Project Progress Report: Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam - APPENDIX 3A" pptx

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 -

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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
130


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 150 g paddy samples were taken from each block to ensure the repetition of each
block. Grains were dehulled by hand to make sure no cracking developed during this
procedure. Fifty dehulled grains were randomly checked to count cracking grains under
microscope. The cracking fraction was calculated over fifty grains.
3.8 Data analysis
Data were analysed by statistical software Statgraphics 3.0.

4 EXPERIMENTAL RESULTS
The cleanliness and grain cracking level of initial paddy samples at three levels of moisture
contents (14, 15, & 16 % wb) are presented in Table 1. It was shown that the cleanliness of
paddy used for this experiment is not high. The cleanliness of 14% moisture content sample
(88.26%) is higher than that of 15% and 16% (Table 1). As cleanness is associated with
milling recovery, it is believed that the milling recovery may not high neither. The
percentage of cracked grain of initial paddy samples at moisture contents of 14%, 15% and
16% are 4.0%, 3.33% and 1.0%, respectively. These figures were used to normalize data by
subtracting from the cracking level of head rice after milling.

131

Table 1. The cleanness and cracking level of paddy samples before milling at three levels of
moisture contents.
Moisture content, % wb Cleanness, % Initial cracking level, %
13.76% 88.26 4.0
14.92% 83.49 3.3
16.22% 83.69 1.0

Table 2 describes the influence of various moisture contents on average output of milling
system and head rice recovery after milling. The ANOVA results (Annex 5) showed that
differences in moisture content of paddy samples before milling has no significant impact
on average output of milling system (P>0.05). However, this conclusion can meet with
Type II Error. Generally, it is accepted that the probability of this error is β ≈ 0.1 ÷ 0.2.
Through statistical infers, we determined: when n ≥ 9 (= number of blocks or repeated
times), and the minimum detectable difference ∆ = 60 kg/h => β = 0.16 (OK). As a result,
number of blocks is very little in these experiments.

Table 2. Average output of milling system and head rice recovery at three levels of moisture
contents.
Milling recovery of white
rice, % *
Moisture
content,
%wb
Average
output, kg
paddy/hr
Head rice Broken rice
whitening rice
in 6 mins, kg
Head rice
recovery, %
(1) (2) (3) (4) (5)
14 691.05
ns
78.11 21.89 41.33 46.71
ns

15 578.47
ns
79.39 20.61 32.73 44.91
ns

16 747.54
ns
67.675 32.325 40.97 37.09
ns



*milling recovery of white rice were 59.63% (14%), 56.60 % (15%), and 54.80 % (16%)
(5)= (2)*(4)*(1); ns: not significant at
α
=0.05

The head rice recovery at 14% moisture content is the highest (46.71%) following by 15%
(44, 90%) and 16% (36.94%). The statistical analysis showed that the head rice recoveries
are not different among the above three different moisture contents with P > 0.05 (Annex
4.2). However, the t test showed that head rice recoveries are significant different between
two samples of MC 14% and 16% at the significant level of 0.1 (Annex 5).

In fact, this experiment was conducted on a milling system made by SINCO, using
rubber-roll dehusker with theoretical capacity of 1 ton/h. This system has been used so far
only as learning facility at Engineering Faculty - Can Tho University. However, it has not
been operated as in whole system conditions, but as single machine during training process;
132

in other words, this system has been stopped operating. Therefore, there are some problems
occurred during conducting experiment as well as the operator was neither skillful nor
specialized with the system. These factors may influence to a certain extent on the records
of experiments.

5 CONCLUSIONS AND RECOMMENDATIONS
In general, the higher the initial moisture content of paddy before milling, the lower the
head rice recovery. The head rice recovery at 14% moisture content is the highest (46.71%)
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<0.1)
when considering between two moisture content levels of 14% and 16%. In addition, the
milling recovery of this 1-ton/h rubber-roll milling system is lower than that of other
current milling systems. This can be explained by the technical problem as discussed
above. It is suggested that this experiment should be repeated by using another milling
system and conducting more experimental repetitions.


133

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






134
APPENDIX 3C. EXPERIMENT ON 7 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 17-18% moisture is not

differentiated clearly by the traders. Thus, the farmers prefer to sun-dry the paddy to final
moisture content of 17-18%. A large amount of high moisture paddy (17-18%) is
demanded for milling. Thus, the milling operators have used the stone-dehusker for
husking of paddy to suit this high moisture content paddy. This system has reduced HRY
and needed to be investigated.

In the first experiment, with 1-ton rubber-roll milling system, it was found that HRY was
not significantly different between 14% and 15% paddy moisture contents (see MS12
report for further information). This may be due to the errors of the experiments (the
difference in moisture was low). However, when the moisture content of paddy increased
to 16%, the HRY reduced significantly from 46.7% to 37% (P < 0.1). This reduction is
quite high and will be discussed in relation to economical issues. In this second
experiment with large-scale milling system (7-ton/h), the main purpose was to evaluate
the current milling performance and find out a new approach for better milling
performance.

2. MATERIALS AND METHODS

2.1 Installation of 7-ton/h rubber-roll dehusker
In this study, milling experiments were carried out at Hung Loi milling plant, Tan Hiep
district, Kien Giang province in August 2009. The technique characteristics of Hung Loi
milling plant were as below:
• Brown rice milling composes of 04 stone dehuskers 1 m and 05 rubber-roll
dehuskers 3000, at milling capacity of 4-6 tons/hr.
• White rice milling has 02 cylinder mills 1,2 m
• Rice polishing includes 02 polishers, followed Bui Van Ngo Co. technique.
To conduct this experiment, a 7-ton/h rubber-roll dehusker (Figure 1) was installed in
Hung Loi milling plant by this CARD project.

2.2 Sample preparation

Approximately 10 tons of paddies were used in this experiment. The rice variety used was
OM2517 harvested by combine harvester. Paddy lot has a large amount of unfilled paddies
visually.



135
2.3 Rice drying
Paddy was divided into two portions: half of paddy mass was dried by air reversible rice
dryer at Tan Phat A co-operative while remaining paddy was sun dried on yard of Hung Loi
milling plant. The average moisture contents of mechanical dried and sun dried rice masses
were 14% and 16,5-17%, respectively.



Figure 1a. Milling line of 7 ton/hour capacity used for milling experiment.


Figure 1b. The rubber-roll dehusker installed in the milling line supported by CARD.

136

2.4 Experimental design
The modified milling technique processes 0-30% and 70-100% of paddy by stone and
rubber roll dehusking, respectively. In this experiment, the modified milling system with 30%
husking by stone dehusker and 70% husking by rubber-roll dehusker is called modified 70%
rubber-roll dehusker and denoted by M70RD. The traditional system is therefore denoted by
M30RD (only 30% of paddy processed by rubber-roll dehusker). Experimental rice batch
comprises of 1.25 tons. After milling, rice was whitened and polished.

2.5 Milling procedure and Head rice yield (HRY) measurements
Paddy was dehusked to obtain brown rice. Head brown rice yield was determined as the
ratio of brown rice over the total amount of paddy mass used. Rice samples then were
subjected to two stages of rice whitening, i.e., whitener 1 and whitener 2. Whitened rice then
were gone through polishing stage. A rice batch was polished two times. Five HRY
measurements were undertaken at the end of each milling stage, namely, dehusking,
whitening 1, 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 18-25 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 2/3 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.



Figure 2. Tray used for rice sample collecting.




Ø 300
Ø 50

137

Table 1. Milling performance of two milling systems M30RD
†
and M70RD
††
for two rice
drying practices sun drying vs. mechanical drying over milling stages
Head rice yield over milling stages, %
N
o
Milling stages
Milling system
Dehusking
Whiten-
ing 1
Whiten
-ing 2
Polish-
ing 1
Polish-
ing 2
1 Sun-dried M30RD 82,66 78,35 76,19 68,15 55,85
2 Sun-dried M70RD 84,53 79,62 74,87 58,69 50,86
3 Mechanical-dried M70RD 86,43 82,81 79,89 73,26 69,07
4 Mechanical-dried M70RD 85,00 80,69 77,98 70,70 62,94
†
: 30% of paddy processed by rubber-roll dehusker and 70% husking by stone dehusker.
††
: the modified milling system with 30% husking by stone dehusker and 70% husking
by rubber-roll dehusker.

3. RESULTS
Figure 3 shows the milling performance of two milling systems M30RD and M70RD for
sun-dried and mechanical dried rice samples. In general, the head rice yield is low due to
the quality of rice with a great deal of unfilled paddy. As can be seen in Figure 3, there is
difference in head rice yield between M30RD and M70RD milling system. For sun-dried
rice samples, brown rice yield of M30RD (processed with 70% stone-dehusking: 40.71%)
was higher than that of M70RD (only 30% stone-dehusking: 35.89%). However,
modified milling system M70RD processed with 70% rubber-stone dehusking is
advantageous for mechanical dried rice samples as head rice yield is the highest among
four milling treatments, at 53.39%. M30RD milling system for mechanical dried rice
obtained higher head rice yield (49.28%) than those of both M30RD and M70RD applied
for sun dried rice samples.

Figure 3. Head rice yield (calculated on the total amount of paddy mass used) of milling
systems M30RD
†
and M70RD
††
for two rice drying practices sun drying vs. mechanical drying
over milling stages

138

4. CONCLUSIONS

+ For sun drying rice (moisture = 17%): HRY of 70% stone dehusker (M30RD) was
higher than that of 30% stone dehusker (40,71% - 35,89%).
+ For mechanical drying rice (moisture = 14-15%): HRY of 70% stone dehusker
(M30RD) was lower than that of 30% stone dehusker ( 49,28% - 53,36%).

+ HRY of mechanical drying rice was higher than that of sun drying rice about 13-14%.
Therefore, dehusking using rubber roll will improve HRY only when the paddy is dried
correctly up to moisture content of 14-15%.

5. APPENDIX

Photographs of milling procedure carried out at Hung Loi milling plant, Tan Hiep district,
Kien Giang province in August 2009.


Mechanical rice drying by air reversible
dryer at Tan Phat A co-operative
Sun drying of rice on yard of Hung Loi
milling plant

Weighting of rice sample for dehusking
Weighting dehusked rice right after
dehusking stage

139

Collecting rice sample Head rice and broken rice separation

Tray used for rice sub-sample collecting
Weighting collected sub-sample by
electric scale