POST HARVEST MANAGEMENT
“What can farmers do to increase the shelf life and maintain the quality and add value to maize grains after harvest?”
By Eunice Sakong
FOOD THAT IS lost means all resources (water, land, energy, labour and capital) that were used to produce that food are wasted. Disposal of food in landfills leads to greenhouse gas emissions contributing to climate change. This impacts on food and nutrition security, contributes to disease burden associated with consumption of unsafe food and affects the economy. Food deficit in Kenya is partly occasioned by food loss and waste with the food import bill standing at about Ksh 200 billion out of which 10% goes to maize imports.
“We need to be reminded that food discarded is in a certain sense stolen from the table of the poor and the starving” (Famous quote from Pope Francis). Food loss negatively impacts income and livelihoods for farmers, to reduce these negative impacts farmers need to do post-harvest management. This is the application of methods and techniques to increase shelf life and maintain quality of produce. In simple terms, post-harvest management in maize is a good agricultural practice that adds value to maize and all maize products. Why is post-harvest management important?
- Ensures food safety and quality assurance
- Contributes to better and longer storage of grains
- Protects harvested maize grains from storage pests and exposure to toxins
- Reduces post-harvest losses in both quality and quantity of grains
- Provides better marketing opportunities for farmers
Practices of post-harvest management
- Harvesting: Good harvesting practice minimizes losses, grain damage and quality deterioration. Harvest at the right time and right moisture content when the maize crop has attained physiological maturity as this influences yield, quality and storage life of produce. Prematurely harvested maize has high moisture content and low quality. De- layed harvesting leads to increased field loss- es due to grain discoloration if mature maize plants are exposed to very moist weather, predisposal to pests and mycotoxin (especially Aflatoxins) produced by fungi especially when maize plants fall or lodge and get in contact with soil. Avoid heaping and putting dehusked maize on the ground; instead place the maize on tarpaulin sheets.
- Sorting and drying maize on cob -: Sort- ing should start at harvesting; separate the clean maize from the rotten or discolored ones then dry on simple matting or tarpaulin laid on bare ground. Avoid drying maize directly on bare ground or tarmac. This is the first step in improving the quality of the grains as drying will facilitate efficient shelling.
- Shelling:- Shelling is the detachment of grains from cobs. This is done manually or mechanically using motorized shellers. The shelling should be done on a clean tarpaulin to reduce scattering losses and grains getting in contact with soil. It should also be done with care not to damage grains as this may predispose grains to insect pests, mould attacks and fungi that produce mycotoxins.
- Winnowing, cleaning and sorting:- Winnowing is based on the principle that lighter materials are blown away by wind and this is used to remove chaff, straw and empty grains. It can be done by hand or mechanically. Damaged grains and any foreign material such as pieces of broken cobs should be removed from the shelled grain. Simple manually operated equipment is now available in the market for winnowing and grading of grains and the grains depend on the size of the tray mesh being used. During winnowing grains may be mixed with straw and chaff may get lost thus winnowing should be done on clean, dry tarpaulin.
- Drying of grains:- Drying is the systematic reduction of grain moisture to safe levels for storage and should be done immediately after harvesting ( before and after shelling, and after winnowing, cleaning and sorting) and it should not be delayed. Dry to remove excess moisture from the grains and aim at having 12 – 14% moisture for the grains as this minimizes storage and post-harvest losses due to moulds and enhances the quality of grains significantly. There are several options for drying grains; Sun dry by placing maize grains on tarpaulin laid on bare ground however in the evening the maize and tarpaulin need to be removed and the same process repeated for some days until grains achieve an average of 13.5 % moisture content. Sun drying can also be done on raised platforms/ drying trays which allows for effective drying. This is further improved by the use of drying on raised mesh/ netting racks and turning the grains at intervals of 1 to 2 hours to expose the grain surface to the wind / surrounding hot air. When using raised platforms grain should be covered at night to protect them against moisture, rain and dew. It is recommended that the grains be covered with 3 layers of covers as follows: – jute that absorbs dew/moisture, followed by shade net that ensures that absorbed moisture by the jute does not get back to the grain and then the plastic cover that ensures moisture from precipitation does not get into the grains.
Using raised mesh racks increases the rate of grains drying significantly while protecting grains from ground dampness thus reducing microbial proliferation and soil contamination. This ensures high quality end products. It is important to note that heavy reliance on ambient or natural air conditions for grain drying can create problems during humid, warm weather as drying might take too long with higher chances of spoilage. Forced ventilation with warm, dry air for example use of solar dryers can increase the drying efficiency.
How to determine grain moisture content
There are several methods to determine the moisture content of grains. Some of the methods are quick and easy but not precise and others require more time and effort but give more accurate results. The sample grains for moisture testing need to be randomly picked from the produce.
- Salt test method:- A sample of grain is vigorously shaken then mixed with dry common salt in a clean dry glass bottle for several minutes and the sample allowed to settle. If damp salt is seen to stick on the walls of the bottle, then the grain is above 15% moisture content. If the jar/ bottle still looks dry, then the moisture content of the grain is less than 15% moisture con- tent.
- Grain moisture meters:- Portable or hand-held moisture meters provide faster accurate results. Grain moisture meters are available in some agricultural offices and some farmers’ grain aggregation centres, ask around within your locality.
6. Storage: Provide safe storage conditions for the grains once they have attained an average moisture content of 12 – 14%. Protect the produce from re-wetting, insect pests, rodents, moulds, birds and theft. The storage structure/ room needs to be well aerated, clean, cool and dry with bagged product placed on pallets above the floor to avoid conditions that may lead to moulds development. Moulds may release mycotoxins such as Aflatoxins which make the grains totally unusable for both human and livestock consumption. Farmers may pack and store the completely dry grains using any of these technologies :-
The second layer of sack with grains
- Drums and plastic containers; – Ensure they are filled with grains to expel air and close lid tightly.
- Hermetic bags;– They are readily available in agro-dealer shops in Kenya. These are specially manufactured bags with sacks lined with a layer of special polythene for safe storage of grains. They are air-tight and moisture-resistant bags and protect grains from air moisture and storage insects for several months and extend storage until the next crop harvest and beyond if well packed.
Twisted and secured special polythene layer
How to keep grains in hermetic storage bags
Open the bag and pour the clean and well dried grains into the bag. Then twist the remaining top of the special polythene to remove air and secure the twist by tying it with a band or twine (sisal or plastic). After that twist the remaining part of the sack and also tie.
Eunice Sakong is a crop officer at the Department of Agriculture in Machakos County. Email: eunicesakong@yahoo.com