower cost.

32. Cryogenic freezing Advantages Low dehydration . Can be simpler to operate because no refrigeration is required. Lower capital cost. Efficient freezing and high product quality. Economical for low to medium capacity production and test runs. Disadvantages High operating cost of expandable refrigerant. Dependence of refrigerant delivery. Should be monitored regularly. Potential operational hazard. Uneconomical for large scale production.

33. C onclusion Preservation by low temperature technique is superior to other methods of long ter m preservation because it is more effective I retaining flavor color and nutritive value of food and moderately effective for preservation of texture. I t is comparatively a less time consuming method.

34. References