Paddy Drying
• Recognizing the need for better drying facilities for both freshly harvested and parboiled paddy, mechanical drying systems were introduced in the late 1960s in India. These dryers were of Louisiana State University (LSU) design, with a holding capacity of 6 tonnes or more. As the heat-generating fuel was furnace oil, these dryers tended to be uneconomical.
• Later, a few portable dryers of small holding capacity that employed rice husk as fuel were developed and are being used commercially (Ojha 1978a).
• Among these, the RPEC recirculatory dryer and LSU dryer coupled with a husk-fired furnace gave good performance
• Bose et al. (1980) developed a system utilizing a fixed-bed LSU dryer coupled with a solar-cum-husk fired heating unit for drying high-moisture paddy. Since these dryers were of about one tonne holding capacity, they were adopted by smaller millers and others.
• The circulatory dryers can be successfully used to dry high-moisture (24 per cent moisture content) paddy to about 16 per cent m.c. in four passes of 30 minutes each. Paddy so dried gave a high head yield due to uniform drying of individual grains.
• A multipass system is used in India for drying. Each pass takes about 30 minutes with the temperature of the heated air being 50 °C for raw paddy and as high as 90 °C for parboiled paddy. About 2 per cent loss of moisture occurs in each pass.
• Moisture removal can be accelerated by tempering the grain in a heap or in a silo at the end of each pass. The most common cause of cracking is believed to be either rapid drying or rapid moistening, or both.
• Cracks are a result of stresses developed in the grains, and they are more frequent in kernels of large sizes.
Pre-milling treatments
• Soaking in cold water and drying in sun, soaking in hot water followed by sun drying or steaming, soaking, steaming, and drying are the pre-milling combinations practised in India to improve the milling, nutritional, and keeping qualities of rice.
• Some varieties of paddy possess poor milling quality for many reasons.
• The weather prevalent during field maturity and harvesting, or unscientific post-harvest practices in handling and storage, render the paddy grains fragile and lead to breakage during milling.
• Proper hydrothermic treatments, as earlier described, can improve the milling qualities of paddy. One such treatment is parboiling, which is given to about 60 per cent of all the paddy produced in India.
• Improved methods of parboiling include the three steps of hot-soaking, steaming, and drying.
• Parboiled paddy is produced either as a small scale, family trade, or at a commercial level in rice mills.
Nutritive Value of Parboiled Rico
• The rice grain is composed of a surface layer called bran (itself consisting of the pericarp and aleurone layers), the starchy endosperm, and the germ. The surface layers are rich in protein, oils, and vitamins compared to the endosperm.
• Parboiling augments the nutritive value, through first translocating vitamins from the peripheral layers to the central core, and oil from the endosperm to the bran layers, followed by heat sealing them.
Milling Quality of Parboiled Rico
• It is well known that parboiling reduces breakage during milling. Thus improvement is usually attributed to increased hardness, or the healing of sun-cracks and other defects resulting from biochemical changes.
• Parboiling leads to an increase in total yield as well as head yield. The performance study report on rice mills reports an increase of about 6.6 per cent in total yield and over 15 per cent in head yield for a few varieties (Mathrani 1971). Varieties that give poor yields in raw milling often show excellent milling quality after parboiling.
• Bran from parboiled rice contains less starch and more oil than raw rice bran. The oil content of parboiled bran varies from 15 to 25 per cent, about 5 per cent higher than in raw bran.
Cooking Quality of Parboiled Rice
• The cooking quality of rice may be defined as the ability of the grain to be cooked to the required texture or tenderness without losing shape. A grain that cooks to a fluffy, non-cohesive, tender texture, and retains its shape, while increasing in size, is said to have good cooking quality.
Milling of grain
• The term milling generally refers to the size-reduction of granular material, but for food grains the term has different connotations. Wheat milling means wheat grinding to prepare flour, maida, suji, etc.
• Rice milling includes operations like dehusking and polishing; dhal milling also involves processing operations such as husk separation, splitting of kernels and polishing, or polishing only.
• The traditional methods employed for milling are wasteful, non-uniform, and do not yield useful by-products.
Modern and the traditional methods can be compared using the outputs obtained.
• About 7 per cent extra yield can be derived by employing modern rice milling machines.
• On an all-India basis, an additional quantity of 5 million tonnes of rice and Rs 6,000 million worth of pure rice bran can be achieved.
• A better quality of rice is produced through modern mills.
• The degree of polish and the percentage of brokers in the final product can be very precisely controlled to suit the specific needs either of industry or of the consumer.
• The most impressive gain that rice mill modernization has brought about is the efficient utilization of by-products of rice. If the total quantity of available bran is solvent-extracted, it will yield about 800,000 tonnes of bran oil for the country.
Milling of grain
• The term milling generally refers to the size-reduction of granular material, but for food grains the term has different connotations. Wheat milling means wheat grinding to prepare flour, maida, suji, etc.
• Rice milling includes operations like dehusking and polishing; dhal milling also involves processing operations such as husk separation, splitting of kernels and polishing, or polishing only.
• The traditional methods employed for milling are wasteful, non-uniform, and do not yield useful by-products.
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