The Nova classification groups food according to different food processing techniques.
Primary food processing is necessary to make most foods edible
while secondary food processing turns ingredients into familiar foods,
such as bread. Tertiary food processing results in ultra-processed foods and has been widely criticized for promoting overnutrition and obesity, containing too much sugar and salt, too little fiber, and otherwise being unhealthful in respect to dietary needs of humans and farm animals.
Processing levels
Primary food processing
These whole, dried bananas in Thailand are an example of primary food processing.
Primary food processing turns agricultural products, such as raw wheat kernels
or livestock, into something that can eventually be eaten. This
category includes ingredients that are produced by ancient processes
such as drying, threshing, winnowing and milling grain, shelling nuts, and butchering animals for meat.It also includes deboning and cutting meat, freezing and smoking fish and meat, extracting and filtering oils, canning food, preserving food through food irradiation, and candling eggs, as well as homogenizing and pasteurizing milk.
Contamination and spoilage problems in primary food processing can lead to significant public health threats, as the resulting foods are used so widely. However, many forms of processing contribute to improved food safety and longer shelf life before the food spoils. Commercial food processing uses control systems such as hazard analysis and critical control points (HACCP) and failure mode and effects analysis (FMEA) to reduce the risk of harm.
Secondary food processing
Baking bread is an example of secondary food processing.
Secondary food processing is the everyday process of creating food from ingredients that are ready to use. Baking bread,
regardless of whether it is made at home, in a small bakery, or in a
large factory, is an example of secondary food processing. Fermenting fish and making wine, beer, and other alcoholic products are traditional forms of secondary food processing. Sausages are a common form of secondary processed meat, formed by comminution (grinding) of meat that has already undergone primary processing. Most of the secondary food processing methods known to humankind are commonly described as cooking methods.
Tertiary food processing
Tertiary food processing is the commercial production of what is commonly called processed food. These are ready-to-eat or heat-and-serve foods, such as frozen meals and re-heated airline meals.
History
Food processing dates back to the prehistoric ages when crude processing incorporated fermenting, sun drying, preserving with salt, and various types of cooking
(such as roasting, smoking, steaming, and oven baking), Such basic food
processing involved chemical enzymatic changes to the basic structure
of food in its natural form, as well served to build a barrier against
surface microbial activity that caused rapid decay. Salt-preservation
was especially common for foods that constituted warrior and sailors'
diets until the introduction of canning methods. Evidence for the existence of these methods can be found in the writings of the ancient Greek, Chaldean, Egyptian and Roman civilizations as well as archaeological evidence from Europe, North and South America and Asia. These tried and tested processing techniques remained essentially the same until the advent of the Industrial Revolution. Examples of ready-meals also date back to before the preindustrial revolution, and include dishes such as Cornish pasty and Haggis. Both during ancient times and today in modern society these are considered processed foods.
Michael Foods egg-processing plant in Wakefield, Nebraska
Modern food processing technology developed in the 19th and 20th
centuries was developed in a large part to serve military needs. In
1809, Nicolas Appert
invented a hermetic bottling technique that would preserve food for
French troops which ultimately contributed to the development of
tinning, and subsequently canning by Peter Durand in 1810. Although
initially expensive and somewhat hazardous due to the lead used in cans,
canned goods would later become a staple around the world. Pasteurization, discovered by Louis Pasteur in 1864, improved the quality and safety of preserved foods and introduced the wine, beer, and milk preservation.
A form of pre-made split-pea soup that has become traditional
In the 20th century, World War II, the space race and the rising consumer society in developed countries contributed to the growth of food processing with such advances as spray drying, evaporation, juice concentrates, freeze drying and the introduction of artificial sweeteners, colouring agents, and such preservatives as sodium benzoate.
In the late 20th century, products such as dried instant soups,
reconstituted fruits and juices, and self cooking meals such as MRE food ration were developed. By the 20th century, automatic appliances like microwave oven, blender, and rotimatic paved way for convenience cooking.
In western Europe and North America, the second half of the 20th
century witnessed a rise in the pursuit of convenience. Food processing
companies marketed their products especially towards middle-class
working wives and mothers. Frozen foods (often credited to Clarence Birdseye) found their success in sales of juice concentrates and "TV dinners". Processors utilised the perceived value of time to appeal to the
postwar population, and this same appeal contributes to the success of convenience foods today.
Also in the late 20th century, food manufacturers began changing
their product model from a single "platonic dish", such as one version
of jarred spaghetti sauce, to offering multiple variations, such as a
plain version, a spicy version, and a chunky version.
Benefits of food processing include toxin removal, preservation,
easing marketing and distribution tasks, and increasing food
consistency. In addition, it increases yearly availability of many
foods, enables transportation of delicate perishable foods across long
distances and makes many kinds of foods safe to eat by de-activating
spoilage and pathogenic micro-organisms. Modern supermarkets would not exist without modern food processing techniques, and long voyages would not be possible.
Processed foods are usually less susceptible to early spoilage
than fresh foods and are better suited for long-distance transportation
from the source to the consumer. When they were first introduced, some processed foods helped to alleviate food shortages and improved the overall nutrition of populations as it made many new foods available to the masses.
Processing can also reduce the incidence of food-borne disease. Fresh materials, such as fresh produce and raw meats, are more likely to harbour pathogenic micro-organisms (e.g. Salmonella) capable of causing serious illnesses.
The extremely varied modern diet is only truly possible on a wide
scale because of food processing. Transportation of more exotic foods,
as well as the elimination of much hard labor gives the modern eater
easy access to a wide variety of food unimaginable to their ancestors.
The act of processing can often improve the taste of food significantly.
Mass production of food is much cheaper overall than individual production of meals from raw ingredients. Therefore, a large profit potential exists for the manufacturers and suppliers of processed food products. Individuals may see a benefit in convenience, but rarely see any direct financial cost benefit in using processed food as compared to home preparation.
Processed food freed people from the large amount of time involved in preparing and cooking "natural" unprocessed foods. The increase in free time allows people much more choice in life style
than previously allowed. In many families the adults are working away
from home and therefore there is little time for the preparation of food
based on fresh ingredients. The food industry offers products that fulfill many different needs: e.g. fully prepared ready meals that can be heated up in the microwave oven within a few minutes.
Modern food processing also improves the quality of life for people with allergies, diabetics, and other people who cannot consume some common food elements. Food processing can also add extra nutrients such as vitamins.
Processing of food can decrease its nutritional density. The amount
of nutrients lost depends on the food and processing method. For
example, heat destroys vitamin C. Therefore, canned fruits possess less vitamin C than their fresh alternatives. The USDA conducted a study of nutrient retention in 2004, creating a table of foods, levels of preparation, and nutrition.
New research highlighting the importance to human health of a
rich microbial environment in the intestine indicates that abundant food
processing (not fermentation of foods) endangers that environment.
Added sodium
One of the main sources for sodium in the diet is processed foods. Sodium, mostly in the form of sodium chloride,
i.e. salt, is added to prevent spoilage, add flavor and enhance the
texture of these foods. Americans consume an average of 3436 milligrams
of sodium per day, which is higher than the recommended limit of 2300
milligrams per day for healthy people, and more than twice the limit of
1500 milligrams per day for those at increased risk for heart disease.
Added sugars
While it is not necessary to limit the sugars found naturally in whole, unprocessed foods like fresh fruit, eating too much added sugar found in many processed foods increases the risk of heart disease, obesity, cavities and Type 2 diabetes. The American Heart Association
recommends women limit added sugars to no more than 420 kilojoules (100
kilocalories), or 25 grams, and men limit added sugars to no more than
650 kJ (155 kcal), or about 38.75 grams, per day. Currently, Americans
consume an average of 1,490 kJ (355 kcal) from added sugars each day.
Nutrient losses
Processing
foods often involves nutrient losses, which can make it harder to meet
the body's needs if these nutrients are not added back through
fortification or enrichment. For example, using high heat during
processing can cause vitamin C losses. Another example is refined
grains, which have less fiber, vitamins and minerals than whole grains.
Eating refined grains, such as those found in many processed foods,
instead of whole grains may increase the risk for high cholesterol, diabetes and obesity, according to a study published in "The American Journal of Clinical Nutrition" in December 2007.
Trans fats
Foods
that have undergone processing, including some commercial baked goods,
desserts, margarine, frozen pizza, microwave popcorn and coffee
creamers, sometimes contain trans fats.
This is the most unhealthy type of fat, and may increase risk for high
cholesterol, heart disease and stroke. The 2010 Dietary Guidelines for
Americans recommends keeping trans fat intake as low as possible.
Other potential disadvantages
Processed foods may actually take less energy to digest than whole foods, according to a study published in "Food & Nutrition Research"
in 2010, meaning more of their food energy content is retained within
the body. Processed foods also tend to be more allergenic than whole
foods, according to a June 2004 "Current Opinion in Allergy and Clinical
Immunology" article. Although the preservatives and other food
additives used in many processed foods are generally recognized as safe,
a few may cause problems for some individuals, including sulfites,
artificial sweeteners, artificial colors and flavors, sodium nitrate,
BHA and BHT, olestra, caffeine and monosodium glutamate — a flavor enhancer.
Wheat is grown on a larger area of land than any other food crop
(220.7 million hectares or 545 million acres in 2021). World trade in
wheat is greater than that of all other crops combined. In 2021, world
wheat production was 771 million tonnes (850 million short tons), making it the second most-produced cereal after maize (known as corn in North America and Australia; wheat is often called corn in countries including Britain). Since 1960, world production of wheat and other grain crops has tripled
and is expected to grow further through the middle of the 21st century.
Global demand for wheat is increasing because of the usefulness of gluten to the food industry.
A: Plant; B ripe ear of corn; 1 spikelet before flowering; 2 the same, flowering and spread, enlarged; 3 flowers with glumes; 4 stamens 5 pollen;
6 and 7 ovaries with juice scales; 8 and 9 parts of the scar; 10 fruit
husks; 11, 12, 13 seeds, natural size and enlarged; 14 the same cut up,
enlarged.
Wheat is a stout grass of medium to tall height. Its stem is jointed
and usually hollow, forming a straw. There can be many stems on one
plant. It has long narrow leaves, their bases sheathing the stem, one
above each joint. At the top of the stem is the flower head, containing
some 20 to 100 flowers. Each flower contains both male and female parts. The flowers are wind-pollinated, with over 99% of pollination events being self-pollinations and the rest cross-pollinations. The flower is housed in a pair of small leaflike glumes. The two (male) stamens and (female) stigmas protrude outside the glumes. The flowers are grouped into spikelets, each with between two and six flowers. Each fertilised carpel develops into a wheat grain or berry; botanically a caryopsis fruit, it is often called a seed. The grains ripen to a golden yellow; a head of grain is called an ear.
Leaves emerge from the shoot apical meristem in a telescoping fashion until the transition to reproduction i.e. flowering. The last leaf produced by a wheat plant is known as the flag leaf. It is denser and has a higher photosynthetic rate than other leaves, to supply carbohydrate
to the developing ear. In temperate countries the flag leaf, along with
the second and third highest leaf on the plant, supply the majority of
carbohydrate in the grain and their condition is paramount to yield
formation. Wheat is unusual among plants in having more stomata on the upper (adaxial) side of the leaf, than on the under (abaxial) side. It has been theorised that this might be an effect of it having been domesticated and cultivated longer than any other plant. Winter wheat generally produces up to 15 leaves per shoot and spring wheat up to 9 and winter crops may have up to 35 tillers (shoots) per plant (depending on cultivar).
Wheat roots are among the deepest of arable crops, extending as far down as 2 metres (6 ft 7 in). While the roots of a wheat plant are growing, the plant also accumulates an energy store in its stem, in the form of fructans, which helps the plant to yield under drought and disease pressure, but it has been observed that there is a trade-off between root growth
and stem non-structural carbohydrate reserves. Root growth is likely to
be prioritised in drought-adapted crops, while stem non-structural
carbohydrate is prioritised in varieties developed for countries where
disease is a bigger issue.
Depending on variety, wheat may be awned or not awned. Producing awns incurs a cost in grain number, but wheat awns photosynthesise more efficiently than their leaves with regards to water usage, so awns are much more frequent in varieties of wheat grown in hot
drought-prone countries than those generally seen in temperate
countries. For this reason, awned varieties could become more widely
grown due to climate change. In Europe, however, a decline in climate resilience of wheat has been observed.
Hunter-gatherers in West Asia harvested wild wheats for thousands of years before they were domesticated, perhaps as early as 21,000 BC, but they formed a minor component of their diets. In this phase of pre-domestication cultivation, early cultivars were
spread around the region and slowly developed the traits that came to
characterise their domesticated forms.
Repeated harvesting and sowing of the grains of wild grasses
led to the creation of domestic strains, as mutant forms ('sports') of
wheat were more amenable to cultivation. In domesticated wheat, grains
are larger, and the seeds (inside the spikelets) remain attached to the ear by a toughened rachis during harvesting. In wild strains, a more fragile rachis allows the ear to shatter easily, dispersing the spikelets. Selection for larger grains and non-shattering heads by farmers might
not have been deliberately intended, but simply have occurred because
these traits made gathering the seeds easier; nevertheless such
'incidental' selection was an important part of crop domestication. As the traits that improve wheat as a food source involve the loss of the plant's natural seed dispersal mechanisms, highly domesticated strains of wheat cannot survive in the wild.
Wild einkorn wheat (T. monococcum subsp. boeoticum) grows across Southwest Asia in open parkland and steppe environments. It comprises three distinct races, only one of which, native to Southeast Anatolia, was domesticated. The main feature that distinguishes domestic einkorn from wild is that its ears do not shatter without pressure, making it dependent on humans for dispersal and reproduction. It also tends to have wider grains. Wild einkorn was collected at sites such as Tell Abu Hureyra (c. 10,700–9000 BC) and Mureybet (c. 9800–9300 BC), but the earliest archaeological evidence for the domestic form comes after c. 8800 BC in southern Turkey, at Çayönü, Cafer Höyük, and possibly Nevalı Çori. Genetic evidence indicates that it was domesticated in multiple places independently.
Wild emmer wheat (T. turgidum subsp. dicoccoides) is less widespread than einkorn, favouring the rocky basaltic and limestone soils found in the hilly flanks of the Fertile Crescent. It is more diverse, with domesticated varieties falling into two major
groups: hulled or non-shattering, in which threshing separates the whole
spikelet;
and free-threshing, where the individual grains are separated. Both
varieties probably existed in prehistory, but over time free-threshing
cultivars became more common. Wild emmer was first cultivated in the southern Levant, as early as 9600 BC.Genetic studies have found that, like einkorn, it was domesticated in southeastern Anatolia, but only once. The earliest secure archaeological evidence for domestic emmer comes from Çayönü, c. 8300–7600 BC, where distinctive scars on the spikelets indicated that they came from a hulled domestic variety. Slightly earlier finds have been reported from Tell Aswad in Syria, c. 8500–8200 BC, but these were identified using a less reliable method based on grain size.
Early farming
Sickles with stone microblades were used to harvest wheat in the Neolithic period, c. 8500–4000 BC
Einkorn and emmer are considered two of the founder crops cultivated by the first farming societies in Neolithic West Asia. These communities also cultivated naked wheats (T. aestivum and T. durum) and a now-extinct domesticated form of Zanduri wheat (T. timopheevii), as well as a wide variety of other cereal and non-cereal crops. Wheat was relatively uncommon for the first thousand years of the Neolithic (when barley predominated), but became a staple after around 8500 BC. Early wheat cultivation did not demand much labour. Initially, farmers
took advantage of wheat's ability to establish itself in annual grasslands
by enclosing fields against grazing animals and re-sowing stands after
they had been harvested, without the need to systematically remove
vegetation or till the soil. They may also have exploited natural wetlands and floodplains to practice décrue farming, sowing seeds in the soil left behind by receding floodwater.It was harvested with stone-bladedsickles. The ease of storing wheat and other cereals led farming households to
become gradually more reliant on it over time, especially after they
developed individual storage facilities that were large enough to hold
more than a year's supply.
Wheat grain was stored after threshing, with the chaff removed. It was then processed into flour using ground stonemortars. Bread made from ground einkorn and the tubers of a form of club rush (Bolboschoenus glaucus) was made as early as 12,400 BC. At Çatalhöyük (c. 7100–6000 BC), both wholegrain wheat and flour was used to prepare bread, porridge and gruel. Apart from food, wheat may also have been important to Neolithic societies as a source of straw, which could be used for fuel, wicker-making, or wattle and daub construction.
Spread
Domestic
wheat was quickly spread to regions where its wild ancestors did not
grow naturally. Emmer was introduced to Cyprus as early as 8600 BC and
einkorn c. 7500 BC; emmer reached Greece by 6500 BC, Egypt shortly after 6000 BC, and Germany and Spain by 5000 BC. "The early Egyptians were developers of bread and the use of the oven and developed baking into one of the first large-scale food production industries." By 4000 BC, wheat had reached the British Isles and Scandinavia.Wheat was also cultivated in India around 3500 BC. Wheat likely appeared in China's lower Yellow River around 2600 BC.
The oldest evidence for hexaploid wheat has been confirmed through DNA analysis of wheat seeds, dating to around 6400–6200 BC, recovered from Çatalhöyük. As of 2023, the earliest known wheat with sufficient gluten for yeasted breads was found in a granary at Assiros in Macedonia dated to 1350 BC. From the Middle East, wheat continued to spread across Europe and to the Americas in the Columbian exchange. In the British Isles, wheat straw (thatch) was used for roofing in the Bronze Age, and remained in common use until the late 19th century. White wheat bread was historically a high status food, but during the
nineteenth century it became in Britain an item of mass consumption,
displacing oats, barley and rye from diets in the North of the country. It became "a sign of a high degree of culture". After 1860, the enormous expansion of wheat production in the United States flooded the world market, lowering prices by 40%, and (along with the expansion of potato growing) made a major contribution to the nutritional welfare of the poor.
Sumeriancylinder seal impression dating to c. 3200 BC showing an ensi and his acolyte feeding a sacred herd wheat stalks; Ninurta was an agricultural deity and, in a poem known as the "Sumerian Georgica", he offers detailed advice on farming
Some wheat species are diploid, with two sets of chromosomes, but many are stable polyploids, with four sets of chromosomes (tetraploid) or six (hexaploid). Einkorn wheat (Triticum monococcum) is diploid (AA, two complements of seven chromosomes, 2n=14). Most tetraploid wheats (e.g. emmer and durum wheat) are derived from wild emmer, T. dicoccoides. Wild emmer is itself the result of a hybridization between two diploid wild grasses, T. urartu and a wild goatgrass such as Ae. speltoides. The hybridization that formed wild emmer (AABB, four complements of
seven chromosomes in two groups, 4n=28) occurred in the wild, long
before domestication, and was driven by natural selection. Hexaploid wheats evolved in farmers' fields as wild emmer hybridized with another goatgrass, Ae. squarrosa or Ae. tauschii, to make the hexaploid wheats including bread wheat.
A 2007 molecular phylogeny of the wheats gives the following not fully-resolved cladogram
of major cultivated species; the large amount of hybridisation makes
resolution difficult. Markings like "6N" indicate the degree of polyploidy of each species:
During 10,000 years of cultivation, numerous forms of wheat, many of them hybrids, have developed under a combination of artificial and natural selection. This complexity and diversity of status has led to much confusion in the naming of wheats.
Major species
Hexaploid species (6N)
Common wheat or bread wheat (T. aestivum) – The most widely cultivated species in the world.
Spelt (T. spelta) – Another species largely replaced by bread wheat, but in the 21st century grown, often organically, for artisanal bread and pasta.
Tetraploid species (4N)
Durum (T. durum) – A wheat widely used today, and the second most widely cultivated wheat.
Emmer (T. turgidum subsp. dicoccum and T. t. conv. durum) – A species cultivated in ancient times, derived from wild emmer, T. dicoccoides, but no longer in widespread use.
Khorasan or Kamut (T. turgidum ssp. turanicum, also called T. turanicum)
is an ancient grain type; Khorasan is a historical region in modern-day
Afghanistan and the northeast of Iran. The grain is twice the size of
modern wheat and has a rich nutty flavor.
Diploid species (2N)
Einkorn (T. monococcum). Domesticated from wild einkorn, T. boeoticum, at the same time as emmer wheat.
Hulled versus free-threshing species
Hulled wheat and einkorn. Note how the einkorn ear breaks down into intact spikelets.
The wild species of wheat, along with the domesticated varieties einkorn, emmer and spelt, have hulls. This more primitive morphology (in evolutionary terms)
consists of toughened glumes that tightly enclose the grains, and (in
domesticated wheats) a semi-brittle rachis that breaks easily on
threshing. The result is that when threshed, the wheat ear breaks up
into spikelets. To obtain the grain, further processing, such as milling
or pounding, is needed to remove the hulls or husks. Hulled wheats are
often stored as spikelets because the toughened glumes give good
protection against pests of stored grain. In free-threshing (or naked) forms, such as durum wheat and common
wheat, the glumes are fragile and the rachis tough. On threshing, the chaff breaks up, releasing the grains.
Classification of wheat greatly varies by the producing country.
Argentina's grain classes were formerly related to the production region or port of shipment: Rosafe (grown in Santa Fe province, shipped through Rosario), Bahia Blanca (grown in Buenos Aires and La Pampa provinces and shipped through Bahia Blanca), Buenos Aires (shipped through the port of Buenos Aires).
While mostly similar to the US Hard Red Spring wheat, the
classification caused inconsistencies, so Argentina introduced three new
classes of wheat, with all names using a prefix Trigo Dura Argentina (TDA) and a number.
The grain classification in Australia is within the purview of its National Pool Classification Panel. Australia chose to measure the protein content at 11% moisture basis.
The decisions on the wheat classification in Canada are coordinated by the Variety Registration Office of the Canadian Food Inspection Agency. Like in the US system, the eight classes in Western Canada and six classes in Eastern Canada
are based on colour, season, and hardness. Canada has a unique
requirement that the varieties of wheat grains should allow for purely
visual identification.
The wheat grain classes used in the United States are named by colour, season, and hardness.
†Percentages estimated using US recommendations for adults, except for potassium, which is estimated based on expert recommendation from the National Academies.
Wheat is a significant source of vegetable proteins in human food, having a relatively high protein content compared to other major cereals. However, wheat proteins have a low quality for human nutrition, according to the DIAAS protein quality evaluation method.Though they contain adequate amounts of the other essential amino
acids, at least for adults, wheat proteins are deficient in the essential amino acidlysine. Because the proteins present in the wheat endosperm (gluten proteins) are particularly poor in lysine, white flours are more deficient in lysine compared with whole grains. Significant efforts in plant breeding are made to develop lysine-rich wheat varieties, without success, as of 2017. Supplementation with proteins from other food sources (mainly legumes) is commonly used to compensate for this deficiency, since the limitation of a single essential amino acid causes the others
to break down and become excreted, which is especially important during
growth.
Health advisories
Consumed worldwide by billions of people, wheat is a significant food for human nutrition, particularly in the least developed countries where wheat products are primary foods. When eaten as the whole grain, wheat supplies multiple nutrients and dietary fiber recommended for children and adults. In genetically susceptible people, wheat gluten can trigger coeliac disease. Coeliac disease affects about 1% of the general population in developed countries. The only known effective treatment is a strict lifelong gluten-free diet. While coeliac disease is caused by a reaction to wheat proteins, it is not the same as a wheat allergy. Other diseases triggered by eating wheat are non-coeliac gluten sensitivity (estimated to affect 0.5% to 13% of the general population), gluten ataxia, and dermatitis herpetiformis. Certain short-chain carbohydrates present in wheat, known as FODMAPs (mainly fructose polymers), may be the cause of non-coeliac gluten sensitivity. As of 2019, reviews have concluded that FODMAPs only explain certain gastrointestinal symptoms, such as bloating, but not the extra-digestive symptoms that people with non-coeliac gluten sensitivity may develop.Other wheat proteins, amylase-trypsin inhibitors, have been identified as the possible activator of the innate immune system in coeliac disease and non-coeliac gluten sensitivity. These proteins are part of the plant's natural defense against insects and may cause intestinal inflammation in humans.
Wheat's share (brown) of world crop production fell in the 21st century.
In 2023, world wheat production was 799 million tonnes, led by China,
India, and Russia which collectively provided 42.4% of the world total. As of 2019, the largest exporters were
Russia (32 million tonnes), United States (27), Canada (23) and France
(20), while the largest importers were Indonesia (11 million tonnes),
Egypt (10.4) and Turkey (10.0). In 2021, wheat was grown on 220.7 million hectares or 545 million acres worldwide, more than any other food crop. World trade in wheat is greater than for all other crops combined. Global demand for wheat is increasing due to the unique viscoelastic and adhesive properties of gluten
proteins, which facilitate the production of processed foods, whose
consumption is increasing as a result of the worldwide industrialization
process and westernization of diets.
19th century
Wheat prices in England, 1264–1996
Wheat became a central agriculture endeavor in the worldwide British Empire in the 19th century, and remains of great importance in Australia, Canada and India. In Australia, with vast lands and a limited work force, expanded
production depended on technological advances, especially regarding
irrigation and machinery. By the 1840s there were 900 growers in South Australia. They used "Ridley's Stripper", a reaper-harvester perfected by John Ridley in 1843, to remove the heads of grain. In Canada, modern farm implements made
large scale wheat farming possible from the late 1840s. By 1879, Saskatchewan was the center, followed by Alberta, Manitoba and Ontario,
as the spread of railway lines allowed easy exports to Britain. By
1910, wheat made up 22% of Canada's exports, rising to 25% in 1930
despite the sharp decline in prices during the worldwide Great Depression. Efforts to expand wheat production in South Africa, Kenya and India
were stymied by low yields and disease. However, by 2000 India had
become the second largest producer of wheat in the world. In the 19th century the American wheat frontier moved rapidly westward.
By the 1880s 70% of American exports went to British ports. The first
successful grain elevator was built in Buffalo in 1842. The cost of transport fell rapidly. In 1869 it cost 37 cents to transport a bushel of wheat from Chicago to Liverpool. In 1905 it was 10 cents.
Late 20th century yields
In
the 20th century, global wheat output expanded by about 5-fold, but
until about 1955 most of this reflected increases in wheat crop area,
with lesser (about 20%) increases in crop yields per unit area. After
1955 however, there was a ten-fold increase in the rate of wheat yield
improvement per year, and this became the major factor allowing global
wheat production to increase. Thus technological innovation and
scientific crop management with synthetic nitrogen fertilizer,
irrigation and wheat breeding were the main drivers of wheat output
growth in the second half of the century. There were some significant
decreases in wheat crop area, for instance in North America. Better seed storage and germination ability (and hence a smaller
requirement to retain harvested crop for next year's seed) is another
20th-century technological innovation. In medieval England, farmers
saved one-quarter of their wheat harvest as seed for the next crop,
leaving only three-quarters for food and feed consumption. By 1999, the
global average seed use of wheat was about 6% of output. In the 21st century, rising temperatures associated with global warming are reducing wheat yield in several locations.
Agronomy
Growing wheat
Wheat is an annual crop. It can be planted in autumn and harvested in early summer as winter wheat in climates that are not too severe, or planted in spring and harvested in autumn as spring wheat. It is normally planted after tilling the soil by ploughing and then harrowing to kill weeds and create an even surface. The seeds are then scattered on the surface, or drilled
into the soil in rows. Winter wheat lies dormant during a winter
freeze. It needs to develop to a height of 10 to 15 cm before the cold
intervenes, so as to be able to survive the winter; it requires a period
with the temperature at or near freezing, its dormancy then being broken by the thaw or rise in temperature. Spring wheat does not undergo dormancy. Wheat requires a deep soil, preferably a loam with organic matter, and available minerals including soil nitrogen, phosphorus, and potassium. An acid and peaty soil is not suitable. Wheat needs some 30 to 38 cm of rain in the growing season to form a good crop of grain.
The farmer may intervene while the crop is growing to add fertilizer, water by irrigation, or pesticides such as herbicides to kill broad-leaved weeds or insecticides
to kill insect pests. The farmer may assess soil minerals, soil water,
weed growth, or the arrival of pests to decide timely and cost-effective
corrective actions, and crop ripeness and water content to select the
right moment to harvest. Harvesting involves reaping, cutting the stems to gather the crop; and threshing, breaking the ears to release the grain; both steps are carried out by a combine harvester. The grain is then dried so that it can be stored safe from mould fungi.
Crop development
Wheat developmental stages on the BBCH and Zadok's scales
Wheat normally needs between 110 and 130 days between sowing and
harvest, depending upon climate, seed type, and soil conditions. Optimal
crop management requires that the farmer have a detailed understanding
of each stage of development in the growing plants. In particular,
spring fertilizers, herbicides, fungicides, and growth regulators
are typically applied only at specific stages of plant development. For
example, it is currently recommended that the second application of
nitrogen is best done when the ear (not visible at this stage) is about
1 cm in size (Z31 on Zadoks scale).
Knowledge of stages is also important to identify periods of higher
risk from the climate. Farmers benefit from knowing when the 'flag leaf'
(last leaf) appears, as this leaf represents about 75% of
photosynthesis reactions during the grain filling period, and so should
be preserved from disease or insect attacks to ensure a good yield.
Several systems exist to identify crop stages, with the Feekes
and Zadoks scales being the most widely used. Each scale is a standard
system which describes successive stages reached by the crop during the
agricultural season. For example, the stage of pollen formation from the mother cell, and the stages between anthesis and maturity, are susceptible to high temperatures, and this adverse effect is made worse by water stress.
Technological advances in soil preparation and seed placement at planting time, use of crop rotation and fertilizers
to improve plant growth, and advances in harvesting methods have all
combined to promote wheat as a viable crop. When the use of seed drills
replaced broadcasting sowing of seed in the 18th century, another great
increase in productivity occurred. Yields of pure wheat per unit area
increased as methods of crop rotation were applied to land that had long
been in cultivation, and the use of fertilizers became widespread.
Improved agricultural husbandry has more recently included pervasive automation, starting with the use of threshing machines, and progressing to large and costly machines like the combine harvester which greatly increased productivity. At the same time, better varieties such as Norin 10 wheat, developed in Japan in the 1930s, or the dwarf wheat developed by Norman Borlaug in the Green Revolution, greatly increased yields.
In addition to gaps in farming system technology and knowledge,
some large wheat grain-producing countries have significant losses after
harvest at the farm and because of poor roads, inadequate storage
technologies, inefficient supply chains and farmers' inability to bring
the produce into retail markets dominated by small shopkeepers. Some 10%
of total wheat production is lost at farm level, another 10% is lost
because of poor storage and road networks, and additional amounts are
lost at the retail level.
In the Punjab region
of the Indian subcontinent, as well as North China, irrigation has been
a major contributor to increased grain output. More widely over the
last 40 years, a massive increase in fertilizer use together with the
increased availability of semi-dwarf varieties in developing countries,
has greatly increased yields per hectare. In developing countries, use of (mainly nitrogenous) fertilizer
increased 25-fold in this period. However, farming systems rely on much
more than fertilizer and breeding to improve productivity. A good
illustration of this is Australian wheat growing in the southern winter
cropping zone, where, despite low rainfall (300 mm), wheat cropping is
successful even with relatively little use of nitrogenous fertilizer.
This is achieved by crop rotation with leguminous pastures. The
inclusion of a canola crop in the rotations has boosted wheat yields by a further 25%. In these low rainfall areas, better use of available soil-water (and
better control of soil erosion) is achieved by retaining the stubble
after harvesting and by minimizing tillage.
Combine harvester cuts the wheat stems, threshes the wheat, crushes the chaff and blows it across the field, and loads the grain onto a tractor trailer.
Pests and diseases
Pests and diseases consume 21.47% of the world's wheat crop annually.
There are many wheat diseases, mainly caused by fungi, bacteria, and viruses. Plant breeding
to develop new disease-resistant varieties, and sound crop management
practices are important for preventing disease. Fungicides, used to
prevent the significant crop losses from fungal disease, can be a
significant variable cost in wheat production. Estimates of the amount
of wheat production lost owing to plant diseases vary between 10 and 25%
in Missouri. A wide range of organisms infect wheat, of which the most important are viruses and fungi.
The main wheat-disease categories are:
Seed-borne diseases: these include seed-borne scab, seed-borne Stagonospora (previously known as Septoria), common bunt (stinking smut), and loose smut. These are managed with fungicides.
Leaf- and head- blight diseases: Powdery mildew, leaf rust, Septoria tritici leaf blotch, Stagonospora (Septoria) nodorum leaf and glume blotch, and Fusarium head scab.
Crown and root rot diseases: Two of the more important of these are 'take-all' and Cephalosporium stripe. Both of these diseases are soil borne.
Stem rust diseases: Caused by Puccinia graminis f. sp. tritici (basidiomycete) fungi e.g. Ug99
Wheat blast: Caused by Magnaporthe oryzae Triticum.
A historically significant disease of cereals including wheat, though commoner in rye is ergot; it is unusual among plant diseases in also causing sickness in humans who ate grain contaminated with the fungus involved, Claviceps purpurea.
Among insect pests of wheat is the wheat stem sawfly,
a chronic pest in the Northern Great Plains of the United States and in the Canadian Prairies. Wheat is the food plant of the larvae of some Lepidoptera (butterfly and moth) species including the flame, rustic shoulder-knot, setaceous Hebrew character and turnip moth.
Early in the season, many species of birds and rodents feed upon wheat
crops. These animals can cause significant damage to a crop by digging
up and eating newly planted seeds or young plants. They can also damage
the crop late in the season by eating the grain from the mature spike.
Recent post-harvest losses in cereals amount to billions of dollars per
year in the United States alone, and damage to wheat by various borers,
beetles and weevils is no exception. Rodents can also cause major losses during storage, and in major grain
growing regions, field mice numbers can sometimes build up explosively
to plague proportions because of the ready availability of food. To reduce the amount of wheat lost to post-harvest pests, Agricultural Research Service
scientists have developed an "insect-o-graph", which can detect insects
in wheat that are not visible to the naked eye. The device uses
electrical signals to detect the insects as the wheat is being milled.
The new technology is so precise that it can detect 5–10 infested seeds
out of 30,000 good ones.
Breeding objectives
In traditional agricultural systems, wheat populations consist of landraces,
informal farmer-maintained populations that often maintain high levels
of morphological diversity. Although landraces of wheat are no longer
extensively grown in Europe and North America, they continue to be
important elsewhere. The origins of formal wheat breeding
lie in the nineteenth century, when single line varieties were created
through selection of seed from a single plant noted to have desired
properties. Modern wheat breeding developed in the first years of the
twentieth century and was closely linked to the development of Mendelian genetics.
The standard method of breeding inbred wheat cultivars is by crossing
two lines using hand emasculation, then selfing or inbreeding the
progeny. Selections are identified (shown to have the genes
responsible for the varietal differences) ten or more generations before
release as a variety or cultivar.
Major breeding objectives include high grain yield, good quality, disease- and insect resistance and tolerance to abiotic stresses, including mineral, moisture and heat tolerance. Wheat has been the subject of mutation breeding, with the use of gamma-, x-rays, ultraviolet light (collectively, radiation breeding),
and sometimes harsh chemicals. The varieties of wheat created through
these methods are in the hundreds (going as far back as 1960), more of
them being created in higher populated countries such as China. Bread wheat with high grain iron and zinc content has been developed through gamma radiation breeding, and through conventional selection breeding. International wheat breeding is led by the International Maize and Wheat Improvement Center in Mexico. ICARDA is another major public sector international wheat breeder, but it was forced to relocate from Syria to Lebanon in the Syrian Civil War.
Pathogens and wheat are in a constant process of coevolution. Spore-producing wheat rusts are substantially adapted towards successful spore propagation, which is essentially to say its R0. These pathogens tend towards high-R0evolutionary attractors.
For higher yields
Breeding has increased yields over time
The presence of certain versions of wheat genes has been important
for crop yields. Genes for the 'dwarfing' trait, first used by Japanese
wheat breeders to produce Norin 10 short-stalked wheat, have had a huge effect on wheat yields worldwide, and were major factors in the success of the Green Revolution in Mexico and Asia, an initiative led by Norman Borlaug. Dwarfing genes enable the carbon that is fixed in the plant during
photosynthesis to be diverted towards seed production, and they also
help prevent the problem of lodging. "Lodging" occurs when an ear stalk falls over in the wind and rots on
the ground, and heavy nitrogenous fertilization of wheat makes the grass
grow taller and become more susceptible to this problem. By 1997, 81% of the developing world's wheat area was planted to
semi-dwarf wheats, giving both increased yields and better response to
nitrogenous fertilizer.
T. turgidum subsp. polonicum, known for its longer glumes and grains, has been bred into main wheat lines for its grain size effect, and likely has contributed these traits to Triticum petropavlovskyi and the Portuguese landrace group Arrancada. As with many plants, MADS-box
influences flower development, and more specifically, as with other
agricultural Poaceae, influences yield. Despite that importance, as of
2021 little research has been done into MADS-box and other such spikelet and flower genetics in wheat specifically.
The world record wheat yield is about 17 tonnes per hectare (15,000 pounds per acre), reached in New Zealand in 2017. A project in the UK, led by Rothamsted Research
has aimed to raise wheat yields in the country to 20 t/ha
(18,000 lb/acre) by 2020, but in 2018 the UK record stood at 16 t/ha
(14,000 lb/acre), and the average yield was just 8 t/ha (7,100 lb/acre).
For disease resistance
Different strains have been infected with the stem rust fungus. The strains bred to be resistant have their leaves unaffected or relatively unaffected by the fungus.
Wild grasses in the genus Triticum and related genera, and grasses such as rye have been a source of many disease-resistance traits for cultivated wheat breeding since the 1930s. Some resistance genes have been identified against Pyrenophora tritici-repentis, especially races 1 and 5, those most problematic in Kazakhstan. Wild relative, Aegilops tauschii is the source of several genes effective against TTKSK/Ug99 - Sr33, Sr45, Sr46, and SrTA1662 - of which Sr33 and SrTA1662 are the work of Olson et al., 2013, and Sr45 and Sr46 are also briefly reviewed therein.
Lr34 is widely deployed in cultivars due to its abnormally broad effectiveness, conferring resistance against leaf- and stripe-rusts, and powdery mildew. An important quantitative resistance gene, Lr34, has been isolated and
used intensively in wheat cultivation worldwide; it provides a novel
resistance mechanism. Krattinger et al. 2009 find Lr34 to be an ABC transporter, and conclude that this is the probable reason for its effectiveness and the reason that it produces a 'slow rusting'/adult resistance phenotype.
In 2003 the first resistance genes against fungal diseases in wheat were isolated. In 2021, novel resistance genes were identified in wheat against powdery mildew and wheat leaf rust.Modified resistance genes have been tested in transgenic wheat and barley plants.
To create hybrid vigor
Because wheat self-pollinates, creating hybrid seed to provide the possible benefits of heterosis,
hybrid vigor (as in the familiar F1 hybrids of maize), is extremely
labor-intensive; the high cost of hybrid wheat seed relative to its
moderate benefits have kept farmers from adopting them widely despite nearly 90 years of effort. Commercial hybrid wheat seed has been produced using chemical hybridizing agents, plant growth regulators that selectively interfere with pollen development, or naturally occurring cytoplasmic male sterility
systems. Hybrid wheat has been a limited commercial success in Europe
(particularly France), the United States and South Africa.
Synthetic hexaploids made by crossing the wild goatgrass wheat ancestor Aegilops tauschii, and other Aegilops, and various durum wheats are now being deployed, and these increase the genetic diversity of cultivated wheats.
For gluten content
Modern bread wheat varieties have been cross-bred to contain greater amounts of gluten, which affords significant advantages for improving the quality of breads and pastas from a functional point of view. However, a 2020 study that grew and analyzed 60 wheat cultivars from
between 1891 and 2010 found no changes in albumin/globulin and gluten
contents over time. "Overall, the harvest year had a more significant
effect on protein composition than the cultivar. At the protein level,
we found no evidence to support an increased immunostimulatory potential of modern winter wheat."
For water efficiency
Stomata
(or leaf pores) are involved in both uptake of carbon dioxide gas from
the atmosphere and water vapor losses from the leaf due to water transpiration. Basic physiological investigation of these gas exchange processes has yielded carbon isotope
based method used for breeding wheat varieties with improved water-use
efficiency. These varieties can improve crop productivity in rain-fed
dry-land wheat farms.
For insect resistance
The
complex genome of wheat has made its improvement difficult. Comparison
of hexaploid wheat genomes using a range of chromosome pseudomolecule
and molecular scaffold assemblies in 2020 has enabled the resistance
potential of its genes to be assessed. Findings include the
identification of "a detailed multi-genome-derived nucleotide-binding
leucine-rich repeat protein repertoire" which contributes to disease
resistance, while the gene Sm1 provides a degree of insect resistance, for instance against the orange wheat blossom midge.
Genomics
Decoding the genome
In 2010, 95% of the genome of Chinese Spring line 42 wheat was decoded. This genome was released in a basic format for scientists and plant breeders to use but was not fully annotated. In 2012, an essentially complete gene set of bread wheat was published. Random shotgun libraries of total DNA and cDNA from the T. aestivum
cv. Chinese Spring (CS42) were sequenced to generate 85 Gb of sequence
(220 million reads) and identified between 94,000 and 96,000 genes. In 2018, a more complete Chinese Spring genome was released by a different team. In 2020, 15 genome sequences from various locations and varieties
around the world were reported, with examples of their own use of the
sequences to localize particular insect and disease resistance factors. Wheat Blast Resistance is controlled by R genes which are highly race-specific.
The Dutch artist Vincent van Gogh created the series Wheat Fields
between 1885 and 1890, consisting of dozens of paintings made mostly in
different parts of rural France. They depict wheat crops, sometimes
with farm workers, in varied seasons and styles, sometimes green,
sometimes at harvest. Wheatfield with Crows was one of his last paintings, and is considered to be among his greatest works.
In 1967, the American artist Thomas Hart Benton made his oil on wood painting Wheat,
showing a row of uncut wheat plants, occupying almost the whole height
of the painting, between rows of freshly-cut stubble. The painting is
held by the Smithsonian American Art Museum.
In 1982, the American conceptual artist Agnes Denes grew a two-acre field of wheat at Battery Park, Manhattan. The ephemeral artwork
has been described as an act of protest. The harvested wheat was
divided and sent to 28 world cities for an exhibition entitled "The
International Art Show for the End of World Hunger".
![Production of wheat (2019)[108]](https://en.wikipedia.org/wiki/File:Production_of_wheat_(2019).svg)
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