120 Ministry of Agriculture & Rural Development Project Completion Report MS14: PROJECT COMPLETION REPORT 026/05VIE Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam APPENDIX 3A DATA COLLECTION OF MILLING LOSSES April 2010 121 APPENDIX 3A. DATA COLLECTION OF MILLING LOSSES The data collection of milling losses in two provinces from more than three milling plants in each province (Kien Giang and Tien Giang) was undertaken in 2007-2008. This work assumed that the head rice recovery will not only depend on the initial rice quality (existing cracks or weaker grain), but also on the efficiency of the milling operation. Therefore, in this work, actual milling loss data were collected in two provinces, Tien Giang and Kien Giang. There exist three systems of rice mills in both provinces: • The traditional white rice milling system: A complete rice milling plant without polishing (accounts for 91%). • The brown rice milling system (accounts for 3%). • The final rice whitening/polishing plant (account for around 6% of total rice mills). In this work, the data collection was done on three milling types: • Small- <1 ton/hr • Medium- 1-4 ton/h • Large- >4 ton/h The data were also collected in three types of hulling mills: • Hulling by stone disc huller • Hulling by rubber roll huller • Hulling by both stone disc huller and rubber roll huller The data were collected by two methods: • Surveying with the millers (all three size rice mills)- in both provinces • Real data collection from the mills (four small and two medium size rice mills)- in only Kien Giang province (the same data set will be collected in other province this season). The results are presented in Tables 2 and 3. The real data and data collected by survey were quite coherent. Both data suggested that the head rice recovery in small scale mills was the lowest and was as low as 33%. Large rice mills had the highest of 55% head rice recovery. In the actual ideal condition the head rice recovery and total rice recovery should be around 59% and 69%, respectively (as rice is comprised of around 10% bran and 20% husk). In literatures, the head rice recovery and total rice recovery have been achieved as high as 60% and 70%. Therefore, there is still a scope of improving the head rice recovery even in large scale mills, let alone a poor performer small scale rice mills. The importance of improving the quality of rice can be substantial. As for example, in Kien Giang province, out of 715 rice mills, 67.6% are small, 28.1% medium scale and 4.3% large 122 scale mills. Similarly in Tien Giang province there are more than 900 small household mills. Simple facilities, product mainly supplied for local demand, not for a commercial production, are the main causes leading to low rice recovery in a small scale factory. By proper awareness, training of operators and maintance of mills the head rice recovery can be substantially improved. In Tien Giang province, the surveying data also found that in the area where the paddy is milled at high moisture content, 16-17% even 18%, has a lower head rice yield than the area where the moisture of the paddy is at 14-15% moisture. Table 2. Head rice recovery data collected by surveying the millers in Kien Giang and Tien Giang provinces Scale Grain moisture (%) Average head rice recovery (%) Broken rice (%) Small 16 47-48 18-22 Medium 16 50-52 17-18 Large 16 52-55 16-17 Table 3. Actual data collected from the mills in Kien Giang province Scale Name of agencies Capacity (tons/hour) Paddy moisture (%) Milled rice moisture (%) Head rice yield (%) Duong Nguyet 0.8 15.5 15.8 48 Huynh Thanh Dung 0.4 15.2 15.1 42 Luu Van Thieu 0.7 14.2 13.7 50 Small Coffee dehusker (mobile) 0.2 15.3 15.2 33 Tan Phat 1.2 16 16.5 52 Medium Luu Thanh Xem 1.5 15.9 15.9 49 In Kien Giang province, the survey results also suggested that the rice mills using rubber roll huller had a better head rice recovery than those using stone disc huller or coffee grain huller (Table 4). Table 4. Head rice recovery (%) in mills having three different types of dehulling systems in Kien Giang Province Rice mill size Stone Disc huller Rubber roll huller Combined (Stone+rubber) Coffee grain huller Small 47 51 49 43 Medium 50 54 53 - Large - - 55 - 123 Conclusion and project intervention methods: • Size of mill is an important factor that determines the losses. The small mills which are used by small farmers showed a low head rice recovery. Medium and large scale plants had a high recovery, but still it was far from ideal. The maximum head rice recovery in large plants is still around 55%, a well below the ideal level (60%). This means that the milling is another important factor to improve the head rice yield. • It is necessary that the millers and farmers are aware of the efficiency of mills in order to augment the value of their produce. • The medium scale rice mills should be promoted even in village level to improve the head rice recovery. The results obtained in this survey were illustrated in leaflets and conveyed to the farmers, millers and mill operators through training and workshops. 124 Ministry of Agriculture & Rural Development Project Completion Report MS14: PROJECT COMPLETION REPORT 026/05VIE Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam APPENDIX 3B EXPERIMENT ON 1 TON/H MILLING SYSTEM April 2010 125 APPENDIX 3B. EXPERIMENT ON 1 TON/H MILLING SYSTEM 1. INTRODUCTION There are many factors accounting for the post harvesting losses of rice and occurring as early as pre-harvesting stage and subsequent periods from harvesting to storage. The occurrence of rice cracking during postharvest stages causes reduction in head rice yield. Rice grains can be damaged or lost quantitatively and qualitatively due to the inappropriate practices during harvesting, reaping, threshing, sun/mechanical drying, loading/unloading, transporting, milling processing and storage conditions. Milling processing is an important stage as it produces the final product (white rice) in the chain of post-production of rice. In addition to the rice grain cracking is potentially occurred in previous postharvest stage, rice kernels can be cracked as a result of unsuitable milling technology applied, i.e., low efficiency of milling system, low quality of paddy before undergoing milling. Few research works pointed out that inappropriate milling system causes more grain cracking meanwhile there is no information reported on the effect of paddy quality on performance of milling system. In this study, the effects of initial moisture content of paddy on the performance of rubber-roll dehusker milling system in terms of milling capacity and rice milling recovery are investigated. Other parameters, such as paddy cleanliness, level of rice cracking before milling, are also considered to have an overall picture of experimental results. 2. OBJECTIVES The purpose of this study was to determine the impact of initial moisture content of paddy on the performance of a 1-ton/h rubber-roll dehusker milling system in terms of milling capacity and rice quality. 3. MATERIALS AND METHODS 3 3 . . 1 1 . .Time and location of experiment The experiment was conducted in July 2007 on a 1-ton/h rubber-roll dehusker milling system (RS10P – SINCO) installed at Can Tho University, Can Tho City, Vietnam. The quality analysis for initial paddy samples was undertaken at the Center of Agriculture Energy and Machinery. Quality analysis of milled rice then was carried out at the Department of Chemical Engineering Nong Lam University of HCMC. 3 3 . . 2 2 . .Rice samples and experimental design Rice variety OM1490 was used for milling experiment. Experimental factor of this study was the initial moisture content (wet basis) with three levels of 14%, 15%, and 16%. Experiments were designed in RCBD (Random Complete Block Design) method with duplicate. 126 Paddy was freshly harvested from paddy field located in Can Tho City. Fresh paddy (moisture content 24 % wb) then was dried mechanically by tray dryers to target moisture contents in this study, i.e., 14%, 15%, and 16%. The data collection was recorded in Annex 1. Practically, the moisture contents of paddy samples after undergoing tray drying were 13.76%, 14.92% and 16.22%. In this study, it was considered these three levels of moisture contents as 14%, 15% and 16%, respectively for convenience. 3 3 . . 3 3 . . Milling system A milling system used in this study was a rubber-roll dehusker with capacity of 1-ton/h RS10P manufactured by SINCO and installed at Engineering Faculty, Can Tho University. The sketch of milling system RS10P-SINCO was illustrated in Figure 1. The elements of this milling system can be seen in Figures 2-5. Figure 1: Scheme of 1-ton/hr Milling System RS10P - SINCO 1- Rice tank; 2- Paddy sort-out sieve; 3- Tank; 4- Husking machine with cylindered rubber; 5- Tank; 6- Rice sort-out sieve; 7- Grit collector; 8- Tank; 9- Whitening machine; 10- Polishing machine; 11- Whiten- rice classifying drum. - E1, E2, E3, E4, E5, E6, and E7: convey buckets. - X1, X2: Cyclones for collecting bran. - F1, F2, F3: separation fans. 127 Operating principle of RS10P-Sinco milling system. At first, paddy is loaded into tank (1); paddy then is conveyed to a sieve (2) by bucket (E1) for separating impurities. After sieving (2), all kinds of impurities such as straws, ropes, soil, stones etc. are removed. Clean paddy is transferred by bucket (E2) to temporary tank (3). This tank has a plate to adjust the quantity of paddy input going to rubber-roll dehusker (4). There is a mixture of brown rice, coarse bran, unfilled paddy, paddy and rice husk after paddy goes through dehusker (4). This mixture is sucked by the centrifugal fan (F1), rice husk and dust are collected to the husk area, coarse bran and unfilled paddy removed out of the mixture at this stage. The remaining of mixture composes of brown rice and paddy which are conveyed to sieve (6) by bucket (E3). At sieve (6), this mixture is separated into three portions: brown rice, paddy and combination of brown rice and paddy. This combination will be re-classified by going back to bucket (E3) while paddy returns to dehusker (4) for the second dehusking. After separation, brown rice is conveyed by bucket (E4) to grit collector (7), and then gone through whitener (9). Here whitening stage is undertaken, removed bran is collected by fan (F2) and taken out via exit at cyclone (X1). White rice is transferred by bucker (E6) to rice polisher (10) for polishing. Bran removed from polishing process is collected by fan (F3) via exit at cyclone (X2). White polished rice then goes to classifying drum (11). Head rice and broken rice are separated from white rice at this last stage via two exits. In addition, other instruments used include of: scales of 60kg, 30kg, 2kg, 1kg; electronic scales 310g ± 0,01g; drying oven, Ampere-Volt meter, chronometer, electric bell, PP bags, samples bags,… 3.4 Determination of rice moisture content Moisture content of paddy is determined by drying (in triplicate) 40-60 g of rough rice in a drying oven at 70 o C for 24 hrs. The moisture content was expressed on a wet basis (wb). 3.5 Determination of milling capacity At first, the total amount of paddy going through rubber-roll dehusker is determined. Note that, there is undehulled paddy mass after dehusking which will be collected and dehusked for the next time. In this study, it is considered that the amount of undehulled paddy (after dehusking) is equal to the amount of paddy for next dehusking. The total mass of dehulled paddy at each exit of milling system is weighted in the testing time (6 minutes). The total amount of rice husk in this study is fixed at 21% the total mass of used paddy as all experiments used the same variety. Milling capacity is calculated as the total mass of dehulled paddy over the amount of undehulled/unfilled paddy and impurities. Output of milling system is expressed as kg/h and calculated as the average value of triplication. 128 Figure 2: the 1- ton/h Milling System RS10P _ SINCO 129 Figure 3: the husking machine and the classifying machine (paddy - brown rice) Figure 4: the whitener and the polisher [...]... repeated by using another milling system and conducting more experimental repetitions 132 Ministry of Agriculture & Rural Development Project Completion Report MS14: PROJECT COMPLETION REPORT 026/05VIE Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam APPENDIX 3C EXPERIMENT ON 7 TON/H MILLING SYSTEM April 2010 133 APPENDIX. ..Figure 5: the bran return system and the classifying machine (tri-e) 3.6 Determination of head rice recovery Head rice recovery is defined by the ratio of the mass of unbroken white rice kernel to the total mass of used paddy (excluding unfilled/undehulled paddy and impurities) The head rice is composed of kernels that maintain 75% of their length after milling 3.7 Determination of grain cracking Three... whitening 2, polishing 1, and polishing 2 Head rice yield and percentage of broken rice were determined About 0. 5-1 .0 kg of rice sample were leveled on tray as described in Figure 2 Five sub-samples of 1 8-2 5 g each were randomly selected at five positions Weight of rice sample was done by electric scale Head rice and broken rice were separated manually (head rice was defined as rice kernel maintaining its. .. TON/H MILLING SYSTEM 1 INTRODUCTION Due to the current post-harvest system in the Mekong River Delta the mechanical drying can cover only 30% of the total wet paddy Most of rice has been processed by sun drying In addition, the price of paddy between 14% and 1 7-1 8% moisture is not differentiated clearly by the traders Thus, the farmers prefer to sun-dry the paddy to final moisture content of 1 7-1 8% A... length) Head rice yield then was calculated as ratio of head rice over the total mass of used white rice Head rice yield over milling stages of rice dehusking, whitening 1, whitening 2, polishing 1, and polishing 2 based on the amount of dehusked rice used can be seen in Table 1 Ø 300 Ø 50 Figure 2 Tray used for rice sample collecting 136 Table 1 Milling performance of two milling systems M30RD† and M70RD††... following by 15% (44, 90%) and 16% (36.94%) The effect of initial moisture content of paddy on the performance of a 1-ton milling system used in this study is significant (P . 026/05VIE Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam APPENDIX 3B EXPERIMENT ON 1 TON/H MILLING SYSTEM. SINCO 1- Rice tank; 2- Paddy sort-out sieve; 3- Tank; 4- Husking machine with cylindered rubber; 5- Tank; 6- Rice sort-out sieve; 7- Grit collector; 8- Tank; 9- Whitening machine; 1 0- Polishing. produces the final product (white rice) in the chain of post-production of rice. In addition to the rice grain cracking is potentially occurred in previous postharvest stage, rice kernels can