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THE EFFECT OF MECHANICAL ADJUSTMENTS
OF A STANDARD RICE HULLING AND
POLISHING MACHINE ON THE
MILLING YIELD OF

PRELUDE RICE

By

LIU YONG-CHI (ROBERT C.)

#

A THESIS

Submitted to the School of Graduate Studies of
Michigan State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of

AASTER OF SCIENCE

Department of Agricultural Engineering

1948

THESIS

 

ACKNOWLEDGEMENT

Appreciation is expressed to the Agricul-
tural Engineering Department of Michigan State
College for the research facilities for this
experiment, and to the Geo. L. Squier Mfg. 00.,
Buffalo, N. Y., who furnished the rice hulling

and polishing machine.

Special acknowledgement is due Prof. D. E.
Wiant of the Agricultural Engineering Department
of Michigan State College, under whose direction
the experiment was made. His valuable sugges«
tions and encouragements were the real motives

to the success.

TABLE OF CONTENTS

ACKNOWLEDGEMENT
Page

INTRODUCTION................................... 1-11
Rice Production and U. S. Contribution..... 2
Varieties or Kinds of Rice................. 2
Structure of Rice Grain and How It Is

Affected in the Process of Milling...... 5

EQUIPMENT AND NATERIAL.........................12-24

The Rice Machine and Its Installation...... 12

Adjustable Parts of the Machine and
Their Range of Settings................. 15

Description of Prelude Rice and Its
Conditions During the Test.............. 20

EXPERILIET‘ITAL RESUL'IIS.OOOOOOOOOOOOOOOOOO0.00000025-32
I‘EethOd Of AnalySi—Sooooooooooooooooooooooooo 25

Effect of Mechanical Adjustments........... SO
DISCUSSIOI‘IO O O O 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 0 054-35
COBICLUSION. C O O O O O O O O O O O O O O O O O O I 0‘. O O 0 O O O O O O O O O 0 036-37

REFERENCES.OOOOOOOOOOOOOOOOOO000.00.00.0000000038-59

INTRODUCTION

In view of the fact that China is an important
rice producing country, growing 60 per cent of the
Oriental production or 29 per cent of the world total,
rice milling is very essential in that country. Since
the war, the Chinese government, private enterprises,
and individual millers are all anxious to have better
mechanical aids in rice milling in order to produce a
better quality product. Orders and arrangements for
the purchase of standard hullers and polishers have been
made with manufacturers all over the world, especially
in the United States. At present, there is no indica-
tion as to whether or not the machine will be adOpted by
the Chinese millers. It is very important that both the
millers and manufacturers know how the adjustments of a
particular machine will affect the milling yield of a pro-
perly conditioned rice. The availability of this detailed
information will determine the extent to which these machines
will be adopted. Previous work has been done on the mechan-
ical effect of a machine as a whole. No results are avail-
able on the effect of various adjustments on the yield
of head rice. Through these tests, some of the charac-

teristics of the machine operation and resulting effect

of adjustments may be determined.

Rice Production and the U. S. Contribution

Rice was first produced commercially in the United
States in 1685 at Charleston, S. C., and is now culti—
vated in Louisiana, Arkansas, Texas and California. The
estimated crOp in the United States in 1945 (l)* amounted
to 70 million bushels, an increase of almost 80 per cent
during the last ten-year period. Of the total world pro-
duction of 7,521 million bushels (2), 4,840 million bu-
shels of rice are produced in the Orient. Sixty per cent
of the Oriental production is in China, 27 per cent in
India, 8.6 per cent in Japan and lesser per cent in other
countries. The U. S. production is not quite one per
cent of the world production and it greatly exceeds the
domestic consumption. However, the U. 8. always leads
the world with new advances and improvements in rice pro-
duction, processing, and marketing. (4), (14), (15), and

(16).

Varieties or Kinds of Rice

Different kinds of rice sold in grocery stores

look very much alike to most peOple, and comparatively

.x.

The numbers in parentheses as hereafter occur
designate the order in References.

few ask for rice by type or variety. There are, how-
ever, a number of varieties of rice marketed commer-
cially which have distinctive appearance and taste. The
rice crop that the farmer grows is commonly called rough
rice after it is thrashed. In India, it is known as
PADDY, and in China as KOO (fiat). There are three
general types of rice in the United States, based prin-
cipally on the length of the grain. They are designated
as short-, medium-, and long-grain types. The short-
grain varieties are grown principally in California and,
to a lesser extent in the southern states. They include
such varieties as Caloro, Colusa, Shinriki, Onsen, etc.,
and their grains have an average length of 7.2 mm. and

a thickness of 3.7 mm. Medium-grain rices include the
Early Prolific, Zenith, Calady 40, Blue Rose, etc. They
are grown principally in the southern rice belt. The
grains average from 8.0-8.7 mm. in length and 3.2-5.4 mm.
in thickness. Long-grain varieties include Rexoro, Nira,
Texas Patna, Bluebonnet, Honduras, Fortuna, etc. They
are grown almost entirely in the southern belt. The
grains average from 9.0-9.8 mm. in length and from 2.4-
3.4 mm. in thickness. Of the 1945 crOp, according to
the Rice Millers' Association statistics, about 20 per

cent was Rexoro, 18.4 per cent was Blue Rose, and 18.2

per cent was short-grain rice. Next in order of
importance came Zenith, comprising about 15.0 per cent
of the crOp, and Early Prolific, 11.5 per cent. All
the other varieties together comprised about 17.0 per
cent.

Rice sold for table use normally consists of head
rice or whole kernels. The quantity of head rice that
can be obtained from a given amount of rough rice is,
therefore, important, and is commonly known as the prin-
cipal milling yield of rice which is also reckoned as the
most important characteristic in the evaluation of rice.
In general, the average yield of head rice is greatest
for the short and medium-grain varieties. In the south-
ern states, the short-grain varieties usually give a
milling yield of head rice from 92 to 97 pounds per bar-
rel of 162 pounds of rough rice. In other words, the
principal milling yield of short-grain rices is 57.8 to
59.9 per cent. The medium-grain varieties yield from 85
to 92 pounds per barrel or 52.5 to 57.8 per cent, and the
long-grain varieties, from 76 to 84 pounds per barrel,
or 46.9 to 51.5 per cent. The average total yield of
milled rice is also slightly higher for the short-grain
than for the medium- and long-grain varieties. The long-

grain varieties, as a group, have the lowest average

total yield of milled rice.

Structure of a Rice Grain and How It Is
Affected in the Process of Milling

In order to visualize the effect of the milling
process on rice, a brief understanding of the physical
and microscopic structure of the rice grain is very
essential (5). In spite of varietal differences, such
as short, medium, and long-grain varieties, the structure
of the grains is virtually the same. The hull (lemma and
pales) which is loosely attached to the edible grain with-
in, is siliceous, hard, and hairy. Directly beneath, but
separated from it, and firmly attached to the starchy body
(endosperm) of the grain, is the bran coat or layer which
reveals seven types of cells under the micros00pe, and
are arranged in enve10ping layers around the endosperm
in the following order from the outside in: (a) epicarp,
(b) mesocarp, (c) cross cells, (d) tube cells, (9) sperm-
odern, (f) perisperm, and (g) aleurone layer. The germ
is located at one end of the grain, and is often too easy
to lose, once the hull is removed. During the process of
milling, most of the outer six layers and a portion of

the seventh are removed.

Rough rice is used for seed and, at times, for
feed, and exclusively for human consumption in the
form of milled rice. Rice with hull removed is known
as brown, clean, or husked rice; after the removal of
part of the bran layers and germ, it is known as under-
milled or unpolished rice; and when practically all of
the bran layers and germ are removed, it is known as
milled or white rice. Brown rice contains more protein,
minerals, and vitamins than milled rice but, on the other
hand, it is reported in the Orient that it causes diges-
tive disturbances. Milled rice is more attractive in
appearance, requires less time to cook, and keeps better
in storage than brown and undermilled rice which becomes
rancid easily. In addition, the practice of milling
reduces the commodity about 50 per cent in bulk and 25
per cent in weight, thus reducing the cost of transpor-
tation (5). Thus, milling is an essential concomitant
of rice production, either as a rural industry, or on a
greater commercial scale.

Due to the common preference for white or milled
rice, beriberi is a rampant disease among the people of
the Orient. It is caused by a pronounced deficiency of
the anti-neuritic vitamin B1 or thiamine. Wise and

Broomell (5) have shown that in modern milling processing,

raw brown rice is reduced approximately 10 per cent

in weight by scouring off of the bran layer, germ and
probably some of the endosperm. About 70 per cent of
ash, 85 per cent of fat or oil, 70 per cent of the crude
fiber, 10 per cent of the protein, and 50 per cent of the
pentosans (anti-gray hair factor) are removed. As to
vitamins, as much as 76.5 per cent of thiamine (anti-
beriberi factor), 56.6 per cent of riboflavin (vitamin
B2), and 65.0 per cent of niacin (vitamin B3 or anti-
pellagra or P.P. factor) are removed and lost for human

consumption.
Milling Methods and Trend of DevelOpment

The methods of rice milling are different in var-
ious localities. In general, we can classify them under
three categories. (a) Simple pounding. This is known as
mortar-and—pestle in the United States, choo-cho (HQ)
in China, and moung in India. It is the most primitive
and crude method in rice milling, used only in the rural
districts for home consumption. (b) The Engelberg or
Plantation Huller. This machine was invented by a German
engineer and named after him. It consists of a perforated
sheet iron wall around a rapid revolving cylinder with

ribbed surface. Based on this principle, standard milling

machines have been develoPed. They are made in units

and applied in batteries, the number of which depend upon
the production capacity. (c) Hulling stones. The appli-
cation of hulling stones in rice milling has been known
in China as noon (jg: ). The stones are made by embedd-
ing bamboo sticks in clay blocks. The rough rice is fed
into the stones from the center and as the grains pass
between them, the revolving action of the upper stone
cracks the hull between bamboo sticks and thus frees the
kernels. Unfortunately, no information has been collec-
ted or recorded, although it is an effective piece of
equipment that is adopted all over the Chinese rural
districts. Hulling stones used in modern mills, are
usually made of steel plates which are set at such a
distance apart that the longest grains of rice are not
broken and, at the same time, a maximum percentage of
grain is hulled. In general, two sets of stones are used
so that the shorter grains that may pass through the first
stones without being hulled, are separated from the brown
rice in a paddy machine and discharged to another set of
stones which is adjusted more closely until all the
grains are hulled. Comparative figures showing the

yield of head rice in percentage of a given amount of

rough rice through different methods, are given in Table I.

Since these figures vary with varieties, moisture
content, pre-treatment, and other conditions of rice
(5), (9), and (14), mechanical means in rice milling is
decidedly not the controlling factor that affects the
milling yield of head rice.

Table I. Yield of Head Rice Obtained by
Different Milling Methods

 

Milling Methods Head Rice Experimenter
in%

Simple Pounding 57.1 Sethi of India

Engelberg Huller 61.9 Sethi of India

Hulling Stones 58.8 Wise and Broomell

 

The development has been made in two directions: the
retention of nutrients in rice, and the improvement of
milling quality of rice. As a result, new terms such as
undermilling, parboiling (14), conversion (15) Malekizing
(15), enriching (4), have been flooded into the rice mill-
ing industry. Outstanding work in this respect has been
done by Converted Rice, Inc., Houston, Texas; Hoffmann-
LaRoche, Inc., Nutley, N. J.: Bureau of Plant Industry,

U. S. Department of Agriculture, and many other Food and
Nutrition Institutions. The principle behind all these
new developments is based on the preservation of the natural

nutrients of whole grain rice by using vaccuum, heat, and

- 10 _

pressure in order to force the water soluble B com-

plex vitamins and minerals from the hull, bran layer

and germ of the rough rice into the endOSperm of the
kernels, to gelatinize the starch of the endOSperm, and
to heat-seal the nutrients within the grains where they
are largely retained after milling, washing, and cooking.
The process used in producing converted rice in Texas,
succeeds in transforming the appearance of the chalkiest
kind of rice into one with a high degree of uniform
translucency, and a tint like that of the highest grades
of rice obtainable. The gelatinization of starch pro-
duces a closeness of structure of the endOSperm superior
to that of even the very highest grades of rice, and pro-
vides a greater resistance to breakage during milling.
Millers of ordinary white rice receive approximately 40
per cent of white head rice from some rough rice, whereas
it is possible to recover 65 per cent or better, of any
variety of converted rice.

In addition, converted rice may be stored for a
longer period without deterioration and it is especially
resistant to infestation of insects. The gelatinized
surface of the grains does not allow a hold for the man-
dibles of weevils for feeding and egg laying purposes.

Since the conversion process employs temperature which

- 11 -

destroys or inactivates the lipase enzyme, any deteriora-
tion during storage and transportation is completely
eliminated.

Furthermore, Jones (14) has shown that the effect
of parboiling treatments on milling quality reveals an
average increase of 26 per cent in head rice yield for
three varieties. Rough rice of low milling quality is
improved much more than rough rice of high milling quality.

The enrichment idea originated through the pOpular
preference for white rice and the cases of beriberi among
the people in rice producing areas. The procedure (4)
is concentrated in the preparation of a premix which pro-
vides thiamine, niacin, and iron in amounts equal to the
enriched flour, after the enriched rice is washed and
cooked. Riboflavin is excluded because of its yellow

color.

- 12 -

EQUIPMENT AND MATERIAL

The Machine and Its Installation

The machine used for this experiment was a Buffalo
No. 4, Combined Rice Huller and Polisher. It was made
upon the Engelberg principle, manufactured and supplied
by the Geo. L. Squier Mfg. 00., Buffalo, N. Y. It has a
10" by 5%" driving pulley. At a pulley Speed range of
750-900 revolutions per minute, the machine has a capac-
ity range for rough rice of 150-250 pounds per hour, and
requires 4-6 horse power to operate. The installation
is shown in Fig. 1.

The machine consists of four principal parts: the
hopper, the huller, the polisher, and the exhauster.
Rough rice flows from the hOpper into the huller through
a 2" by 2" opening controlled by a sliding feed gate, E.
The cylindrical huller chamber is a two-piece steel cast-
ing with the upper half hinged to the lower. A fluted or
grooved cylinder (Fig. 2), mounted on the main pulley shaft,
forces the grains against a stationary adjustable hulling
knife (Fig. 5). Hulled rice passes from the hulling cham-
ber through a 1%" by 2" controlled Opening to the test
spout, L, when the operator wishes to examine the product.

The lower half of the hulling chamber, which acts as a

                              
                                 

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hulling screen, is made of perforated sheet steel and has
a case-hardened surface (Fig. 4). The hulling action is
accomplished in two ways; first, by means of the hulling
knife rubbing up against the grains, removing the outside
hull; and secondly, by means of friction between the
grains as they pass through the cylinder, removing the
bran and under coat. Before starting the machine, feed
gate B should be closed, and discharge gate M about half
Open. Test gate R is set so that rice will discharge into
test Spout and not into the polisher section of the ma-
chine. The hulling knife is adjusted by loosening clamps
O, turning the adjusting screws N, so that the knife
touches the outer diameter of the cylinder. Then the
knife is backed away from the cylinder the desired dis-
tance, making sure that the Spacing between the cylinder
and knife is the same at all points. When starting the
machine, Open the feed gate slowly until wide Open. Ad-
just the knife away from the cylinder slowly by turning
the adjusting screws until a point is reached where some
Of the rice is not hulled. This can be observed by exam-
ining the rice discharged into the test spout. After the
hulling knife is properly set and adjusted, clamps 0

should be tightened.

 

 

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If the color Of the rice leaving the machine does
not meet specifications, slowly decrease discharge gate
Opening by screwing down the slide M, which will cause
rice to remain inside the cylinder longer. Friction
between the rice itself will bring up the color of the
finished rice to the desired standard. When this is
accomplished, test gate B should be set back so the rice
will be discharged into the polisher, in which a tapered
drum, covered with leather strips, is revolving at a
speed Of 360 revolutions per minute within a casing Of
perforated sheet steel which makes up the polishing screen.
All the loose hulls, bran, polish and trash that passed
through.both the hulling and polishing screens, are col-
ilected into the lower part of the machine or the exhauster,
in which a fan U, revolving at 2,500 revolutions per min-
ute, is mounted to discharge the by-products out of the
machine. Heavy stuff may accumulate in the base of the
machine and is removed, manually, through the slide
gate T.

When the machine arrived from the factory in Buf-
falo, it was uncrated and set on a wooden base with a
single phase 5 h.p., 250 volt, G.E. Repulsion Induction

motor, as shown in Fig. l. The huller was driven first

- 15 -

by means of a 5" 5-ply hinge jointed Balata belt, accord-
ing to the specifications. The generation of static
electricity through the belt and pulley made it necessary
to ground the machine to the motor. The power input was
measured with a 1.5 kw Reston wattmeter in series with a
5:1 current transformer. Thus, the actual power input
was always five times the meter reading. The circuit

sketch is shown in Fig. 5.

Adjustable Parts of the Nachine and
Their Range of Settings.

As previously stated, the machine has three pos-
sible adjustments. They are:

(a) Feed Gate under the hopper. The size Of this
Opening regulates the capacity Of the machine. The feed
gate has a range from 0" tO 2". As the motor used was
not large enough to drive the machine at its full capac-
ity, the settings made are limited to the lower half of
the range. For convenience, a home made scale is attached
in front of the slide, as shown in Fig. 6.

(b) Hulling Knife. This is a i" by 1-3/4" by 13"
NO. 1090 tool steel plate, hardened to Rockwell NO. 47-50

with l" of each end annealed. It is double-edged and

-15..

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- 17 -

 

 

 

Fig. 6. Adjustable Parts of the
Huller and Polisher

_ 18 -

reversible, and has a clearance range with the cylinder
from O" to 0.15". The adjustments are made by means Of

two knurled screws, one on each end. The screw has 20
threads per inch, which means that a complete turn of the
screw will give the knife a displacement of 1/20 Of an inch
(1.27 mm.). The clearance space is closely related to the
width and thickness Of the rough rice. Hulling will not be
completed if the clearance is greater than the width of the
grain, and, at the same time, will cause excessive breakage
if the clearance is less than the thickness of the grain.
The settings made were limited to the upper half of the
range.

(0) Discharge Gate. This is the outlet for hulled
rice to reach the polishing chamber. The Opening controls
the rate of output, degree of hulling, and color of fin-
ished rice and has a range from O" tO 2". The settings
made were limited to the upper half of the range.

With these three adjustments of the machine, four
settings of each were planned to be tested. In order to
facilitate labelling in sample taking, the adjustments
were represented by capital letters A, B, and C, and set-
tings by Arabic numerals 1, 2, 5, and 4. Thus the set-
tings in detail were as follows: shown in next page.

Total number of settings would be the cube of four or 64.

- 19 -

"A" - Feed Gate Opening

A1 - Feed Gate at an Opening Of 0.25"
A 2 _ N N N N " " O . 50 N
A - " " " " " " o. 75"
A: _ n N N N I? I! l . OO "

"B" - Hulling Knife Clearance

B1 - Hulling Knife at a Clearance Of 0.075"

B _ n n n n n n O 100 n
2 .

B3 - I! N N It 1! N O . 12 5"

B _ N N fl '1 9! N O 1 50 fl
4 O

"C" - Discharge Gate Opening

Cl - Discharge Gate at an Opening of 1.00"

C - fl " N n N N 1.25"
2

C _ n n n n n n 1.50"
3

C _ n fl " " '1 fl 1 .75"
4

Through the trial test, it was known that the feed gate
at Al was not effective. The Opening was too small to
perform a prOper feed function. Also, when the feed
gate went up to A4, the machine choked easily, making it

necessary to eliminate the settings in combination with

A1 and A4, This eliminated 52 tests and thus halved the

time and material required to conduct the test.

- 20 -

Description of Prelude Rice and
Its Conditions During the Test

For this experiment, rough rice was ordered from
the Arkansas Rice Growers COOperative Association, Stut-
tgart, Arkansas. It arrived in two bags Of about 100
pounds each with no specification or description. That
was Nov. 1947, at which time the machine had not yet
arrived. Actually, the machine was not shipped until the
first part of February, 1948. While waiting for the
machine, the rice was identified by the Arkansas Rice
Growers COOperative Association as PRELUDE. The follow-
ing description Of Prelude rice was Obtained from Dr.

J. O. Dockins, Superintendent, Rice Branch Experiment
Station, University of Arkansas, Stuttgart.

"The parent varieties were Improved Blue Rose
(medium-grain) and Fortuna (long-grain). The cross was
made by Jenkin W. Jones at the Biggs Rice Field Station,
Biggs, California, in 1929. The F1 plant was grown at
Biggs, California, in 1950. The F2 generation was grown
at the Texas Agricultural Substation NO. 4, Beaumont,
Texas, in 1951. The F5 and all subsequent generations
were grown at the Rice Branch Experiment Station, Stutt-

gart, Arkansas."

- 21 _

"Selections were made from the F5 line, number
2920Al7-4, in 1955. Selections from that line were grown
and re-selected each year until 1957. One of the lines
from this family was selected in 1956 and designated as
number 2920Al7-4-4-1-1. This line was quite uniform, so
it was grown in a yield nursery in 1957. Selections were
made from that line in an effort to Obtain a line more
resistant to diseases and more uniform in grain type.

The final selection was made in 1957, and designated as
number 2920Al7-4-4-1-1-1. The selecting was done by C.
Roy Adair with the assistance of other employees of the

U. S. Department of Agriculture, Bureau of Plant Industry,
Division of Cereal Crops and Diseases, and employees of
the Arkansas Agricultural Experiment Station, working on
the COOperative rice improvement project."

"Description of the plant:

1) The leaves are hairy, semi-erect, acuminate,
medium to wide, medium to long, and medium-light green.

2) The leaf sheaths are green on the surface,
lighter green at the nodes and very light green (almost
white) on the inside.

5) The ligules are acute, split, medium long and

white or very pale green.

- 22 -

4) The auricles persist and they are hairy, horny,
and white or very pale green.

5) The gglmg are large, erect, sturdy, green on
the surface, lighter green at the nodes, and white or very
pale green inside.

6) The panicles are medium in compactness and
drOOping.

7) The glumes are flat, toothed, hairy, and green
before maturity, and straw colored when ripe.

8) The 13mmg and 23133 are hairy, partially tip-
awned, and they are green before maturity, and straw
colored when ripe.

9) The stigma is green and the anthers are yellow.

10) The gagig is long, medium thick, medium wide,
and there is very little shattering.

11) The kernel is very light brown before milling.
The grooves are shallow and it is common and vitreous with
an occasional chalky Spot in the center.

12) Reaction to disease organisms:

 

 

 

a) HelminsthOSporium oryzae - Susceptible
b) Cerocospora oryzae - Resistant

c) Leptosphaeria salvinii - Susceptible
d) Piricularia oryzae - Moderately

 

resistant

- 25 _

e) White tip, - Susceptible

 

15) Grain yield and days from seeding to maturity

when sown at different dates; five year average 1957-41.

 

SeedinggDate
April 20 May 10 May 50 June 20

Seeding to maturity 145 155 150 121
(dayS)
Yield per acre (bu.) 40.5 42.5 48.4 47.6

 

From the above description, it is evident that
Prelude rice is a rather new variety. According to the
U. S. Standards of rough rice (8), it belongs to Class X
rough rice with a test weight Of 41 pounds per bushel
not cleaned, and that Of 45 pounds per bushel when 6.1
per cent Of dockage is excluded at a moisture content
of 8.7 per cent. The grain and kernel measurements, as
compared with other types Of rice in general, are as

shown in Table II.

- 24 -

Table II. The Grain and Kernel Measurements
of Prelude Rice as Compared
with Other Types Of Rice

 

Length Width Thickness

 

Inch mm . Inc h m. Inch mm.

 

Prelude: Grain 0.597 10.10 0.124 5.14 0.079 2.01
Kernel 0.518 8.07 0.108 2.74 0.071 1.81

Long Type:GI‘ain 900-908 In; 0 """"- 2.4‘504 mm.
Kernel 6.6-7.7 m. "'""- 2.0-2.6 mm.

Ti'xedim Grain 800‘807 min. "" 302‘304 mm.
type: Kernel 6.1-6.7 mm. ---- 2.6-2.9 mm.
Short Grain 0.285 7.20 ---- 0.145 5.70
type: Kernel 0.216 5.50 ---- 0.126 5.20

 

Note: For Prelude, the measurements were made by the
writer.

For other types of rice, from Jones (2)

-25-'

EXPERIMENTAL RESULTS

Method of Analysis

Strictly speaking, milling yield includes two
products: one is the total amount of clean rice, the
other is that of by-products. The former consists of
head rice, second head rice, screening and brewer's rice
and the latter, bran, hull, and polish. Since this exper-
iment deals with the effect of the mechanical adjustments
on rice, the yield Of head rice from the samples taken at
the two spouts would be sufficient to show the effect Of
mechanical adjustments. But, because the by-products
from the machine were all mixed up through the exhauster,
the standard method, used in determining the milling
yield of rice (7), could not be directly applied. For
each setting Of the machine, five to ten pounds Of rough
rice were fed through the feed hOpper, according to the
size Of the feed gate Opening. After the machine ran
for a few seconds, the feed gate slide was slowly Opened
to the desired scale, the power input was recorded, and
the time for a given amount of rough rice to run through
was determined by means Of a stop watch. Duplicate sam-

ples of about 100 grams each were taken at each Spout in

- 25 _

airtight bottles and they were analyzed in three ways.

(a) Yield Of head rice. The sample was weighed
and the head rice was separated by passing over a 11" by
11" NO. 7 sieve four times. Any unhulled rice was picked
up by hand and weighed. The difference in the amount of
head rice, Screening and unhulled rice would be one way
Of evaluating the effect Of various settings.

(b) Weight per 1,000 kernels. As the degree of
polish can be distinguished by weight Of a given number
of whole kernels, 250 Of which were counted and weighed
with a precision balance in the Chemistry Department for
each sample, and the 1,000-kernel weight was Obtained by
multiplying the actual weight of sample by four.

(0) Color and general appearance. According to
the United States Standards for Milled Rice, Prelude
should be classified as Class XI. Since it was produced
east of the Rocky Mountains, the grade requirements
shall be in accord with those Specified for Classes I to
VIII, inclusive. Other factors (8) being equal, the
effect of broken kernels and color and general appearance
_On grading is given in Table III. 2

Within the available power range, the following

settings were made. The average percentage Of head rice,

Table III. Important Grading Requirements
for Class XI Milled Rice

 

 

.-l -—-

Max. limit
Grades of broken Color and General Appearance
kernels %

 

U. S. NO. 1 4 White or creamy, and well
milled.
U. S. NO. 2 7 White, creamy, or Slightly

grayish, and well milled.

U. S. NO. 5 15 White, creamy, or light gray,
and reasonably well milled.

U. S. NO. 4 20 White, creamy, or gray, and
may be slightly rosy, and
reasonably well milled.

('1'!

U. S. NO. 55 May be dark gray or rosy,

and reasonably well milled.

U. S. NO. 6 50 May be dark gray or rosy,
and reasonably well milled.

 

screenings, and unhulled rice, if there were any, were tab-
ulated under the column, Yield Of Rice in Per Cent, Table
IV. Then came weight per 1,000 kernels in grams, loss of
weight in per cent, based on the heaviest sample Obtained,
and the capacity of rough rice in pounds per hour. The
details are found in Table IV in which it is seen that there
are two series of figures for each setting. Figures in the
upper row are average values Obtained from the analysis of

the duplicate sample taken at the test Spout, and those in

the lower, at the discharge spout.

_ 28 -

This table can be

rearranged for the convenience of graphical expressions

so that curves can be drawn more easily.

 

 

 

Table IV. Yield Of Head Rice, Specific Weight,
and Grade of Prelude Rice as
Effected by Different Settings
Vt. per Loss
Set- Yield of Rice in % 1,000 of c & A Capa-
tings Uhhul- Head Scree- kernels’ wt. by cit
led rice ning Grade in gms. % Grade lb. hr.
A2B101 14.90 85.10 X 21.6728 12.70 1 72
6.82 95.18 x 21.6250 12.98 1
A B c 21.61 78.59 x 21.9744 11.58 1 81
2 1 2 22.55 77.67 x 21.9452 11.70 1
A B c 29.52 70.48 x 22.2552 10.45 1 89
2 1 5 55.55 64.45 X 22.2517 10.55 1
A B c 52.41 67.59 x 22.4592 9.65 1 95
2 1 4 29.79 70.21 x 22.4158 9.82 1
A2B201 67.11 52.89 5 22.0048 11.45 1 116
75.45 24.55 5 21.9812 11.54 1
A B c 76.25 25.75 5 22.1740 10.77 2 121
2 2 2 78.75 21.25 5 22.1555 10.94 1
A B c 0.51 68.78 50.71 5 25.0544 7.25 4 126
2 2 3 0.21 77.51 22.48 5 25.0241 7.56 5
A B2C4 1.42 85.70 12.88 5 24.2552 2.42 5 140
2 2.56 81.70 15.74 4 24.2085 2.58 5
A B c 75.85 24.15 5 22.5752 9.18 2 177
2 5 1 79.00 21.00 5 22.5586 9.51 2

 

(continued on next

page)

Table IV (continued)

-29..

 

A2B5C2

‘8
A27505

A B
2 504

A234(31

A2B4C2

A2B4C5

0.48
0.20

5.67
2.54

5.24
2.67

5.70
1.76

A B c 10.40
2 4 4 9.21

A381C

A5B2C

A513501

A B C
5 5 2

A5B5C5

A 8,0
5 o

1.26
0.85

A B c 25.60
5 4 126.10

78.60
81.60

84.12
84.50

85.55
82.20

78.62
78.05

79.60
80.02

81.00
81.24

85.78
82.56

These two series of tests

21.40
18.40

15.40
15.50

10.98
15.26

21.58
21.95

17.16
17.51

15.15
17.10

5.82
8.45

um 55 5» mm pm 9» 5m

22.8808
22.8545

25.0792
25.0546

24.5976
24.5587

22.8964
22.8497

25.8680
25.8521

24.5944
24.5611

24.8544

24.8158

to insufficient power

77.50
74.00

79.60
75.50

68.50
77.20

79.70
69.80

60.52
61.50

22.50
26.00

20.40
16.70

51.70
25.80

19.04
29.57

15.88
12.60

0101 011?- mm #301 0101

21.6512
21.6108

22.4524
22.4010

22.8672
22.8556

25.4528
25.4148

21.9744
21.9219

7.94
8.05

7.14
7.51

1.06
1.19

7.88
8.05

8.00
4.12

1.05
1.18

0.00
0.16

failed

12.90
15.00

9.75
9.85

7.99
8.05

5.65
5.78

11.60
11.80

0305 010) 0101 0‘01 030) $01 (003

due

1
1
1
1
4
5
6
5
2
2

216

242

504

257

515

562

446

No record
hereon

 

(continued on next

page)

- 30 -

Table IV (continued)

A B C 54.78 51.76 15.46

25.4194 5.78
5 4 2 56.05 52.80 11.17

25.5788 5.95

A B C 50.70 57.15 12.15

24.5820 1.90
3 4 3 50.12 54.86 15.02

24.5601 1.98

A B C 72.58 17.54 10.58

24.7096 4.60
3 4 4 71.61 15.65 15.76

25.6719 4.76

0303 “>03 0‘01
0101 0101 0103

 

Effect of Mechanical Adjustments

The best known example showing the mechanical effect
of milling on rice was the work of Rise and Broomell who
took samples at different milling stages and determined the
percentage of head rice and specific weight (weight of 1,000
kernels). The differences tell the effect of the machine on
rice at different milling stages, whereas, in this experiment,
the effect of different settings of the same machine were
analyzed, so that the inherent ability of the machine upon
the specific type of rice can be realized. Fig. 7 shows the
effect of hulling knife clearance on the yield of head rice
at various settings. The curves are plotted by arranging the
figures in the first row of each setting in Table IV with
the hulling knife clearance, B against the yield of head
rice in per cent. .

A204at B2 and A2B5 at B5 are undoubtedly the best

 

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. . .

 

- 31 -

settings for the Prelude rice, so far as the yield of
head rice is concerned. But, when they are referred
back to Table IV again, both settings produce 1.42 per
cent and 0.4 per cent of unhulled rice respectively, and
also, the color and general appearance are dark gray or
rosy and not reasonably well milled. By so checking,
curve A2C2 at B5 gives the best setting for Prelude rice,
and the product is white, creamy or gray in color and
good in general appearance. This indicates that the set-
ting of the machine for Prelude rice at a feed gate opening
0.5" and a discharge gate opening of 1.25" should have a
hulling knife clearance 0.125".

Fig. 8 is made out the same way by plotting the
hulling knife clearance against the specific weight (gms.
per 1,000 kernels) at various settings. The curves
infallibly Show that the winder the clearance Space, the
heavier the kernels will be, and the same is true if the
discharge gate is Opened wider. For the retention of
food value in rice, both the knife clearance and the dis-
charge opening should be so adjusted that the product
would be at maximum specific weight and yet reasonably
well milled.

By rearranging the figures in Table IV, Fig. 9 and

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Fig. 10 are obtained. The yield of head rice for curve
A3B4 at various settings of the discharge Opening gives
an inverse result. It shows that the unhulled rice per-
centage increases as the knife clearance and the discharge
Opening increase. Any adjustment which gives such a
result should be carefully avoided.

Fig. 11 shows the color and general appearance of
the product from two complete series of the settings.
This is one of the important factors in grading of milled
rice. The picture not only shows the differences within
the discharge gate openings, but also the differences in

knife clearances.

 

Fig. 11 Color and General Appearance of Products
As Affected by Different Settings.

- 34 -

DISCUSSION

As the method used for the analysis of head rice
in this experiment deviated somewhat from the standard
method (7), (9), (10), (11), and (12), some results may
be questionable, but, in general, the analysis checks
closely with Wise and Broomell's result on head rice at
different milling stages. In addition, the differences
in 1,000-kernel weight and color-appearance of the pro-
ducts verify the result to a great extent.

The moisture content of rough rice, as determined
by Gehl (9) in his "Shelling Device" study, has signifi-
cant affect on the milling yield of rice. Due to lim-
ited supply of rice, it was not possible to determine
the effect of mechanical adjustments on Prelude rice of
different moisture content. Low moisture content in rice
always gives high milling yield. The Prelude rice used
had been stored in a heated room for more than two months
before the tests were made, and had a moisture content
of less than 9 per cent. This would make for favorable
results.

During the tests, considerable trouble was caused
by poor power transmission which led to clogging or

choking of the machine. The drive was changed back and

forth from a flat belt drive to a V—flat drive several
times. No improvement was made even with the aid of
belt dressing. The use of a V-belt drive proved that
the motor was not big enough for the service, and also,
the design for flat belt transmission of the machine

is somewhat questionable. The forfeiting of the settings
related with A4 and those with A3B1 and A5B2 made the
experiment not as complete as desired. Also, some of
the rejections, due to over-load, rendered the curve
plotting impossible or meaningless. In some of the fig-
ures, only four characteristic curves were drawn instead

of six because of the forfeited settings.

_ 35 -
CONCLUSION

The quality of product in rice milling is dependent
on the resultant effect of all possible adjustments that
can be made on the machine. Every single change in the
adjustable parts will be shown in some way by the product.
The most important reSponses to machine adjustments are:
(a) yield of head rice, (b) specific weight of the kernel,
and (c) color and general appearance. If these charac-
teristics can be correlated with various adjustments of
the machine, then there is no doubt but that the limits
and effectiveness of the machine can be pre-determined.
Prelude is a long-grain type rice of recent development.
Information about its milling quality is rather limited.
The grain has an average length 10.10 mm., width, 5.14 mm.,
and thickness, 2.01 mm. Its test weight at a moisture con-
tent of 8.7 per cent was 41 pounds per bushel. Maximum
yield of head rice was obtained with a hulling knife clear-
ance of 0.100 inch and a discharge gate opening of 1.75
inches when the feed gate was at 0.50 inch, and maximum
retention of food value (1,000-kernel weight) was at a
hulling knife clearance of 0.150 inch and a discharge gate
opening of 1.75 inch when the feed gate was at 0.50 inch.

The products thus obtained were dark gray or rosy in color

and usually contained some unhulled rice. For high
grade products, careful study of the characteristic

curves should be followed.

(l)

(2)

(4)

-58é

REFERENCE

Collier, G. A.
1947 Rice Production and Marketing in the
United States. U.S.D.A. Misc. Pub.
No. 615?

 

 

Jones, J. W.
1941 Rice Varieties and Their Comparative
Yields in the UnitedSStates.
U}S.D.A. Cir.7No. 612.

 

 

Wise, F. B. and Broomell, A. W.
1916 The Milling of Rice and Its Mechanical
and Chemical Effect upon the Grain.
U.S.D.A. Bul. No. 350.

 

 

Furter, M. F., Lauter, W. M., Ritter, E. De.,
and Rubin, S. H.
1945 Enrichment of Rice with Synthetic Vitamins
and Iron. ‘Industrial and Engineering
Chemistry Vol. 58, No. 5

 

Sethi, R. L., Sethi, B. L., Mehta, T. R., and
Gupta, P. S. -
1957 Observations of the Milling of Rice in the
United Provinces. Indian Journal of*—
Ag. Sc., Vol. VII, Part V, Oct., 1957.

 

Reed, J. B.
1917 The Byeproducts of Rice-milling;
UfS.D.A. Bul. No. 570

 

1928 Handbook of Official Standards for Milled
'Rice, Brown Rice, and RougthICe.
USGSA-GISFOrm No. 179.

 

 

1945 United States Standards for Milled Rice,
Brown Rice, and Rough Rice. U.S.D.A.
Production and Marketing Administration.

 

 

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

- 59 -

Smith, w. D.

1928 Im roved A aratus and Method for Making
“Shellingfi of Rough Rice.

U.STD.A. Cir. NO. 48.

 

 

Gehl, R. M.
1950 The Gehl Laboratory Rice-scourinngevice.
‘U.SID.A. Cir. No. 156.

 

Bates, E. N.
1927 The Bates Laboratory Aspirator.
U.S.D.A. Cir. No. 9.

 

Bates, E. N.
1942 The Improved Bates Laboratory A5pirator.
U.S.D.A. Cir. No. 650.

 

Kik, M. C., and William, R. R.
1945 The Nutritional Improvement of White Rice.
National Research CounciIWBul. No. 112.

 

Jones, J. W.

1946 Effect of Parboiling and Related Treatments
on Milling,'Nutritionall_and COOking
‘Qfiality of Rice. U.S.D.A. Cir. No. 752.

 

 

O'Donnell, W. W.
1947 Conversion Process Retains Rice Vitamins.
Food Industries,fiVo1. p. 7654769.

 

Kik’ hi. CO
1945 Vitamin Retention and Processing.
'Rice Journal. 46:14-16.

 

Jones, J. W.

1947 New Ricesi New Practices.
Reprint of the 1945—47 Yearbook of
Agriculture, pages 575-578.

 

Mac Rae's
1947 Mac Rae's Blue Book, 1947.

AP 22 .”
MAR 131961 a!

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