Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DRUM COOKER
The present invention relates to a drum cooker for cooking
granular products, especially corn grits for the production of
cornflakes, having a vessel mounted to rotate about an axis
with nozzles that open into the vessel and that are connected
with lines through which a gaseous heat-carrying medium can be
introduced into the vessel, there being provided at least two
circumferentially distributed nozzles so that at least one noz-
zle opens into the area covered by the product while at least
one nozzle opens into the area not covered by the product.
A drum cooker of this type is known, for example, under the
designation DSCK from Gebr. Biihler AG, Uzwil, Switzerland.
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A comparable drum cooker is also known from APV Baker, Peter-
borough, England, under the designation "Rotary cereal cooker".
The axis of the rotary vessel extends horizontally, the vessel
as such has a substantially barrel-shaped contour. Inside the
vessel, the product to be treated, for example corn grits, is
mixed with water, the vessel being filled with that product-
water mixture up to more than half its volume.
The heat supply is realized by nozzles arranged in the wall of
the vessel, that are supplied with a hot gaseous medium, namely
hot water steam, through lines extending along the outside of
the vessel. The arrangement of the nozzles is such that the
nozzle groups are located substantially diametrically opposite
one to the other. All lines and/or nozzle groups are supplied
form a common supply source via communicating lines. This means
that the steam is supplied to all lines and all nozzles simul-
taneously.
In practical use it has, however, been found that the steam en-
ters the interior of the vessel only through those nozzles that
open into the area not covered by the product-water mixture at
that time. These are the nozzles that occupy a position above
the product-water mixture during the rotary movement.
Those nozzles that open into the area just covered by the prod-
uct-water mixture hardly admit any steam since the counter-
pressure of the product-water mixture present in the vessel is
so high as to prevent the steam from entering through those
nozzles in any quantity worth mentioning.
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This is due to the fact that the gas, being supplied simultane-
ously via all lines, tends to follow the line of least resis-
tance, which is through the nozzles that are not immersed in
the product-water mixture.
Even increasing the pressure does not cause the gas to enter
through the nozzles in the area covered by the product.
This now leads to the effect that very poor heat transmission
is achieved from the admitted heat-carrying medium to the prod-
uct-water mixture revolving in the vessel, i.e. the mixture of
water and the corn grits to be treated. The heat exchange oc-
curs substantially at the surface of the product, which in re-
volving condition has a kidney-shaped cross-section, and the
upper steam-filled space.
However, since it is necessary to continuously supply fresh
heat-carrying medium for the cooking process, additional ar-
rangements must be provided for carrying off the gaseous medium
from the vessel, which is effected through openings arranged
above the product-water mixture. This then creates the risk
that fresh medium is carried off without a considerable heat
exchange having taken place with the revolving product-water
mixture.
This is connected with the considerable disadvantage that very
long cooking times are necessary, with the risk that the starch
shows gelatinizing phenomena in the outer areas of the corn
grains, that have been cooked for a long time, while inside the
grain the cooking process has not yet led to the desired re-
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suit, so that a so-called "white spot" of uncooked starch is
still left.
During further processing, this then leads to the result that
after the grains have been rolled to flakes, these contain non-
gelatinized spots. The roasting process that follows then leads
to cornflakes which exhibit pale discoloring in the area not
thoroughly cooked (white spot), and which instead of containing
the desired blisters, exhibit in this area a baked structure,
i.e. a closed structure similar to puff pastry.
With respect to energy balance, this cooking process is ex-
tremely unfavorable.
According to the present invention, there is provided a
drum cooker for cooking granular products, comprising:
a vessel mounted to rotate about an axis;
at least two nozzle groups opening into said vessel;
each of said nozzle groups being connected to supply lines;
a gaseous heat-carrying medium is feedable via said supply
lines and said nozzle group into said vessel;
said at least two nozzle groups are arranged
circumferentially distributed one to another, in a manner
that:
a first nozzle group opens into a first area of said
vessel covered by said granular product contained in said
vessel,
while a second nozzle group opens into a second area
of said vessel not covered by said granular product
contained in said vessel,
wherein:
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a control means is provided for supplying said gaseous
heat-carrying medium at any time to that nozzle group only
that opens into said first area covered by the product.
It is, therefore, the object of the present invention to
improve a drum cooker of the before-mentioned kind so that
an efficient heat exchange and/or cooking process takes
place that leads to reduced cooking times and by which, in
addition, a good and uniform cooking result is achieved.
Preferably, this object is achieved by the invention due to
the fact that a control means is provided which ensures
that the medium will be supplied at any time to those
nozzles only that open into the area covered by the
product.
Preferably, this feature provides the advantage that the
gaseous medium is now exclusively introduced through the
nozzles that open into the area covered by the product,
i.e. that are located below the water level so that the
medium is blown directly into the water where it gets into
intimate heat-exchanging relationship with both the water
and the product to be treated.
Preferably, this positive control results in much more
purposeful, quicker and more effective heat transmission
which leads to a uniform and excellent cooking result in
considerably less time. The medium being introduced enters
the product-water mixture to be heated through the nozzles
in the form of uniformly distributed bubbles.
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Preferably, the purposeful introduction of the medium into
the product-water mixture allows the vessel to be filled to
a considerably higher level so that much more product can
be treated with the same overall drum size. A voluminous
pressure cushion, as required in equipment of the prior
art, is now no longer necessary, the steam space serving
exclusively venting purposes.
Preferably, according to a further embodiment of the
invention, the design of the control means is such that the
vessel can be vented via those nozzles that open at any
time into the area not covered by the product.
Preferably, this feature provides the additional
considerable advantage that the heat-carrying medium is
guided through the vessel very directly and uniformly, that
it enters the product-water mixture directly, flows through
the mixture and is evacuated from the vessel through those
nozzles which at that time are located above the product-
water mixture level.
This permits the pressure build-up in the cooker to be
adjusted in an easy way.
The nozzles, therefore, act as injection nozzles in the
immersed condition and as venting nozzles when they are
located above the water level.
Preferably, according to a further embodiment of the
invention, diametrically opposite nozzles are provided.
Preferably, this feature, which is known as such, provides
the advantage under control aspects that switching-over
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operations can be effected in a purposeful and simple way
so that in a given angular area a nozzle works in the
injection mode while in the next defined angular area it
works in the venting mode.
Preferably, according to a further embodiment of the
invention, a plurality of nozzles are arranged along the
axis of rotation of the vessel.
Preferably, this feature provides the advantage, especially
in the case of very large drum cookers, that the plurality
of nozzles permit the heat-carrying medium to be injected
at a plurality of positions so that especially uniform and
quick heat distribution is guaranteed.
Preferably, according to a still further embodiment of the
invention, the control means comprises a multiple line
distribution through which media are guided into and out of
the vessel.
Preferably, multiple line distributions designed as
stationary units for supplying a plurality of media
separately into a rotating vessel, are commercially
available as complete compact units so that a simple and
little complex control system can be realized.
Preferably, such a multiple line distribution allows not
only the heat-carrying medium to be introduced and carried
off, but also the water in which the corn grits are cooked
and, if desired, even flavor agents and dulcifiants to be
gradually added, for example. Additionally, line
distributions for rinsing media may be provided so that
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after draining of the drum cooker a cleaning operation may
also be carried out through the control means.
The invention will now be described and explained in more detail
with reference to a selected exemplary embodiment in connection
with the attached drawings, in which:
Fig. 1 shows a very diagrammatic view, partly sectioned, of a
drum cooker;
Fig. 2 shows a representation of a corn grit to be treated;
Fig. 3 shows another processing step of such a grit, after it
has been pressed between rollers;
Fig. 4 shows a finished cornflake, in the desired form; and
Fig. 5 shows a cornflake as it results from corn grit not uni-
formly cooked.
p, drum cooker shown in Fig. 1 is indicated generally by refer-
ence numeral 10.
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The drum cooker 10 comprises a horizontal, essentially barrel-
shaped vessel 12 that can rotate about a horizontal axis of ro-
tation 13.
The vessel 12 is rotatably seated in columns 16 and 18, via
lateral bearings 14, 15. The vessel is driven for rotary move-
ment about an axis of rotation 13 via a chain drive 20 con-
nected with a drive motor 22.
A first line 24 is guided along a surface line on the outside
of the vessel 12 and connects two nozzles 26 and 27 that open
into the interior of the vessel 12. Each nozzle 26, 27 is pro-
vided with a filter 28.
Diametrically opposite to that line and nozzle arrangement a
further line is guided along the outside for supplying two noz-
zles 30 and 31, likewise opening into the vessel 12.
Both lines 24 and 29 end in a control means 32 provided with a
multiple line distribution 34.
The control means 32 is connected with a supply and control
unit 40 through which the media and control operations, which
will be described in more detail further below, are supplied
and/or controlled.
The vessel 12 is provided with a lid, not shown, through which
the product to be treated, for example corn grits, can be
filled in and/or discharged.
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Corn grits are corn grains from which the germs and shells have
been removed.
In addition to the corn grits, water is filled into the vessel
12 up to a level considerably above the level of the axis of
rotation 13, as indicated in Fig. 1.
For cooking the water and corn grit mixture contained in the
vessel 12, hot steam is introduced at approximately 120° Cel-
sius and a pressure of approximately 1 to 2 bar.
According to the invention, the system is switched and/or con-
trolled via the control means 32 in a manner such that the me-
dium 35 is at any time introduced only through the line that
supplies those nozzles that open into the area 33 covered by
the product.
In the representation of Fig. 1, it is the line 24 that sup-
plies the nozzles 26 and 27.
Thus, the medium 35 is introduced via the supply line 38, the
control means 32, which for this purpose comprises a multiple
line distribution, to the line 24 and from there to the nozzles
26 and 27. The medium 35 then enters the product via the fil-
ters 28 in very finely distributed bubbles, as indicated in
Fig. 1 by the flow arrows and the bubbles. This permits inti-
mate, quick and uniform heat transmission from the medium 35 to
the product-water mixture contained in the vessel 12. Once the
medium 35 has passed the mixture, i.e. left the liquid volume,
it flows to the diametrically opposite nozzles 30 and 31 and
can be discharged from the vessel 12 through the nozzles 30 and
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31 and the line 29. The line 29, therefore, carries the medium
through the multiple line distribution 34 to a venting opening
36.
In the position illustrated in Fig. 1, which corresponds to an
instantaneous condition of the rotating drum cooker 10, the
nozzles 26 and 27 therefore work in an injection mode, while
the nozzles 30 and 31 work in a venting mode. This situation is
maintained so long as the nozzles 26 and 27 open into the area
33 covered by the product. Once the nozzles 26 and 27 have left
that area, they are again switched to the venting mode; in the
meantime, the nozzles 30 and 31 have reached the area 33 cov-
ered by the product and are switched over from the venting mode
to the injection mode, which is effected automatically and un-
der positive control by the multiple line distribution 34 of
the control means 32. It is thus possible to convert a granular
product, for example the corn grits 42, to the desired cooked
state within short time.
Compared with the comparable prior art apparatuses of the kind
described at the outset, i.e. of equal size and volume through-
put, where the treating times are in the range of 120 to 150
minutes, a reduction of the treating time by 20 to 30 % could
be achieved. In addition to achieving a reduction in treating
time, a perfectly cooked product was obtained already after
that short treating time. Further, the charge can be increased
by approximately 20 % as compared with conventional drum cook-
ers.
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Fig. 2 shows a corn grit 42 as it is obtained when the cooking
process is conducted for an excessively long time and with in-
sufficient heat exchange.
The resulting grit exhibits outer areas 46, where the starch
has already gelatinized due to the long treating time, i.e.
where a sticky outer layer has been produced.
The inner core has not yet been cooked at all, i.e. there still
exists the so-called white spot 44.
If such a grit 42 is then subjected to further treatment, i.e.
pressed between rollers, the flake 48 obtained, as illustrated
in Fig. 3, contains areas 50 that are still uncooked. When such
a flake is then roasted to obtain the desired cornflake, one
obtains the cornflake 56 as illustrated in Fig. 5, which exhib-
its in the incompletely cooked areas a surface 55 with a baked
structure similar to puff pastry. The cornflake 56 shows an un-
desirable pale discoloring in these areas.
The desired blisters 58 are produced in small numbers only.
With the aid of the drum cooker 10 equipped according to the
invention, it is now possible to produce a corn grit that is
cooked thoroughly, much more uniformly and more quickly so that
it exhibits neither any sticky outer areas 46, nor a white spot
44 in its inner core.
If such a uniformly treated corn grit is then further proc-
essed, a cornflake 52, as illustrated in Fig. 4, is obtained
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after the roasting process which exhibits fine, small blisters
54 uniformly distribution over its surface.
For the sake of clarity, the lid and also the additional supply
lines, for example for introducing syrup or cleaning water or
the like, have been omitted in Fig. 1; these lines can be
suitably guided along the outside of the vessel.
