Post-harvest technology: Cleaning rice

Harvested at 18 – 25% moisture, rice is mechanically dried to less than 15% moisture on the farm, at a commercial dryer, or at the mill before storage or processing.

Several stages of post-harvest handling of rice grains include field-drying, threshing, shed drying, cleaning, grading, storing, weighing, and milling before making it fit for human consumption. These can be done individually or a combine harvester can be used to perform the operations simultaneously.

The paddy rice from the warehouse or store must be dry cleaned to remove pieces of straws, stones and other foreign materials before processing.

High percentage of chaff, foreign matters include the soil piece, sand, small stones, metal debris, plastic or paper pieces, twig and branches, wood piece, weed seed, other grains, chemical and poisonous matters, etc., will unnecessarily increase the number of sack of rice and weight of paddy, which may cost the grower avoidable transport fees and milling fees paid the mill operator; and for the rice mill operator the cost of wear-and-tear and spoilage to his machine.

Most cleaners separate three groups of materials:
• The first separation is done by scalping or removing the objects that are larger than the grain. Either a flat oscillating screen or a rotary drum screen that allows the grain to pass through but retains straw can do this.
• The second separation retains the grains but allows broken grains, small stones and weed seeds to pass through. An air aspirator may also be incorporated to remove the dust and the light empty grains
Post-harvest technology: Cleaning rice

Watermelon post-harvest

Watermelons in most of the world are customarily handled postharvest under nonrefrigerated conditions. Shelf life for watermelon is 2–3 weeks at 10–15C depending on cultivar.

Watermelons should be harvested at full maturity to ensure that good quality fruit are delivered to the market. The fruit do not develop internal color or increase in sugar content after being removed from the vine. Harvesting usually begins 3-4 months after planting.

The ground spot (the portion of the melon resting on the soil) changes from pale white to a creamy yellow at the proper harvest maturity. The ground spot color is easily revealed by gently rolling the fruit over to one side while still attached to the vine. Also, tendrils near fruit stem have changed color from green to brown.

Very experienced workers can determine ripeness stage based on the sound produced when the fruit is thumped or rapped with the knuckles. Immature fruit will give off a metallic ringing sound whereas mature fruit will sound dull or hollow.

Sugar content (measured as soluble solids by use of hand held refractometer) of 10 % or more in the flesh near the center of the melon.

Lycopene content peaked 7 days postharvest and intensity of flesh color increased concomitantly; yellowing of flesh was detected at 14 days.

Rootstocks improved postharvest flesh firmness and lycopene content and enhanced flesh color. Rind was minimally thickened by rootstocks and declined with storage.

The harvest operation is a manual process which is the most labor-intensive part of producing watermelons. Due to their large size and susceptibility to splitting or cracking under mechanical stress, watermelons should not be harvested in the early morning when they are most turgid.

Handling should minimize fruit injury which may be caused by impact or abrasion. Shading is necessary in order to protect watermelon from direct sunlight which causes sunburn.
Watermelon post-harvest

Postharvest of oats grain

After harvest, oats are generally marketed through local and /or terminal elevators except that which is used on farm.

A large portion of the oat crop is used in livestock feed. This grain may be pulled out of the marketing channel at any point. A high-yielding, quality oat crops needs careful postharvest handling and storage to ensure or improve its milling and nutritional quality.

Humidity and temperature are the main factors influencing the biological activity of the grain nd the interaction of microorganism and animal organisms with the stored grain.

Seed of oats is usually dry (10-12% moisture content) at harvest time of the grain moisture content is high at harvest, the seeds must be dried to a safe moisture level (below 13.5 %( to avoid biodeterioration).

In the tropical countries, sun drying is a common practice for small quantities of produce. Mechanical drying is essential in large-scale production to avoid seed losses due to birds, rodents and unexpected rains and to ensure uniform drying of seeds.

The seed of oats must be cleaned, treated and bagged immediately after threshing and drying to maintain their high quality. The cleaning of oats begins with a weighing scale, followed by magnet for removal of any ferrous metal or its alloy from the oat stream.

A grain separator or classifier is used next, with an air-recycling aspiration system attached. This would help remove larger, finer and lighter foreign material form oats.

Grading function can be accomplished using drum graders which make separations on the basis of width. In the older oat processing plants grading is also carried out using a grading sifter with a various screen sizes to sort small, medium and large oats.
Postharvest of oats grain