Wheat is a grass that is widely cultivated for its cereal grain seed and is a worldwide staple food.  It has been cultivated on earth for over ten thousand years, with the earliest evidence from the Middle East Fertile Crescent region around 9600 BC.  The grain is often milled into flour and used to make foods like bread, pasta, noodles, cereals, crackers, pancakes, numerous dessert foods, and many others.  Wheat straw is used as an animal feed and in the manufacture of carpets, baskets, packing, bedding, and paper.  Wheat is grown on more land area than any other food crop and world trade in wheat is greater than that of all other crops combined.  Per the United Nations Food and Agriculture Organization, wheat crop land area was 220.4 million hectares in 2014 and estimated production of wheat in 2019 was 766 million metric tons, making it the second most produced cereal food after maize. Production of wheat has tripled since 1960 and is expected to continue to grow. Global demand for wheat is increasing due to a number of factors.  It is a major source of starch, carbohydrates, and energy as well as a number of healthy nutritional components, such as protein, vitamins, dietary fiber, and phytochemicals.  It is the leading source of vegetable protein in human food with a protein content of around 13%.  This is relatively high compared to other cereals, but low in protein quality for supplying essential amino acids.  The unique properties of gluten proteins help facilitate the production of processed foods.  Consumption of processed foods is increasing due to worldwide industrialization and the “Western Diet” phenomenon, marked by an increased consumption of processed foods.  It is an important food for livestock as well as humans.  There are numerous wheat species which differ in nutritional value as well as the type of food they are used to make.  It is estimated that around 30,000 wheat varieties of fourteen different species are grown worldwide and approximately one thousand are considered commercially significant.  Different areas are suited to growing specific species of wheat based on climate, soil, and other environmental factors.  The major wheat species grown throughout the world is known as Triticum aestivum, better known as common or bread wheat.  Another major species is T. turgidum var. durum, a species well adapted to the hot and dry conditions around the Mediterranean Sea and regions with similar climates.  It is commonly known as pasta wheat or durum wheat.  As is the case with all agricultural products, disease and pests are problems when growing wheat.  The different types and severity of diseases and pests vary in different parts of the world and farmers can employ different strategies for minimizing effects, such as choosing resistant varieties, good seed quality, selective field planting, crop rotation, delayed planting, and proper application of pesticides and fungicides when needed.  Many advances in soil preparation, seed placement, crop rotation, fertilization, harvesting methods, and more recently, breeding and genetics, have combined to increase the viability of wheat as a major worldwide food product.  

Wheat Growing, Harvesting, Processing 

Many varieties of wheat are grown in two seasons: spring wheat and winter wheat.  Spring wheat is typically planted in early spring and harvested in the late summer. Winter wheat is planted in the fall and harvested in the summer.  Spring wheat is often referred to as a “tough crop” because it keeps its growing point below the ground during early spring, preventing it from being harmed by late spring frost.  The first step in growing wheat is choosing a suitable location with fertile soil with a loam texture, good structure, and moderate water holding capacity.  Soil is prepared by plowing and adding natural fertilizers.  For commercial wheat farming, an average of 50 kg Nitrogen, 25 kg Phosphorus, and 12 kg Potash is sufficient in one acre of land.  It is important to select a variety of wheat that is suitable for growing in the climatic conditions of the farm area.  Typically, 40 kg to 50 kg of seeds are required per acre of land.  Seeds are cleaned before sowing and if necessary, fungicide can be applied after cleaning.  Wheat seeds are sown in 4 cm to 5 cm of soil in rows that are spaced out at 20 cm between the rows.  With proper preparation, additional fertilization and weeding are minimal once the seeds are planted.  Irrigation is important and must be first done twenty to twenty-five days after planting.  Additional irrigation is required every twenty days or so until harvesting.  

Spring wheat is typically ready for harvesting about four months after planting.  Winter wheat takes about seven to eight months because of the dormant winter period.  Before harvesting, the moisture level must be tested and should be between 14% and 20%. The green color in the wheat should be gone before harvesting.  Traditional methods of harvesting wheat were by hand or with a horse-drawn binder but these are quite labor-intensive and only done on small farms these days. A machine called a combine is used for harvesting.  It is designed for efficient harvesting of mass quantities of grain and the largest modern combines can cut through an area in the field more than forty feet wide.  Combines can be fitted with different heads to harvest many different types of grains including wheat, corn, soybeans, oats, rye, barley, sunflowers, and canola.  The name combine comes from combining three essential harvest functions into a single process: reaping, threshing, and winnowing.  Reaping is the cutting of the grain.  It is important to adjust the combine header in relation to the height of the wheat to get the most wheat with the least amount of straw as well as adjust the reel speed relative to the ground speed.  Going too fast will either knock the wheat down or cut it poorly. Going too slow can cause the wheat to fall to the ground or not enter the combine correctly.  Threshing is the process of loosening the edible part of the grain from the straw.  Winnowing is the method for separating grain from chaff.  The cut crop is fed into the threshing cylinder, which consists of a series of horizontal rasp bars fixed across the path of the crop and in the shape of a quarter cylinder.  These bars pull the crop through concave grates that separate the grain from the straw.  The grain heads then fall through the fixed concaves. During this process, the grain husks are not removed from the paddy grain.  Combine concaves perform both the threshing and winnowing processes and afterwards, usable grains are loaded into the grain tank.  The wheat is then put into a grain cart for transport for storage in a grain elevator.  Proper storage before transport for sale is essential to avoid both disease infection and pest infestation. 

Transgenic Wheat and Genetic Engineering 

Transgenic wheat is wheat that has been genetically engineered by the direct manipulation of its genome using biotechnology.  Like other genetically engineered foods, transgenic wheat is a source of controversy and debate and resistance to the use of genetically modified wheat has been particularly strong.  No genetically modified wheat is grown commercially anywhere in the world although field trials have taken place.  Modifications to wheat that have been tested in transgenic field trials include resistance to herbicides, insects, and fungal pathogens, drought and heat tolerance, both increased and decreased content of gliadin and glutenin, improved nutrition content, increased water-soluble dietary fiber, increased plant yield, and improved qualities for use as a biofuel.  The use of transgenic wheat to create low-gliadin strains is of particular interest as wheat and flour consumed by people with celiac disease and non-celiac gluten sensitivity (NCGS) must have a minimal amount of gluten in their diets. It is estimated that 1% of the world’s population suffers from celiac disease and up to 6% of the population in the United States suffers from NCGS.  One genetically modified wheat, Bioceres HB4, has been approved for commercial use in Argentina.  The variety is named for its expression of a transcription factor from sunflowers, known as HaHB4.  It is said to be able to withstand drought as well as provide high yield.  Commercial introduction is pending approval of the crop by Brazil, Argentina’s major wheat export partner.   

One cause of major controversy and debate in transgenic wheat has been the discovery of genetically modified wheats in shipments even though genetically modified wheat is not approved for human consumption anywhere in the world with the exception of Bioceres HB4 in Argentina.  In 1999, scientists in Thailand claimed to have found herbicide-resistant wheat in a shipment from the United States.  The source of the claimed contamination was never found.  In 2013, a similar strain which was tested extensively by Monsanto and approved by the FDA for use as food was found on a farm in Oregon.  MON 71800 is the transgenic wheat strain that went the furthest in the approval process for commercial use in the United States, but the EPA application was withdrawn after market analysis in Europe and Asia showed that public resistance to the product was strong enough to have a large potential loss of these markets.  After the discovery, Japan suspended soft white wheat imports from the United States and Monsanto was sued by a Kansas farmer who claimed the controversy caused a price drop in wheat in the market.  Ultimately, the cause was never determined although Monsanto suggested that it was likely an act of sabotage and framed the incident as an isolated one.  No evidence was ever found that the wheat had entered commercial supply.  Imports returned to normal and market disruption was minimal.  Other similar incidents have occurred with less press and fanfare and despite the fact that there have been few real consequences thus far from cross-contamination from unapproved transgenic wheat products, the fear for consumer safety and market disruption does remain a hindrance to commercialization of transgenic wheat.   


Wheat and NIR Spectroscopy  

NIR spectroscopy has emerged as a tool for rapid, non-invasive, and cost-effective analysis of parameters of interest in wheat that could potentially replace traditional reference methods.  There are a number of quality parameters in both whole wheat kernels and wheat flour that have been studied and predicted with NIR spectroscopy with results suitable for process control purposes, such as moisture and protein. Other parameters have shown results good enough for screening purposes and more study and calibration work could improve the prediction results. These include total gluten content, glutenin and gliadin content, particle size, and baking water absorption.  Particle size is directly correlated to hardness and determining hardness in wheat using NIR spectroscopy is an AACC certified method.  Wheat straw residue decomposition potential is important for managing straw residue depending on rainfall levels in the region of planning. NIR spectroscopy has been examined for determining the fiber and chemical constituents in wheat straw that determine decomposition potential, such as neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), cellulose, hemicellulose, carbon, and nitrogen.  Both wheat and oat straw are strong sources of carbohydrates which can be hydrolyzed to fermentable sugars that are precursor substances for biofuels or building blocks for chemical syntheses.  However, chemical pre-treatment is necessary to open up the lignocellulose structure and to increase the accessibility to microbial enzymes.  NIR spectroscopy has been examined for determining key parameters of precursors of biofuel production, such as weight loss, residual lignin content, and hydrolysable sugars.  Geographical origin of wheat is an important factor in determining quality, cost, and particular suitability for the products that will be manufactured from it.  One study determined the feasibility of discriminating Durum Wheat samples from different regions of Italy from each other as well as from samples from other parts of the world.  While not approved for commercial use, research is being conducted on transgenic wheat and developing wheat lines with low gliadin content is of particular interest because of the large number of people with celiac and related diseases.  NIR spectroscopy has been studied for discriminating between wild wheat and transgenic wheat lines with low gliadin content using both whole grain and flour.  All of these parameters and measurements have been studied using NIR spectroscopy with results showing the potential to replace traditional reference methods. 



 The Contribution of Wheat to Human Diet and Health 

 How To Grow Wheat? 

 Farming 101: Planting Wheat 

 How Long Do Wheat Plants Take Before the Harvest? 

 The Combine: King of the Harvest,%E2%80%93%20reaping%2C%20threshing%20and%20winnowing. 

 Transgenic Solutions to Increase Yield and Stability in Wheat: Shining Hope or Flash In the Pan? 
 Monsanto Wheat Scandal: What The Discovery of Unapproved Genetically Engineered Wheat Means For Our Food