Note: Descriptions are shown in the official language in which they were submitted.
1133;~53
GRAIN MILL,I~G AND DEGERMINATION
PROCESS A~D EQUIPMENT FOR SAME
~ his invention relates to grain ~illing 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 degerminating grain such as corn.
Conventional milling techniques utilize a gradual
reduction process wherein successive differential grinding and
shifting separates the basic components of the whole kernel
grain, namely bran, endosperm and germ. The grain is first
cleaned with care being taken to maintain the grain intact.
With relatively tough grains such as wheat, impact
deinfestation may be utilized under proper conditions without
the danger of cracking the grain. With most brittle grains
such 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 tempering wherein water absorption magnifies the
differences in grinding characteristics of the grain
components. Finally, the gradual reduction process subjects
the grain to multiple grinding 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 5Q to 60 separate steps before the end products are
reached.
3. s 5 3
~ n ad(~ition to the expense of 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. Again, 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 process. In the Beall degerminator, which is 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
purposes such as 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 of recovered oil; however, the separation
of the gerrn that is achieved with impact machines is poor and
for this reason they have not been widely used. All
3~53
degerminators that have been proposed or used in the past break
the 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 which 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 of milling
grain wherein the fines resulting from the degermination need
not be removed in an extra separate step as is required in
conventional processes. The fines from the degerminator are
normally left in the stock and removed after milling together
with the later germinated fines, thus eliminating the necessity
for removing the degerminator fines as an added step.
It is also an important aim of this invention to
provide a milling process for grain which allows the use of
impact deinfestation machines on relatively brittle grain such
as corn thereby eliminating the need for a water wash or
gravity table cleaning and providing for 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 quantity of "black specks" in the end
product making it of higher grade and making it more desirable
for cereal grits and meal.
Yet another object of the invention is to provide a
milling process for corn 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.
~ n 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 become
apparent from a reading of the following specification and
claims:
The invention encompasses a milling process for grain
kernels which includes the steps of fracturing the grain
kernels into a plurality of relatively large particles and then
grinding the endosperm portion of each fractured particle while
substantially avoiding grinding of the germ thereby effecting
separation of the endosperm from the germ without substantial
size reduction of the germ. The ground particles are then
il~3,~53
separated within a preselected size range and the separated
particles are subjected to a grinding action applied in a
manner to grind the endosperm while substantially avoiding
grinding of the germ thereby effecting size reduction of the
endosperm without substantilaly reducing the size of the
germ. Finally, the ground particles are sorted into a portion
rich in endosperm and a portion rich in germ and bran.
The invention also encompasses a machine for
degerminating a kernel of grain such as corn having relatively
large side surfaces and relatively thin side and end edges.
The machine comprises a pair of disc members and means mounting
the disc members for relative rotation with facing surfaces
thereof oriented generally parallel to one another. Also
included is means providing a plurality of corrugations in the
facing surfaces of the disc members with the groove areas of
opposed corrugations in the disc members being spaced apart a
distance less than the width dimension of the kernel between
the opposite side edges thereof. There is also means for
effecting relative rotation of the disc members so that when a
kernel is inserted between the disc members and caught between
opposed corrugations, it is subjected to compressive crushing
forces applied to the side edges which fracture the endosperm
portion of the kernel away from the germ portion.
In another embodiment, the invention encompasses a
machine for degerminating a kernel of grain such as corn having
relatively large side surfaces and relatively thin side
edges. The machine comprises a frame, a disc member supported
on the frame in a generally horizontal orientation for rotation
about a substantially vertical axis, and a plurality of guide
vanes on the upper surface of the disc member for guiding the
kernel generally outwardly thereon. An impact surface is
supported on the frame at a location outwardly of the vane and
~3~ 3
means is provided for rotating the disc member about its axis
at a speed sufficient to centrifugally propel a kernel disposed
on the disc member outwardly along one of the guide vanes and
against the impact surface. There is also means for orien~ing
the kernel such that one of its thin side edges impacts against
the impact surface whereby a compressive crushing force is
applied to the kernel from one edge toward the center to
fracture the endosperm portion away from the germ portion.
In the accompanying drawings which form a part of the
specification and are to be read in conjunction therewith and
in which like reference numerals are used to indicate like
parts of the various views:
Fig. 1 is a top plan view showing one of the
corrugated disc members included in a degerminator machine
constructed according to a first embodiment of the present
invention, 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 of 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 according
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 employed in the prior art;
Fig. 6 is a diagrammatic flow sheet of a milling
process carried out according to one embodiment of the present
invention;
Fig. 7 is a diagrammatic flow sheet of a modified
milling process carried out according to the present invention;
1~33~3
Fig. ~ is a diagrammatic flow sheet of another
modified rnilling process of the present invention,
Fig. 9 is a diagrammatic flow sheet o~ 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
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
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
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 steps over given time periods using simple water
absorption or a combination of water and heat as hot water or
S3
steam.
The ternperiny process results in a relatively highly
absorptive germ and bran becoming tough and pliable as these
components take on water. On the other hand, the endosperm,
which absorbs moisture much more slowly, will remain relatively
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
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
the degree of degermination and debranning sought. Also used
at times is an impact type degerminator which generates less
fines although the degree of germ 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 possible 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 of the degerminator, namely to
remove the germ without grinding it unduly, is not actually
reached with existing degerminators, and an additional problem
is that low quality fines are produced which must be removed
prior to further processing of the stock.
Generally the produc-t 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
streams are preferably placed on gravity tables (or aspirators~
as indicated in the flow diagram to achieve sorne 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, the various sets
of roller mills are indicated diagrammatically and given the
conventional designation of break ("brk") rollers and germ
rollers.
The concept utilized in each series of roller mills
in the conventional milling process is to match particle size
with individual roller mill characteristics. Thus, relatively
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 finer 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
inch. The roller corrugation used for this stock is 6 per
inch. Next, stock passing through a ~ wires per inch mesh but
passing over one with 8 per inch is passed to a break roll with
8 corrugations per inch of roll circumference. 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
grinding the germ rich streams, the reason being that the
~3~ 3
relatively fragile germ requires the gentler treatment afforded
~y a lower roll speed differential. This is the reason that
two series of roller mills are employed.
Because of the different grinding characteristics of
the components, as discussed above, the roller mills in each
series will proceed to reduce the size of the endosperm
relative to the size of the germ and bran. The mill stock that
does not meet final product specification (excepting moisture)
is continuously reclassified by size, aspirated to remove bran,
and then passed to the next roller mill which is set up to
receive the stock according to its primary component and
particle size. The process is repeated over and over until the
desired separating and sorting 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 product
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 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
11;3335~
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 14
realtive to the stationary upper disc 12. The discs are
parallel to one another in horizontal planes, and their facing
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 12a and 14a, respectively. The
corrugations 12a and 14a extend over the entire facing surfaces
of the discs. As shown in Fig. 1, the corrugations are greater
in number on the outer portion of the discs than on the inner
portions to accommodate the larger surface areas of the outer
disc portions.
Referring to 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 in the groove of a
lower corrugation 14a (see the kernel in the right portion of
11
1 IL3~;~53
E`iq. 2). Ilowever, when the grc)oves of the corruga-tiorls are
located ~irec-~ly above o~e another, they ~re spaced apart a
distance less than t~e width of 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 contact. 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
10 12a and 14a is about 1/2the width of the kernel (or sliyhtly
longer), and the depth of each corrugation is approximately
equal to the thickness of the kernel. The corrugations are
smoothly rounded on their ridges and grooves to avoid
presenting sharp edges or corners that might cut the grain.
In operation, grain is introduced between discs 12
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. 2. 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. Elowever, 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. 2.
~ ontinued motion of disc 14 relative to disc 12
subjects the kernel caught between the corrugations to a
¦ 30 compressive crushing force that is applied from the thin
- opposite side edges of ~he kernel toward -the center. The
magnitude of this crushing force is sufficient to fracture the
12
11~33;~3
endosperm under and arouncl the germ 20a to thereby squeeze or
pop t~e germ 20a out of ~he 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 20a is small enough to pass freely between
the ridges of the corrugations, it is not crushed and is
carried outwardly 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 undamayed germ that is released and the extent to
which the germ and endosperm are separated is a function of a
number of factors, including the moisture content of the germ,
the type and condition of the corn, the configuration of the
corrugations 12a and 14a, or combinations of these and other
factors.
~ xemplifying the improved results obtained by the
degerminating method of this invention, it has been found that
midwestern hybrid corn of about 12~ moisture and average
condition and age yields approximately 85% whole ~erm and
slightly 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 yield 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 5~, depending on the tepmering process, the moisture
content of the germ and endosperm, the kind of corn, the
condition and age of the corn, the relative speed of rotation
13
1~33;~53
of discs 12 and 14, the spacing between the discs, the
configuration and arrangement of the corrugations, and the
condition of ~he disc surfaces.
Athough the degerminator machine 10 is similar in
construction to a conventional attrition mill, its operational
characteristics differ considerably. The main difference is
that the discs 12 and 14 are carefully spaced and the
corrugations are arranged to achieve only a crushing effect on
the kernel which is applied only 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
parallel to the planes of the discs passes freely between the
ridges of the corrugations, the machine avoids crushing the
kernels from the relatively large flat sides thereof, thus
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
2Q 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. ~ 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 (not shown).
14
113~33S3
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 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 grain kernel. The inside surface of the wall is formed 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 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 rotated 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 off 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
crushing force to the grain from the thin edge toward the
center and not at one of the relatively large side surfaces of
the kernel. ~s each kernel is propelled outwardly along vane
34, it may be oriented either with one of its large flat sides
il333~i3
against the vane or with one of its thin side edges against the
vane. In eithe~ case, the top or bottom edge of the kernel
will be on its leading portion in ~he 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, thè
thin top or bottom edge of the kernel impinges on surface 24a
and a crushing force is thereby applied 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
between the wall and the edge of the disc for further
processing. Unbroken kernels are too large to fall between 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 effectiveness 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
of about 2% to 8% by weight of the corn, 90% to 98% of the bran
is removed by the degerminating process as a result of the
16
11;~3353
crushing forces applied to the corn. The de~ree of debranning
is affected by the ki~d and condition of the corn, the amount
of water and heat added and the length of time held, the speed
of the discs, and the configuration of corrugations 12a and 14a
or the shape of vanes 34. Since on a practical level only the
bran is tempered and not the remainder of the corn, drying is
simplified because only the bran needs to be sorted out by
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 of 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-
minating process of this invention is the relatively high
quality of the degerminator fines which, as previously indi-
cated, have a fat content of about 1% to 5%. In comparison,
the fines generated in conventional degerminating processes are
so high in fat that they are either sold as 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 quality of
the fines with such devices allows the fines to move into
industrial 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. 6-9. The whole grain or a major part of it may be
17
11;~33~3
tempered in some of the processes, although tempering is not
always required if the preferred degerminating process des-
cribed above i5 used, due to the high degree of degermination
and the high quality of the fines. The particular process that
may be employed to the best advantage in each set of
circumstances depends upon a variety of factors, including the
end products desired, the type and condition of the grain, and
economic considerations such as operating costs and marketing
objectives.
Referring first to Fig. 6, the process shown therein
involves cleaning of the corn followed by a prebreaking in a
prebreak mill. The prebreak mill may be any suitable type that
breaks the grain by subjecting it to a crushing action that
breaks the endosperm while preferably although not necessarily
maintaining a substantial amount of the germ in a whole
condition. The grain should be broken along the germ so the
germ is exposed. The crushing action should fracture the grain
into at least four and preferably six or more major pieces.
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 prebreak 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 fat content than corn
having a moisture content below about ]5~. The tempering can
be carried out using known techniques.
18
1~3~
Tempering after prebreaking may be carried out if the
moi~ture content of the germ and bran was not adjusted by a
tempering step prior to prebreak, or if additional moisture
adjustment is necessary or desired after prebreak. The
moisture 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
water requirements for the tempering step. This can be done in
a sifter which sifts the stock 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 i5 desirable to simplify the flow.
The present invention departs from the technique of
the conventional grain milling process which, as previously
indicated, attempts 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 germ, bran and endosperm
19
11;~3~.~5;~
exceedingly difficult.
Instead of passing the grain through a long
succession of rollers as is done in the conventional process,
grinding is accomplished in the present invention by passing
the broken grain directly to fine rollers of the type that
normally characterize only the end of a differential milling
process.
In accordance with the invention, the prebreaking and
tempering steps are effected, and the grain is then passed
through a first set of break rolls which may be of the modified
Dawson type having 20 corrugations per inch and a spiral of
aboutl/2 inch per linear foot. The rollers are arranged dull to
dull and have a differential roll speed of 2 to 1. The first
break roller milL is adjusted so that at least appro~imately
50~ of the product through is small enough to pass through a U.
S. #12 sieve. rrhe 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 practice 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 "fines", 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 excessively. 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. S. ~12 sieve. The relatively large size particles over
~1~33S3
the #8 sieve are primarily germ and bran and may be directed to
feed or oil recovery or to further processing as described
below. The portion passing through the #12 screen is less than
1~ in fat content, and it is therefore passed to finished pro-
duct. Par'cicles through the #8 screen but over the #12 screen
are principally endosperm, although there is enough germ
present that this 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
corrugations of the same size as the first set or slightly
smaller, and the spacing between the rolls is again sufficient
to avoid excessive penetration of the germ. The differential
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
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 lowers
the fat content of the throughs from the sifter wires, and it
aids in making the milling process superior to conventional
processes both in quality and product yield.
Although the specific operating parameters for the
process depend upon the age of the grain, its moisture content
21
3;~ 3
and grade, and the end products desired, it has been found, by
way of example, that U. S. grade #2 corn having a moisture
content of 13~ yields approximately 62% brewer's grits on a U.
S. #30 sieve at 1% maximum oil, 8% meal through a U. S. #30
sieve at less than 1.5~ oil, 3~ flour through a U. S. #80 sieve
at about 2~ maximum oil, and a brewer's extract on the grits of
80.5% as 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 conventional proceed of Fig. 5 is 47% brewer's grits,
9~ meal and 5~ flour. The total prime product yield is 63% in
the conventional process. In addition to providing a higher
yield in the more valuable brewer's grits, the process of this
invention yields a cereal grit and flour product of higher
quality because of a reduction in "black specks". This is
attributable 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 involves 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
thereby crushed from its thin edges toward the center to
achieve a high degree of separation of the germ from the
endosperm while maintaining the germ in a substantially whole
condition.
The degerminator stock is passed to a degerminator
sifter which grades it into four streams containing particles
of different sizes. A first stream consists of relatively
large particles of whole corn or incompletely degerminated
22
1133,..?~3
pieces of corn. It may not be necessary to separate out this
first stream or fraction, depending on the scalp sieve size,
the degerminator setting, the condition of the corn, and/or the
object of the milling operation. The first stream is recycled
or passed again 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 particles, 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 endosperm 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
obtained by closer si~ing of stream #2 into several streams
and/or employing aspiration prior to passing the streams to the
gravity tables. This will upgrade the finished product in both
quality and quantity.
The third fraction includes 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
combined with the endosperm rich stream from gravity table #l
and passed to break rolls having fine corrugations that may be
identical with those of the first break roll mill described in
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 grits grade sifter, most of the germ and bran
still remaining in stock are scalped off and directed to feed
23
or oil recovery. The scalp sieve i5 about 10 to 16 mesh,
depending upon the mesh of the sieve for the fourth fraction
from the degermlnator sifter~ The grits grade sifter size
classifies the remainder 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 U.S. #30 sieve and over a
10 U.S. #80 sieve with 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 total weight
of the cleaned corn, as compared to about 63% for the
conventional milling process.
Referring now to Fig. 8, the milling process shown
therein employs tempering and the preferred degerminating
method described above. The object of the process is to
produce a maximum yield of brewer's grits. The process 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
and before degermination. Tempering 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 relatively long and extensive drying
is required. A small amount of tempering is particularly
beneficial if the moisture of the corn is low because in this
case the degermination is enhanced appreciably due to the
tempering step.
24
3~
Degen~ination is effected by the preferre~
degerminating method described above, and the degerminator
stock is fed to a ~egerminator sifter which provides four
fractions as in the process of Eig. 7. ~lowever, instead of
directing fraction #3 to a gravity table, it is tempered, if
there was no tempering previously, to bring its germ moisture
content in the range of about 15% to 35%.
After tempering of the #3 fraction, it is combined
with 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 employ~d in the
process of Fig~ 7. The stream from the roller mill may be
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
degermination, the fine 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 manner as in the process of Fig. 7.
Minimal tempering yields results similar to and
usually somewhat better than are obtained with the process of
Fig. 7. More complete tempering gives results better than
those of the process of Fig. 6, with yields 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 degerminate. This process is used
primarily to produce extra coarse grits such as those used to
~3~
make cereal cornflakes in the breakfast food industry. If the
objective of the process is to maximize grit size, impact
deinfestation is not used to advantage in the corn cleaning
operation because the broken corn that results from impact
deinfestation is not debranned easily and the yield of larger
grits is reduced accordingly.
After the corn is cleaned, it is tempered using
water, hot water, and/or steam and is held long enough for the
moisture to penetrate and loosen the bran. Unlike the
conventional debranning processes which require tempering of
the entire kernel, on]y 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 endosperm and the endosperm being crushed out of the
pliable tempered bran.
The degerminator stock is sifted by the degerminator
sifter wherein the top or coarsest fraction is scalped off and
passed through an aspirator to remove the bran. The bran that
i~ removed may be sent to a dryer if necessary before it is
directed tG animal feed or to another use. Undegerminated 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 according to market and/or
use objectives and efficient gravity table operation. These
fractions are sent to gravity tables which may be preceded 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
particularly efficient bran removal, most of the bran is
26
~13~
scalped off in the recycle fraction from the degerminator
sifter.
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 grits not
used as grits can be reduced in size for brewer's grits and/or
meal and added to the products of the degerminating process.
In each of the processes of the present invention,
the fines from the degerminator are relatively low in fat
content since the germ is maintained in a substantially whole
condition. 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
a result primarily of the high degree of degermination and
debranning that is achieved in the degermination process.
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 having 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.
By virtue of the reduced number of steps required,
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 does 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
27
~1333S~
roller mills are needed, and the reduced length of the Elow
path corresponclingly reduces the need for conveying
equipment. Further economic benefits result from the reduced
power requirements and the decreased need for heating, cooling
and drying equipment. ~he 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
milo, rollers having finer corrugations are utilized to achieve
the desired separation of components in a minimum number of
steps.
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 with
the process of Fig. 6 that more than one or two breaks may be
made in the prebreak mill and that higher yields or higher
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 benefits obtained by using
the milling processes of the present invention, dry milling
techniques may be extended into areas that have heretofore been
thought to be economically impractical. For example, since
yields of prime products over 70% are obtained with fat content
as 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
invention is the high rate of germ recovery which results in a
28
~3~53
higher oil yield per bushel of corn than is obtained with
conventional dry milling processes.
E'rom the foregoing, it will be seen that this
invention is one well adapted to attain all the ends and
objects hereinabove set forth together with other advantages
which are obvious 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
contemplated by and is within the scope of the claims.
Since many possible embodiments may be made of the
invention without departing from 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.
