Engineering, 2010, 2, 97-102
doi:10.4236/eng.2010.22013 Published Online February 2010 (
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The Quantized Characterization of Cooked Rice Hardness
and Research on the Automatic Measurement Technology
Nan Jiang1, Yuan Gao2, Jiping Zhou1, Longqin Gao1, Jianhua Zhou1, Qigen Dai2
1Mechanical Engineering College, Yangzhou University, Yangzhou, China
2Agricultural College, Yangzhou University, Yangzhou, Jiangsu, China
Received August 27, 2009; revised September 19, 2009; accepted October 4, 2009
The hardness of cooked rice is one of the most important criteria which determine the rice quality. The
commonly used near-infrared reflectance (NIR) method is still in argument due to its indirectness and possi-
ble error. In this paper, a mechanical method was proposed and its principle, automation, components and
operative reliability were evaluated and compared with the NIR method. The results showed that the me-
chanical testing method can accurately detect the rice quality and were consistent with the NIR testing data.
This new mechanical method can be effectively used in rice quality testing and branding with the advantage
of simplicity, accuracy and reliability.
Keywords: Rice Hardness, Measurement System, Stress-Strain
1. Introduction
Rice is one of the most important food crops in China,
and China also is the biggest country of production and
consumption of rice. The people’s requirement of high
quality rice is increased with time [1]. The requirement
of high quality rice will be substantially increasing in
market demand. Therefore, the study and identification
of rice eating quality will be more emphasized.
The rice hardness is one of the important factors af-
fecting rice eating quality. The existing detection methods
of rice hardness are sensory evaluation [2] and physi-
cal-chemical analysis [3]. The former has established a
series of the evaluation standards, and these have some
guiding effects to the rice quality testing. But it also has
some uncertain factors and thus is lack of public reliabil-
ity and persuasion. Researchers are searching a conform-
able and scientific method to test the quality of rice and
other organic solids. Procter (1955) have putted forward
the standard of chew food, and use the human tactility to
research the physical characteristics of food [4]. Procter
and Szczeniak (1963) have confirmed the Texture Profile
Analysis to describe the quality of food, and use the
stress-time curve to show the food quality [5]. Recent
years researchers use the Texture Analyzer and Instron
Universal Texting Machine to test the cooked-rice quality
especially the hardness and viscosity, but the method’s
adaptability is few to testify. Meanwhile the Taste Ana-
lyzer has been developed to test the rice quality [6],
which is based on the NIR (Near-Infrared Reflectance)
technique, analyzes the rice quality components (protein,
starch, oil, sugar and water etc), and finally indirectly get
the appearance, hardness, viscosity, equilibrium degree
and taste data of rice., This method obtains the result from
conversion of a rage of experiential formulas, not through
the press the rice directly to get the testing result, so its
analysis result is not very precise. Besides, another tech-
nique is use the Image Reconstruction based on Analytic
Method to test the brightness and glossiness of rice, to be
brief is through the appearance to judge the eating quality
of cooked rice [7].
Therefore, the establishment of a new method and
technique to reflect accurately the rice hardness and
other characteristic parameters is very important for rice
grade identification and quality breeding through modern
genetic engineering.
2. The Measurement and Analysis of Rice
2.1. The Rice Hardness and Stress Analysis
The rice hardness means the resistance of the cooked rice
to external-introduced pressure. When people chew the
rice, they can intuitively feel its hardness or softness.
When the external pressure reaches a critical value, the
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rice will break thoroughly, and this critical value that can
be used to characterize the rice hardness is usually be-
tween 0~150g force and the strain is between 0~3mm, so
the key point is to get the stress-strain relationship of the
2.2. The Basic Ideas of Measurement
Now there is still not a mature and reliable method and
technique for micro-stress and displacement measure-
ment. Based on analysis of existing methods and tech-
nology of food testing [8–10], correct understanding and
grasp of rice relationship between the material properties,
machinery mechanics measurement techniques were
used to establish a measurement of rice stress-strain, ac-
cording to the characteristics of small size, displacement
and force. The method developed in this study could
measure the rice force which could be conversed to ex-
press the rice hardness.
2.3. The Basic Principles of Measurement
The basic principles of measurement are the double can-
tilevers stress and strain measurement techniques as
shown in Figure 1(a). The rice to be measured is put on
the pallet between the double cantilevers, external force
push the indenter, which fixed on the up-cantilever, to
oppress the rice, then the rice will press the down-canti-
lever. There are 8 resistance strain gauges (BHF350-
3AA type) in Figure 1(b), and the Figure 1(c) shows that
the strain gauges 1~4 are linked with differential circuit
to detect the double cantilevers relative deformation that
is the strain of rice; meanwhile, the strain gauges 5~8 are
linked with another differential circuit to detect the force
of down-cantilever that is the stress of the tested rice.
Then through the data wire transfer the stress-strain sig-
nal of rice, which acquired by the data acquisition board,
then analysis the data to obtain the rice hardness finally.
3. The Measurement System
Figure 2 shows the basic ideas and principles for the
measurement of the rice, and the automatic system used
to measure the rice hardness.
3.1 The Machinery of Automatic Force
The rice automatic measurement system is composed by
motor, transmission shaft, cam, guide rod and spring etc.
as shown in Figure 3. The principle is that when the mo-
tion control system sends a signal to the motor, the motor
drives the cam to rotate through the transmission shaft,
the cam presses the up-cantilever through the guide rod,
meanwhile press the rice. The loading stroke decided by
the size of the rice (usually is the 85% of the rice), and the
maximum loading stroke is the net volume of the cam.
The control program detects the deformation of the rice to
judge whether it reaches the loading stroke. When the
deformation reaches the stroke, the motor will stop load-
ing and drive the cam to reverses to the initial position.
3.2. Measurement and Date Acquisition System
In order to get the measured value of micro-stress and
strain of different materials, the double cantilevers’ high
Figure 1. Schematic diagram of measurement principle.
The machinery of
automatic force
Force sensor
manage system
Figure 2. The components of automatic measurement system.
ratio of length and width is 200:15:1 determined prelimi-
narily. Besides, we choose the AAA resistance strain gauge,
and the requirements of patch, substrate and cure are very
strictly designed, and measurement accuracy is ensured by
means of the differential circuit and compensation (Figure
1(c)). The deformation signals of the double cantilevers are
collected by the special data acquisition board, and then
through the data wire linked to the computer.
3.3. Data Analysis System
Language Delphi 7 is used to compile the program of data
analysis system, draw the “stress-strain”, “stress-time”
and “strain-time” curves, and to calculate the maximum
stress and eigenvalue, record and save the data of the rice
(Figure 4).
4. The System Operation and Test Verification
4.1. The Initialization of the Measurement
Figure 5 shows that the automatic measurement system
designed and manufactured by ourselves, composed by
automatic measurement equipment, data wire and com-
4.1.1. Stress-Strain Parameter Calibration
In order to get the relationship between stress-strain, mi-
cro-force and deformation, and to ensure the accuracy
before the first time to run the system, we demarcate both
force signal and strain signal. The force signal of the
up-cantilever is demarcated by the spiral micrometer, it
presses the up-cantilever 0.2mm each time, and the strain
signal of the down-cantilever is demarcated by weights,
they press the down-cantilever 10g each time. The demar-
cation value of force and strain signal is listed in Table 1
and Table 2. The average of the three demarcation values
is used as the basis. According to the Table 1 and Table 2
the linearity of the demarcation values is good, the data
acquisition system can meet the requirement.
4.1.2 System Self-Check
After demarcating, the system must self-check. Accord-
ing to the theory, without the test object, the double can-
tilevers are rigid connection, when the machinery of
automatic force application press the double cantilevers
the relative deformation should be zero, and the stress-
strain curve is straight line of which the angle is 45° with
the coordinate axis, meanwhile the curves of loading and
unloading should be coincident in Figure 6 which shows
that the system is accurate and reliable.
4.2. The Preparation of Test
4.2.1. Testing Scheme
According to the evaluation standard of the rice quality,
in order to verify the adaptability, reliability and accu-
racy of the rice hardness test system, we establish the
testing scheme as follows:
Firstly, aiming at the same variety rice using the dif-
ferent types of indenters to test the rice, and analysis the
Figure 3. The machinery of automatic force application.
Figure 4. The interface of data analysis system.
Figure 5. Automatic measurement system.
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Table 1. Force demarcation.
Table 2. Strain demarcation.
Figure 6. The graph of system self-check.
consistency of the rice under the same indenter;
Secondly, aiming at the varied rice varieties, using the
same type of the indenter to test the stress-strain, and
verifying if the test system can discriminate the differ-
ence of varied rice varieties;
Thirdly, using one of the indenters to test the same va-
riety at different time, and verifying if the test system
could discriminate the change of the results with differ-
ent time.
We select the five rice varieties randomly, and take the
average of the test results as the measured value of the
4.2.2. Preparation of Need Checking Sample
1) Preparation of the test rice
According to the standard cooking method [11] to pre-
pare the test rice: 1) use the electronic balance to weigh
30g rice; 2) wash the rice four times, and add the
1.33-times water; 3) immersing the rice 30 minutes, then
cooking 30 minutes; 4) after the rice cooked standing it
10 minutes, then cooling it 20 minutes in the cooling
equipment; 5) extract the sample to test during which the
sample is stirred to maintain uniformly.
0 0.0 90 1033.3
10 86.0 100 1166.7
20 255.0 110 1213.3
30 335.3 120 1350.0
40 465.7 130 1500.0
50 563.3 140 1636.7
60 686.7 150 1716.7
70 813.3 160 1843.3
80 920.0
2) Preparation of the indenters
For the requirement of the test, at the beginning of the
scheme establishment we use the different indenters to
test the rice hardness, in order to get the suitable one. We
prepare the Φ2mm and Φ3mm spherical indenter, Φ2mm
and Φ3mm plane indenter, Φ10mm and Φ15mm cylin-
drical indenter, 10mm×1mm tool form indenter, respec-
tively, while the cylindrical indenter is used to test the
rice-flour dough mainly.
Strain signal
Strain signal
0 0.0 1.6 175.3
0.2 22.5 1.8 197.0
0.4 42.7 2.0 219.0
0.6 65.8 2.2 241.0
0.8 86.0 2.4 262.0
1.0 112.7 2.6 280.0
1.2 131.7 2.8 301.3
1.4 153.7 3.0 322.0
4.3 Measurement Results and Analysis
1) Choose the first class rice (according to National Stan-
dard), and use the different indenters to test it, the meas-
ured results are showed in Table 3. We can educe that the
stresses are different with the different indenters, and the
average stresses exhibit a obvious difference. But the slope
of the stress-strain curves has a good consistency. There-
fore, we could use the slope to express the hardness of the
cooked rice, and the big slope indicates a high hardness.
Note: the average is the ratio of maximum force to
area of the indenter
2) Table 4 shows data of using the Φ3mm plane in-
denter to test the first class rice and the data of Baoying
lake organic rice at the different time is also listed in
Table 4. The all listed results show that the testing sys-
tem can distinguish the difference of the hardness of the
rice at the different time.
3) Table 5 shows data of using the Φ10mm cylindrical
indenter to test the six different breed rices. We can see
that the testing system could distinguish the variance of
the rice hardness.
4) Comparison with the Japanese taste analyzer
According to the test results of hardness which is
tested through the Taste Analyzer STA 1A indirectly, we
use the rice under the same cooking standard to test, the
results are in Table 5. The hardness of the same variety
exhibits the consistency between the automatic testing
system and the Japanese taste analyzer, which prove the
correctness of the system.
5) Analysis of system measuring error
According to the test scheme, every variety repeats 5
times. Take the first class rice as example, use the Φ3mm
plane indenter to test, under the cooking standard the test
values are in Table 7. The absolute error is 0.2691, and
the average of the relative error is 1.35%, which shows
that the error and the reproducibility of the measuring
system can meet the test requirement.
Table 3. The data of the same breed rice with different pressure head.
Table 4. The data of the same rice variety at different time.
Time First class according rice Baoying lake organic rice
0 hour 19.7433 20.7861
1 hour 19.7503 21.1354
2 hour 19.9474 21.4977
6 hour 20.3053 21.8576
Table 5. The data of contrast experiment.
Auto-test system Taste analyzer
Rice breed
The slope Hardness
Daoya rice 21.5191 8.1
Baoying lake organic rice 21.0686 7.9
San’an rice 20.9645 7.6
Yueguang rice 20.8404 6.8
Xinxie rice 20.3684 6.5
The first class rice 20.3248 6.3
Table 7. The data of error analysis.
No. 1 2 3 4 5 Average
Test values 19.7433 19.9509 19.9876 20.0124 19.9473 19.9283
Absolute error 0.2691 Relative error 1.35%
5. Conclusions
A mechanical automatic testing system is established to
quantitatively characterize the rice quality such as its
hardness. Through test the deformation of the rice, we
can use the slope of the curve to express the rice hard-
ness as the evaluation standard of the rice. The test re-
sults show that the automatic testing system could detect
the hardness difference of varied rice varieties, and it
also could detect the change of one variety hardness with
time, the testing errors and reproducibility are in accor-
dance with the demand of the rice identification. The test
results are in consistent with that of the Taste Analyzer.
This automatic testing method based on mechanical
theory is feasible, it can provides a convenient, accurate
and reliable method to quantitatively obtain the rice pa-
rameters, and is important for studying and characteriz-
ing the quality of organic solid substance. Further im-
provements are still needed in testing precision, reducing
testing error, and using in other parameter measurement
of rice.
6. Acknowledgement
This research is supported by the National Technology
R&D Program of China (Contract No. 2006BAD02A03)
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