All stages of producing peanuts to trade this product 5
Continuous flow dryers
These consist essentially of tall towers down which the produce moves, usually by gravity and are designed to enable heated air to be blown through the produce. Alternatively, they are tray-type dryers with the tray inclined to take advantage of gravity or cause movement of the produce from one end to other. Usually these dryers have a cooling section in which only ambient temperature air is used. Various types of batch dryers have been used successfully, particularly in the USA, providing the drying air temperature does not consistently exceed about 38°C with an air flow rate of 5 to 100 f.p.m (c.f. sq-1 ft. effective floor area) and provided that the final moisture content does not exceed below 7 percent. Following are some general recommendations from America on the conditions for artificial drying of groundnuts. Although fresh nuts can be safely dried artificially if adequate care is taken, most of the workers seem to agree that windrow-cured pods can be dried artificially with great success and economy as long as the conditions are properly controlled. Over-drying should be avoided, otherwise the shelling quality is lowered, the flavour impaired and viability reduced; for this reason consistent drying temperature above 38°C should not be employed.
Intermittent artificial drying is considered optimum procedure, where feasible. Under certain conditions it may be advisable to use slightly higher temperatures for a faster drying rate even at the expense of the quality of the pods. In the tropics, where ambient temperatures can be above 30°C the use of forced air without additional heat may be sufficient for drying groundnuts. If the airflow rate is higher it even without heating the ambient air increases the temperature of the pods during drying. After curing and picking up the pods from the vine they must be dried promptly to safe moisture level for storage. Failure to reduce the moisture content to a marketable level of less than 10 percent (w.b.) with in a period of two or three days may result in quality losses from biological activity.
When groundnuts are harvested they contain wide range of foreign material. This impacts quality, beginning with airflow restrictions and uneven moisture distribution during curing.
Foreign material at 5 percent and above results in a deduction in the value of farmer’s stock groundnut brought to market.
During storage, foreign material interferes with airflow, reducing the ventilation that is necessary to removemoisture from the warehouse. To improve the quality of groundnuts, further modifications are needed in the threshers being used in the developing countries. Still, threshers used in India perform asatisfactory job of cleaning. The cleaning of threshed groundnut is normally done when there is no blower in the thresher or the cleaning efficiency of the thresher is low. In general most of the threshers have blowers, which perform the cleaning operation by the process of winnowing.
In the developing countries, less attention has been paid to cleaning material by the machines before storage. For the benefit of readers of this report, the cleaning operations of a typical peanut pre-cleaner and the methods to reduce the incidences of foreign material in groundnuts are displayed in Table 8.
Foreign material and loose-shelled kernels (LSK), groundnut seed inadvertently shelled by harvesting and handling operations cause problems in storage and processing (Dickens and Hutchison, 1976). LSK are often dirty, mouldy, mechanically damaged, or insect damaged.
They deteriorate more rapidly during storage than in shell groundnuts. Small-shrivelled pods (raisins) contain high concentrations of moisture and often mould during storage. The incidence of foreign material in the farmers’ stock groundnut may be reduced with a program of prevention and removal.
Table 8. Methods to reduce the incidence of foreign material in groundnuts.
|Foreign material(s)||Best conventional method(s) of prevention||Best conventional method(s) of removal|
|Dirt||Harvest when soil is not too wet or dry. Control weeds.||Screening|
|Rocks pieces||Avoid planting on rocky or pebble-type soil||Specific gravity|
|Sticks/previous crop residue||Remove of burry old crop residue before planting. Set groundnut digger to cut taproots as shallow as possible||Aspiration and screening|
|Immature pods||Harvesting at optimum maturity. Remove immature pods||Screening, aspiration and specific gravity|
|Pops, leaves, stems and hulls||Harvest at optimum maturity||Aspiration|
|Weed fruit/seed/nut grass and rhizomes||Control weed||Screening and colour sorting|
|Metal||Maintain machinery in good condition||Screening and magnetic separation|
Despite the obvious advantages, most of the groundnuts are not cleaned before storage. Doing so requires a large investment in equipment and labour, provides another significant cause of breakdowns and delays during the rapid harvest season and usually results in a small loss of marketable groundnuts. Developing countries have manufactured cleaning equipment and created methods to remove some of the foreign material that segregate in storage . Cleaning with sand-screens at ground level and employing additional elevators is also an effective cleaning method. In Senegal, a rotary cleaner made by SISMAR®, is used which can be operated by hand. This machine has a double sieve designed to separate groundnuts from husk and other rubbish. It is fitted with a large hopper, having a capacity of 80 kg (approximately one sack)plus two outlet spouts allowing the independent or simultaneous filling of two sacks. Output is 155 to 2 000 kg h-1. The sieve axle is mounted on ball bearings. Recommended turning speed is 15 rpm, weight 212 kg.
Decorticating or shelling
Due to the lack of an efficient machine to shell groundnut, small farmers generally depend upon mouth shelling or employing labour to prepare seed for sowing purpose. This is a time consuming operation and does not match the shelling requirements within a limited period of time to retain seed viability. A small machine is required for this purpose, which may also meet the shelling needs of the farmers for their domestic consumption of kernels. This can also facilitate the shelling of graded kernels by the farmers instead of pods. Sale of kernels in graded quality will also fetch them more price for the produce. In Gujarat, a small manually operated sheller is available in the market for the use of small farmers and for shelling of groundnut at the time of sowing (Figure 18).
Figure 18:Groundnut hand-sheller.
A power operated groundnut pod opener (decorticator) has been developed at Zonal Research Centre, Tamil Nadu Agricultural University, Coimbatore. The decorticator is used to shell groundnut pods and to separate kernels with least injury or damage for use as seed. The unit consists of a hopper, double crank lever mechanism, an oscillating sector and blower assembly, all fixed on a frame. In the oscillating sector unit, a number of cast iron peg assemblies are fitted. The whole sector assembly oscillates close to a concave sieve fitted just below. A hopper is fitted at the top of the unit and the pods are fed through it gradually. The groundnut pods are broken between the oscillating sector and the fixed perforated concave sieve. The blower separates the kernels and shells; kernels are collected through a spout at
the bottom of the machine, while the blower blows off the lighter materials. The clearance between the concave and the oscillating sector is adjustable to decorticate the pods with the different varieties of groundnut. Similarly, the sieves are also replaceable thus avoiding the damage to the kernels at any time. Power required: 1 hp motor. The machine output is shelling 400 kg of pods per hour. Percentage of breakage is only 4 kg.
The cultivated groundnut is defined as one of four types: i.) runner: runner have become the dominant type, because of their attractive size range which makes them useful for a variety of products; ii.) Virginia: Virginias have the largest kernels and account for most of the groundnuts roasted and eaten as in-shell. When shelled, the larger kernels are sold as saltedgroundnuts. They are also used in confectionery products; iii.) Spanish: Spanish type groundnuts have small kernels covered with a reddish-brown skin. They used predominately in groundnut candy, with significant quantities used for salted nuts and groundnut butter.
They have a higher oil contents than others types iv.) Valencia: Valencia’s usually have three or more small kernels to a pod. They are very sweet groundnut and are usually roasted and sold in the shell. They are excellent for fresh use as boiled groundnuts.
After drying, groundnut pods are graded at a prescribed moisture level in the kernels such as 9 percent. Undersized pods, chaff, inert matter, if any, is separated. The factors such as foreign material over 4 percent, moisture over 7 percent, damage over 1 percent, loose shelled kernel content, and split percent over 4 percent determines the value of the produce in the national and international markets. Seed size is another important characteristic that also determines both quality and value. The 100-seed weight may differ among genotypes from <30 g to >150 g. Size also varies within a genotype, and cultivars with more uniform seed size are desired for improved processing efficiency and marketing of groundnut products.
Figure 19. Groundnut grader line diagram (Source: NDDB, Manual on Groundnut).
India produces two sizes of groundnut kernel, medium and small. The medium-size kernels, known as “Bombay Bolds”, generally count 50/55 kernels per ounce. They can also be graded to 40/50 kernels per ounce, though availability at this size is not unlimited. The small-size kernel are called the “Java” type, is equivalent to the US “Spanish” or the South African “Red Natal”. The generally traded grade of Java is 70/80 kernels per ounce. In internal trade the quality of pods and kernels is judged by a visual examination except in contract sale when the proportion of damage kernels, nooks, broken and splits, percentage of foreign matter, and moisture content is determined. The ISI has prescribed certain grades for groundnuts (kernels for oil milling and handpicked selections) produced and marketed in the country. These standards are based on the trade practices followed in the country in respect of the type and grades. The specifications are given in Table 9. A line diagram of groundnut grader is shown in Figure 19.
Table 9. ISI specification for groundnut kernels for oil milling.
|Requirement for milling|
|Damaged kernels and weevil kernels, % by weight (max)||0.5||1.5||3.0|
|Slightly damaged kernels, % by weight (max)||1.0||2.0||4.0|
|Shrivelled and immature kernels, % by weight (max)||1.0||30.||6.0|
|Split and broken kernels, % by weight (max)||5.0||10.0||15.0|
|Nooks, % by weight (max)||1.0||2.0||3.0|
|Impurities, % by weight (max)||1.0||2.0||3.0|
|Admixture with other types, % by weight (max)||1.0||2.0||5.0|
|Total of 1-7 above (max)||6.0||12.0||30.0|
|Moisture content, % by weight (max)||6.0||6.0||6.0|
|Oil content on moisture free basis, % by weight ( max )||48.8||46.0||42.0|
|Acid value of extracted oil (max)||2.0||4.0||6.0|
For preparing export grade edible groundnut, “Hand Picking and selection” (HPS) through hired labour is still in practice. Although, in the Indian context, human endeavour is worthy of appreciation and encouragement, the need to install mechanical graders cannot be over emphasized. Use of machine for grading groundnuts will not only be faster and more reliable but hygienic also. Optical sorting machine grading is not used at present, but colour sorters are now in use in some developing countries to remove aflatoxin-infested kernels. The ISI (Indian Standard Institute) specifications for the HPS are given in the following Table 10.
Table 10. ISI specifications for groundnut kernels- handpicked selection (HPS).
|Characteristics||HPS Bold 1||HPS Bold|
|Number of kernels per 25 g of the material||Max 40||45 to 53||54 to 58||71 to 75|
|Broken, damaged and slightly damaged kernels, % by weight (max)||Nil||1||1||1|
Note: The groundnut kernels shall also be free from non-edible oils such as mahua, castor, neem and argemone.
Pods after grading to the requisite normal size are packed in gunny bags. Seed are seldom shelled and packed because in the kernel (seed) form they lose viability quickly than in-shell (pod) form. Therefore, seed is mainly sold in the form of pods and a small pack of thiram or captan is also kept in the gunny bag with the instruction to treat the seed (kernels) at the time of sowing. Packing for the milling or seed purpose in polyethylene bags is generally recommended, as it helps in maintaining the quality during storage. Similarly in several developing countries the roasted kernels are sold loose in the market, packaging of the confectionery groundnut in polyethylene bags may add to the value and quality of the product in the local markets. Other value-added product should also be sold with proper packaging to maintain the moisture content and the crunchy and crispy nature of groundnuts (Figure 20).
Figure 20. Confectionery groundnut available in polyethylene packages.
After filtration groundnut oil is packed in big drums or tanks, and in tins of 15 kg capacity. A part of the population in the developing countries, living below the poverty line, purchase unbottled or unpackaged groundnut oil for their consumption from the market daily. This practice boosts the risks of adulteration. Recently the Government of Gujarat has decided to make packaging compulsory for groundnut oil sold in the market. Even quantities as small as 50g of groundnut oil will require packaging before sale. This will have a major impact on the state’s edible oil market, leading to a 10 to 15 percent price increase in this politically sensitive commodity. Similar regulations are desirable from other governments in the developing world.
Smallholder farmers store groundnut in-shell, in earthen pots, mud bins, bamboo baskets or in other types of wicker receptacles. These containers are often plastered with mud and cow dung with little or no use of pesticides. For long-term storage the containers are sealed with mud after the addition of ashes, ground pepper, dried neem leaves or other local herbs to control storage pests. In Andhra Pradesh groundnuts are stored in big earthen pots and the mouth of the container is sealed with the sand or mud or cow dung. Daily storage of groundnuts in gunny bag is a common practice requiring utmost care to protect the produce from the pests. For consumption and seed purposes, groundnuts are stored for longer periods up to 8 to 10 months. Farmers generally have inadequate facilities and use their houses to keep bags of groundnuts over long periods of time. This finding calls for an effort on the part of governments in the developing countries to improve facilities for storage. Farmer level storage conditions for groundnut in gunny bag is shown in Figure 21.
Figure 21. Storage of groundnuts in gunny bags under farmers’ storage conditions.
Groundnuts following proper drying are either packed in gunny bags or stored in heaps in big rooms in the farmhouse. Eighty percent of the farm produce reaches the market to be crushed for oil extraction by the millers via the local market or cooperative societies. Due to storage problems, the oil mills also do not store groundnuts for a long time. When pods are stored at ambient farm storage conditions, they interact with the storage humidity (RH percent) and temperatures. At high RH >80 percent and temperatures >40°C the process of ageing accelerates and the kernels start deteriorating.
Groundnut pods are generally stored at the moisture content between 6 and 8 percent. In India summer season groundnut is harvested in the month of May to June, and the environmental RH increases immediately after storage, and may reach up to 80 to 90 percent on the onset of monsoon in the month of June to July. Consequently the pod moisture also increases and may reach between 10 and 15 percent, depending on the RH of storage environment. Pod moisture percent >10 percent is harmful for the maintenance of seed viability and quality. The RH of the storage environment may be reduced with the help of dehumidifiers or use of desiccants like silica gel and calcium chloride (anhydrous or fused). On the other hand the rainy season produce is harvested in the month of October to November, when monsoon resides and the temperature and RH of the storage environment become favourable for the storage of groundnuts. Thus the storage environment between December and March remains quite favourable, under such situations farmers can store their produce in ordinary gunny bags at the ambient storage conditions, provided care is take to protect the produce from the storage pests. It is recommended that the summer season produce either should be processed immediately after harvest or may be stored for 1 to 2 months taking utmost care. For example the produce may be stored in polyethylene bags with desiccant like silica gel or calcium chloride (CaCl2, anhydrous) and sealed.
In the assembling markets, decorticating factories and oil mills, produce is generally stored in the form of pods, either loose or in bags. The period of storage may be very short. Beside storage in godowns, pods are often heaped loose or stacked in bags in the open in places where the risk of damage by rain is minimal. If it does rain, the sacks are covered with tarpaulin. Wooden planks or matting must be arranged on the floor to prevent damage from damp. The pile of bags in the godowns should be kept to 4 to 5 feet below the roof to allow free circulation of air. The period of storage of individual lots in most cases may not exceed two to three months. Storage conditions may very in the terminals markets and ports. At these centres invariably storage is in the form of kernels, which are most often packed in gunny bags. Sometimes, it becomes imperative to store kernels at ports for longer periods, waiting for the shipment, such situations lead to serious damage to the kernels.
Groundnuts are semi-perishable and are subject to quality losses during storage through microbial proliferation, insect and rodent infestation, biochemical changes, i.e. flavour change, rancidity, viability loss; physical changes, i.e. shrinkage, weight loss, and absorption of odours and chemicals. When subjected to suitable storage environments, clean groundnuts can be stored for several years. High moisture and temperature regulates the rate of deterioration of kernels in storage. During shelling serious losses in milling quality may result, if groundnut kernels are dried below 7 percent moisture content (w.b.) or stored at a temperature less then 7°C. Thus, best storage conditions for normal dry bulk storage of unshelled groundnuts is about 7.5 percent kernel moisture content (w.b.) at 10°C and 65 percent RH. If these storage conditions are maintained, unshelled groundnuts can be stored without significant loss in quality for about 10 months (Patee and Young, 1982). Some groundnut varieties have been noted to have poor storability for example in Gujarat cultivar GG 2 loses its viability rapidly than any other cultivar. The methods of cultivation, harvesting, curing, and post-harvest handling of the groundnuts may affect their storability. In developing countries the conditions of most farmers stock warehouses are not good, practically they don’t have the warehouses. The warehouses require ventilation and/or aeration system to help in maintaining the quality of groundnuts. These systems remove excessive heat and moisture, equalize groundnut moisture content and temperature throughout the mass of stored groundnuts and reduce the differences between the ambient and groundnuts temperature. The aim should be to keep the conditions of the air in the pile of groundnuts within the limits and to prevent moisture migration and condensation inside the storage structure. In Ghana mature groundnut kernels, following harvesting and drying are stored in jute bags and kept in barns built of mud or thatch. The major problems in stored groundnuts in Nigeria include weather, insects, rodents, and infestation by toxicogenic fungi. In South Africa the recommended maximum drying temperature is 35°C, however, commercial cultivars react differently to drying temperature. In India groundnuts in-shell and seed of cv. Big Japan and M 13 were stored in polyethylene bags for up to 14 months (Sinha, et al. 1997). Groundnut stored in polyvinyl bag at 7 percent moisture content showed the highest germination. Seed treated with an insecticide/fungicide, were stored successfully for one year without significant loss of viability in laminated polyvinyl bags (Krishnappa, et al.
Certain factors known to accelerate the ageing process are: i.) soil moisture content during pod development, harvest stage; ii.) drying methods mainly the temperatures during curing of pods, and iii.) ambient relative humidity during storage. Based on these principles a simple and economic storage technology has been developed to prevent the exposure of pods to high humidity during monsoon season. In this technology CaCl2 is used as a desiccant in side a polyethylene-lined gunny bag containing the groundnut pods (Figure 22).