Allen Paul W. Industrial Fermentations
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CORN PRODUCTS
171
Theoretically Practically
Starch 38.0lbs. 32JJlbs.
Feed:
Gluten meal 7.0 lbs. QDlbe.
Corn bran 5.01ba. 7.0lbe.
Germ oil meal 2.2 lba. 2.0lbe.
Steep water 4.0 lbs. 401be.
Com oil
1.81bfl.
lJ5Ibfl.
Very little starch is made in the United States from any other
grain than corn. Corn starch has proven most satisfactory as to quality
and as to cost.
FIG.
26.—Staroh settling tables.
In the manufacture of starch there are different methods of
separating it from com but there is only one process, the wet process,
which produces a starch of high quality from corn.
In the wet process shelled oorn is purchased by the oarload and is
cleaned by fanning mills and sieves. After the cleaning it goes
to the steeps whioh are upright tanks holding about two thousand
bushels each. In these large tanks the corn is steeped for about
forty hours with warm water containing sulphurous acid. The sul-
phurous acid is used to prevent fermentation and to soften the
glutenous part of the corn. From the steeps the softened corn goes
to the degenninating
millf*,
which tear the corn so that the germs
are freed from the kernels. The mass from the degerminatmg mills is
passed into long vats where the germs are separated by taking ad-
vantage of the fact that they are lighter than the other parts of
the corn and thus float while the remainder winim. The germs float
172
INDUSTRIAL FERMENTATIONS
over a weir and are sent to the oil house to have their oil expelled.
The remainder of, the corn constituents mnirpf and passes down to fine
grinding mills of the Buhr Stone type which disintegrates the starch,
gluten, and fiber very thoroughly.
From the Buhr Stone milk the finely ground mass of starch,
PLATE 6
DRY STARCH HOUSE
Simplified
flow
sheet of a
dry
etaroh house.
gluten and fiber goes down through the mill house, story by story,
passing first through perforated copper and then silk reels. The
fineness
1
of these is increased on each lower floor. These reels separate
first the coarser material from the starch, as the skins or bran of
the corn kernel. The finest silk reels separate from the starch
everything but the liquefied gluten. The material separated from the
starch by the reels is passed on to the feed house. The separation of
liquefied gluten from the starch is accomplished by passing the dilute
CORN PRODUCTS 173
starch and gluten mixture slowly over long narrow tables which have a
very gentle slope. The starch settles on these tables and the gluten
flows off at the end. After tabling, the starch goes to large presses in
which it is washed with filtered water until a starch of purity is
obtained.
Steeping the Corn. The purpose in steeping the corn as already
mentioned is to soften the glutenous part of the kernel and to facilitate
the removal of the flVin and germ and to hasten the disintegration
of the starch grains. There has been much study on the process of
steeping corn in the manufacture of corn products, but nearly all
manufacturers steep their corn differently. While no one method
has ever become standard still practically all corn at the present time
is
1
steeped in the presence of sulphurous acid. The sulphurous acid is
used both for its softening effect on the glutenous part of the corn,
and because it is a strong germicide and checks to a great degree
putrefaction in the steep tanks. The amount of sulphurous aoid placed
in the steep water is between 25% and .4%. The mechanics whereby
this amount of sulphur dioxide is added to water consists' of a sulphur
burner and a tower containing baffles over which water trickles. The
water in the sulphur tower cofiecte the sulphur dioxide gas as it passes
upward.
The steep tanks as a rule hold about 2,000 bushels of oorn each.
After they are filled with, shelled corn, water at about 110 degrees' F.
and charged with sulphur dioxide as above mentioned, is added to
each until the corn is completely covered. The corn is steeped at this
temperature for about 40 hours. The temperature is kept oonstant
throughout the different parts of the tank by circulating the sulphur
water.
The present practice in steeping corn has grown up .almost of
itself,
that is, no one person has ever studied it enough to master it
but numerous superintendents have each contributed small points.
It may be said tnat at present the steeping of corn is carried on in
a .crude way.
There are oertain controlling factors which have to be observed
in steeping. The temperature must be high enough to rapidly soften
the corn, as time is money in the operation of large plants. Still
the temperature must not be high enough to start in any way the
gelatinization of starch or in any manner injure the amylo-cellulofle
walls of the starch granules. In steeping, temperatures are necessarily
used at which putrefactive bacteria flourish. In the earlier factories
the corn in the steep tanks was a foul putrefying mass causing a
nuisance in the neighborhood. Because of this condition corn starch
manufacturers in looking about for germicides to place in the steep
tanks decided on the use of sulphur dioxide and this practice has
become quite universal.
There are three important results obtained by the use of sulphurous
aoid in steep water., First, the foulness of the steep tanks is eliminated.
Seoondly, the sulphurous acid is found to soften the corn more effi-
174 INDUSTRIAL FERMENTATIONS
ciently than just warm water alone. This is due to the action of
sulphurous acid on the proteins of the com. Thirdly sulphurous
acid reduces the loss of corn proteins in steeping. This is due to the
elimination of putrefaction which in the absence of a germicide con-
verts much protein into foul gases.
This reduction of protein putrefaction is a great improvement over
the early factories in which 60% of the constituents of the corn was
lost. At present only Vfo to 5% of the total constituents of the corn
is lost in the processes of manufacture.
While sulphurous acid does keep down putrefaction, that is, the
growth of putrefactive organisms, still many bacteria do grow in the
steep tanks during steeping with sulphurous acid and a certain amount
of proteolysis is continuously going on as is shown by the following
data:
BACTHHIA IN STHHP-WATBE AT END OF STEEPING.
Samples BS.
Boot,
per cc.
1 2 187,000
2 IS 102,500
3 2.5 168,000
4 21 172,000
5 2.7 412,000
6 22 297,000
Kind oj Bacteria in Steep-water. Out of 60 oultures inoculated into
litmus milk 28% peptonized the casein. Of these 60 oultures examined
53 were spore-formers.
That there is considerable corn protein (zein) liquefied by the
presence of sulphurous acid during steeping is indicated by the fol-
lowing figures:
LKJTJHFACUON OF PHOTBEN IN COEN D-OH TO .188% SOa DOTING 40 HBS.
Brmpma
AT 110 F.
Protein
Liquefied Protein Liquefied
lOg
Samples
in
SO»
Water in
Distilled
Water
1 4160% 2.518%
2 4.386% 2.328%
3 4.250% 2.014%
NOTH.—There
were considerable numbers of bacteria in the samples flteeped in
distilled water.
The chemical analysis of an average sample of corn is:
Moisture 14%
Aflh 1.85% DS.
Protein 1010% DJ3.
Starch
80.63%
DJS.
g£ 4J2%DJ9.
£*« 3-50%DJ3.
Soluble 4.70% DJ3.
CORN PRODUCTS 176
During steeping, some of the salts, proteins, and soluble carbo-
hydrates pass out through the covering membranes of the corn kernel
and are recovered only by evaporating the steep water down to 18
degrees B6. and spraying this syrupy mass upon the corn gluten feed
during drying.
Bacterial action sets in immediately upon starting a steep as
mentioned above. In spite of the sulphurous acid the germ count,
goes to hundreds of thousands per oubic oentimeter. Considerable
amounts of lactic and acetic acid also accumulate during steeping.
Also a certain more or less uniform amount of protein is liquefied due
to bacterial action, to the liquefying effect of sulphurous acid, or to
the proteolytic enzymes of the corn. The steep water which is drained
from the steeped corn is generally from 2 to 6 degrees Be\, depend-
ing on whether a oiroulating system or a simple holding system of
steeping is employed. The bacteria of the steep tanks are very
largely high aoid resisting types, B. bulgaricus being readily isolated
from the steeps when lactose agar plates containing .4% lactic aoid
are used for oulturing. It is this organism which often produces ropi-
ness of the corn further on in the process, that is, in the starch and feed
reels.
From each 2,000 bushel steep tank there is obtained after
steeping about 9,000 gallons of light steep water. The analysis of
this light steep water may be as follows:
BaumS 3D
Aah 20. %
Protein 38. %
Organio not protein 49. %
Acidity, figured as HQ 4J5%
SO.
0.0%
NOTB.—Elements
present in the above ash are Ca, Mg, P, Al, Fe, Na, K
r
and Cl.
The "Sweet Process" or "Alkaline Process" is an older method of
steeping than the sulphurous acid method. The nature of this process
is indicated by the name. This method was in use for many years and
is in use to some extent to-day. By this process the corn was placed
in large tanks of lukewarm water to Which alkali had been added.
The corn in these tanks of alkali was allowed to rot for Beveral days.
The putrefaction became very foul and only the starch was used as a
commercial product. The remainder of the constituents of corn were
made useless by the alkali or were destroyed by the putrefaction. A
starch of high purity was made by this process but the process was
too foul and wasteful to be practiced to any extent. It should be
noted that this process utilized a combination of the actions of alkali
and of bacteria. Little starch was lost in this form of steeping due
to the fact that bacteria are practically helpless in their attack
upon the starch granule so long BB the starch cellulose wall remains
intact.
Still another method of steeping corn used some years' ago was
176 INDUSTRIAL FERMENTATIONS
the "Durgen Process" which was the steeping of corn by allowing a
stream of water heated to just below the gelatinizing point of corn
starch, to pass continuously through the corn in the steep tanks for
about three or four days or until the grain had softened properly.
This method had advantages over the "Rotting Process" and the
"Sweet Prooess," in that the glutenous matter of the corn could be used
for feed. However, it is not as satisfactory as the "Sulphurous Acid
Process" in that it requires more time and fuel. Also large amounts
of corn solubles are lost, the volume «of water passing
^
out of the
steeps being too great to be condensed for the retention of corn
solubles.
In any process of steeping it must be remembered that whatever
amounts of oarbohydrates, proteins, or of salts are in solution inside of
the swelled corn kernels at the end of the steeping process are lost
as the kernel is then craoked in the degerminator and only solid matter
is recovered. This is partly the reason why in the modern process of
the manufacture of corn products it is impossible to do better than to
reclaim from 95% to 97% of the weight of corn taken into the factory.
Under the subject of gluten settlers it will be mentioned that the
waste water flowing away from the corn products plant oontains
about 350 grains of solid matter per gallon or nearly a ton of material
lost for every thousand bushels taken into the plant. This
1
solid
matter in the waste water is about one-half protein. This material
is in a oolloidal condition to a considerable extent and has resisted
all attempts directed toward its reclamation.
The secret of high efficiency in reclaiming corn constituents in
the wet process of corn products manufacture, and also the proper
separation of the different parts of corn, lies in the control of steeping.
If the steeping is wrong, the whole system goes wrong. The subjeot
of steeping invites much study and research. In other words the steep
tanks should be reduced to both chemical and bacteriological control.
The separation of the germ, gluten and starch is accomplished
in the wet process by the reels. These are long open cylinders covered
with perforated copper or silk depending upon the work to be done
by the reel. The germs are separated by the coarse copper reels. The
starch is separated from the coarse and fine feed, by the coarse feed
reels,
the No. 9, the No. 12 and the No. 17 silk reels. Sometimes even
No.
20 silk reels are used.
FTNBNBSS
OF
RBHL
CovBamas.
Perforationa in ooarse copper reels 8 per inch
Perforations in fine copper reels.......,,.. 20perinch
Mesh of No. 9 silk 86 per inch
Mesh of No. 12 silk 122 per inch
Mesh of No. 17 silk 167 per inch
Meeh of No. 20 silk 178perinch
There are many problems to be considered in the operation of the
reels but perhaps the worst is a bacteriologioal trouble, that is, ropiness
PLATE
7
-pnoccs*
ERHA
STPAM
MILL
HOUSE
T«*t
Simplified
flow
sheet
of
mill
house.
Houre
2d
177
178 INDUSTRIAL FERMENTATIONS
whioh absolutely stops up the silk on the reels. There are many
"rope"
producing organisms. Many of these have been investigated
in connection with milk but little work has been done in connection
with com products plants. However, it is safe to say that any organism
which can produce ropiness at all can produce it in the presence of
com.
In the sulphurous acid process of com products manufacture many
"rope"
producing organisms are unable to survive at all in the presence
of a slight amount of sulphurous aoid. This is not true of B. bulgaricus
and a few spore bearing members of the "rope" producing group of
bacteria which have been found to stand 18% SO
a
in a solution con-
taining ground corn.
The "rope" producing organisms of milk as given by Hummer
are:
Bact. visco-fucatum
Bact. album
Bact. healii (sp. nov.)
Baot. bulgaricum
Bact. casei
Baot. Burgeri
Bact. lactis acidi
Bact. visco-doccoidium
Bact. lactis viscosum (Adametz)
Baot. para viscoBum (sp. nov.)
Bact. lactis pituitosi
Bact. aerogenes (Escherich)
Baot. cartilagineum
Baot. peptogenes
B.
rubefaoiens
B.
droseraB
B.
harisonii
B.
viscosymbioticum (sp. nov.)
B.
hesaii
B.
vulgatus
B.
kleinii
B.
pruchii
Str. taette
Str. pyogenes
Str. lacticus var. hollandicus (comb, nov.)
Str. viscosus
M. rosaceus
M. viscosus b.
M. pituitoparus
M. mucofaoiens
M. freudenreichii
CORN PRODUCTS
The "Uquor-containing" ground oorn going to the reels for separa-
tion is made up with water which has been tempered to between 86
degrees and 87 degrees F. The factor of temperature is carefully
controlled in reeling in order to have uniform separation by the reels
and a definite yield of starch. As 86 degrees F. is a very suitable
temperature for the growth of bacteria more SO» gas is added to the
starch liquor and feed liquor to prevent the production of ropiness
in the reels. It is found that at the end of steeping the percentage
of SO, in the steep water has dropped from 26% to 10% and at the
separator heads the SO
a
is .032%. Thus it can be seen that in the
feed reels especially, more sulphur dioxide must be added as the
gluten ferments very quickly unless there is a germicidal agent
present.
The gluten settlers are large tanks usually made of cement into
which the gluten which flows from the tables passes and is allowed
to stand until the gluten has settled out. It generally requires 14 to 24
hours for the gluten to settle from the water. The supernatant water
is then drawn off and runs away as waste water. As mentioned under
steeping this waste water or "gluten settlers water" contains about
360 grains of solid matter per gallon. To reduce this amount of solid
matter per gallon is one of the big problems yet unsolved in the corn
products industry. About half of this 360 grains per gallon is protein
in the water soluble state. This protein is very likely the result of
bacterial action on the protein of corn in the steep tanks.
TABLE HE.
THMFERATUBEB OF SOMH COMMON STAHGHBS AS
DmmtMXNn)
BT THB
THHBMO-SUDH AND WATBB-BATH METHODS.
/—Temperatures Are Degrees
Centigrade—\
Thermo- Water-
Slide Bath
Kind of Starch Method Average Method Average
f 74.41
Arrowroot {745
74J6
74to75 74-6
|.74J6
f70,6 .
Corn {715 70.9 71 to 72 71.5
1.71.0
f76.0
Navy bean {76.4- 76.6 75to76 75JS
175.4)
[82J6"
Sweet potato {82.6 82.5 82 to
83
82.5
182.4 ]
f67j6
Irish potato { 67.8
V
67.7 87to68 67.5
(.67.8
[66.5
Wheat {65.0 652 65 to 66 65.5
165.1
180
INDUSTRIAL FERMENTATIONS
THMFHRATUBB
07
STABCHBS
THOM
THH QBAIN
SOEGHTJMS.
Kinds of Starch
White kaoliang
Brown kaoliang
Feterjta
Orange cane
Red kafir
White kafir
Pink
White milo
After C. K. Francis and 0. C. Francis.
Thermo
SUde Readings
f78J)C.
{78.0°C.
I rare.
f762°C.
{76.4°C.
[76.4° C.
f75.4°C
{7B£°C.
175^0.
[72.2° C/
{72.4°C.
1.72.6°
C.
f745°C.
J7°0
J75.00.
176.0° C.
?72.0°C.
\ 72.1° C.
1.72.4°
C.
64:6°
66.0° C. •
64J6°O.
f74.0°C.
\ 735° C. •
[ 74.4° C.
Average
78.0° C.
763° C.
76.6° C.
72.4° C.
76.0° 0.
72.2° C.
64.7° C.
741"
C.
An analysis of a sample of "gluten settlers water" resulted as
follows:
Ash 12.196%
Protein 40.600%
Organic not protein 38507%
NOTB:
Half of the ash is composed of phosphorus and potassium salts.
Glucose and Corn
Sugar.
The two most important products manu-
factured from corn starch are gluoose and corn sugar. When a starch
solution containing a mineral aoid as hydroohloric acid is. heated, the
hydrolysis of the starch takes place. Brown and Morris represent
this fact by the following group of reactions:
Starch
to
= (C
ia
H
ao
Oio)ao + (i
2ao
io)ao
Stable Dextrin Amylin Groups
eto.,
etc.
r (CiaH
sa
Oii)i&
+ 19 H
8
O = j (Maltose)
CuHaaOu + H
a
O = 2C
a
H
ia
O
8
Maltose Dextrose.