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ice crystal may vary with method of freezing i.e. quick freezing or slow freezing. Quick freezing is defined as the process where the temperature of the food passes through the zone of ice crystal formation in 10 minutes or less. The process removes quick removal of water and small ice crystals are formed in it.
Lecture Notes and Handouts. The handouts contain graphs that are referenced during each lecture. Handouts are not available for lectures 14, 24, and 25. Notes for Lectures 1–7 (PDF) Topics: Supply and Demand. Consumer Theory.
Freezing process is divided into two broad categories viz. slow freezing and quick freezing. Slow freezing : when thermal arrest time is more than 30 min. Quick freezing : Thermal arrest time is less than 30 min.
- Frozen Food Industry and Markets
- Basic Principles of Food Freezing
- Freezing Equipment
- General Considerations of Food Freezing Preservation
- Cold Supply Chain
- Pre-Processing Foods For Freezing
- Packaging Frozen Foods
- Frozen Food Quality
- Freezing and Food Safety
3.1.1 The US Frozen Food Industry
Freezing is one of three key methods for preserving fruits and vegetable (NAIC3114) commercially, alongside canning (NAIC311421) and food drying (NAICS 311423). The frozen food industry also extends to specialty foods (NAICS 311412). A listing of the main frozen foods groups are shown the Tables 13.7 and 13.8. The scope of the freezing industry is wide because virtually all food groups can be frozen. Economic information related to some of these industries can be found in the chapters coverin...
3.1.2 Global Frozen Food Markets
The global frozen food sector is worth 260 US$ billion per year (MarketsandMarkets 2014). The sector is currently valued in excess of US$26 billion for the European Union with the major segments being frozen ready meals, frozen fish and ice cream (Fig. 13.5). The benefits of freezing as compared to canning and drying are apparently, that the former retains more of the original quality of fresh foodstuffs. The processing time for food freezing is short compared other preservation methods (Barb...
3.2.1 The Preservation Effect of Freezing
Food is frozen and then maintained at lower temperatures compared with chilled foods. Differences in storage temperature aside, the longer shelf life of frozen products, (about 24 months) compared with chilled foods (max 1 month), is also due a water activity (AW) difference. For frozen food at –20 °C, the value AW was approximately 0.82 (Miyawaki 2018). Freezing will remove water from the bulk food in the form of ice, which can be physically separated from the liquid phase leaving behind a c...
3.2.2 Food Freezing Curves
The physical changes displayed by water during the freezing process can be summarized graphically (Fig. 13. 6B). For convenience the cooling curve is divided into four distinct stages; (1) removal of sensible heat and the cooling of liquid water, (2) freezing of the liquid water and removal of insensible heat also known as the latent heat for crystallization. During ice formation the temperature remains constant, (3) cooling of the solid ice mass, and (4) formation of a freeze concentrated ph...
3.2.3 Rapid Versus Slow Freezing
When foods are allowed to freeze slowly, water molecules migrate from smaller ice crystals to large ice crystals. This process called Ostwald ripening produces a more heterogeneous mass of ice, which impairs product quality. By comparison, when foods are frozen rapidly, sluggish water molecules do not have enough time to migrate to ice crystals at far distances and instead are “frozen in their tracks,” so to speak, forming relatively small ice crystals. To maintain top quality, small ice crys...
The earliest recorded use of artificial freezing appear to in the mid- 1800s, when fish was frozen in pans surrounded by ice and salt. In the late 1800s, fish, meat and poultry were frozen by ammonia refrigeration equipment, with fish being the most important in terms of volume. The commercial freezing of fruits and vegetables started in the early ...
There are three recognized methods of freezing foods: fast or quick freezing, sharp freezing, and slow freezing. There is no generally accepted definition for differentiating among the various freezing rates. It is obvious that with some methods, such as for food frozen in bulk, the product is frozen slowly. It is generally agreed that the quality ...
Although changes often take place in frozen foods during storage after freezing, the major changes take place during the distribution. Frozen foods may be carried to retail outlets in trucks that are not refrigerated or in which the refrigeration is not adequate to hold the temperature at 0 °F (−17.8 °C). Frozen foods may be delivered to the retail...
3.6.1 Blanching
Many foods require pretreatment before freezing. With a few exceptions, such as onions, vegetables must be blanched before they are frozen and stored. Vegetables are blanched by heating in steam or hot water (about 210 °F [98.9 °C]), while being carried along a perforated metal belt or screw conveyor, until the temperature of all parts reaches 185–200 °F (85–93.3 °C), then cooling with sprays of water or in water flumes. Vegetables are blanched prior to freezing in order to deactivate enzymes...
3.6.2 Other Pre-processes for Freezing
Citrus juices are often concentrated to about one-fifth of their original volumes, and then diluted back to one-fourth of the original volumes with fresh juice prior to freezing. This dilution with fresh juice is done to add back flavor components because most of the flavor compounds are removed during vacuum concentration of the juice. When this product is to be reconstituted, it requires the addition of water equal to three times its volume. Other solid natural products undergo simple pre-p...
Packaging is an important factor in the freezing of foods. It is not possible to maintain high humidity in frozen storage rooms because moisture present in the atmosphere of freezer storage rooms tends to condense and freeze on the expansion pipes or other apparatus used to cool the room, thereby reducing the cooling efficiency of the system. Packa...
A number of changes occur during the frozen storage of foods, which affects the sensory, nutritional, storage life and safety (Erickson and Yen-Con 1997). These changes may be physical, chemical, enzymatic, and, in rare cases, microbial. Microbial changes occur when refrigeration is inadequate. The storage life of frozen foods, at temperatures that...
Recent advice from the USDA (USDA Food Inspection Services 2010) suggests that freezing food will preserve safety “indefinitely”. Under ideal conditions, most microorganisms will not grow in frozen foods held at temperatures of 0 °F. At below freezing temperatures food borne microbes are “inactivated” or held in “suspended animation”. In technical ...
quick freezing. Since liquid are good heat conductor s, a product can be frozen rapidly by direct immersion in low temperature liquid for exam ple brine and sugar solutions.
Sep 30, 2020 · This paper describes studies to investigate the effects of a range of different OMF freezing settings using an ABI Cells Alive System (CAS) freezer on characteristics of the freezing...
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quick freezing. Slow freezing refers to formation of big ice crystals as a result of slow freezing. On the other hand, quick freezing refers to formation of small ice crystals and the time taken to freeze will be quick. The temperature of chamber during freezing will be -30o to -40oC. Immediately after fish is frozen, the fish is kept
