Freezing
Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...
food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved grains and produce in unheated buildings during the winter season. Freezing food slows decomposition by turning residual moisture into ice, inhibiting the growth of most bacterial species. In the
food commodity industry, there are two processes: mechanical and cryogenic (or
flash freezing
In physics and chemistry, flash freezing is the process whereby objects are frozen in just a few hours by subjecting them to cryogenic temperatures, or through direct contact with liquid nitrogen at . It is commonly used in the food industry.
Fl ...
). The freezing kinetics is important to preserve the food quality and texture. Quicker freezing generates smaller ice crystals and maintains cellular structure.
Cryogenic freezing is the quickest freezing technology available due to the ultra low liquid nitrogen temperature .
Preserving food in domestic kitchens during modern times is achieved using household
freezer
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
s. Accepted advice to householders was to freeze food on the day of purchase. An initiative by a supermarket group in 2012 (backed by the UK's
Waste & Resources Action Programme
WRAP (Waste & Resources Action Programme) is a British registered charity. It works with businesses, individuals and communities to achieve a circular economy, by helping them reduce waste, develop sustainable products and use resources in an effi ...
) promotes the freezing of food "as soon as possible up to the product's 'use by' date". The
Food Standards Agency
, type = Non-ministerial government department
, nativename =
, nativename_a =
, nativename_r =
, logo = Food Standards Agency.svg
, logo_width =
, logo_caption =
, seal =
, seal_width =
, seal_caption =
, picture =
, picture_width =
, ...
was reported as supporting the change, provided the food had been stored correctly up to that time.
Preservatives
Frozen products do not require any added
preservatives
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
because
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s do not grow when the temperature of the food is below , which is sufficient on its own in preventing food spoilage. Long-term
preservation
Preservation may refer to:
Heritage and conservation
* Preservation (library and archival science), activities aimed at prolonging the life of a record while making as few changes as possible
* ''Preservation'' (magazine), published by the Nat ...
of food may call for food storage at even lower temperatures.
Carboxymethylcellulose
Carboxymethyl cellulose (CMC) or cellulose gum is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose backbone. It is often used as its sodiu ...
(CMC), a tasteless and odorless stabilizer, is typically added to frozen food because it does not adulterate the quality of the product.
History
Natural food freezing (using winter frosts) had been in use by people in cold climates for centuries.
In 1861
Thomas Sutcliffe Mort
Thomas Sutcliffe Mort (23 December 18169 May 1878) was an Australian industrialist who improved the refrigeration of meat. He was renowned for speculation in the local pastoral industry as well as industrial activities such as his Ice-Works in ...
established at
Darling Harbour
Darling Harbour is a harbour adjacent to the city centre of Sydney, New South Wales, Australia that is made up of a large recreational and pedestrian precinct that is situated on western outskirts of the Sydney central business district.
Origin ...
in Sydney, Australia, the world's first freezing works, which later became the New South Wales Fresh Food and Ice Company. Mort financed experiments by
Eugene Dominic Nicolle, a French born engineer who had arrived in Sydney in 1853 and registered his first ice-making patent in 1861. The first trial shipment of frozen meat to London was in 1868. Although their machinery was never used in the frozen meat trade, Mort and Nicolle developed commercially viable systems for domestic trade. The financial return on that investment was minimal for Mort.
By 1885 a small number of chickens and geese were being shipped from Russia to London in insulated cases using this technique. By March 1899, the "British Refrigeration and Allied Interests" reported that a food importing business, "Baerselman Bros", was shipping some 200,000 frozen geese and chickens per week from three Russian depots to New Star Wharf, Lower Shadwell, London over three or four winter months. This trade in frozen food was enabled by the introduction of Linde cold air freezing plants in three Russian depots and the London warehouse. The Shadwell warehouse stored the frozen goods until they were shipped to markets in London, Birmingham, Liverpool and Manchester. The techniques were later expanded to the
meat-packing industry
The meat-packing industry (also spelled meatpacking industry or meat packing industry) handles the slaughtering, processing, packaging, and distribution of meat from animals such as cattle, pigs, sheep and other livestock. Poultry is generally no ...
.
From 1929,
Clarence Birdseye
Clarence Birdseye (December 9, 1886 – October 7, 1956) was an American inventor, entrepreneur, and naturalist, considered the founder of the modern frozen food industry. He founded the frozen food company Birds Eye. Among his inventions during h ...
introduced "
flash freezing
In physics and chemistry, flash freezing is the process whereby objects are frozen in just a few hours by subjecting them to cryogenic temperatures, or through direct contact with liquid nitrogen at . It is commonly used in the food industry.
Fl ...
" to the American public. Birdseye first became interested in food freezing during fur-trapping expeditions to
Labrador
, nickname = "The Big Land"
, etymology =
, subdivision_type = Country
, subdivision_name = Canada
, subdivision_type1 = Province
, subdivision_name1 ...
in 1912 and 1916, where he saw the natives use natural freezing to preserve foods.
The Icelandic Fisheries Commission was created in 1934 to initiate innovation in the industry, and encouraged fishermen to start quick-freezing their catch.
Íshúsfélag Ísfirðinga, one of the first frozen fish companies, was formed in
Ísafjörður
Ísafjörður (pronounced , meaning ''ice fjord'', literally ''fjord of ices'') is a town in the northwest of Iceland.
The oldest part of Ísafjörður with the town centre is located on a spit of sand, or ''eyri'', in Skutulsfjörður, a fjord ...
, Iceland, by a merger in 1937.
More advanced attempts include food frozen for
Eleanor Roosevelt
Anna Eleanor Roosevelt () (October 11, 1884November 7, 1962) was an American political figure, diplomat, and activist. She was the first lady of the United States from 1933 to 1945, during her husband President Franklin D. Roosevelt's four ...
on her trip to Russia. Other experiments involving orange juice, ice cream and vegetables were conducted by the military near the end of World War II.
Technology
![Tsukiji](https://upload.wikimedia.org/wikipedia/commons/8/84/Tsukiji.CuttingFrozenTuna.jpg)
The freezing technique itself, just like the frozen food market, is developing to become faster, more efficient and more cost-effective. As demonstrated by Birdeye's work, faster freezing means smaller ice crystals and a better-preserved product.
Birdeye's original cryogenic freezing approach using immersion in
liquid nitrogen
Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...
is still used. Due to its cost, however, use is limited to fish fillets, seafood, fruits, and berries. It is also possible to freeze food by immersion in the warmer (at ), but cheaper,
liquid carbon dioxide
Liquid carbon dioxide is the liquid state of carbon dioxide (), which cannot occur under atmospheric pressure. It can only exist at a pressure above , under (temperature of critical point) and above (temperature of triple point). Low-temperatu ...
, which can be produced by mechanical freezing (see below).
[
Most frozen food is instead frozen using a ''mechanical'' process using the ]vapor-compression refrigeration
Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings ...
technology similar to ordinary freezer
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
s. Such a process is cheaper at scale, but is usually slower. (There is also more upfront investment in the form of construction.) Nevertheless, a wide variety of processes have been devised to achieve faster heat transfer
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
from the food to the refrigerant:[
* Air-blast freezing is the oldest and cheapest approach. Food is placed into freezing rooms where the air is cold. Air is either forced ("blasted") onto the food or left static. This setup allows large chunks of food (usually meat or fish) to be easily processed compared to other methods, but is quite slow.
** Belt freezers simply put a ]conveyor belt
A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred to ...
inside a cold room.
** Tunnel freezing is a variant of air-blast freezing where food is put onto trolley racks and sent into a tunnel where cold air is continuously circulated.
** Fluidized bed freezing is a variant of air-blast freezing where pelletized food is blown by fast-moving cold air from below, forming a fluidized bed
A fluidized bed is a physical phenomenon that occurs when a solid particulate substance (usually present in a holding vessel) is under the right conditions so that it behaves like a fluid. The usual way to achieve a fluidize bed is to pump pressur ...
. The small size of the food combined with the fast-flowing air provides good heat transfer and therefore quick freezing.
* Contact freezing uses physical contact other than air to transfer the heat. Direct contact freezing puts the product directly in contact with the refrigerant, while indirect contact freezing uses a plate in between.
** Plate freezing is the most common form of contact freezing. Food is put between cold metal plates and then lightly pressed to maintain contact.
** Contact belt freezing combines a conveyor belt with plate freezing. It is usually used for fruit pulps, egg yolk, sauces and soups.
** Immersion freezing dips the product into a cold refrigerant liquid to freeze it, usually on a conveyor belt. The product may be in direct contact with the liquid, or be separated by a membrane. It can be used for freezing the outer shell of large particles to reduce water loss.
Individual Quick Freezing
Individual Quick Freezing, usually abbreviated IQF, is a descriptive term for freezing methods used in the food processing industry. The food is in individual pieces, and is frozen quickly. Products commonly frozen with IQF technologies are typical ...
is a descriptive term that includes all forms of freezing that is "individual" (not in a whole block) and "quick" (taking a maximum of several minutes). It may correspond to cryogenic freezing, fluidized bed freezing, or any other technique that meets the definition.
Packaging
Frozen food packaging
Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...
must maintain its integrity throughout filling, sealing, freezing, storage, transportation, thawing, and often cooking. As many frozen foods are cooked in a microwave oven
A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce t ...
, manufacturers have developed packaging that can go directly from freezer to the microwave.
In 1974, the first differential heating container (DHC) was sold to the public. A DHC is a sleeve of metal designed to allow frozen foods to receive the correct amount of heat. Various sized apertures were positioned around the sleeve. The consumer would put the frozen dinner into the sleeve according to what needed the most heat. This ensured proper cooking.
Today there are multiple options for packaging frozen foods. Boxes, cartons, bags, pouches, Boil-in-Bags, lidded trays and pans, crystallized PET
A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence, ...
trays, and composite and plastic cans.
Scientists continue to research new aspects of frozen food packaging. Active packaging
The terms active packaging, intelligent packaging, smart packaging and connected packaging refer to packaging systems used with foods, pharmaceuticals, and several other types of products. They help extend shelf life, monitor freshness, display inf ...
offers many new technologies that can actively sense and then neutralize the presence of bacteria or other harmful species. Active packaging can extend shelf-life, maintain product safety, and help preserve the food over a longer period of time. Several functions of active packaging are being researched:
* Oxygen scavenger
Oxygen scavengers or oxygen absorbers are added to enclosed packaging to help remove or decrease the level of oxygen in the package. They are used to help maintain product safety and extend shelf life.
There are many types of oxygen absorbers ...
s
* Time Temperature Indicator
A time temperature indicator (TTI) is a device or smart label that shows the accumulated time-temperature history of a product. Time temperature indicators are commonly used on food, pharmaceutical, and medical products to indicate exposure to ex ...
s and digital temperature data logger A temperature data logger, also called temperature monitor, is a portable measurement instrument that is capable of autonomously recording temperature over a defined period of time. The digital data can be retrieved, viewed and evaluated after it h ...
s
* Antimicrobials
* Carbon Dioxide controllers
* Microwave susceptor
A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which in some cases is re-emitted as infrared thermal radiation). The electromagnetic energy is typically radiofrequency or microwave radiation ...
s
* Moisture control: Water activity
Water activity (''aw'') is the partial vapor pressure of water in a solution divided by the standard state partial vapor pressure of water. In the field of food science, the standard state is most often defined as pure water at the same tempera ...
, Moisture vapor transmission rate
Moisture vapor transmission rate (MVTR), also water vapor transmission rate (WVTR), is a measure of the passage of water vapor through a substance. It is a measure of the permeability for vapor barriers.
There are many industries where moisture c ...
, etc.
* Flavor enhancers
* Odor generators
* Oxygen-permeable films
* Oxygen generators
Effects on nutrients
The process of flash freezing itself generally effectively retain the nutrient content of foodstuff with minor losses of vitamin, making them a cost-effective and nutritious substitute for fresh equivalents. However, pre-seasoned frozen food, such as packaged meals, may have a significant amounts of salt and fats added. It is therefore recommended to read the nutrition label.
Vitamin content of frozen fruits and vegetables
* Vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
: Usually lost in a higher concentration than any other vitamin. A study was performed on peas to determine the cause of vitamin C loss. A vitamin loss of 10% occurred during the blanching phase with the rest of the loss occurring during the cooling and washing stages. The vitamin loss was not actually accredited to the freezing process. Another experiment was performed involving peas and lima beans. Frozen and canned vegetables were both used in the experiment. The frozen vegetables were stored at and the canned vegetables were stored at room temperature . After 0, 3, 6, and 12 months of storage, the vegetables were analyzed with and without cooking. O'Hara, the scientist performing the experiment said, "From the view point of the vitamin content of the two vegetables when they were ready for the plate of the consumer, there did not appear to be any marked advantages attributable to method of preservation, frozen storage, processed in a tin, or processed in glass."
* Vitamin B1 (Thiamin): A vitamin loss of 25% is normal. Thiamin is easily soluble in water and is destroyed by heat.
* Vitamin B2 (Riboflavin): Not much research has been done to determine how freezing affects Riboflavin levels. Studies that have been performed are inconclusive. One study found an 18% vitamin loss in green vegetables, while another found a 4% loss. It is commonly accepted that the loss of Riboflavin has to do with the preparation for freezing rather than the freezing process itself.
* Vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
(Carotene): There is little loss of carotene during preparation for freezing and freezing of most vegetables. Much of the vitamin loss is incurred during the extended storage period.
Effectiveness
Freezing is an effective form of food preservation because the pathogens that cause food spoilage are killed or do not grow very rapidly at reduced temperatures. The process is less effective in food preservation than are thermal techniques, such as boiling, because pathogens are more likely to be able to survive cold temperatures rather than hot temperatures. One of the problems surrounding the use of freezing as a method of food preservation is the danger that pathogens deactivated (but not killed) by the process will once again become active when the frozen food thaws.
Foods may be preserved for several months by freezing. Long-term frozen storage requires a constant temperature of or less.
Defrosting
To be used, many cooked foods that have been previously frozen require defrosting prior to consumption. Preferably, some frozen meats should be defrosted prior to cooking to achieve the best outcome: cooked through evenly and of good texture.
The defrost system in freezers helps the equipment to perform properly, without thick layers of ice developing, thus preventing the evaporator coil from absorbing heat and cooling the cabinet.
Ideally, most frozen foods should be defrosted in a refrigerator
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
to avoid significant growth of pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s. However, this can require considerable time.
Food is often defrosted in one of several ways:
* at room temperature; this is dangerous since the outside may be defrosted while the inside remains frozen[
* in a refrigerator]
* in a microwave oven
A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce t ...
[
* wrapped in plastic and placed in cold water][ or under cold running water
People sometimes defrost frozen foods at ]room temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
because of time constraints or ignorance. Such foods should be promptly consumed after cooking or discarded and never be refrozen or refrigerated since pathogens are not killed by the refreezing process.
Quality
The speed of freezing has a direct impact on the size and the number of ice crystals formed within a food product's cells and extracellular space. Slow freezing leads to fewer but larger ice crystals while fast freezing leads to smaller but more numerous ice crystals. This difference in ice crystal size can affect the degree of residual enzymatic activity during frozen storage via the process of freeze concentration, which occurs when enzymes and solutes present in a fluid medium are concentrated between ice crystal formations. Increased levels of freeze concentration, mediated by the formation of large ice crystals, can promote enzymatic browning
Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regardin ...
.
Large ice crystals can also puncture the walls of the cells of the food product which will cause a degradation of the texture of the product as well as the loss of its natural juices during thawing. That is why there will be a qualitative difference observed between food products frozen by ventilated mechanical freezing, non-ventilated mechanical freezing or cryogenic freezing with liquid nitrogen.
Reaction
According to a 2007 study, an American consumes frozen food on average 71 times a year, most of which are pre-cooked frozen meals.
See also
* List of frozen food brands
This is a list of frozen food brands. Frozen food is food that is frozen from the time it is produced to the time it is
either defrosted or cooked by the consumer, or eaten while still frozen.
Frozen food brands
* Amy's Kitchen
* Aunt ...
** List of frozen dessert brands
This is a list of frozen dessert brands. Frozen dessert is the generic name for desserts made by freezing liquids, semi-solids, and sometimes even solids. They may be based on flavored water (shave ice, sorbet, snow cones, etc.), fruit purées (suc ...
** List of ice cream brands
This is a list of notable ice cream brands. Ice cream is a frozen dessert, usually made from dairy products such as milk and cream, and often combined with fruits or other ingredients and flavors. However, not all frozen desserts can be called ice ...
* Refrigerator
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
* Boil-in-bag
* Cold chain
A cold chain is a low temperature-controlled supply chain network. An unbroken cold chain is an uninterrupted series of refrigerated production, storage and distribution activities, along with associated equipment and logistics, which maintain qu ...
References
* Arsdel, Wallace, B. Van, Michael, J Copley, and Robert, L. Olson. ''Quality and Stability of Frozen Foods: Time-Temperature Tolerance and its Significance''. New York, NY: John Wiley & Sons,INC, 1968.
* "Clarence Birdseye.
Encyclopedia of World Biography
Vol. 19. 2nd ed. Detroit: Gale, 2004. 25-27. Gale Virtual Reference Library. Gale. Brigham Young University - Utah. 3 November 2009.
* Copson, David. ''Microwave Heating''. 2nd ed.. Westport, CT: The AVI Publishing Company, INC., 1975.
* Decareau, Robert. ''Microwave Foods: New Product Development''. Trumbull, CT: Food & Nutrition Press, INC., 1992.
* Gould, Grahame. ''New Methods of Food Preservation''. New York, NY: Chapman & Hall, 2000.
* Mathlouthi, Mohamed. ''Food Packaging and Preservation''. New York, NY: Chapman & Hall, 1994.*^Robinson, Richard. Microbiology of Frozen Foods. New York, NY: Elsevier Applied Science Publishers LTD, 1985.
* Russell, Nicholas J., and Grahame W. Gould. ''Food Preservatives''. 2nd ed. New York, NY: Kluwer Academic/Plenum Publishers, New York, 2003.
* Sun, Da-Wen. Handbook of Frozen Food Processing and Packaging. Boca Raton, Fl: Taylor & Francis Group, LLC, 2006.
* Tressler, Donald K., Clifford F. Evers, and Barbara, Hutchings Evers. ''Into the Freezer - and Out''. 2nd ed. New York, NY: The AVI Publishing Company, INC., 1953.
* Tressler, Donald K., and Clifford F. Evers. ''The Freezing Preservation of Foods''. 3rd ed. 1st volume. Westport, CT: The AVI Publishing Company, INC., 1957.
* Whelan, Elizabeth M., and Fredrick J. Stare. ''Panic in the Pantry: Facts and Fallacies About the Food You Buy''. Buffalo, NY: Prometheus Books, 1998.
External links
*
Food and Agriculture
Waste less by using frozen food
{{DEFAULTSORT:Frozen Food
Convenience foods
Food preservation
Food storage
Food and drink introduced in 1863
Food and drink introduced in 1923