Note: Descriptions are shown in the official language in which they were submitted.
GRAIN MILLING AND DEGE~MINATION
PROCESS AND EQVIPMENT FOR SAME :`
Background and Summary of the Invention
' ';'
This invention relates to grain milling generally,
and more particularly to improved milling processes which
accomplish separation of the grain components in a novel manner
.
resulting in substantial economic savings and increased
yield~ The invention also deals with an improved method and
apparatus for degerminatiny grain such as corn. ;
Conventional milling~techniques utillze a gradual
~ reduction process wherein successive differential grinding and ~ ;
;~shifting separates the baslc components of the whole kernel
. : . - ,
grain, na~ y bran, endosperm and germ. The grain is first
cleaned witil care being taken to maintain the grain intact. `~
; With~ r~ iat.i~!21y tough grains such as wheat, impact
d~ein~es~tatlon may be utilized under proper conditions without
the clanger of cracking the gra1n~ With most brittle grains
uch as corn under most conditions, a water wash is normally
performed to remove foreign materials while protecting the
grain from damage.
Using prior art procedures, the cleaned grain is then
subjected to temperlng wherein water absorptlon magnifies the
dif~erences in grinding~characteristics of the grain
componentsO Finally, the gradual reduction process subjects
the grain to multiple grindiDg and separating steps until the
components have been ground to the desired size and purity.
The ground product is dried if necessary to meet market
specifications, cooled and graded~ A typical milling process
for highly purified products utilizing conventional techniques
has from 50 to 60 separate steps before the end products are
reached.
~: .
æ~
In addition to the expense o the large number of
rollers needed in the gradual reduction process, the stock must
` be elevated each time it is to be passed through another set of
rollers, thus requiring expensive conveying equipment.
~ Further, since tempering is necessary to achieve separation of
;- the grain components, the components must be dried to the
proper moisture content. ~gain, this increases the cost and
complexity of the milling process and delays its completion.
The high fat content and consequent low quality of the "fines" -
resulting from the conventional process necessitates that they
be separated and removed from the stock, which further adds to
the difficulty and expense involved~
The degree of separation of germ from endosperm that ;~
is achieved with conventional degerminating machines is lacking
somewhat and this incompleteness of the degermination causes
many of the problems that are encountered in the overall
milling prvcess~. In` the Beall degerminator, which lS used
extensively in the United States, the grain kernels are rubbed
more against one another`than against the metal of the
machine. As a consequence~ even though relatively good
separation of the germ is achieved, a large~ quantity of fines
is generated and~the fines are high in fat content since they
contain much germ. `~
Impact type degerminators are used for specific
purp~es such a~ where finished products having high fat
content are acceptable (table meal) and where smaller
~ granulation of the finished products is involved (no large
; grits). The impact degerminators that have been used in the
past generate fewer fines than the Beall degerminator and
provide higher yields o~ recovered oil; however, the separation
of the germ ~hat is achieved with impact machines is poor and
for this reason they have not ~een widely used. All
-2-
~: :
;~
degerminators that have been proposed or used in the past breakthe germ and the quality of the product is thus reduced in
comparison to products in which the germ is in a whole
condition.
It is a primary object of the present invention to
provide a method of milling grain whlch completes the milling ;;
process in a minimum number of steps and is therefore more
economical than processes employing gradual differential ~;
grinding techniques~
As a corollary to the above object, a further
objective of the invention is to provide a method oE milling
grain wherein the fines resulting from the degermination need
; not be removed in an éxtra separate step as is required in
conventional processes. The f~ines from the degerminator are
normally left in the stock and removed after milling together
with the later germinated finesl thus eliminating the necessity
for remo~ing the degerminator fines as an added step. ~ ;
It is~also an~important;aim of this invention to
provide a mil~ing process for grain which allows the use of
~impact deinfestatlon machines on rélatively brittle grain such
as corn thereby eliminating the need for a water wash or
; gravity table cleaning and providing Eor substantial economic
savings in the equipment utilized in carrying out the cleaning
; operation.
A further aim of the invention is to provide a
milling process for corn which accomplishes more effective
separation of the black germ tip from the endosperm as a result
of reduced grinding of the whole kernel grain and thereby
results in a reduced ~uantity of "black spe~ks" in the end `
product making i of~higher grade and making it more desirable
for cereal grits and meal.
Yet another object of the invention is to provide a
-3~ ~
, . : ;;. ; ~ . .. , :,:
Z~
milling process for coxn wherein the need for tempering the
grain is eliminated in some situations and cut down in other
situations. Accordingly, the expense and delay associated with
drying the grain is avoided or reduced appreciably.
In conjunction with the preceding object, it is still
another object of the invention to provide a milling process in
which only a portion of the grain is tempered, such as the
bran, so that only a portion of the grain needs to be dried.
An additional object of the invention is to provide
an improved method and apparatus for degerminating grain
wherein a high degree of separation of the germ is achieved
without the germ being broken.
A still further object of the invention is to provide
a method and apparatus for degerminating grain wherein the
grain kernels are crushed from the thin edges toward the center
in a manner to pop the germ component out of the kernel in a
substantially whole condition.
Yet another object of the invention is to provide a
degerminating apparatus of the character described which
assures that crushing forces are applied only to the thin edges
and not to the relatively large side surfaces.
There are numerous other advantages and objects of
the present invention which will be discussed or hecome
apparent from a reading of the following specification and
claims~ !
The invention encompasses a method of degerminating a
kernel of grain such as corn having relatively large side
surfaces and relatively thin side edges. The method comprises
subjecting the kernel to a compressive crushing force applied
substantially simultaneously to two opposed side edges in a
direction generally toward the center of the kernel while
avoiding the application of any crushing forces to the side
~3 , ' ,~,, ",.
~ ` ~
:` :
surfaces. The crushing force applied to the side edges is of
suf~icient magnitude to fracture the endosperm portion of the
kernel while maintaining the germ portion in a substantially
whole condition. An optional step in the proeess is to
initially temper the grain prior to subjecting the kernels to
compressive crushing force with the tempering taking place a
suffieient length of time for moisture to penetrate and loosen
the bran but without substantially penetrating the endosperm
and the germ.
In the accompanying drawinys which form a pa~t of the
specification and are to be read in conjunction therewith and
in which like reference numerals are used to indieate like
parts of the various views:
Fig. 1 is a top plan view showing one of the
eorrugated dise members lneluded in a degerminator machine
aonstructed according to a first embodiment of the present
`:
- -4a-
B
z~
inventionr with the broken lines indicating that the
corrugations extend along the entire surface of the disc;
Fig. 2 is a fragmentary sectional view on an enlarged
scale taken generally along line 2-2 o~ Fig. 1 in the direction
of the arrows, with corn kernels shown in broken lines;
Fig. 3 iS a side elevational view, partially in
section, showing a degerminator machine constructed accordinq
to a second embodiment of the invention;
Fig. 4 is a sectional view taken generally along line
4-4 of Fig. 3 in the direction of the arrows;
Fig~ 5 is a diagrammatic flow sheet of~a conventional
milling process of the type commonly employéd in the prior art;
Fig. 6 is a diagrammatic flow sheet of a milling
process carried out according to one embodiment of the present
inventlon; --
Fig. 7 is a diagrammatic flow sheet of a modified
milling process carried out according to the present invention;
Fig, 8 is a diagrammatic flow sheet of another
modified milling process of the present invention;
Fig. 9 is a diagrammatic flow~sheet of still another
~ modified milling process of the present invention;
.:
Fig. lO is a side elevational~ view the grain kernel
shown in Fig, 2; and
Fig. 11 is a top plan view of the kernel shown in
Fig, 10~
Referring initially to Fig. 5 which depicts the
'
conventional milling process described briefly above~ it is to
- be emphasized that the illustration of Fig. 5 forms no part of
the present invention and is included herein merely for
30 ~ purposes of comparison to allow for a more complete
understanding of the present invention, In the interest of
`brevity, the process shown in Fig~ 5 will not be described in
- ~5-
:, :
~4~
intricate detail as a complete understanding will be readily
apparent to anyone skilled in the art. Briefly, however~
referring to Fig. 5, it is seen that corn is first introduced
to a cleaning station wherein foreign materials such as stones~
sticks, sand and foreign seeds are removed. The grain is then
subjected to a water wash for removal of dirt and other foreign
materials. Next, a tempering step is utilized to condition the
.:
grain for the subsequent grinding operations. The tempering
procedure allows the whole kernel grain to absorb moisture and
10 thereby magnifies the different grinding characteristics of the ;-
:
grain components. Since;moisture is absorbed primarily through
the germ tip of the grain, the tempering procedure normally ~;
lasts~for about one and up to~several hours depending upon the
end product desired and ~the age and moisture content of the
grain being processed. Tempering is achieved in a single or
several s~teps over given time periods using simple water
absorp~ion or a combination of water and heat as hot water or
r
steam
The tempering process~results in a relatively highly
20 ~absorptive germ and bran becoming tough and pliable as these
components take on waterO On the other hand~ the endosperm,
~which absorbs moisture much more slowly, will remain relatively ~;~
. 1 . ~ , ,
unchanged although somewhat less brittle. This procedure also
.~ '
helps to commence parting of the endosperm from the germ and`~
bran components.
,: ~
~The next step in the convention process is to pass
- the tempered grain to a degerminator which breaks the whole
kernel grain in;a manner to achieve initial separation of germ,
:~:
bran and endosperm. By far the most widely used type of
30 degerminator is the Beall degerminator which is well known to ;
those in the trade and which generally requires tempering of
the grain to a moisture level of from 19% to 25%, depending on
~ -6
: . '
,:,
. . .
the degree of degermination and debranning sought. Also used
at times is an impact type degermina-tor which generates less
fines although the degree of yerm separation is reduced in
comparison to the Beall machine~ In any case, the design of
the degerminator is such that the germ is intended to be broken
out from the endosperm to the extent possihle without
excessively grinding the germ component. Consideration is
given to bran removal in this step depending on the final use
of the end product. The goal o~ the degerminator, namely to
remove the germ without grinding it undulyr is not actually
reached with existing degerminators r and an additional problem
is that low q~lality fines are produced which must be removed
prior to further processin~ of the stock.
. .
Generally the product~out of the degerminator is
separated into "tail" and "thru" streams, the former being
relatively rich in endosperm and the latter being relatively
rich in germ and bran. The two streams are then dried and
cooled to reduce the moisture~content to approximately 17%.
Prior to commencing the grinding steps~ the two degerminator
streàms are preferably placed on gravity tables (or aspirators)
~- as indicated in the flow diagram to achieve some further
initial sorting out of germ and endosperm.
~- The roll grinders in the conventional milling process
are set up in two series as indicated in the drawing. One
series is for the endosperm rich streams and the other series
is for the germ rich streams. In the drawing t the various sets
of roller mills are indicated dlagrammatically and given the
conventional designation of break ("brk"~ rollers and germ
rollers.
The concept utili~ed in each series of rvller mills
in the conventional milling process is to match partlcle size
with individual roller mill characteristics. Thus, relatively
-7~ ;
large particles from the gravity tables (or aspirators) are
directed to the first break and germ rollers respectively,
according to particle size classification. These first rollers
are characterized by relatively large corrugations with
"
inherent coarse grinding characteristics. The smaller
particles from the gravity tables are directed according to the
` successively flner series of~rollers. For example, the stock
` going to the number one break roll may~be that passing through
a sieve with 31/2 wires per~inch and over one with 5 wires per
13 inch.~ The roller corrugRtion used for this stock is 6 per
nch. ~Next, stock passing through~a~5 wires per inch mesh but -
passing over one with 8 per inch is~pas~sed to~a break roll with
8 corrugations per inch of roll circum~erence. The procedure
, ~ .
-~ is continued;up to rolls with 20-24 corrugations per inch.
~; In general, rollers grinding the streams rich in
endosperm have a higher roll speed differential than those
~; ~ , . . ..
grin-ding~the~;germ rich streams, the reason being that~the
;relatlvely~fraqile~gsrm requlres the gentler treatment afforded
by a lower~roll speed differential. This is the reason that
two series of roller mills are employed.
Because of the cliffe~rent grinding characteristics of
the components,~as dlscussed above, the ro~ller mills in each
~series~will proceed to reduce the~ size of the endosperm
~relatlve to thè size of th yerm and bran. The mill stock that
does not meet final product specification (exceptin~ moisture)
is continuously reclassified by size, aspirated to remove~bran,
and ~hen passed to the next roll~r mill which is set up to
receive the stock according to its primary component and
~;particle size. The procsss is repeated over and over until the
3Q desired separating and s~rtin~ is accomplished.
The final steps~in the conventional milling process
are to dry the milled grain to~a maximum moisture content of
" .
,
:
.. , .. . .. . ~ . . ..... . . . . . . .
approximately 12% or to marketing and end use specifications, cooL
it, and aspirate off any remaining bran. The end procluct is then
graded according to size into various component products.
With a view to understanding the present invention,
reference is first of all made to Figs. 10 and 11 where it is seen
that a corn kernel is designated by the numeral 20 and has a germ ~;
portion 20a that is surrounded by an endosperm portion 20b. Fig. 11
shows in full one of the relatively large flat side surfaces of the
kernel which has been designated by the numeral 21. A second large
~` 10 flat side surface (not shown) is opposite and parallel surface 21.
The two side surfaces 21 are separated by relatively thin side
edges 23a~ 23b and 23c. Side edge 23a extends the length of the
kernel on opposite sides ~only one side being visible in Fig. 10).
The top side edge is designated 23b and the bottom side edge or tip
is designated 23c. Manifestly, the width of the side edges is equal
to the thickness of the grain kernel. ``
With reference now to Figs. 1 and 2, the present invention ~;
provides an improved degerminator 10 which is constructed to crush
the grain from its thin edges toward the center area of the kernel.
The compressive force accompanying this crushing action fractures the
endosperm under and around the germ to release it in a manner providing
approximately 95% separation from the endosperm while maintaining
the germ in a substantially whole condition.
The degerminator machine 10 includes a stationary upper
metal disc 12 and a lower disc 14 which is mounted on a vertical
shaft 16. The shaft may be driven by any type of drive system
~not shown) in order to rotate the lower disc 1~ relative to the
~ stationary upper disc 12. The discs are parallel to one another
- in horizontal planes, and their facing
,.
g
surfaces are spaced apart in a manner that will be more fully
explained~
The stationary upper disc 12 has a central opening 18
through which the grain is introduced to the area between the
discs. Each disc 12 and 14 is provided with a plurality of
radially extending corrugations l2a and 14a, respec~ively. The
corrugations 12a and 14a extend over the entire facing surfaces
of the disc5. As shown in Fig. 1, the corrugations are greater
... ,: :
in number on the outer portion of the discs than on the inner
portion~ to accommodate the larger surface areas of th~ outer
disc portions.
:
Referriny ~o Fig. 2 particularly, corrugations 12a
and 14a are inclined and are sized so that a corn kernel 20 in
an inclined orientation can fit with one of its thin side edges
23a in the groove of an upper corrugation 12a and with the
opposite side edge 23a of the kernel located ln khe groove of a
lower corrugation I4a (see the kernel in the right portion oE
Fig. 2). However, when the grooves of the corrugations are
located~directly above one another~ they are spaced apart a ~ ;
~distance less than the width~o kernel 20 between its opposite
side edges 23a. The respective peaks and valleys of each --
corrugation are rounded to avoid piercing the kernel at the
point of contactO The ridges of corrugations 12a and 14a are
-
vertically spaced apart a distance at least as great as the
thickness of kernel 20 between its relatively large opposite
side surfaces 21. Preferably, the pitch of each corrugation
12a and 14a is about 1/2 the width of the kernel (or slightly
longerl, and the depth of each~oorrugation is approximately
equal to the thickness of the kernelO The corrugations are
smoothly rounded on their ridges and~grooves to avoid
presenting sharp ed~es or corners that might cut the grain.
~ In operation, grain is introduced between discs 12
: -10-
, . . . ~ .; . . ~ . ., ":
Z ;~:
and 14 through opening 18, and shaft 16 is rotated to rotate disc
14 relative to disc 12 in the direction indicated by the directional
arrow in Fig. Z. When a kernel positioned between the discs is
oriented with its large flat sides 21 facing up and down (as shown
for the kernel in the left hand portion of Fig. 2), the kernel
passes freely between the ridges of corrugations 12a and 14a and
no crushing occurs. However, when the kernel is displaced in
any fashion from this orientation, the thin opposite side edges
23a or 23b and 23c of the kernel catch in the grooves of opposed ~`
corrugations 12a and 14a. This is the position of the kernel shown
in the right hand portion~of Fig. ~.
Continued motion of disc 14 relative to disc 12 subjects
the kernel caught between the corrugations to a compressive crushing
force that is applied from the thin opposite side edges of the
kernel toward the center. The magnitude of this crushing force is ;
sufficient to fracture the endosperm under and around the germ 20a
to thereby squeeze or pop the germ 20a out of the side of the kernel
` In a substantially whole, undamaged condition. The crushing action
terminates when the corrugations move past one another. Since
the released germ 2Qa is small enough to pass freely between the
ridges of the corrugatlons, it is not crushed and is carried out-
wardly by centrifugal force along with the fragments of the endosperm `
resulting from the crushing action. The fines resulting from the
degermination contain very little germ since the germ is maintained
whole.
The grain may be tempered prior to the degermination,
although tempering is not essential. The amount of whole and relatively
undamaged germ that is released and the ex~ent to which the germ
and endosperm are separated is a functlon of a number of factors,
including the moisture content of the germ,
B !, :, " . ,, ,, ~
$Z
the type and condition of the corn, the configuration of the
corrugations 12a and 14a, or combinations of these and other
factors.
Exemplifying the improved results obtained by the
degerminating method of this invention, it has been found that
midwestern hybrid cor~ of about 12% moisture and a~erage
condition and age yields approximately 85~ whole germ and
sIightly more than 95% separation of germ and endosperm.
Tempering the same type of corn to about 17% moisture content `~
for about 3 hours increases the yleld to about 95% whole germ
and about 97% complete separation of germ and endosperm. The
degerminator fines that will pass through a 16 mess screen vary
in quantity from a high of about 20% of the corn degerminated
to a low of about 10%~ and from a fat content of about 1% to
about`S%, depending on the tepmering process, the moisture
content of the germ and endosperm, the kind of corn, the
. . ~
condltion and age of the corn, the~relative speed of rotation
o~ discs~12 and 14, the spacing between the discs, the
con~iguration and arrangement of the corrugatlons, and the
Z0 condition of the disc surfaces.
Athough the degerminator machine 10 is similar in
construction to a conventional attritlon mill, its operational
characteriskics differ considerablyO The main difference is -
that the discs 12 and 14 are carefully space~d and the
corrugations are arranged to achieve only a crushing effect on
the kernel which is applied ~ from the opposite thin edges
inwardly toward the center, in contrast to the grinding and
cutting action of an attrition mill Since discs 12 and 14 are
spaced apart such that a kernel oriented with its flat sides
~ 30 paralIel to the planes of the discs passe~s freely between the
ridges of the corrugations, the machine avoids crushing the
kernels from the relatively large flat sides thereof, thus
12~
, , :
; ,: ~
~9LO;Z 2
assuring that the crushing occurs only at the thin edges in a manner
to squeeze the germ free of the endosperm.
Referring now to Figs. 3 and 4, a degerminator constructed
in accordance with a second embodiment of the invention is
generally designated by numeral 22. Degerminator 22 applies
a crushing force similar to that applied by degerminator 10,
although in the case of degerminator 22, the force is applied -from
only one of the thin edges of the kernel toward the center. ;
The degerminator 22 includes an upright wall 24 having
a generally cylindrical shape and surmounted by a frustoconical
roof portion 26. A vertical tube 28 extends through roof 26 and is ~ `~
hollow in order to receive and direct grain into the machine.
The lower end of tube 28 is open and is located centrally above a
horizontal disc 30. Disc 30 is rigidly mounted on top of a `~
::~
~- vertical shaft 32 which may be rotated by any suitable drive
:. :
system ~now shown~
A plurality of spaced apart guide vanes 34 are located
on the upper surface of disc 30. Each vane 34 extends outwardly
; along the disc from the tube 28 to the periphery of the disc.
Vanes 34 are curved members each having a sharply curving outer
: . :
end portion which approaches a tangent line at the edge of the
disc.
The inside surface of wall 24 is located outwardly of
~ the periphery of disc 30 a distance less than the thickness of a
- graln kernel. The inside surface of the wall is formad in a
manner to present a plurality of flat linear surfaces 24a against
which the corn kernels impact when propelled outwardly off of
disc 30. Each impact surface 24a is oriented such that a kernel
; propelled off of the periphery of disc 30 and moving in a direction -
generally tangent to the disc impacts against surface 24a at a right
angle. Surfaces 24b of wall 24 extend between each adjacent pair
of impact surfaces 24a to assist in directing the grain kernels
:
- 13
22
against surfaces 24a at substantially a right angle.
In operation, grain is introduced through the tube 28
and onto the upper surface of disc 30. The disc is rot~ted at
a rate of speed high enough to propel the grain outwardly thereon
by centrifugal force. As it moves outwardly, the grain is
guided along the curved leading surfaces of the guide vanes 34
until the grain is eventually propelled of:E of the edge of the
disc against the impact surfaces 24a.
The guide vanes are constructed to orient the grain
such that one of the thin top or bottom edges of each kernel impacts
against surface 24a, thereby applying a compressive crushin~ force
to the grain from the thin edge toward the center and not at
one of the relatively large side surfaces of the kernel. As
-. each kernel is prqpelled outwardly along vane 34, it may be oriented
'r`l either with one of its large flat sides against the vane or with
- one of its thin side edges against the vane. In either case, the
top or bottom edge of the kernel will be on its leading portion
in the direction of motion at the time it leaves the disc, by
virtue of the sharply curving shape of the outer portions of vanes
34. Consequently, the thin top or bottom edge of the kernel
impinges on surface 24a and a crushing force is thereby appIied
from the edge toward the center. In this manner, vanes 34 orient the ~-
~; kernel so that only thin edges engage surfaces 24a, and the crushing
~: force is not applied to the flat sides as would sometimes occur
with straight radial vanes.
The crushing force applied on the edge of the kernel
toward the center squeezes the germ out from the endosperm in a
,~ substantially whole condition. Due to the space between wall
24 and disc 30, only the fragments of broken kernels can pass
- 14 -
B :
, . , . . .................................. ~ .. ,
.. ~- . . ... , ~, . ,.. ;.. .. .... . .
~U~2
between the wall and the edge of the disc for further -~
processing. Unbroken kernels are too large to fall ~etween the
wall and disc and may be recirculated through the machine.
It is to be understood that various additional types
of machines may be employed to carry out the degerminating
method of this invention. However, the machines 10 and 22 are
preferred since they effectively apply crushing forces to the
side edges of the grain while avoiding the application of
crushing forces to the relatively large side surfaces~
In addition to the eLÇectiveness of the germ
separation, the process of this invention separates the bran
from the endosperm with excellent results. As the moisture
; content of the bran increases, its separation becomes more
complete. It has been found that if dry corn of about 14~
moisture is tempered for 4 to 8 minutes with addition of water
o about ~% to 8~ by weight of the corn, 90~ to 98~ of the bran
is removed by the degerminating process as a result of the
crushing forces applied to the corn. The degree of debranning
is af~ected by the kind and condition of the cornt the amount
~20 ~ of water and heat~added an~ the length of time held~, the speed
of the discs, and the con~iguration of corrugations 12a and 14a
or the~sh~ape~of vanes 34. Since on a practical level only the~
bran is tempere~d and not the remainder of the corn, drying is
`~ simpllfied because only the bran needs to be sorted out hy
screens and/or aspiration and sent to dryers. Conventional
methods of debranning require tempering of the germ also and/or
~` separate~equipment to perform this function. In carrying out
the method of the present invention, the power requirements are
about ~/2 HP per hour per ton oF corn, as compared with
requirements o~ conventional processes of from 15 to 25 HP per
hour per ton of corn for degerming and debranning.
Another important result obtained by the deger-
z~ .
minating process of this invention is the relatively highquality of the degerminator fines which, as pre~iously indi-
cate~, have a fat ~ontent of about l~ to 5%. In comparison,
the fines generated in conventional degerminating processes are
so high in fat that they are either sold às a low value
byproduct animal feed or are reprocessed to upgrade their
quality. Such reprocessing involves the use of sifters,
aspirators, gravity tables, purifiers or various combinations
of these and other costly devices. Upgrading the quali~y of
the fines with such devices allows the fines to move into
ndustrial uses or other markets where they yield a higher
price than animal feed but~a lower price~ than prime products
from the mill. In addition, separation of the fines from the
prime product is costly and time consuming. ~;
The present invention also~provides improved grain
milling processes~which are illustrated in flow sheet form in
; ~ Fig. ~6-9o The whole graln or a major part of~it may be ;~
te~mpered in some of the processes, although tempering is not
always~required if the preferred degerminating process des-
crlbed~above is used, due to the high degree of degerminatlon
~ and the high quality of the fines. The pa~rticular process that
; may be~employed to the best advantage in each set of
circumstances depends upon a variety of factors, including the
end products~deslred, the type and condition of the grain, and
economic considerations such as operating costs and marketing
objectives.
Referr~lng first to Pig. 6, the~process shown therein
involves cleaning of the corn followed by a prebreaking in a
prebreak mill. ~The prebreak mill~ may bè any suitable type that
breaks the grain by subjecti~g it to a crushing action that
breaks the endosperm while preferably~although not necessarily
maintaining a substantial amount of the germ in a whole
-16-
, ~
- . , ,. . . , ,~ . , ,, ,, :
'~ iZ
condition. The grain should be broken along the germ so the
germ is exposed. The crushing action showld fracture the grain
into at least four and preferably six or more major piecesO
The germ should be separated from the endosperm to as great an
extent as possible because the fat content of the finished
products is reduced as the degree of separation increases. The
actual degree of separation of the germ and the extent to which
the germ remains whole depend upon the particular prebreaking
process utilized and the end product desired.
Tempering of the grain may be carried out in advance
. ,
of the prebrea~ or after the prebreak, or both. Tempering ~ ~'
before the prebreak better controls the germ separation. For
example, corn having a moisture content of 15~ to 20% by weight
will, when broken, provide better release of the germ with a
.~
corresponding reduction in fines and at content than corn
having a moisture ccntent below about 15~A The tempering can
be carried out using known techniques.
~ ~Tempering after prebreaking may be carried out if the
`~ moisture content of the germ and bran was not adjusted by a
tempering s~ep prior tv~prebreak, or if additional moisture
adjustment is necessary or desired after prebreak~ The
molsture;content of the~germ and bran prior to passage of the
stock to the first roller mill should be about 15% to 35% by
weight. Tempering after prebreak results in an appreciable ;~
shortening of the tempering time because the prebreaking
exposes the germ and bran. Tempering can be as short as 2
minutes if heat is used and in no case will it exceed about 30
minutes when performed subsequent to prebreak~
Although a main advantage of the process of this
invention is that it avoids the need to remove fines prior to
milling, it may be desirable in some~instances to remove the
fines after prebreak and before milling in order to reduce the
-17-
water requirements for the tempering step. This can be done in
a sifter which sifts the ~tock after prebreak and before
tempering if tempering occurs only after prebreak. The fines
are then separated and returned to the stock after it has been
tempered and passed through the first set of break rolls if
this is desirable to simplify the flow.
The present invention departs frGm the technique of
the conventional grain milling p~ocess which, as previously -~
indicated, ~ttempts to match particle size with individual
roller mill characteristics. In the conventional gradual
reduction process, the particles are first passed through
roller mills having relatively large corrugations and then to
:: .:
successive additional roller mills having increasingly finer ~ ;
corrugations. It has heretofore been~thought that any atempt
to utilize rollers having fine corrugations at the front end of
the mill would result in smashing of the grain kernels which
would make ultimate separation of germr bran and endosperm
exceedlngly diff~cult.
Instead of passing the grain through a long
20 suacession of rollers as is done in the~conventlonal process,
grinding is accomplished in the present invention by ~assing
the broken grain directly to fine rollers of the type that
normally characterize only the end of a different~al milling
process.
In accordance with the invention r the prebreaking and `
tempering steps are effected, and the grain is then passed
through a first set of break rolls which rnay be of the modified
Dawson type hav~ng 20 carrugations per inch and a spiral of
about 1/2 inch per linear foot. The rollers are arranged dull to
dull and have a di~ferential roll speed o~ 2 to 1. The first
break roller mill is adjusted so that at least approximately
50% of the product through is small enough to pass through a U.
-18-
: ~ :
.. . ~. . .
S. #12 sieve. The spacing between the rollers is sufficient to
substantially prevent appreciable penetration of the roller
corrugations into the germ, thereby avoiding size reduction of
the germ in contrast to the conventional prac~ice of placing ~`;
fine rollers closer together in accordance with the fine
particles being processed. Those particles from the prebreak
mill, with the exception of the "finesl', are large enough so
that they are subjected to a grinding action when passed
between the rollers of the first break mill and those of the
second break mill.
Due to the fineness of the roller corrugations and ;~
~; their spacing, the endosperm is severely and abruptly ground up -
-~ and thereby separated from the germ and bran without resulting ~
in the germ being fractured excessivelyO The product from the ~ -
first break rolls, together with the fines if they have been
removed prior to temper, is sifted through a U. S. ~8 sieve and
a U. 5. #12 sieve. The relatively large size particles over
the #8 sieve are primarily germ and bran and may be directed to
feed or oil recovery or to further pr~ocessing as described
~20 below. The portion passing ~hrough the #12 screen is less than
1% in fat content, and it is therefore passed to finished pro-
` duct. Particles through the #8 screen but over the ~12 screen
; are principally endosperm, although there is enough germ
present that thi~ portion is not marketable as a prime
product. This portion is passed to a second set of break rolls
which effect further size reduction of the endosperm and which
further separate the endosperm from the germ and bran
components.
The rollers of the second break mill have
30 corrugations of the same size as the first set or slightly~;
smaller, and the spacing between the rolls is again sufflcient
to avoid excessive penetration of the germ. The differential
~- ~ ~19
,~
speed of the rollers in the second break mill may be reduced to
about 1, 75 to 1. After passing through the second set of break
rolls, the product is sifted through a ~14 wire. The particles
over the wire are rich in germ and bran and go to animal feed
or oil recovery. The stock passing through the wire is rich in
endosperm and goes to finished product along with the endosperm ~ !
rich stock from the first break mill~ The endosperm rich
stream is dried and cooled if necessary and is finally passed
to a grading station where grits and meal are graded according
l~ to a size and~any remaining bran is removed by aspiration.
The free germ may be removed prior to the first break
rolls by utilizing gravity tables. This optional~step lowèrs ~ ;~
the fat content of the throughs from the sifter wires, and it
aids in making the milling process superior to conventional
processes both ln quality and product yield.
~- Although the specific operating parameters for the
process depend upon the age of the gra~in, its moisture content
~and~grade, and the end products desired, it has been ound, by
way ~ X~ample, that U.~S. grade #2 corn having a moisture
content~o~ 13~ yi21ds~approximately 62% brewer's grits on a U.
S~. #30 si~i7e at~ maximum oil, 8% meal through a U~ S. #30
sleve~at;~le~ss~hàn~1~.5% ol1, 3% flour through a U. S. #80 sieve
at about~2~maximum oll, and a brewer's extract on the grits of
~80~5% a~ is basic and prescribed by the American Association of
~Brewing Chemist Methods. The total prime product yield is
73%. In comparison, a typical yield of equal quality products
from the conventlonal proceed of Fig. 5 1s 47~ brewer's grits,
9% meal and S~ flour. The total prime product yield is 63~ in
the conventional process. In addition to providlng a higher
yield~in the more valuable brewer's ~rits, the process of this
invention yields a cereal grit and flour product oE higher
quality because of a reduction in "black specks"l This is
` ~ ''
attributahle to the reduced grinding which leaves most of the
germ tip (black speck) attached to the bran or germ, although
the extent to which this occurs decreases with a diminishing of
the tempering.
Fig. 7 illustrates a modified grain milling process
which involYes no tempering and has the objective of producing
a maximum amount of brewer's grits. After the corn is cleaned,
it is degerminated by subjecting it to the preferred ~ -
degermination process described previously. The grain is /~
L0 thereby crushed from its thin edges toward the center to
~achieve a high degree of separation o~ the germ from the
endosperm while maintaining bhe germ in a substantially whole
condition.
The degerminator-stock is~passed to a degerminator
s~ which gradbs it into four streams containing particles
of different sizes. A~ first stream consists of relatively
large particles of whole corn or incomplete~ly degerminated
piec~G o~qorn. It may not be necessary to separate ou~t tnis `~
first str~am or fraction, depénding~ on~the scalp sieve size,
~20 ~h~ germlnatoL setting, the condition of the corn, and/or the
~; vbject of t~e milling operation. ~The first stream is recycled
OL' ~passed aq~in through the degerminator.
The bulk of the degerminator stock is the second
coarsest fraction which contains bran, the whole germ and the
-~ ~ larger broken germ parti~1es, as well as the pieces of broken
endosperm passing over the second sieve. ~ Depending upon a
variety of factors, the second sieve can be from 5 to 9 mesh.
The second fraction is passed to gravity table ~l where the
germ and bran are sorted from the ~ndosperm and directed to
::
feed or oil recovery, If large ~quantities of corn are being
processed so that sheer volume requires the use of a number of
gravity tables, more efficient gravity table operation can be
-21~
;~ ' '
.
- - -
obtained by closer sixing of stream #2 into several streams
and/or employing aspiration prior to passing the streams to the
gravity tables. This will upgrade the flnished product in both
quality and quantity.
The third fraction in ludes broken germ, endosperm
and bran normally making up between 5~ and 25% of the total
weight of the corn. This stream goes to gravity table ~2 which
sorts the germ and bran from the endosperm and directs them to
animal feed or an oil recovery system. The endosperm is
10 combined with ~he endosperm rich stream from gravity table ~1
and passed to break rolls having fine corrugations that may be i
identical with those of the first break roll mill described in
.:
.J~'; connection with the process of Fig. 6. The stock from the
.,~ .
break rolls is combined with the fourth and finest fraction
from the degerminator sifter. ;
In a irits grade sifter,~most of the germ and bran
stiIl remaining in stock are scalped off and directed to feed
or oil recovery. The scalp sieve is about 10 to 16 mesh,
depending upon the mesh of the sleve for the Eourth fraction
20~ ~from the degerminator sifter. The grits grade sifter size
classlfles the rema~lnder of the roller mill stock which is
aspirated conventionally.
- It has been found that with U.S~ Grade #2 corn having
a moisture content of 13%, the process of Fig. 7 yields about
57% brewer's grits over a U.S. #30 sieve with a fat content of
1% or less, about 9% meal through a V.S. ~30 sieve and over a ;~
U.S. #80 sieve~wlth 1 5% fat or less, and about 5% flour
through a ~80 sieve at 2.~5% maximum fat and a low at less than
1% The prime product yield-is about 71% of the t~tal weight
30 of the cleaned corn, as compared to about 63~ for the ;~
conventional milling process.
Referring now to Fig~ &, the milling process shown
-22
:~ :
~u~z
therein employs tempering and the preferred degerminating
method described above. The object of the process is to
produce a maximum yield of brewerls grits. The proce~s of Fig.
8 is similar to that of Fig. 7, the main difference being that
only one gravity table is needed and optional tempering of all
or part of the grain may be carried out.
If a particularly high quantity of whole germ is
desired from the degerminator or if a small amount of fines and
low fat is sought, the grain is tempered after being cleaned
10 and beore degermination. Tempeling at this point produces
high yields and oil quality as compared to the process of Fig.
7~ However, the moisture added penetrates deeply into all
parts of the corn so that relatlvely long and e~tensive drying
is required. A small amount of tempering is particularly
beneficial if the moisture of the corn is low because in this
case the deg~rmination is enhanced appreciably due to the
tempering step.
~;~ ; Degermination is ef~ected by the preferred
degerminating method described above, and the degerminator
gtock 1s fed to a degerminator sifter which provides four
fractions as in the process of Fig. 7. However, instead of
directing fraction ~3 to a gravity table, it is tempered, if
there was no tempering previously, to bring its germ moisture
content~1h the range of abou~ 15% to; 35%.
After tempering of the #3 fraction, it is combined
ith the endosperm rich grit stream from the gravity table of
fraction #2, and the combined streams are then sent to fine
break rolls which may be identical with those employed in the
; process of Fig. 7~ The stream from the roller mill may be
33 passed directly to the grits grader sifter or to a drying
station and a cooling station if necessary due to marketing or
end use objectives. If the grain was~tempered before
23-
j degermination, the ~ine fraction #4 is combined with the roller
mill stock before drying and cooling. The fine fraction ~4
from the degerminator sifter can bypass the drying and cooling
stations in a situation where only fraction #3 was tempered~
since fraction #4 need not be dried in this case~ Fraction #4
is then combined with the roller mill stock after drying and
cooling. The grits grader sifter and aspiration operations are
carried out in the same manler as in the process of Fig. 7.
Minimal tempering yields results similar to and
usually somewhat be~ter than are obtained with the process of
Fig. 7. More complete tempering gives results better than
those of the process of Fig. 6, with ylelds of prime products
running as high as 75~ of the cleaned corn.
Fig, 9 illustrates still another milling process in
which the degermination process of the invention is used to
debran as well as to de~erminate. This process is used
primarily to produce extra coarse grits such as those used to
make cereal cornflakes in the breakfast food industry, If the
~ ~ ob]ective~of the process is to maximlze grit size, impact
-` 20 deinfestation is not used to advantage in the corn cleaning
operation because the broken corn that results from impact
deinfestatlon is not debranned~easlly and the yield of larger
grits is reduced accordingly.
~ After the corn is cleaned, it~is tempered using ~;
water, hot waterl and/or steam~and is held long enough for the
moisture to penetrate and loosen the~bran. Unlike the
conventional debranning processes which re~uire tempering of
. :
~; the entire kernel, only the bran is tempered and the tempering
time is reduced appreciably as a result. After tempering, the
~ ~,: . : . .
grain is degerminated by the preferred method of degermination
described previously, resulting in the germ being separated
from the endospe~rm and the endosperm being crushed out of the
2~
pliable tempered bran.
The degerminator stock is sifted by the degerminator
sifter wherein the top or coarsest frac~tion is scalped off and
passed through an aspirator to remove the bran~ ~he bran that
is removed may be sent to a dryer if necessary before it is
directed to animal feed or to another use. Undeg~rminated corn
or large particles that need to be degermed and/or debranned
are recycled from the aspirator back to the degerminator.
The remaining fractions from the degerminator sifter
are separated according to size and aGcording to market and/or
:
use objectives~and efficient gravity table operation. These~
fractions are sent to gravity tables which~ may be precede~ by
aspirators depending upon ~the desired efficiency of the gravity
tables for separating the grain for drying or other reasons.
The aspirating, sifting and gravity table operations are
carried out conventionally. It has been found that for `~
part1cuIarly efficient bran removal, most of the bran is
;scalped off in~the~recycle fraction from the degerminator
ifter.
2G ~ ~ The process of Fig~ 9 efficiently and economically
produces extra large grits meeting the marketing specifications
of fat and bran content. The fraction of extra large g~its not
used as grits can be reduced in size for brewer's grits and/or
meal and added to the products o the degerminating process.
In each of the proc~esses of the present invention,
the fines from the degerminator are relatively low in fat ~ ;
content since the germ is maintained in a substantially whole
conditlon~ Accordingly, the~fines are high enough in quality
that they can remain in the prime product stock and need not be
separated out and sent to feed~as is necessary in the
conventional milling process. It is also apparent that fewer
:
steps are required in the milling process of this invention as
-25-
:~ :
zz l
a result primarily of the high degree of degermination and
debranning that is achieved in the degermination process n
- The processes illustrated in Figs~ 6-9 can be
; combined to produce virtually all dry corn milled products with
~ a maximum of flexibility and economy. In addition, in ~-
'~ situations where the desired product is cornmeal haviny a fat
level of about 1.2% to 1.5%, even higher yields than those with
lower fat products can be achieved by using size reduction
equipment to break down the grits.
,
;~ 10 By virtue of the reduced number of steps requird, the
process of this invention permits the overall size of the mill
to be reduced substantially. Also, the reduction in the amount
of equipment~provides considerable economy and decreases the
maintenance and~repair requirements. Since the process stock
doe~ not need to be sifted repeatedly as is necessary in the
conventional gradual reduction method of milling, only a
relatively small amount of sifter cloth is required. Fewer
,
~`~ roller mills are neededr and the reduced length of the flow
-~ path correspondingly reduces the need for conveying
equipment. Further economic benefits result from the reduced
power requirements and the decreased need for heatin~, cooling
and drying equipment~ The simplicity of the processes has the
added benefit of reducing the level of skill and training
necessary to operate a mill in which the pocesses are carried
out.
While the processes have been described with
particular reference to corn milling, they find application
also in connection with other grains such as wheat and grain
sorghum. Manifestly, with a much smaller sized grain such as
mllol rollers having finer corrugations are utilized to achieve
the desired separation of components in a minimum number of
steps.
~26-
,
The processes of this invention may find application
for "clean up" of a stream of broken grain in a conventional
milling process. It should also be apparent in connection wîth
~- the process of Fig. 6 that more than one or two breaks may be
- made in the prebreak mill and thak higher yields or higher
r~ quality products may be obtained by using three or more breaks
depending upon the results desired and-the nature of the grain.
` By virtue of the economic benefiks obtained by using
the milling processes of the present invention, dry milling
` 10 techniques may be extended into areas that have heretoEore been
thought to be economically impractical. -For example, since
yields of prime products over 70~%~are obta1ned with fat content
; a~ low as .4~, it is practical to apply the dry milling
processes to replace the long, extensive steeping step employed
in the wet milling of corn, thereby shortening the process and
cutting costs. Another economic advantage of the present
inventlon is the high rate~of qerm recovery which results in a
~higher oil yield per bushel of corn than is obtained with
;~ conventional dry milling processes~ ~
~ ~ From the foregoing, it wi31 be seen that this
invention is one well adapted to attain all the ends and
objects hereinabove set orth together with other advantages
which are obvioas and which are inherent to the structure.
~ It will be~understood that certain features and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. This is
con~emplated by and is within the scope of the claims.
Since many possible embodiments may be made of the
invention without departing ~rom the scope thereof, it is to be
understood that all matter herein set forth or shown in the
accompanying drawings is to be interpreted as illustrative and
not in a limiting sense.
-27
"~
: .
