Sorghum bicolor, commonly called sorghum and also known as durra or jowari, is a grass species cultivated for its edible grain. Sorghum originated in Northern Africa, and is now cultivated widely in tropical and subtropical regions. Sorghum bicolor is typically an annual, but some cultivars are typically perennial. It grows in clumps that may reach over 4 meters high. The grain is small, ranging from 3 to 4 mm in diameter. Sweet sorghum cultivars that are primarily grown for foliage; they are shorter than those grown for grain.
- Uses of Sorghum
- Malted beverages
- Animal feed
- Organic acids
- Cellulose and paper from stalk
Soil and Climatic conditions required for Sorghum Production:
Sorghum is uniquely adapted to adverse ecological conditions such as mild drought, poor soil fertility, waterlogging, high altitudes and salinity. It can thus grow on wider soil range than maize. It also tolerates a pH range from 5.5 to 8.5 and is more suitable than maize to acid soils. It is generally grown on sandy loams as well as on heavy black soils.
It requires an annual rainfall of between 500 and 1,500mm. Sorghum grows best at temperatures of 28° ± 3°C. It can grow and produce well in higher temperatures than maize. Depending on the soil nature and evapotranspiration rate, 500 – 800mm of evenly distributed rainfall during the cropping season is adequate for cultivars maturing in 100 – 130 days.
In Nigeria, sorghum is grown mainly as a rainfed crop by small-scale farmers using traditional practices common to subsistence agriculture. Local land races are generally grown. They are chosen for their grain and stalk qualities, adaptation to low fertility and most importantly, to match the length of the growing season.
- Planting Materials:
Nigeria has a number of improved sorghum varieties and management techniques capable of significantly increasing sorghum yields. Breeder seeds of officially registered and released varieties of sorghum are available at the research institutes such as the Institute for Agricultural Research (IAR) Samaru, Zaria. Foundation seeds can be found in the National Seed Service (NSS) and private seed companies sell seeds certified by the NSS. Many local farmers, however, use seeds saved from previous planting as well as local varieties. The IAR, Samaru has developed a total of 41 improved pureline varieties and 4 hybrids of sorghum all of which had been released to the Nigerian farmers between 1970 to 2001. The varieties identified to be suitable for industrial utilization include, among others: Samsorg 14 (KSV 8) called farafara; Samsorg 19 (SK 5912) locally called kaura; Samsorg 40 (ICSV 400); Samsorg 41 (ICSV 111); Samsorg 3 (KSV 4); Samsorg 6 (KSV 12); Samsorg 7 (KSV 13); NR 71176. Other local varieties planted by farmers include: yarwasha, yar gaya, and extra early genotype called Peugeot.
- Sorghum Processing
Traditionally, sorghum is dehulled in households by the mortar and pestle method followed by grinding on a stone mill. With the advent of small power driven plate mills, the bulk of the sorghum is custom milled to whole flour. The ban on wheat imports initiated rapid changes in sorghum milling technology in Nigeria (ICRISAT, 1990). There are basically two major processes- dry milling and malting.
- Dry Milling:
Dry milling of sorghum involves three operations: cleaning, decorticating and grinding. In the cleaning section, impurities like foreign matter, stones, sand, metallic objects, and light impurities are eliminated. The decomatic decorticator is a vertical machine with a capacity of pearling 1.5t/h of grain and is equipped with six rotor mounted carborundum discs and a screen mantle. The decortication principle is abrasion and the extent of decortication can be adjusted. It was found that 20% decortication could be optimum. Tempering of grain prior to decortication decreased throughput and increased the amount of broken grains, ash and fat contents of the product.
At the same mill, a combination of a roller stand with two passages and a hammer mill were adopted for grinding pearled sorghum. This grinding system can produce either brewers grits or dour, or both if needed.
During malting, the sorghum grains are washed and steeped in water for 24 – 48hrs. Appropriate chemicals are added during the steeping process to prevent the growth of molds. At the end of steeping, the grains are further washed. The moisture content of the grain should be between 40 – 46% at the time of transfer to an aseptically clean floor (100 x 40m). The grains are heaped to a thickness of 152 – 221mm and left to germinate for 3 – 5 days with frequent aeration. Temperature is maintained at 25 – 35°C and relative humidity at 85 – 95%. The resulting malt is dried to a moisture level of 8 – 10% in a rotary drier at 75°C. The dried malt is mechanically agitated and the sprouts are removed by screening. Grains of sorghum varieties SK 5912 and farafara are used for malting.
Flow Chart of grain sorghum processing.