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Effect of Drying and Tempering on the Milling Quality of Long Grain Aromatic Paddy Processing in Bangladesh

M. Syedul Islam
FMPHT Division, Bangladesh Rice Research Institute, Gazipur-l701, Bangladesh

M. Abdul Ghani
PETRRA/IRRI, House-39, Road- 23, Block-J, Banani, Dhaka, Bangladesh

AKM Saiful Islam
FMPHT Division, Bangladesh Rice Research Institute, Gazipur-l701, Bangladesh

M. Anisur Rahman
DEMFRIPT Project, PROVA, GPO Box-I5, Rajshahi-6000, Bangladesh

Abstract/ Executive Summary:

Rice production, processing and consumption are part of culture of the Bangladesh population. However, their experiences are very much limited to parboiled paddy for home consumption. Recently, the country attained almost self sufficiency in paddy production and heading towards production and export of long grain aromatic rice. The milling yield of locally available aromatic rice processed in automatic mills ranged from 50 to 54%, which may be improved by adopting proper processing technology. Two recently developed aromatic rice i.e. BRRI dhan37 and BRN dhan 38 are comparatively longer than the existing aromatic varieties which need better processing technology in order to minimize breakage and improve product quality. An industry level experiment was conducted at a rubber roll type automatic rice mill located at North-west region of Bangladesh for processing BRRI dhan 37 and BRRI dhan 38. The initial moisture content of BRRI dhan 37 and BRRI dhan 38 were 13.39 and 12.86 percents respectively. The paddy was sun dried for 4 hours followed by 20 hours tempering everyday; and were dried for 3, 4, 5, and 6 days. The ranges of temperature and relative humidity during drying of paddy were 34-42T and 42-79%, respectively. After two days of drying, the moisture content of the paddy reduced to 9%. However, in the following morning the paddy moisture increased up to 10% due to condensation. But the hardness of the kernel was on increasing trend, which is necessary to reduce breakage during milling. The highest crushing strengths of BRRI dhan 37 and BRRI dhan 38 were found 8.0 and 6.T6kg,respectively at 3 days of drying and tempering which are attributed as the proper milling condition for better head rice recovery. Kernel translucency increased with drying duration irrespective of the variety. The highest milling yield of BRRI dhan 37 was 60.2% when samples were dried for 4 days and the highest milling yield of BRRI dhan 3 8 was 60. 1% when samples were dried for 3 days. The highest head rice recovery based on milled rice of BRRI dhan 37 was 90.4o/o when samples were dried for 4 days whereas that of BRRI dhan 38 was 84.1% when samples were dried for 3 days.

Keywords: BRRI dhan 37, BRRI dhan 38, Long grain paddy, Sun drying, ternpering, Unparboiled, Rubber roll huller, Milline vield, Head rice, Crushing strength and kernel translucency

Location: Chapai Nawabganj district, Bangladesh

Start Date: 01-07-2001

End Date: 30-06-2002

Program Area: Postharvest and Agro-processing

Commodity: Rice

Objectives:

To examine the Effect of Drying and Tempering on the Milling Quality of Long Grain Aromatic Paddy Processing in Bangladesh

Methodology:

Industry level experiment on long grain fine rice processing was conducted in M/s Minar Auto Rice Mill, Namosankarbati area of Chapai Nawabganj district through participatory approach among researcher, mill owner, operator and NGO personnel during May, 2003. Rice mill owner and mill operators have long experience on rice processing technology. Therefore, it was essential to conduct research through participatory method in order to find out the improved processing technology of long grain aromatic rice. Initially, a baseline survey of M/s Minar Auto Rice Mill was conducted to observe the parameters i.e. drying capacity, milling capacity' head rice, recovery, percentage of broken rice, husking efficiency etc. Both parboiled and unparboiled rice was processed in the mill. Basically, they processed chinigura as unparboiled rice. Parboiled as well as a part of unparboiled paddy was sun dried in mill yard. One Lousiana State University (LSU) type mechanical drier with capacity of 12000 kg was installed in the mill yard' In LSU type drier, about 8 hrs times is needed to make the paddy in optimum quality suitable for milling. The milling parameters of chinigura as unparboiled rice were: maximum input capacity 2400 kg h^-1, output capacity 1344 kg h-', milling yield 50-54%, co-efficient of husking 71%, broken rice 20- 24%. In sun drying, chinigura needs about 5-7 days to make the paddy suitable for quality milling' The paddy was dried in low temperature and the moisture content was maintained about 11-12%. The paddy was dried up to a maximum removal of white portion (white belly) of the kernel. The removal of white portion is important for two reasons i.e. to maximize the translucent area of kernel and to minimize breakage during milling. Although less time is required in LSU type drier but more head rice can be obtained from the paddy dried under sunshine. Two varieties of fine rice i.e. BRRI dhan 37 and BRRI dhan 38 were used in the experiment. The paddy was procured from the grower during January 2003 and kept in the mill yard storehouse for about two months' At the time of procurement, the moisture content of the paddy was 14%.

Source of Information: Pakistan Joumal of Biological Sciences 6 (19):1675-1680, 2003; ISSN 1028-8880

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The initial moisture contents of BRRI dhan 37 and BRRI dhan 38 were 13.93 and 12.86%, respectively. The temperature and relative humidity ranged 34 to 42^oC and 42 to 79%, respectively, at 10:00 and 13:00 hours in the last week of May, 2003. During sun drying, moisture content, crushing strength and kernel translucency values were monitored everyday. After two days of drying, the moisture content of both the varieties reduced to 9%, however, in the following morning the grain moisture content increased up to 10% due to condensation. The ranges of temperature and relative humidity during drying of paddy were 34-42^oT and 42-79%, respectively. After two days of drying, the moisture content of the paddy reduced to 9%. However, in the following morning the paddy moisture increased up to 10% due to condensation. But the hardness of the kernel was on increasing trend, which is necessary to reduce breakage during milling. The highest crushing strengths of BRRI dhan 37 and BRRI dhan 38 were found 8.0 and 6.T6kg,respectively at 3 days of drying and tempering which are attributed as the proper milling condition for better head rice recovery. Kernel translucency increased with drying duration irrespective of the variety. The highest milling yield of BRRI dhan 37 was 60.2% when samples were dried for 4 days and the highest milling yield of BRRI dhan 3 8 was 60. 1% when samples were dried for 3 days. The highest head rice recovery based on milled rice of BRRI dhan 37 was 90.4o/o when samples were dried for 4 days whereas that of BRRI dhan 38 was 84.1% when samples were dried for 3 days.

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