Post harvest processing encompasses an array of handling and processing system from the stage of maturation till consumption of the produce and includes threshing, cleaning, grading, drying, parboiling, curing, milling, preservation, storage, processing, packaging, transportation, marketing and consumption systems.
The most important factor deciding the storability of the produce is moisture content of the produce. High moisture content invites pest and disease and induce pre-germination. Moisture content for safe storage of grains of most crops is about 14% (raw rice), 15% for parboiled rice, 12% for wheat, barley, other millets and pulses, 10% for coriander, chillies and 6% for groundnut, rapeseed and mustard.
• To minimize post harvest losses which is around 10–25% in cereals and 20–30% in perishables.
• To get good quality products.
• To get maximum quantity of materials by way of proper PHT.
• To get value added products by way of processing.
• For proper utilization of water from food industries.
• To create employment opportunities.
• To eliminate or minimize the pollution.
(i) Threshing: Involves the detachment of grains from the panicle.
(ii) Drying: Reduction of 12–14% or 8% by evaporation. i.e., it involves heat and mass transfer operations simultaneously.
(iii) Parboiling: Is a hydrothermal treatment followed by drying before milling for the production of milled parboiled grain. The most important change during parboiling is the gelatinization of starch and disintegration of protein bodies in the endosperm.
(iv) Milling: Refers to the size reduction and separation operations used for processing of food grains into edible form by removing and separating the inedible and undesirable portions from them, Milling may involve cleaning/separating husk (dehusking), sorting, whitening, polishing, grinding etc.
(v) Storage: Proper storage in storage structures is necessary to prevent the grains from storage pest and to maintain the quality of seeds.
Methods involved in Post Harvest Technology
The quantitative losses encountered at various stages are 1 to 3%, during harvest, 2 to 6% during threshing, 1 to 5% during drying 2 to 7% during handling 2 to 10% during milling and 2 to 6% during handling 2 to 10% during milling and 2 to 6% during storage. To overcome these losses the following improved practices can be adopted.
(i) Harvesting: Paddy if not harvested at the optimum time, results in loss of quality and quantity. To reduce these losses, machines like combines and reapers are being introduced to harvest paddy at an appropriate stage.
(ii) Threshing: Threshing, done by bullocks, tractors and by hand, result in poor drying, storage and milling. The multicrop threshers have been developed to reduce these losses.
(iii) Transport: Poor transport facilities result in losses to the farmers, millers, and eventually food grain to the country, sometimes as much as 2–3 per cent. Good transport facilities should be used to minimize these losses.
When once the grain is threshed and dried, it will be transported from the field to store houses by bullock carts, or tractors by the growers. Sometimes if the market price is favourable, the produce is disposed to the traders soon after drying. The disposal of the produce, either at the village or at the market yard is, however often closely connected with financial needs of the growers and sometimes indebtedness.
The traders on purchasing, transport the produce to go-down, or shops for sale to the consumers. This transport mainly uses trucks i.e., lorries. Government agencies like Food Corporation of India etc., transport the produce from one place to another place either by road or rail (waggons) for long-term storage and sometimes to export to other countries by sea (cargo). If the produce is not properly bagged and handled there will be some loss during transport.
(iv) Drying: Sun drying methods cause more breakage of grain than other factor, resulting in low head yields and low milling yields. Moist paddy in storage deteriorates rapidly. With the introduction of heated air dryers, the losses can be reduced considerably.
(v) Storage: Uncleaned wet paddy accounts for the largest losses during storage. This is followed by losses due to rodents, birds, mould, fungus, insects and pilferage. These losses can be minimized by storing in good storage structures.
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