Technical Bulletin

Drying and Storage Practices of Maize Cobs and Grains ICAR-Central Institute of Post-Harvest Engineering and Technology P.O. PAU Campus, Ludhiana-141004 (Punjab) (An ISO 9001:2015 Certified Institution)

Technical Bulletin No.: ICAR-CIPHET/Pub./2020-21/06 Drying and Storage Practices of Maize Cobs and Grains Dr. Pankaj Kumar Dr. Mridula D. Dr. Nachiket Kotwaliwale ICAR-CIPHET भा.कृ .अन.ु प.-कंे द्रीय कटाई उपरातंा अभभयांात्रिकी एवां प्रौद्योत्रिकी सां स्थान, डाकघर-पी.ए.यू., लभु ियाना-141004 (पंा जाब) ICAR-Central Institute of Post-Harvest Engineering and Technology Ludhiana-141004 (Punjab), India (An ISO 9001:2015)

Citation: Pankaj, K., Mridula, D. and Kotwaliwale N. (2021). Drying and Storage Practices of Maize Cobs and Grains. ICAR-Central Institute of Post-Harvest Engineering and Technology, Ludhiana (Punjab). Technical bulletin no. Technical Bulletin No.: ICAR-CIPHET/Pub./2020- 21/06. Pp.29. Published by: Dr. Nachiket Kotwaliwale Director ICAR-CIPHET, P. O. PAU Campus Ludhiana-141004 (Punjab), India Ph: 01612313101; Fax: 0161-2308672 www.ciphet.in Email: [email protected] © 2021, ICAR-CIPHET, Ludhiana Disclaimer: All possible efforts have been made to ensure the correctness of the contents. However, ICAR- CIPHET, Ludhiana shall not be accountable for any inadvertent error in the content. The corrective measures shall be taken up once such errors are brought to notice. The data and photos, including graphs and figures used in this bulletin, are taken from the available open resources and copyright information is vomited.

PREFACE Maize is one of the important cereal crops of India for human consumption, animal feed and industrial usage. It is being grown worldwide due to high yield and its unique biochemical properties. However, it suffers from major quantitative as well as qualitative losses after harvest due to improper post-harvest practices. Immediately after harvest, proper drying and storage of maize are important for maintaining the grain quality and reduction of quantitative and qualitative losses. From harvest till consumption, a variety of biotic and abiotic factors including insect pests, microorganisms, rodents, birds, temperature, humidity and physical damage vitiate maize and shorten the shelf life. Fungi, especially aspergillus spices, is a major quality issue in maize at higher moisture content. Therefore, optimum drying and good storage practices for maize become inevitable for reduction of quantitative and qualitative post-harvest losses. ICAR-CIPHET is serving as a nodal institute in the area of the Post-Harvest Engineering & Technology with a major focus on post-harvest mechanisation, processing and value addition of agricultural produce to mitigate the post-harvest losses of agricultural produces. This bulletin is intended to be a short reference for different conventional and contemporary methods for drying and storage of maize cobs and grains. Authors

TABLE OF CONTENTS PAGE No. 01 S. NO. CONTENT 03 1. INTRODUCTION 05 2. POST-HARVEST PROCESSING 18 3. DRYING PRACTISES 27 4. STORAGE OF MAIZE 27 5. CONCLUSION 6. REFERENCES

I. Introduction Maize (Zea mays L.) also called corn is one of the important staple foods, it is also used for animal feed and industrial purposes (Fig. 3). It is high yielding, processable, easily digested, and comparatively less expensive than many other cereals. In India, it is the third most important cereal crop after rice and wheat. Maize production in India has grown from 18.96 MT in 2007- 08 to 28.75 MT in 2017-181. In 2018-2019, India's production volume of maize was over 27.72 MT2 (Fig. 1). The fourth advance estimate estimated 28.64 MT in Fig. 1 Maize production, area and yield of India23 2019-20. Maize is an important source of industrial raw material. The starch from maize is employed in the manufacture of ceramics, dyes, Rabi Summer plastics, paper boards, textiles, 8% 2% cosmetics, pharmaceuticals products etc. Besides this, every part of the maize viz. Kernel, leaves, stalk, tassel, cobs, is used to produce various food and non-food Kharif products. In India, it is grown in all 90% seasons i.e. Kharif, Rabi and Zaid. Fig. 2 Production of maize in India3 The production of maize (Fig. 2) from the Kharif, Rabi and Zaid CATTLE FEED BREWERY seasons is 90%, 7-8% and 1-2%, 12% 1% respectively 3. The maize crop is harvested when it FOOD reaches physiological maturity and 23% contains 25-30% moisture content POULTRY 52% (wb)3. At the time of harvesting in STARCH Kharif season, the environmental 12% conditions; high temperature and relative humidity favour the growth of Fig. 3 Maize uses in India 1

some fungal species that produce toxic by-products called mycotoxins. The fungal species associated with the contamination of maize is Aspergillus flavus that synthesises a poisonous mycotoxin called aflatoxin. Fungal infection and synthesis of mycotoxins may start during the crop growing, harvesting, handling, storage, and processing. The critical factors for fungal infection and subsequent production of mycotoxins in maize are the initial moisture content of kernel, timeliness of harvest, length of wet holding before drying, the ratio of kernel and foreign material, the type of storage structure, maize kernel temperature, the interstitial air relative humidity (RH), headspace condensation, moisture migration during bulk storage, and insect infestation. The condition of the kernel during storage is one of the main factors for the growth of mycotoxins. The main factors that favour fungal growth and mycotoxin biosynthesis in the stored kernel are high kernel moisture, above 17.5% is conducive for the growth of A. flavus28, warm kernel temperature (25-32C), and high air RH (80-100%). The production of aflatoxin continues, if the post-harvest operations like drying and storage are not properly managed as per the requirement of the grain. Contamination of the crop with aflatoxin leads to economic loss, food security problems and has a detrimental effect on human and animal health. The consumption of food containing strains of aflatoxin causes hepatic and gastrointestinal injury and is immunosuppressive, teratogenic, carcinogenic and mutagenic. The synthesis of mycotoxins deteriorates the appearance and quality of stored kernels, hence, reducing the value of maize for food, feed and biofuels. Even large doses of aflatoxins, a type of mycotoxin produced by Aspergillus flavus, cause acute poisoning (aflatoxicosis), which can be lethal if the liver is damaged. Fig. 4 Spoilage of maize due to delayed drying practices 4 2

Various techniques are being used to prevent and control the growth of mould and mycotoxin production in maize. Good postharvest and processing techniques to control mycotoxins begin with harvesting. Thus, the drying of maize after harvesting is necessary to reduce the grain moisture to the optimum level to retard the fungal growth. Drying is the most effective unit operation for the safe storage of agricultural produce and their products. Proper drying makes the material stable and the attack of insects and microorganisms can be kept at a negligible level due to reduction of moisture content. II. Post-harvest processing Post-harvest processing is crucial for better storability of maize for longer duration. Drying is one of the oldest methods for preserving the quality of agricultural produce in order to reduce post-harvest losses. It is the elimination of moisture from agricultural produce to the degree that can arrest the mould’s action and insects’ infestation. The material is generally dried to improve its transportability and storability. The moisture movement into or from a product is dependent on the variance in vapour pressure between atmosphere and product. If the vapour pressure of the kernel is higher than atmospheric vapour pressure, moisture moves from the kernel to the atmosphere. But when the vapour pressure of the atmosphere is higher than that of the kernel, the kernel absorbs moisture from the atmosphere. The drying process involves both heat and mass transfer. Heat is supplied to the material to provide latent heat of vaporisation and thus moisture gets vaporised from the material to the surrounding air through diffusion. The removal of moisture by evaporation depends on the rate of heat and mass transfer. In order to preserve the quality and prevent the maize from damage by mould growth, the maize must be dried to the moisture content of about 12% (wb) for safe year-round storage 6,7. Preservation of maize through drying can prevent huge wastage and make the material available in the off-season at remunerative prices. Different methods are used to dry the maize cob and kernels that preserves the quality, nutritive value and viability of the kernel, suitable for different purposes. 3

Fig. 5 Different Drying Methods of Maize Cobs and Grains 4

III. Drying Practices of Maize Cob and Grain Field drying The traditional methods for maize drying include exposing the crop to direct sunlight; it depends on the natural movement of air to reduce moisture content for storage. It permits the drying of maize while the yield is as yet remaining in the field (Fig. 6). Generally, in the sun drying method maize cobs drying takes 10-15 days. However it is dependent on weather conditions. It is Fig. 6 Field drying of maize cob 8 anticipated that 15-20 labourers are required per acre of maize cob based on stakeholder inputs. The cost of maize cob drying has been calculated to be around ₹ 1590 per ton of maize cobs. Advantages  Simplest method that does not require any input. Disadvantages  Exposed to attack by insects, birds, rodents, wild animals.  Strong winds and occasional rain showers, and mould growth.  Clearing of the field is also delayed and the land could not be prepared for the next crop.  Not feasible in irrigated fields where higher cropping intensity requires early and/or timely harvesting. Shallow layer natural drying Drying in the sun is a well-known method in tropical agricultural nations. The sun-drying in the field is carried out after harvesting the crop. It involves the spreading of the maize cob on the bare ground, roofs, on purpose-built platforms or trays (Fig. 7). The produce is openly exposed to the sun for its drying, depending on the humidity of dried air. The crop is to be stirred repeatedly to ensure even drying. The maize kernel after Fig. 7 Sun drying of maize cob 9 5

shelling is also dried in the same way by spreading the kernels open in direct sunlight (Fig. 8). Advantages  Easy and does not require any kind of machinery.  No expenditure of fuel or energy Disadvantages  A labour intensive process as the crop must be covered on every evening or before onset of rain.  The material is contaminated with dust that cannot be easily avoided in this method.  Due to difficulty in proper monitoring Fig. 8 Sun-drying of kernel 11 of the drying process, weather uncertainty, higher labour costs, wide area requirements for drying, insect infestation, and contamination with dust and other foreign materials, it is quite challenging to dry large quantities of maize on time.  It is the slowest drying method and has Fig. 9 Tray dryer for natural drying of crops in shallow layer 10 the greatest potential for corn spoilage by mycotoxin.  Likely damage from birds, rodents and other animals.  Uneven drying. The labour requirements can be significantly reduced by using a plastic or tarpaulin sheet for easy handling or a clear plastic-covered platform/tray, as shown in Fig. 9. Drying the kernels on plastic sheets, ideally black, yields clean dried kernels. 6

Ventilated structures for natural drying Small producers may hang crop bundles from trees or poles so that they are freely exposed to the air, while large quantities of harvested crops may be heaped on platforms or racks and protected from rain by a layer of straw. It's best to make the heap as open as possible. The crop for drying is heaped in a permanent ventilated structure in which the crop is well protected from rain. A ventilated maize crib is used for this purpose, which is a Fig. 10 Ventilated maize crib 10 rectangular structure with slatted walls and a floor (Fig. 10). Crib drying Maize cob has high moisture content and drying with natural ventilation takes a longer time for drying. The crib allows the maize cob to dry by natural aeration. The sides of the crib are made of wire meshed, or any convenient material such as loose-woven wattles that does not obstruct the airflow (Fig. 11). Natural aeration dries the cob slowly and safely whether the cobs shells are removed or not. After harvesting, if the climate is Fig. 11 Corn crib 12 dry then the crib is at least 2 m wide. On the other hand, in a humid area, the width should not be reduced to 1 m at most, and possibly to 60 cm12. The damage by rodents is prevented by building the crib at least 1 m above the ground. Corn crib is often used in Europe and The United States. Since the following season is winter, the Indian environment, especially during the Kharif season, is not conducive to crib drying. Solar dryers 7

The solar dryers are classified as direct, indirect and mixed-mode. Indirect solar dryers, the kernels are placed in the air heater and solar energy is passed through a transparent cover and absorbed by the kernels (Fig. 12). Indirect type solar dryers, in which air is heated in a solar collector and then passed through a bed of kernels, are a better way to use solar energy for drying of maize kernels also. Natural convection dryers, in which airflow is caused by thermal gradients while in forced convection dryers, air is Fig. 12 Direct solar dryer 13 forced through a solar collector to the kernels by a fan, are the two basic types of solar dryers suitable for drying of kernels. The forced convection solar dryer is similar to a traditional mechanical dryer in that air is forced through a bed of kernels, but the air is heated by a flat plate solar collector instead of more traditional means. The heated air from a separate solar collector passes through a bed of kernels in the mixed-mode form, while the drying chamber absorbs solar energy directly through the transparent walls or roof. The bare plate collector, which can operate at a collection efficiency of 40-50% with an airflow of 0.10 kg/s.m2, is possibly the best configuration for use on farmers’ fields in developing countries. Covered plate collectors with efficiencies of 60-70% can provide air temperature elevations of 10-30°C with lesser airflow. Solar Bubble Dryer The Solar Bubble Dryer (SBD), developed by IRRI, Hohenheim University and GrainPro, is the newest low cost drying method. The SBD is transportable and totally separate from the fuel or power system and hence has very low running costs. It is available in several sizes and with current variants with a capacity of 0.5 and 1t. The SBD takes advantage of solar energy in two ways. First, the drying tunnel acts as a solar collector, converting the energy contained in the sun rays that enter the transparent top of the drying tunnel into heat, which raises the temperature of the drying air and speeds up the drying process. Second, it has a photovoltaic system that includes a solar panel, a deep cycle rechargeable battery, and a controller that generates electricity to power a small blower that moves air through the drying tunnel, inflates it, and removes the water evaporated from the grains within. The SBD improves the conventional sun drying process by protecting the crops from animals, insects, contamination, 8

and rain. The drying tunnel also acts as a temperature buffer, protecting the grains from overheating, which is frequent while sun drying around midday. The SBD completely eliminates the re-wetting of grains during rain and losses due to animals, spillage and cars running over the grains if they are spread on roads. In a newly constructed SBD, the drying behaviour of freshly harvested maize grain was investigated. In this drier, the initial moisture content of freshly harvested maize grain was decreased from 28 to 41 percent (db) to a final moisture content of 11 to 18 percent (db), with the whole drying process taking place during the falling rate phase. They suggested that it be used to dry cereal crops like as maize grain in tropical and subtropical climates (Asemu et al. 2020). Fig. 13 Solar Bubble Dryer Solar tunnel dryer Solar tunnel dryers absorb solar energy from the sun's rays and atmospheric air to dry agricultural materials such as tomatoes, onions, and agro waste leaves. The material to be dried is spread out in an even layer on treys on the tunnel's racks. The sun heats the air beneath the semi-transparent collector, which then circulates throughout the tunnel. The temperature within the tunnel rises to 65-70 degrees Celsius. The higher temperature within the tunnel drier lowers the relative humidity of the air, allowing it to dry the material inside more efficiently. 9

It does not require much supervision and only requires minor maintenance, which may usually be handled by the end-user. Solar tunnel dryers are a better way for small and medium-scale farmers to dry their crops. A typical solar tunnel dryer lowers the time it takes to dry products from 1 to 5 days, depending on the crop, can enhance harvest productivity by decreasing product loss due to moisture, and minimises the amount of labour necessary to dry products. It has some advantages over direct sun drying- Drying in direct sunlight has the potential to degrade the product's quality. Traditional open- air drying can contaminate products with dust, bugs, and airborne microorganisms, among other things. Direct sun drying does not protect food from fluctuations in humidity or precipitation. A solar tunnel dryer can be a time and cost effective alternative to direct sun drying. Products dried in a solar tunnel have a superior colour, flavour, and taste than those dried in the sun. Fig. 14 Solar Tunnel Dryer Batch-in-bin dryer In a batch-in bin dryer, a specific amount of kernels are dried at a time according to the capacity of the dryer. The batch-in-bin dryer, also known as the flat-bed dryer, was built for use on farms and in villages. The dryer has a capacity of 1-3 tonnes per day, which can be dried in 6- 12 hours. 10

Batch dryers are easy to build out using readily available materials and operated by unskilled labour. The drying bin's walls can be made of wood, stone, or metal, and the floor can be made of fine wire mesh, properly supported, or perforated metal. To ensure an even flow of air through the bed of kernels, the length of the drying chamber should be 2-3 times the width. The height of the plenum chamber is about 0.3 m. Unloading ports are fitted at the walls of the drying chamber. The dryer has a demerit of over-drying the kernel nearest to the wall of the incoming hot air. The excessive moisture gradient in the bed of maize can be prevented by keeping the depth of kernel in the bin Fig. 15 Isometric view of developed dryer 15 relatively shallow, 0.4-0.7 m and the air velocity in the range of 0.08-0.15 m/s. The dryer is loaded easily from sacks by hands whereas, unloading of the kernels is a time and labour intensive process. The advantage of this method is that it can be used for both drying and storing the kernels thus saving both capital and operational cost. A small scale batch-in-bin dryer of 100 kg capacity was developed by Bola et al. 15 to dry maize kernels at varying drying temperatures and air velocity. The drying chamber was a cylindrical bin with a slanting and perforated floor. An agitation shaft with spikes at the alternate site was placed at the centre of the cylinder (Fig. 13). A centrifugal fan was used to force air heated by a set of heater elements to the drying chamber. The agitating shaft ensures the even distribution of heated air by reducing the resistance to airflow. 11

Re-circulating type batch dryer The re-circulating type batch dryer is designed to overcome the problem of moisture gradients experienced in the flat bed dryer. The dryer is a self- contained device with a 500 mm thick annular drying chamber encircling a central plenum chamber, a fan and heater, and a central auger for transporting Fig. 16 Re-circulating batch dryer 17 the kernel from bottom to top. The kernels are discharged from the top after the drying process is completed. The majority of these dryers are compact and can be easily moved from farm to farm. Hot air at 60-80°C is used, with airflow rates of 0.9-1.6 m3/s per tonne of the kernel, which is twice that of flat-bed dryers. Since the kernels are only exposed to the flow of hot air for a limited time during each cycle, excessively fast drying rates are prevented in this method. Adjusting the auger speed to regulate the flow of kernel through the dryer will monitor the drying rate. Rectangular batch dryers with drying chambers on either side of the heater, fan, and plenum chamber are another form of the re-circulating batch dryer (Fig. 14). A horizontal screw conveyor collects the kernel under each drying chamber and returns it to a screw auger at one end, which raises the kernel to a holding section at the top. The kernel is distributed uniformly in each drying chamber by a screw conveyor in the holding section. The dryer's throughput is higher because the drying period is shorter, and the dried kernels are of higher quality. Recirculating batch dryers need specialised construction skills and skilled operators to operate successfully, thus making them unsuitable for use by small-scale farmers or businesses. 12

Continuous-flow dryer Recirculating batch dryers are expanded into continuous-flow dryers. In a continuous flow dryer, rather than recirculating the kernel from bottom to top, the kernels are collected from the bottom, cooled, and then conveyed to tempering or storage bins (Fig. 15). Continuous-flow dryers have a holding bin atop a tall drying compartment in a simple design. Some dryers have a cooling portion under the drying compartment, which blows ambient air through the kernel. Fig. 17 Continuous flow dryer 18 The bottom of the dryer has a flow control portion that controls both the movement of the kernel and its discharge. Based on the exposure of kernels to the drying air, the continuous-flow dryer is categorised as follows: I. Crossflow is a process in which the kernel travels downward in a column between two perforated metal sheets when air is pushed horizontally through the kernel. Although this form of the dryer is easy and inexpensive, moisture gradients are created around the bed due to the lack of mixing systems. II. In a counter flow system, a circular bin with an unloading system is used at the bottom, and the airflow is upward. Since the air exhausts via the wettest kernel, these dryers are relatively effective. For effective drying of the kernels, bed depths of up to 3-4 m can be used. III. Concurrent flow is the opposite of counter-flow drying. The air travels down through the bed of kernels in this dryer. When the air first comes into contact with wet and often cold kernels, high air temperatures can be used. The upper layers dry quickly, while the lower layers dry more slowly, with some tempering action. The crossflow columnar form dryer is the most widely used continuous-flow dryer, and it comes in two types: non-mixing and mixing.  Drying occurs between two parallel screens 150-250 mm apart on either side of the plenum chamber in a non-mixing dryer (Continuous Flow Dryers) (Fig. 15).  The air is vented from the dryer via louvres on either side. 13

 A regulator gate, at the bottom of the drying column regulates the flow rate of the kernel.  The kernel drying portion has a plug-like flow, with the kernel layer closest to the plenum chamber being dried by hotter and drier air than the kernel on the outside. When the kernel is discharged and conveyed to tempering and storage containers, the mixing is influenced to some extent.  Air temperatures of 45-55°C are used, with a flow rate of 2-4 m3/s per tonne of the kernel.  Kernels that are very wet and dirty can clog, posing a problem with flow.  A baffle system is used in a mixing continuous-flow dryer to allow kernel mixing and prevent moisture gradients from developing across the drying bed (Fig. 14).  To prevent kernels from being blown out of drying chambers without a screen on the outside of the drying section, a lower airflow of 1-1.5 m3/s per tonne of the kernel must be used.  Continuous-flow dryers offer the largest drying capacity as compared to batch-in-bin dryers and recirculating batch dryers.  It is considered a priority when large volumes of wet kernels are to be dried in a single site.  They are generally used in a multi-pass drying operation (Large drying system using Continuous-flow Dryer, Conveying Equipment, and tempering bins).  While the initial investment is substantial, the operating costs per tonne are lower than those of larger batch-in-bin and re-circulating dryers due to the high throughput.  Continuous-flow dryers are used in conjunction with tempering bins in a multi-pass drying system.  The kernels are dried for 15-30 minutes during each run through the dryer, with a moisture content reduction of 1-3%.  The kernels are kept in a tempering bin after each run, where the moisture inside the kernel equalises due to moisture diffusion from the interior to the surface.  Repeat the process of rapid drying and tempering until the desired moisture content is achieved.  The actual residence time of the kernel inside the continuous-flow dryer in this process is 2-3 hours to achieve a 10% moisture reduction. 14

 The number of passes chosen is a trade-off between dryer performance and drying time, with fewer passes resulting in a longer drying time.  To cool the kernel and remove some moisture, the tempering bins can be aerated with ambient air.  To ensure optimum throughput and performance, the drying and tempering operations must be meticulously designed and controlled. In a study in Ghana a Crossflow column dryer with a biomass burner heat source was studied for maize kernels in this study. To evaluate its performance, the drying rate, drying efficiency, and moisture extraction rate were examined. The moisture content of maize was reduced from 22.3 % to 13.4 2.6 % in 5 hours at an average drying rate of 1.81 % per hour and a drying efficiency of 64.7 %, according to the findings(Obeng-Akrofi31) 15

Fig. 18 ICAR-CIPHET developed Maize Cobs Dryer ICAR-CIPHET developed Maize Cobs Dryer Corn quality can be maintained by immediately drying of corn cobs after harvesting, as this stage is more vulnerable to microbial infection at high moisture content, especially in Kharif harvests. On those days, the weather is also cold, and drying it out in the open field using sun drying techniques is difficult due to the occasional rain. In this line, A hot air dryer for maize cobs has been designed and developed by ICAR-CIPHET, Ludhiana for dropping the moisture 16

content from approximately 35 to 17% (wb) (Fig. 16). It can accommodate 150 kg of cobs with husk per batch. The heating unit, drying bin, and control panel are the three major components of the dryer. The designed dryer's overall dimensions (L×W×H) are 1.815× 0.912× 2.800 m, while the drying bin has a circular form with dimensions (H×D) of 0.990 ×0.834 m. The heating unit measures 0.827 m in length, 0.750 m in width, and 2.800 m in height. An electronic panel controls the air flow rate, RPM blower and the temperature in the heating unit. To minimize the dryer's heat losses, insulation has been placed over the heating unit and the drying bin. The loading and unloading of maize cobs is performed manually. At the climatic conditions of 36.86°C and RH 51.37 %, it took 24-27 hours to reach the desired moisture content. Meanwhile, six hours of maize cob tempering has been supplied to maintain the dryer’s heat utilisation factor (HUF). The dryer consumes 1.2±3 kWh of electricity. Where corn cobs take 7.75 ± 0.43 minutes to load, it takes 9.85 ± 0.85 minutes to unload. As the most important performance parameters of the dryer, the HUF and thermal efficiency of the dryer have been found to be 0.86 - 0.47 and 79.63 ± 1.54%, respectively. When it comes to drying corn cobs, the total cost of each batch is about Rs.300, or Rs.2.0 per kg of corn cobs. The capital cost, on the other hand, is approximately 1.06 lakhs. Certainly, it is a mechanical drier that consumes energy, which raises drying costs and makes it more expensive than sun drying methods, but it also allows corn cobs to be dried immediately after harvesting without having weather glitches. PAU Portable Maize Dryer The Punjab Agricultural University (PAU), Ludhiana, Punjab has developed a portable maize dryer (Fig.17), which can dry maize grain from 25% moisture to 15% moisture in 8-10 hours. This cross-flow dryer has a three-pass, indirect diesel-fired heating system that keeps the grain at 45°C for seed and 60°C for other than seeds. For better operation, a control panel with variable frequency drive is given to regulate and view the temperature of heated air, exit air, and air blower speed. The dryer dries maize grain at a rate of 1-1.5% per hour while using no 17

more than 4 litres of diesel per hour for the first hour. Heat recovery from flue gases enables higher fuel efficiency, resulting in a 2 litre/h reduction in diesel consumption later on. Both tractor PTO and electricity can be used to power this PAU maize dryer. This dyer can be operated by one skilled and unskilled worker. Fig. 19 PAU Portable Maize Dryer 19 IV. Storage Practices of Maize Grain Reducing post‐harvest losses is considered a major step towards the food security of the country. However, losses vary significantly by climatic region, country, crop and of course the infrastructure and methods of storage practices. After harvesting, farmers keep maize on cob either wet or dry due to lack of storage facilities. In India, the post‐harvest losses of maize grain have been estimated as 4.65%, thereby losing around 1.3 million tons per year.29. This can be attributed to the poor infrastructural facility and unscientific methodologies followed for food kernel storage in the country. Safe kernel storage methods play a crucial role in preventing losses caused mainly by weevils, beetles, moths and rodents. It is estimated that 60-70% of the food kernel produced in the country is stored at a domestic level30. To ensure safe and scientific storage, careful selection of storage site, storage structure and proper aeration of kernels, regular inspection of kernel stock, cleaning and fumigation needs to be performed whenever required. 18

The most critical factor for the successful storage of maize is moisture content. High moisture causes storage problems as it encourages fungal and insect problems, respiration and germination. Another factor is the temperature, which affects the activity of fungal species and insects. Being biologically active, kernels respire during storage and generate heat. Thus, reducing the temperature of the kernels during storage diminishes the rate of respiration, thereby lengthening the storage life by lessening the possibility of germination. Moreover, the lower temperature also decreases the metabolic rate of insects and fungi thus restricting their spoilage activity during storage. Any warm spot in bulk storage increases the rate of respiration, which produces the heat along with moisture. The heat and moisture from such a ‘hot spot’ spread by convection thus encourage the growth and development of moulds and bacteria, which in turn respire and give off more heat and moisture to the stored grain. This spoilage mechanism during storage deteriorates the quality of the kernels. Therefore, proper storage structures are necessary to preserve the quality of stored kernels for a longer time. Traditionally, two approaches are employed for storage of maize/ grain in India: i) temporary and ii) long‐term storage methods. In temporary storage, the methods such as aerial storage, storage on the ground or on drying floors and open timber platforms are followed at farm level, whereas, under long term storage methods, storage baskets (cribs) made exclusively of plant materials, calabashes, gourds, earthenware pots, jars, solid wall bins and underground storage are employed. The storage of grain in bulk is done in warehouses owned by the Food Corporation of India (FCI) and the Central and State Warehousing Corporation (CWC/SWC). Warehouses are scientific storage structures especially constructed for the protection of the quantity and quality of stored material. Under bulk storage, sealing and aeration play an important role in safe storage of grains. Depending on the requirements of the stored product, aeration might be ambient or controlled. Underground pits Underground pits, it is said, can safely store kernels for many years. The closed pits keep the kernels cold. The kernel on top and towards the sides, on the other hand, turns mouldy. Pits come in a variety of shapes and sizes, with the most common being flask-shaped and coated with sticks, cow dung, and mud, or a huge stone stuck in soft mud. Termites should not be present, and the area should be reasonably dry. A better lining of straw and mud, the use of 19

plastic sheets and concrete, the use of plastic bags in the pit, increased pit covering, and adequate surface drainage may all help to improve the design of pits. (Fig. 18). Brick-walled silo Small and medium-sized stores use brick-walled silos or bins. It's cost- effective up to a height of 7-8 metres. Bricks or mud blocks, burnt clay, stones, or cement are used to build the walls. The walls must be reinforced in Fig. 20 Underground pit 10 proportion to the size and strength of the building materials to sustain the pressure from the kernel. Building thick, heavy walls can decrease or eliminate the need for reinforcement (gravity walls). The moisture in the air is absorbed by brick walls constructed of mud or cement. Moisture barriers are installed to the silo walls in locations with high relative humidity to protect the kernel.Outside, plaster burned bricks or cement walls with cement–lime–sand (1:1:5) mortar, and mud walls with cement–sand–mud mortar (1:2:6). Plastic paint or coal tar 10 can be used to protect the walls if more protection is required. Instead of plastering and painting the silo, a liner of plastic Fig. 21 Brick-walled silo 10 sheeting in the middle of the wall, floor, and roof can be used to make the container airtight. (Fig. 19). Pusa Bin The Indian Agricultural Research Institute (IARI), New Delhi developed the Pusa bin27. The rectangular silos are built of earth or sun-dried bricks and have a capacity of 1 to 3 tonnes. A brick, compacted earth, or stable earth foundation is usually of a \"Pusa\" bin. Over this, a polyethene sheet is placed, followed by a 10-cm-thick concrete slab floor. A 1.5 to 2 metre 20

high interior wall is made of bricks or compacted earth, with a polyethene sheet wrapped around it. The exterior wall is then built once this sheet is heat-sealed to the basal layer. An outflow pipe is placed into the base of the wall during construction.The concrete slab roof, like the floor, is supported by a wooden frame and is made up of two layers divided by a polyethene sheet. A 60 × 60 cm manhole is placed into one corner of the structure during construction (Fig. 20). In India, the \"Pusa\" bin is extensively used, and it has also been exhibited in various African nations. When loaded with a well-dried kernel, it provides good results. The system may be utilised for silos of any design and, if built properly, would provide good air and moisture protection. 21

Reinforced concrete silos Because concrete bears relatively little tension, it must be reinforced when used for silos. Small silos used for a single farm are reinforced with chicken wire. As depicted in Fig. 21, the ferrocement store, or ‘ferrumbu,' is an example of such a storage structure. One or two layers of 12 mm chicken wire are woven into a circle of vertical sticks or rods. After that, both the interior and Fig. 23 Ferro cement store 10 exterior of the chicken wire is plastered. The verticals are removed when the exterior has been completed. Welded mesh wire and 12 mm chicken wire connected to the outer frame the silos with a height of 3-4 metre or higher. The bags or plastics are fastened to the exterior, and then the inside of the silo is plastered first, followed by the outside a few days later once the bags have been removed. This allows for the construction of walls with a thickness of 3-6 cm. A sliding mould, which is pushed upwards continuously or step by step, is used to construct larger concrete silos. From the top, reinforcement and concrete are poured. The concrete silos can be made airtight by sealing the holes. Storage baskets/ cribs When the kernel cannot be thoroughly dried before storage due to humid weather conditions, it must be kept sufficiently aired during the storage period. Traditional granaries (cribs) are generally made completely of locally available plant materials, such as wood, reeds, bamboo, and so on, and are used to store maize. Most plant material decays rapidly in prevailing climate, so most cribs need to be changed every two or three years - however bamboo structures may survive up to 15 years with proper care. Traditional storage structures include mud-plastered 22

baskets and cement-plastered baskets. There are a few upgraded storages, such as the brick and the ferrocement bin. Fig. 24 Maize crib used for storing shelled maize grain in bags24 Walls of light branches, split bamboo, or other woven material are used to construct traditional basket storage. Both the inner and outer walls of an improved structure are plastered with mud or cement mortar. A plastered basket adds another layer of defence against the Larger Kernel Borer. A wooden platform at least 75 cm above the ground is the standard basis for this type of storage. If you utilise a wooden platform, make sure the posts are treated for termites and have rat guards fitted. However, a stone base covered with either mud or cement mortar can enhance storage even more. An overhanging detachable roof or perhaps a permanent roof structure should cover the entire basket. After the maize has been dried on the cob, a rectangular drying and storage crib is used to store shelled maize in bags. The crib should ideally be rectangular, with an internal width of 60-70 cm but no more than 1 metre, and a floor structure that is at least 75 cm above the ground (Fig. 22). Termite treatment and rat guards should be applied to the posts. To minimise pest infestation, cribs should be placed far away from fields, away from grass, shrubs, waste corn, and water. 23

Metal bins/silos Metal silos are sometimes thought to be too expensive for small-scale storage. Nonetheless, several initiatives in developing countries, such as Swaziland (Walker24) and India (Anon25), have been successful in establishing tiny metal silos of 0.4 to 10 tonne capacity at farm/village level. For almost 50 years, metal silos have been claimed to have been utilised on farms and in villages in Guatemala (Breth26), and on a smaller scale in Swaziland for perhaps longer storage. It has a storage capacity of thousands of tonnes.Metal silos are more expensive than concrete silos, but they offer the benefits of being easier to build, smaller in size, and transportable. The welded steel silo is typically airtight, and even a silo composed of corrugated iron sheets may be made airtight by using rubber gaskets or bitumen to seal all seams. (Fig. 23). Bag storage Bag storage is the most common grain storage method, and it may be done in a number of structures, including stone, local brick, corrugated iron, mud and wattle, with or without plastered walls, earth, stone, or cement floors, and corrugated iron or Fig. 26 Storage warehouse 10 thatched roofs. To avoid spoiling from translocating water or termites, grains in bags must be kept off the ground. Low platforms, tarpaulins, or plastic sheeting can be used for this, but elevated platforms with rodent barriers should be utilised to avoid damage from rats or other animals (Fig. 24). As a result, the bags are stacked atop a perforated panel tunnel that serves as the stack's foundation, distributing air evenly. If it rains during the temporary storage period, the bags should be covered with waterproof sheeting (although not all of the time if the grain has a moisture content greater than 12%). Alternatively, the bags should be placed in a rodent-proofed building on dunnage or waterproof sheeting away from walls. The jute bag has drawbacks in that it provides little bug protection, necessitating the application of insecticide. If the storage time is short, there should be no need for chemical pest management. Similar conservation measures should be implemented when sacks are used for domestic grain storage. It will, however, be required to use some type of insect pest control. Before using a secondhand bag, it must be carefully cleaned and disinfected. For temporary storage in dry climates, the bags are stacked on plinths and covered with a tarpaulin. The bags are stored in the building if the kernel has to be 24

maintained for a long time. In warehouses, a huge quantity of bagged kernels are stored. The design of warehouses depends upon the specific volume of the main product to be stored (m3 /tonne), the maximum tonnage of the product to be stored, the maximum stack height desired and the extent to which separation of lots is desired (Fig. 25). Fig. 27 Storage of food grain in bags in warehouse 22 General Considerations: The stored maize can be protected from mould or insect infestation by incorporating integrated pest management practices, which are based on the understanding of the ecology of kernel pests. The preventive practices have to be applied to pest control that includes cleaning of kernel bins and the area surrounding them before harvest, cleaning of dried corn before storage to remove broken kernels and trash, controlling temperature throughout storage, managing the depth of kernel in the bin to permit uniform airflow, and monitoring kernel during storage for temperature, moisture, and mould and insect populations. By following these measures, a post-harvest Integrated Pest Management (IPM) approach can be substituted with the use of chemicals that have traditionally been used to control pests in the stored kernel. Maize containing a high amount of trash and/or not dried uniformly can cause problems during storage. Thus, it is necessary to check the topmost layer of the grain in all the storage bins about a week after drying and ensure that no moisture build-up occurs. If a rise in temperature or moisture migration is unchecked, mould and insect growth can flourish in cold weather too, as its activity leads to the production of heat, which accelerates the deterioration of kernels. 25

Controlling the moisture content and temperature of maize throughout the storage period is the most cost-effective method to prevent spoilage problems and potential dockage from musty odours, insects, low test weight, and poor condition. Stored maize can spoil, if it is dried uniformly to appropriate moisture content but not cooled thoroughly. Uneven kernel temperatures can lead to moisture migration (which usually occurs in the top centre of the bin), which promotes mould growth and insect activity. Here, aeration is necessary to equalise kernel temperatures throughout the bin that prevents moisture migration. The time required to aerate the kernels depends primarily on the size of the fan relative to the amount of kernel. Another good grain management practice is to remove the top cone of maize that occupies the upper portion of the bin. This method is not commonly followed as it is viewed as a loss of storage capacity. Most problems during the storage of maize arise in overfilled bins and begin in the upper centre of the kernel mass because that area gets little airflow as air follows the path of least resistance and bypasses the deepest grain. While removing the top cone of maize, trash and fines that tend to accumulate in the centre of the bin are reduced, which allows the movement of air through the centre of the bin much more easily. Maize from this area should be held in a separate bin and fed to livestock or sold quickly since it has a relatively high concentration of broken corn, trash, and fine material. The removal of the top cone of maize has improved airflow and created adequate space for workers to probe the bin and check for possible problems. The stored maize is to be inspected every 1 to 2 weeks in the fall and spring and once every 2 to 4 weeks after conditions in the bin have stabilised during the winter months. All workers should be made aware of the suffocation and entrapment hazards that exist with the flowing of the kernels as the personal safety risks associated with kernel dust. The kernel moisture, temperature and condition should be inspected at regular intervals and the recorded data should be compared with the previous samples. If the condition changes towards an increase in temperature or moisture level that favours mould growth or insect activity, run aeration fans to cool the kernels thoroughly. If conditions continue to worsen, transfer the kernel to another bin and collect a sample every two to five minutes during unloading. Re-dry the moist kernels to a safe level as quickly as possible or sell the lot if drying is not an option. 26

V. Conclusion Post-harvest management practices are necessary to preserve the quality of the maize. Drying is one of the oldest and inexpensive methods to preserve the various agricultural commodities. Several methods are being practised for drying of maize cob and maize kernels viz. sun drying, solar drying, mechanical drying and so on. Along with drying methods, storage conditions also affect the quality of the maize. If maize is not properly dried and stored, it is susceptible to growth and development of fungus, mainly Aspergillus flavus, which not only leads to qualitative loss to the maize cobs and kernels but also severely damages the health of the consumers. Several dryers have been designed and developed but still a cost effective maize cob dryer for on-farm drying of maize cobs is the urgent need of the Indian farmers. Furthermore, inhibition of the growth and development of aflatoxin-producing fungi in maize cobs as well as in maize kernel by efficient means of drying, immediately after harvesting should be followed by the producers for preventing the quantitative and qualitative losses in maize. References 1. Agricultural Statistics at a Glance 2019. Directorate of Economics and Statistics, Department of Agriculture, Cooperation and Farmers Welfare, Ministry of Agriculture and Farmers Welfare, Government of India. 2. https://www.statista.com/statistics/1140254/india-production-volume-of-maize/. Accessed 23 January 2021. 3. Singh, S. P., Singh, S., Singh, P. 2011. Status of maize threshing in India. Agricultural Mechanization in Asia, Africa, and Latin America, 42(3): 21-28. 4. https://agfax.com/2018/10/11/iowa-corn-mycotoxins-smartphone-app-available/. Accessed 23 January 2021. 27

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