Drying (food)
Encyclopedia
Drying is a method of food preservation
that works by removing water
from the food, which inhibits the growth of microorganism
s and hinders quality decay
. Drying food using sun and wind to prevent spoilage has been practised since ancient times, and was the earliest form of food curing. Water is usually removed by evaporation
(air drying, sun drying, smoking or wind drying) but, in the case of freeze-drying, food is first frozen
and then the water is removed by sublimation. Bacteria, yeasts and molds need the water in the food to grow, and drying effectively prevents them from surviving in the food.
Many different foods are prepared by dehydration. Good examples are meat such as prosciutto
(a.k.a. Parma ham), bresaola
, and beef jerky. Dried and salted reindeer
meat is a traditional Sami
food
. First the meat is soaked / pickled in saltwater for a couple of days to guarantee the conservation of the meat. Then the meat is dried in the sun in spring when the air temperature is below zero. The dried meat can be further processed to make soup
.
Fruit
s change character completely when dried: the plum becomes a prune, the grape a raisin
; fig
s and date
s are also transformed in new, different products, that can be eaten as they are or else after rehydration. chilis
are frequently dried.
Home drying of vegetables, fruit and even meat (to produce jerky) can be carried out in the home employing sun drying or using electrical dehydrators (household appliance). Preservatives such as potassium metabisulphite, or BHA, BHT for meats may be used. These preservatives are not required, however dried products without these preservatives may required refrigerator or freezing to ensure a long period of storage.
Freeze dried vegetables are often found in backpackers food, hunters, military, etc. The exception to this rule are bulb
s, such as garlic
and onion
, which are often dried. Edible and psilocybin mushroom
s, as well as other fungi, are also sometimes dried for preservation purposes, to affect the potency of chemical components, or so they can be used as seasonings.
For centuries, much of the European diet depended on dried cod
, known as salt cod
or bacalhau
(with salt) or stockfish
(without). It formed the main protein source for the slaves
on the West Indian plantations, and was a major economic force within the triangular trade
. Dried shark
meat, known as Hákarl
, is a delicacy in Iceland
.
, corn
, soybean
, rice
and other grain
s as sorghum
, sunflower seed
s, rapeseed
/canola
, barley
, oats
, etc., are dried in grain dryers. In the main agricultural countries, drying comprises the reduction of moisture from about 17-30%w/w to values between 8 and 15%w/w, depending on the grain. The final moisture content for drying must be adequate for storage. The more oil the grain has, the lower its storage moisture content will be (though its initial moisture for drying will also be lower). Cereals are often dried to 14% w/w, while oilseeds, to 12.5% (soybeans), 8% (sunflower) and 9% (peanuts). Drying is carried out as a requisite for safe storage, in order to inhibit microbial growth. However, low temperatures in storage are also highly recommended to avoid degradative reactions and, especially, the growth of insects and mites. A good maximum storage temperature is about 18°C.
The largest dryers are normally used "Off-farm", in elevators, and are of the continuous type: Mixed-flow dryers are preferred in Europe, while Cross-flow dryers in the USA. In Argentina, both types are commonly found. Continuous flow dryers may produce up to 100 metric tonnes of dried grain per hour. The depth of grain the air must traverse in continuous dryers range from some 0.15 m in Mixed flow dryers to some 0.30 m in Cross-Flow.
Batch dryers are mainly used "On-Farm", particularly in the USA and Europe. They normally consist of a bin, with heated air flowing horizontally from an internal cylinder through an inner perforated metal sheet, then through an annular grain bed, some 0.50 m thick (coaxial with the internal cylinder) in radial direction, and finally across the outer perforated metal sheet, before being discharged to the atmosphere. The usual drying times range from 1 h to 4 h depending on how much water must be removed, type of grain, air temperature and the grain depth. In the USA, continuous counterflow dryers may be found on-farm, adapting a bin to slowly drying grain fed at the top and removed at the bottom of the bin by a sweeping auger. Grain drying is an active area of manufacturing and research. The performance of a dryer can be simulated with computer programs based on mathematical models that represent the phenomena involved in drying: physics, physical chemistry, thermodynamics and heat and mass transfer. Most recently computer models have been used to predict product quality by achieving a compromise between drying rate, energy consumption, and grain quality. A typical quality parameter in wheat drying is breadmaking quality and germination percentage whose reductions in \ are somewhat related.
Food preservation
Food preservation is the process of treating and handling food to stop or slow down spoilage and thus allow for longer storage....
that works by removing water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
from the food, which inhibits the growth of microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s and hinders quality decay
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
. Drying food using sun and wind to prevent spoilage has been practised since ancient times, and was the earliest form of food curing. Water is usually removed by evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
(air drying, sun drying, smoking or wind drying) but, in the case of freeze-drying, food is first frozen
Frozen food
Freezing food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved their game and produce in unheated buildings during the winter season. Freezing food slows down decomposition by turning water to ice, making it...
and then the water is removed by sublimation. Bacteria, yeasts and molds need the water in the food to grow, and drying effectively prevents them from surviving in the food.
Food types
Prosciutto
Prosciutto |ham]]) or Parma ham is a dry-cured ham that is usually thinly sliced and served uncooked; this style is called prosciutto crudo in Italian and is distinguished from cooked ham, prosciutto cotto....
(a.k.a. Parma ham), bresaola
Bresaola
Bresaola or brisaola is air-dried, salted beef that has been aged two or three months until it becomes hard and turns a dark red, almost purple colour. It is made from top round, and is lean and tender, with a sweet, musty smell...
, and beef jerky. Dried and salted reindeer
Reindeer
The reindeer , also known as the caribou in North America, is a deer from the Arctic and Subarctic, including both resident and migratory populations. While overall widespread and numerous, some of its subspecies are rare and one has already gone extinct.Reindeer vary considerably in color and size...
meat is a traditional Sami
Sami people
The Sami people, also spelled Sámi, or Saami, are the arctic indigenous people inhabiting Sápmi, which today encompasses parts of far northern Sweden, Norway, Finland, the Kola Peninsula of Russia, and the border area between south and middle Sweden and Norway. The Sámi are Europe’s northernmost...
food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
. First the meat is soaked / pickled in saltwater for a couple of days to guarantee the conservation of the meat. Then the meat is dried in the sun in spring when the air temperature is below zero. The dried meat can be further processed to make soup
Soup
Soup is a generally warm food that is made by combining ingredients such as meat and vegetables with stock, juice, water, or another liquid. Hot soups are additionally characterized by boiling solid ingredients in liquids in a pot until the flavors are extracted, forming a broth.Traditionally,...
.
Fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
s change character completely when dried: the plum becomes a prune, the grape a raisin
Raisin
Raisins are dried grapes. They are produced in many regions of the world. Raisins may be eaten raw or used in cooking, baking and brewing...
; fig
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
s and date
Date Palm
The date palm is a palm in the genus Phoenix, cultivated for its edible sweet fruit. Although its place of origin is unknown because of long cultivation, it probably originated from lands around the Persian Gulf. It is a medium-sized plant, 15–25 m tall, growing singly or forming a clump with...
s are also transformed in new, different products, that can be eaten as they are or else after rehydration. chilis
Chili pepper
Chili pepper is the fruit of plants from the genus Capsicum, members of the nightshade family, Solanaceae. The term in British English and in Australia, New Zealand, India, Malaysia and other Asian countries is just chilli without pepper.Chili peppers originated in the Americas...
are frequently dried.
Home drying of vegetables, fruit and even meat (to produce jerky) can be carried out in the home employing sun drying or using electrical dehydrators (household appliance). Preservatives such as potassium metabisulphite, or BHA, BHT for meats may be used. These preservatives are not required, however dried products without these preservatives may required refrigerator or freezing to ensure a long period of storage.
Freeze dried vegetables are often found in backpackers food, hunters, military, etc. The exception to this rule are bulb
Bulb
A bulb is a short stem with fleshy leaves or leaf bases. The leaves often function as food storage organs during dormancy.A bulb's leaf bases, known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. At the center of the bulb is...
s, such as garlic
Garlic
Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...
and onion
Onion
The onion , also known as the bulb onion, common onion and garden onion, is the most widely cultivated species of the genus Allium. The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion The onion...
, which are often dried. Edible and psilocybin mushroom
Mushroom
A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
s, as well as other fungi, are also sometimes dried for preservation purposes, to affect the potency of chemical components, or so they can be used as seasonings.
For centuries, much of the European diet depended on dried cod
Cod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...
, known as salt cod
Dried and salted cod
Dried and salted cod, often called salt cod or clipfish , is cod which has been preserved by drying after salting. Cod which has been dried without the addition of salt is called stockfish....
or bacalhau
Bacalhau
Bacalhau is the Portuguese word for codfish and—in a culinary context—dried and salted codfish. Fresh cod is referred to as bacalhau fresco .-Use:...
(with salt) or stockfish
Stockfish
Stockfish is unsalted fish, especially cod, dried by cold air and wind on wooden racks on the foreshore, called "hjell". The drying of food is the world's oldest known preservation method, and dried fish has a storage life of several years...
(without). It formed the main protein source for the slaves
Slavery
Slavery is a system under which people are treated as property to be bought and sold, and are forced to work. Slaves can be held against their will from the time of their capture, purchase or birth, and deprived of the right to leave, to refuse to work, or to demand compensation...
on the West Indian plantations, and was a major economic force within the triangular trade
Triangular trade
Triangular trade, or triangle trade, is a historical term indicating among three ports or regions. Triangular trade usually evolves when a region has export commodities that are not required in the region from which its major imports come...
. Dried shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
meat, known as Hákarl
Hákarl
Hákarl or kæstur hákarl is a food from Iceland. It is a Greenland or basking shark which has been cured with a particular fermentation process and hung to dry for four to five months...
, is a delicacy in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
.
Grain drying
Hundreds of millions of tonnes of wheatWheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, corn
Corn
Corn is the name used in the United States, Canada, and Australia for the grain maize.In much of the English-speaking world, the term "corn" is a generic term for cereal crops, such as* Barley* Oats* Wheat* Rye- Places :...
, soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
, rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
and other grain
GRAIN
GRAIN is a small international non-profit organisation that works to support small farmers and social movements in their struggles for community-controlled and biodiversity-based food systems. Our support takes the form of independent research and analysis, networking at local, regional and...
s as sorghum
Sorghum
Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...
, sunflower seed
Sunflower seed
The sunflower seed is the fruit of the sunflower . The term "sunflower seed" is actually a misnomer when applied to the seed in its pericarp . Botanically speaking, it is more properly referred to as an achene. When dehulled, the edible remainder is called the sunflower kernel.There are three types...
s, rapeseed
Rapeseed
Rapeseed , also known as rape, oilseed rape, rapa, rappi, rapaseed is a bright yellow flowering member of the family Brassicaceae...
/canola
Canola
Canola refers to a cultivar of either Rapeseed or Field Mustard . Its seeds are used to produce edible oil suitable for consumption by humans and livestock. The oil is also suitable for use as biodiesel.Originally, Canola was bred naturally from rapeseed in Canada by Keith Downey and Baldur R...
, barley
Barley
Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...
, oats
OATS
OATS - Open Source Assistive Technology Software - is a source code repository or "forge" for assistive technology software. It was launched in 2006 with the goal to provide a one-stop “shop” for end users, clinicians and open-source developers to promote and develop open source assistive...
, etc., are dried in grain dryers. In the main agricultural countries, drying comprises the reduction of moisture from about 17-30%w/w to values between 8 and 15%w/w, depending on the grain. The final moisture content for drying must be adequate for storage. The more oil the grain has, the lower its storage moisture content will be (though its initial moisture for drying will also be lower). Cereals are often dried to 14% w/w, while oilseeds, to 12.5% (soybeans), 8% (sunflower) and 9% (peanuts). Drying is carried out as a requisite for safe storage, in order to inhibit microbial growth. However, low temperatures in storage are also highly recommended to avoid degradative reactions and, especially, the growth of insects and mites. A good maximum storage temperature is about 18°C.
The largest dryers are normally used "Off-farm", in elevators, and are of the continuous type: Mixed-flow dryers are preferred in Europe, while Cross-flow dryers in the USA. In Argentina, both types are commonly found. Continuous flow dryers may produce up to 100 metric tonnes of dried grain per hour. The depth of grain the air must traverse in continuous dryers range from some 0.15 m in Mixed flow dryers to some 0.30 m in Cross-Flow.
Batch dryers are mainly used "On-Farm", particularly in the USA and Europe. They normally consist of a bin, with heated air flowing horizontally from an internal cylinder through an inner perforated metal sheet, then through an annular grain bed, some 0.50 m thick (coaxial with the internal cylinder) in radial direction, and finally across the outer perforated metal sheet, before being discharged to the atmosphere. The usual drying times range from 1 h to 4 h depending on how much water must be removed, type of grain, air temperature and the grain depth. In the USA, continuous counterflow dryers may be found on-farm, adapting a bin to slowly drying grain fed at the top and removed at the bottom of the bin by a sweeping auger. Grain drying is an active area of manufacturing and research. The performance of a dryer can be simulated with computer programs based on mathematical models that represent the phenomena involved in drying: physics, physical chemistry, thermodynamics and heat and mass transfer. Most recently computer models have been used to predict product quality by achieving a compromise between drying rate, energy consumption, and grain quality. A typical quality parameter in wheat drying is breadmaking quality and germination percentage whose reductions in \ are somewhat related.
Methods
There are many different methods for drying, each with their own advantages for particular applications; these include:- Bed dryers
- Drum dryingDrum dryingDrum drying is a method used for drying out liquids; for example, milk is applied as a thin film to the surface of a heated drum, and the dried milk solids are then scraped off with a knife...
- Freeze DryingFreeze dryingFreeze-drying is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport...
- Shelf dryers
- Spray dryingSpray dryingSpray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some...
- SunlightSunlightSunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
- Commercial food dehydratorFood dehydratorFood drying is a practice used to preserve fruit, vegetables and animal proteins after harvest since antiquity, and a food dehydrator refers to a device that removes moisture from food to aid in its preservation. A food dehydrator uses a heat source and air flow to reduce the water content of foods...
s - Household ovenOvenAn oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...
See also
- Dried fruitDried fruitDried fruit is fruit where the majority of the original water content has been removed either naturally, through sun drying, or through the use of specialized dryers or dehydrators. Dried fruit has a long tradition of use dating back to the fourth millennium BC in Mesopotamia, and is prized...
- Meat extractMeat extractMeat extract is highly concentrated meat stock, usually made from beef. It is used to add meat flavor in cooking, and to make broth for drinking....
- Bouillon cubeBouillon cubeA bouillon cube [ˈbuːjɒn kjuːb] or stock cube is dehydrated bouillon or stock formed into a small cube about 15 mm wide. It is made by dehydrating vegetables, meat stock, a small portion of fat, salt and seasonings and shaping them into a small cube...
- Instant soupInstant soupInstant soups are a kind of soup. They are produced on an industrial scale and treated in different ways for preservation. Usually instant soups, especially instant noodles, are dried, canned, or treated by freezing....
- Instant noodlesInstant noodlesInstant noodles are dried or precooked noodles and are often sold with packets of flavoring including seasoning oil. Dried noodles are usually eaten after being cooked or soaked in boiling water for 2 to 5 minutes, while precooked noodles can be reheated or eaten straight from the packet...