Hi leofind,
Briefly, milling (removal of the husk) is needed to make it edible and
if one prefers white rice, the bran layer needs to be removed also.
I've copied and pasted relevant sections from rice websites, but
please click on the links for complete details, photos, and
illustrations.
>>> What is Rice Milling?
4.2.1 Paddy grain [see illustration]
"Paddy grain basically consists of a husk (or hull) and a grain of
brown rice. Brown rice consists of a bran layer (including pericarp,
seed coat, and aleurone layer), a germ and scutellum connected on the
ventral side of the grain, and an edible portion or endosperm.
Basically, paddy grain is not suitable for eating. It becomes edible
only if the husk and the bran are removed."
Rice milling involves the removal of the husk and the bran layer to
produce the edible portion for consumption. Rice-milling process
embraces two basic operations. One operation is the removal of the
husk to produce brown rice; this operation is called dehusking (or
dehulling). The other operation is the removal of the bran layer from
brown rice to produce polished (or white) rice; this operation is
called polishing or whitening. Milling also removes the germ and a
portion of the endosperm as broken kernels and powdery materials."
http://www.ub.rug.nl/eldoc/dis/eco/l.khuong.ninh/c4.pdf
"The basic objective of a rice milling system is to remove the husk
and the bran layers, and produce an edible, white rice kernel that is
sufficiently milled and free of impurities."
"A rice milling system can be a simple one or two step process, or a
multi stage process. In a one step milling process, husk and bran
removal are done in one pass and milled or white rice is produced
directly out of paddy. In a two step process, removing husk and
removing bran are done separately, and brown rice is produced as an
intermediate product. In multistage milling, rice will undergo a
number of different processing steps."
http://www.knowledgebank.irri.org/ppfm/riceMilling/WebHelp/Milling_lesson01.htm
"To get from paddy to rice needed to pass through several steps namely
: husking, husk separating, paddy separating, polishing and grading.
All these steps together is called milling."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"Milling of the rice involves; removing the trash and then the husk
from the rice, milling the bran off of the endosperm (leaving white
rice), and then removing broken kernels and other defects. There are
many ways that rice can be stored and milled. In much of the world,
the rice is milled in very small mills near the farm and stored in the
form of milled rice until consumed. Sometimes it is stored as paddy or
brown rice and then milled fresh prior to consumption. Thailand,
Japan, and the U.S. are good examples of how different the systems can
be."
"IN THAILAND, most rice is milled to white in small mills near the
point of harvest and very soon after harvest."
"IN JAPAN, the rice will be husked and made into brown rice near the
field soon after harvest. These brown mills can be very small or can
be as large as 100 ton per day (brown mills are usually operated by a
cooperative). "
"IN THE UNITED STATES, most of the rice is dried and then stored in
large commercial dryers."
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
>>> Milling Steps
1. PADDY CLEANER
"The paddy rice is passed through coarse screens to remove all straw,
stones, and other objects that are larger than the rice. The rice
passes over fine screens to remove small weed seed, sand and dirt,
stones, and other objects smaller than the rice. Air separation
systems are sometimes used in this process." [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Machinery - Photos - Illustrations - Specs
http://www.rice-machinery.com.tw/e_p_rice_01.htm
2. STONE SEPARATOR
"The rice is passed through a specific gravity table that separates
the product by density. Stones are separated from the rice." [see
photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Machinery - Photos - Specs
http://www.rice-machinery.com.tw/e_p_rice_02.htm
3. PADDY HUSKER
"Husk is a layer of cellulose protecting rice grain. Each paddy grain
has 2 "half husk" interlocking each other, so it is easier to break
the interlock and release 2 half husks from each paddy, this is the
concept of Husking machine."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"The husk is removed from the rice. This is most often done by passing
the rice through two spinning rubber roles. One roll is spinning
faster than the other. The rubber rolls are tightly pressing against
the rice from both sides and strip the husk off." [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Machinery - Photos - Specs
http://www.rice-machinery.com.tw/e_p_rice_03.htm
4. HUSK / PADDY SEPARATING: :
"After husking, brown rice/husk/paddy passed through husk separating
step, which is separating husk (lighter in density) from the rest
(heaver density). This can be done by sieve or ventilation."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"There are many machines and methods designed to remove bran from the
rice. The Japanese milling system is most often used in the most
modern mills. With this system, the rice is first passes through a
milling chamber that has an abrasive stone spinning in the center and
a scarified metal screen on the outside. (The abrasive system). The
rice then passes through a milling chamber that has a metal roller
spinning in the center and a scarified metal screen on the outside.
This machine is rubbing the many kernels of rice against themselves
and the screen in order to remove the bran. (The frictional system.)
The last pass (sometimes all frictional passes) is basically another
frictional machine that is applying a mist of water to facilitate
milling and add a smooth polished surface to the rice. (The water
polishing system.) This Japanese system can be done in three passes as
described here, or as many as seven passes." [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
"Brown rice/paddy mixture is feed into paddy separator."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"A portion of the rice leaving the husking operation still has the
husk on the kernel. A paddy separation machine that works with
specific gravity separates the light paddy kernels from the heavy
brown (husks removed) kernels. The paddy kernels go back to the
huskers." [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Machinery - Photos - Illustrations - Specs
http://www.rice-machinery.com.tw/e_p_rice_04.htm
5. RICE POLISHER
"Brown rice is covered with bran layer which densely wrap around each
grain. Polishing machine use rubbing technique to remove bran layer
from each grain."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
Machinery - Photos - Specs
http://www.rice-machinery.com.tw/e_p_rice_07.htm
6. GRADING
"Milled rice is passed through different type of sieve to take out broken rice."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"The milled whole kernel rice is passed through an electronic sorter
to remove defects. The rice is passed before an electronic eye that
detects any difference in color. A jet of air removes defects. Usually
damaged kernels (with black specks), yellow kernels, and stones are
removed. The very best mills pass the rice through two breaks of
sorters. Sorters can be adjusted to remove green immature kernels from
brown rice, chalky rice from white (more translucent kernels) rice, or
regular medium grain rice from chalky mochi rice. There are special
sorters to remove glass from rice." [see photo]
"Milling the rice can yield as many as 4 to 40 percent broken kernels
depending on the quality of the incoming rice and the milling
equipment. Most high quality rice is sold with less than 4 percent
brokens and so brokens must be removed in the milling process. The
rice is passed through indent graders. These can be cylinders with
small pockets too small for whole grain to fit into, but just right
for brokens, or disks within a trough that have similar indents.
Either way, the idea is for the brokens kernels to temporarily fit
into the indent so that they will be picked out of the whole kernels
and then thrown into a separate flow. The brokens can then be passed
over screens or additional indent graders to be further separated into
various sizes. (brewers, screening, and second heads). " [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Magnet
"There are usually magnets throughout the milling system to remove
metal that can damage machinery and get into the rice. Many have a non
ferrous metal detectors (can remove all metal including aluminum and
stainless steel) just before packaging as a final safeguard."
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Photos - Diagram - Specs
http://www.rice-machinery.com.tw/e_p_rice_12.htm
>>> Overview and Flow Chart
Commercial rice milling systems: an overview
http://www.knowledgebank.irri.org/ppfm/riceMilling/WebHelp/Milling_lesson07.htm
>>> Additional Links of Interest
EQUIPMENT - PHOTOS & SPECS
Automatic Paddy Husker
Paddy Separator
Rice Sheller
Paddy Separator
http://members.commerce.com.tw/pic/1013439515.jpg
HUSKERS - automatic and manual
http://www.rice-machinery.com.tw/e_p_rice_03.htm
The rice-milling industry in the Mekong River Delta:
http://www.ub.rug.nl/eldoc/dis/eco/l.khuong.ninh/c4.pdf
TOUR
The following pages take you on a tour of our state-of-the-art rice
milling factory in Woodland, California
http://www.pirmi.com/docs/tour.html
GAME: Rice Rampage:
http://www.riceromp.com/teachers/games.cfm?sId=2
I hope I've been able to sort the process out for you in an easy to
understand format. If you have any questions, please post a
clarification request *before* closing/rating my answer and I'll be
happy to reply.
Thank you,
hummer
Google Search Terms Used:
rice milling
rice milling process
rice mill equipment |
Clarification of Answer by
hummer-ga
on
13 May 2005 19:55 PDT
Hi leofind,
There are whole industries built around the by-products of rice.
Commercial rice milling systems: byproducts and their utilization
"The main byproducts of rice milling are rice hulls or husk, rice
bran, and brewer?s rice. Rice hulls are generated during the first
stage of rice milling, when rough rice or paddy rice is husked. Rice
bran is generated when brown rice moves through the whiteners and
polishers. When paddy is hand-pounded or milled in a one-pass
Engleberg steel huller, rice bran is not produced separately but mixed
with rice hulls. Brewer?s rice is separated produced when milled rice
is sifted."
http://www.knowledgebank.irri.org/ppfm/riceMilling/WebHelp/Milling_lesson13.htm
3. PADDY HUSKER - by product: RICE HULLS
"The husk is removed from the rice. This is most often done by passing
the rice through two spinning rubber roles. One roll is spinning
faster than the other. The rubber rolls are tightly pressing against
the rice from both sides and strip the husk off." [see photo]
http://www.sagevfoods.com/MainPages/Rice101/Milling.htm
Rice hull as Animal feed
[note: "rice millfeed" usually contains about two-thirds rice hulls
and one-third rice bran]
Rice hull as fertilizer
Fuel: Rice hull combustion
Fuel: Rice hull gasification
Industrial use of Rice hull and Rice hull ash
http://www.knowledgebank.irri.org/troprice/Rice_hull_uses.htm
"Common use of rice hulls are as bedding materials, and as source of
energy for grain dryers or electric power stations. In the modern
rice milling industry, rice hulls are used as a fuel source for grain
drying and parboiling, and for electricity generation. In Bangladesh,
rice hulls are the preferred fuel for parboiling, and rice hulls are
widely used for grain drying in the larger rice mills in Northern
India. Rice hulls, once ground, are also used as ingredient in animal
feeds. In some rice mill hulls are ground prior to piling or storage.
Grinding reduces space needed for storage, and reduces transportation
costs. Grinding an abrasive material like rice hulls however is not
cheap."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
5. RICE POLISHER - by product: RICE BRAN
"Brown rice is covered with bran layer which densely wrap around each
grain. Polishing machine use rubbing technique to remove bran layer
from each grain."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"The conventional use of rice bran is as ingredient for animal feeds,
in particular ruminants and poultry. In recent years however,
advances in stabilization techniques have been made which has led to
new uses for bran and its derivatives, most notably bran oil for
cooking and waxes for cosmetic products. In the developing countries,
rice bran is underutilized due to a lack of suitable stabilization
techniques."
http://www.knowledgebank.irri.org/ppfm/riceMilling/WebHelp/Milling_lesson13.htm
6. GRADING - by product: BREWER'S RICE
"Milled rice is passed through different type of sieve to take out broken rice."
http://www.therice.org/articles/Rice%20milling%20in%20brief.html
"Brewer?s rice is often used as ingredient for beer brewing, hence the
name. In rural areas, brewer?s rice has a variety of uses including
ingredient for rice flour."
http://www.knowledgebank.irri.org/ppfm/riceMilling/WebHelp/Milling_lesson13.htm
Extended Use of Rice (Processing Rice by-products)
"Besides consuming with main courses, rice and its parts have various
other uses. The unedible parts, that are discarded through the milling
process, and the edible part could be transformed into some of the
following suggested products:
RICE HUSKS
"To increase the fuel's effectiveness, rice husks are burned and
compressed into briquettes. If carbonized, these briquettes could
become a high-quality charcoal."
RICE BRAN
"The bran is the most nutritious part of rice and provides a good
natural source of vitamin B."
RICE BRAN OIL (extracted from the rice bran)
"Rice bran oil is a high-quality cooking oil because it could decrease
the blood cholesterol level."
BROKEN RICE
"Approximatele 70% of the broken rice produced in Thailand is used as
feeding ingredients or made into instant noodles and snacks."
RICE FLOUR
"Rice flour, made from 30% of the broken rice produced in Thailand, is
used to produce rice pasta, chips, and other snacks, as well as
cereals."
RICE STARCH (main component of milled rice)
"Rice starch is used as a thickener in making sauces, desserts, and sweet syrup."
RICE STRAW
"Rice straw has various uses in Thailand. Approximately 10% of the
straw are utilized as a medium to grow mushrooms, 50% are used for
animal feeds, 30% are used in paper making, and the rest are burnt
away in other food production process."
BEVERAGE MAKING
"Many alcoholic beverages are made from rice (i.e. broken rice). Some
of the examples include sake or saki, traditionally called rice wine,
and beer."
RICE PAPER
"The pith of rice paper trees is used to make rice paper. This type of
rice product is particularly used in cigarette wrapping; some are
edible, such as those used in wrapping candies."
RICE GLUE
"Rice glude is made by dissoving a proportional ratio of rice in boiling water."
http://www.foodmarketexchange.com/datacenter/product/grain/rice/detail/dc_pi_gr_rice0604_01.htm
Composting the Wastes from a Rice Processing Plant
http://www.fftc.agnet.org/library/article/pt2001037.html
Please let me know if you have any other questions.
hummer
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