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Study on Coarse Rice Processing in a Commercial Rice Mill

A.K.M. Saiful Islam
Senior Scientific Officer
Farm Machinery and Post-harvest Technology Division, Bangladesh Rice Research Institue, Gazipur

M.A. Zaman
Professor
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M.P. lslam
Lecturer
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M.z.A.Vhutto
Post graduate student
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

This study was conducted in the Minar auto rice mill located at Chapai Nawabgonj district of Bangladesh during November 2003. The variety Parija was processed as parboiled and non-parboiled rice. Parboiled paddy ias dried in the sun and milled in engelburg huller whereas, non-parboiled paddy was dried in Lousiana State University (LSU) drier and milled in rubber roll huller. The initial moisture content of rough rice was 15.2.h. After soaking for 36-his the moisture content of paddy was increased to 29.8% (wb). Steaming was done twice before and after soaking for complete gelatinization of the rice kernels. The paddy was sun dried for 3 days followed by l8 hours tempering every day to reduce moisture content of the paddy from 29.8o% to 9.3% (wb). Non-parboiled paddy was dried in LSU drier for 6 hours and moisture content was reduced from 15.2% to 9.0% (wb). The range of hot air temperature was 60 to 90⁰C. The crushing strength of parboiled paddy was 6.2 kg after three days of sun drying The crushing strength of non-parboiled paddy wal 4.8 kg after 6 hours of drying in LSU dryer. The milling yield and head rice recovery of parboiled rice were 64.25% and 62.25 %, respectively, whereas those of non-parboiled rice were 65.50% and64.25%, respectively. Head rice yield was 2% higher in non-parboiled rice due to milling in rubber roll huller. The non-parboiled rice was fine than the parboiled rice due to polishing after dehusking. The production of non-parboiled rice was more profitable than the parboiled rice.

Keywords: Parboiled rice, Non-parboiled rice, Crushing strength, Head rice

Location: Bangladesh Rice Research Institute, Gazipur

Start Date: 00-11-2003

End Date: 00-00-2004

Program Area: Postharvest and Agro-processing

Commodity: Rice

Objectives:

(a) To study the processing system of coarse rice in commercial rice mills.

(b) To study the milling yield, head rice recovery and by products of both parboiled and non-parboiled rice.

Methodology:

Field study was conducted in November 2003. The selected site was Namosankarbati, Chapai Nawabganj, which is a leading rice growing area and has a large number of rice mills. The Minar Auto Rice Mill of Namosankarabati was selected for the study as because the mill owner agreed to provide facility in their mill premise. The rice mill has a large drying yard for sun drying and Lousiana State University (LSU) drier for mechanical drying Parija variety was selected for processing as parboiled and non-parboiled rice. Parboiled paddy was dried in the sun and milled in the engelburg steel huller, whereas non-parboiled paddy was dried in the LSU drier and milled in the rubber roll huller. Paddy was sun dried for a total of 16.5 hrs in three consecutive days followed by tempering of 18 hrs a day. Paddy was dried for 6 5 hrs, 7.0 hrs and 3.0 hrs in the first, second and third day, respectively. ln LSU drier, only six hours was required to complete drying. Physical dimensions of the paddy and corresponding rice kernel was measured by a vernier calipers. Paddy samples were collected at random and measured the dimensions to obtain the average length and breadth of the kernels. Paddy and rice shape was determined by length breadth ratio. Length-breadth ratio is an index of the grain quality whether the grain is coarser, medium or fine. A Kett moisture meter (Kett Electric Co. Ltd., Japan) was used to measure the moisture content of the grain samples. Temperatures of heated-air, drying floor, grain and atmosphere were measured by a digital thermometer. Hygrometer was used to measure the relative humidity of ambient air. The breaking strength of the rice kernels was measured by a hardness testing machine (Kiya Seisakusho Ltd., Japan) following the standard procedure. Data on temperature, relative humidity, moisture content and hardness of the grain were taken at 30-min interval during drying. Drying rate was calculated. Paddy was soaked at normal temperature in brick built tanks. Soaking was done for 36 hours to obtain moisture content of 29.8 % (wb). After soaking, paddy was loaded into two 200 kg capacity steaming vessels. Rice husks were used as fuel in husk-fired furnace to produce steam in a boiler. Steam was passed through the perforated pipe placed at the middle of the steaming vessels. Paddy was steamed once before soaking and once after soaking. The temperature of the steam was 102"C. Before soaking, first steaming was done for 3 to 4 minutes. After full soaking, paddy was again poured into steaming vessel. Steaming process for each batch was stopped when steam was found coming out from the top and bottom of the vessel. Time required for steaming soaked paddy was 5 to 6 minutes. The parboiled paddy was then unloaded from the steaming vessel. The paddy was dried by spreading on cemented floor and exposed to the sun. The thickness of the layer was about 15 to 20 mm. The female and male workers moved the paddy by a rake locally called as 'naingla' for about 10 to 15 minutes. The paddy was turned every half an hour. After 2 hours of drying, paddy was gathered in rows by 'shapta'. This process allowed the moisture absorbed by the drying floor to be evaporated. The paddy was frequently stirred to make uniform drying. Frequent stirring and turning of the grain reduced the overheating and over drying, and improved the uniformity of drying. Non-parboiled paddy was dried in LSU drier. Heat was produced in the furnace by firing husk. Hot air was collected by a blower and forced into the drying chamber. The grains were exposed to forced ventilation of air that was heated to certain degree. As the air was heated its relative humidity was reduced and thus its moisture absorbing capacity was increased. The paddy falling vertically downward was subjected to a continuous flow of heat. The operator maintained the air temperature by controlling the supply of fuel. The input and output costs for parboiled and nonparboiled rice were estimated and the benefit-cost ratios were determined based on the market price of rice and the by-products. The total cost of inputs included the price of paddy, carrying cost, milling and processing charges. On the other hand, cost of outputs were the prices of rice, brokens and byproducts.

Source of Information: J. Agric. Mach. Bioresour. Eng. 4(1&2),2006:47-56 , rssN 1993-4041

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The parboiled paddy required 3 days of sun drying to reduce its moisture content from 29.8% to 9.3% (wb) Sun drying was followed by 18 hours tempering every day. Drying of non-parboiled paddy in LSU drier required 6 hours drying time, when the moisture content was reduced from 15.2% lo 9.0% (wb). ln sun drying the average drying rate gradually decreased from 1.71 lo 132 percent per hr and in LSU drier 1.0% per hr. The crushing strength of parboiled rice was 6.2 kgf al 9.3% (wb) moisture content after 3 days of sun drying, whereas the crushing strength of nonparboiled rice was 4.8 kgf at 9.0% (wb) moisture content. The milling yield and head rice yield of parboiled rice were 64.25 percent and 62.25 percent, respectively and the corresponding values of nonparboiled rice were 65.50 percent and 64.25 percent, respectively. Head rice yield was higher in non-parboiled rice due to milling in rubber roll huller.

Knowledge Management: Journal