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Processing of cereals, pulses and millets, the stages and more
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Sunday, 01 March, 2020, 08 : 00 AM [IST]
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Annette Gowda, Dinkar Pange, Sachin Shewalkar
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India is the world’s second-largest producer of rice, wheat and other cereals. The huge demand for cereals in the global market is creating an excellent environment for the export of Indian cereal products.
General information
Each type of cereal requires a specific post-harvest treatment, however, there are certain general principles that apply to most of them. Cereals undergo a number of processing stages between harvest and consumption. This chain of processes is often referred to as the total post-harvest system. The post-harvest system can be split into three distinct areas. The first is the preparation of harvested grain for storage. The second, which is referred to as primary processing, involves further treatment of the grain to clean it, remove the husk or reduce the size. The products from primary processing are still not consumable. The third stage (secondary processing) transforms the grains into edible products.
Primary processing - It involves several different processes, designed to clean, sort and remove the inedible fractions from the grains. Primary processing of cereals includes cleaning, grading, hulling, milling, pounding, grinding, tempering, parboiling, soaking, drying, sieving. Secondary processing of cereals (or ‘adding value’ to cereals) is the utilisation of the primary products (whole grains, flakes or flour) to make more interesting products and add variety to the diet. Secondary processing of cereals includes the following processes: fermentation, baking, puffing, flaking, frying and extrusion.
Puffing - Puffed grains are often used as breakfast cereals or as snack food. During puffing, grains are exposed to a very high steam pressure which causes the grain to burst open. The puffed grains can be further processed by toasting, coating or mixing with other ingredients.
Flaking - Flaked cereals are partially cooked and can be used as quick-cooking or ready-to-eat foods. The grains are softened by partially cooking in steam. They are then pressed or rolled into flakes which are dried. The flakes are eaten crisp and should have a moisture content of below 7%.
Fermentation - Doughs made from cereal flour can be fermented to make a range of products. Baking - Doughs and batters made from cereal flours are baked to produce a range of goods.
Extrusion - Extrusion involves heating and forcing food (usually a dough) through a small hole to make strands or other shapes. The extruded shapes then undergo further processing such as frying, boiling or drying. Extruded products include pastas, noodles, snack foods and breakfast cereals.
Harvesting - There is an optimum time for harvesting cereals, depending on the maturity of the crop and the climatic conditions. This has a significant effect on the quality of the grain during storage.
Threshing - It is the removal of grains from the rest of the plant. It involves three different operations: Separating the grain from the panicle; sorting the grain from the straw; winnowing the chaff from the grain. Separation of the grain from the panicle is the most energy-demanding of the three processes.
Winnowing - It is the separation of the grains from the chaff or straw. Some of these contain sieves and screens that grade the grains as well.
Drying - Prior to storage or further processing, cereal grains need to be dried. The most cost-effective method is to spread out in the sun to dry. In humid climates it may be necessary to use an artificial dryer. Cereal grains should be dried to 10-15% moisture before storage.
Storage - Dried grains are stored in bulk until required for processing. The grains should be inspected regularly for signs of spoilage and the moisture content tested. If the grain has picked up moisture it should be redried. Grains are often protected with insecticides and must be stored in rodent-proof containers.
Primary processing
Cleaning and grading - Before further processing, grains are cleaned and graded according to size. Winnowing machines can be used to separate out the chaff, soil and dirt. Some machines have integral sieves that combine cleaning with grading.
Hulling - Several grains have an unpalatable husk or shell that needs to be removed by a decorticator.
Pounding/Milling - Three main types of grain mill are available: Plate mill; Hammer mill; Roller mill. The choice of mill depends on the raw material and the scale of production. Hammer mills are almost universally used throughout the developing world. It is important to ensure that the grains have optimum moisture content before milling.
Paraboiling - Paraboiling rice is an optional step, but one that improves the quality of hulling as it results in fewer broken grains. About 50% of all rice grown is parboiled.
Secondary Processing
Dried grains are stored in bulk until required for processing. The grains should be inspected regularly for signs of spoilage and the moisture content tested. The quality of raw materials has an influence over the quality of the products. High quality raw materials should be used.
Flour can be milled from a variety of cereals. The type available in each country or region may depend upon the types of cereal grown, although wheat flour tends to be available in most places.
Wheat flour contains proteins known as glutens. These are capable of forming a strong elastic network within the dough, which is very useful when making leavened bread. The protein network traps the gas that is given off by the yeast during fermentation. This causes the dough to increase in volume and produces a bread with a light texture.
Maize can either be wet or dry milled. In dry milling, maize is ground between stones or by using a hand-powered plate mill or at a larger scale, using a hammer mill or powered plate mill. In wet milling, the grain is soaked and allowed to ferment slightly to improve the flavour before milling with a hand or powered plate mill. Maize is sometimes soaked in alkaline water to facilitate removal of the bran before it is milled.
Paddy rice is parboiled before the husk is removed. Parboiling is the partial cooking of the rice to gelatinise the starch, which makes the grain tougher. There is also a slight change in flavour which some people prefer.
The toughening process makes the seed more resistant to insect attack and to shattering during husking. It also helps to prevent absorption of moisture from the air during storage.
The parboiling process involves three stages: - soaking or steeping of the paddy in cold or hot water to increase its moisture content - steaming to gelatinise the starch in the kernel - drying. The rice should be dried carefully after parboiling to minimise losses. Husking paddy, which is sometimes referred to as dehusking or milling is the process of removing the outer husk. Husked paddy is referred to as brown rice, whereas dehusked (or polished) rice is white rice. Brown rice is nutritionally superior to white rice as it contains some of the bran which contains protein and vitamin B1 (thiamine).
Millet: The outer layers of some varieties of sorghum seed (usually the red seed varieties) contain tannins that are slightly toxic, have a bitter taste and inhibit the digestion of proteins. For this reason, sorghum is generally hulled before grinding into a flour. Traditionally sorghum and millet is ground by hand using querns or hand plate mills. The seed is winnowed to remove foreign matter, then put into a large mortar and wetted. It is then pounded to strip the bran or shell from the grain, followed by winnowing to get rid of the bran. Pounding and winnowing are repeated several times to get a good quality milled seed. The milled seed is washed to remove any small pieces of bran and soaked in water for 24 hours to condition or temper it. The grain is dried to the correct moisture content then reground using a pestle and mortar.
Cereals, pulses and millets are distinguished by the below tests:
1. Description
2. Essential composition and quality factors
- Moisture
- Extraneous matter
- Toxic or noxious seeds
3. Contaminants
- Heavy metals
- Pesticide residue
- Mycotoxins
4. Hygiene
5. Packaging
6. Labelling
7. Methods of analysis and
sampling
Codex standards for cereals, pulses, legumes and vegetable proteins too allow their wide use and understanding by governments, regulatory authorities, food industries and retailers, and consumers, which are intended for direct human consumption.
Most important factor that accelerates the competitiveness of the millets and pulses in the international as well as domestic markets is the grain quality and organic produce. Use of pest- and disease-resistant, nutritional-rich varieties and organic production could create more opportunities. Enhancement of export competitiveness of these crops in the international as well as targeted domestic markets will help the farmers to fetch good returns for their produces in long term.
(Gowda is manager, customer coordination, Pange is sales executive-survey & inspections, and Shewalkar is sr customer support executive (survey & inspections) at Envirocare Labs Pvt. Ltd, Mumbai. They can be contacted at annette.g@envirocare.co.in)
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