Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FOOD PROCESSING METHOD AND APPRISE
The present invention relates to the field of food
processing and, in particular, to the process of deep
frying food snack items.
Methods used for deep frying foods on an industrial
scale, particularly snack foods such as potato chips,
banana chips and the like, include batch processing
and continuous processing. A batch process, for
example, to prepare potato chips involves cooking a
10 batch of either washed or unwashed potato slices in a
cooker containing a cooking medium, such as, hot oil,
then removing the entire batch from the oil for
further processing, such as de-oiling, seasoning and
80 forth. The cooking medium may be oil, lard or
other conventional materials. For convenience,
hereinafter, the cooking medium will be referred to as
oil, but it is understood that any conventional
rooking material may be utilized.
Continuous processing, of potato chips, for example,
usually involves conveying the uncooked potato slices
: through a cooker containing hot oil such that the
length of time the potato slices are in the oil and
the oil temperature are appropriate for the desired
potato chip. There are several configurations for
cookers, the most common one employing linear
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conveyors. In such a cooker, the slices are continue
ouzel placed in the oil at one end of the cooker and
advanced under control through the cooker where potato
chips are continuously withdrawn from the other end.
In either batch or continuous processing, the oil may
be heated by heaters directly submerged in the oil or
by circulating the oil to an external heater and
returning the heated oil into the cooker.
Conventional potato chips may be characterized by
10 reference to standardized color charts oil content,
water content, number of folds, clumps, blisters, and
the like. The capability of a particular type of
potato to achieve desirable chip qualities is defined
as its chipping quality. Usually, conventional chips
15 have a fat content in the range of about 32-40% by
weight and may be cooked either by batch or continuous
processing. The usual cooking conditions for a
conventional potato chip in a continuous process
utilize external heating means and continuous oil
20 circulation. The chip is immersed initially into hot
oil at a temperature of about 360 to 390F and
conveyed through the cooker such that there is a drop
in temperature of the oil along the cooking path. The
cooked chips are withdrawn from the oil at a tempera-
25 lure of about 320 to 350F. There is usually a Tao 45 D drop in temperature during the course of
continuous cooking of conventional potato chips. In
Rome instances, multi-zone cookers are used wherein
the temperature drops along the cooking path in one
30 zone, then rises as the next zone is entered, result-
ins in a "sawtooth" temperature profile along the
cooking path.
Other continuous rooking systems for conventional
potato chips include direct fired and immersion tube
ISLES 03
cookers. The time-temperature profile through the
cooker can be altered by modifying the cooker design
but there are severe limitations imposed by the fact
that the heat transfer capability it limited by the
heat transfer surface available within the cooker.
These types of cookers are usually necessarily larger
than external heat exchanger cookers for equivalent
production rates, and more importantly they unneces-
sanity contain much more cooking oil than required to
10 cook the food product The oil turnover rate, meaning
the time in which all the volume of cooking oil
contained in the system is absorbed into the chips and
replaced with fresh oil, is extremely important in
maintaining low free fatty acid cooking oil. Another
15 fact effecting cooking oil quality is the film temper-
azure which the oil is subjected to on the heat
transfer surfaces. The internally heated cookers
cannot achieve both low oil volume and low oil film
temperatures compared to externally heated systems.
20 however, particularly in the area of potato chip
processing, there are types of potato chips which vary
from what may be considered to be conventional chips
in terms of color, texture, oil content, number of
folds, salt content and lack of defects. These types
25 of chips are recognized and preferred by some con-
supers. These preferences for certain variations of
chips may be related to ethnic or regional habits, to
fad or to the consumer's desire to reduce fat intake.
One of these variations of chips is the low fat potato
30 chip, which ha been processed by a continuous cooking
system whereby the oil temperature remains relatively
constant or increases during the entire cooking
period, i.e., usually at a temperature range of about
275 to 350F. The low fat potato chips are cooked
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for about 2-3 minutes, however, the cooking time will
depend upon the type of potato used, slice thickness,
and the cooking temperature. The fat content of a low
fat potato chip may be in the range of about 22-24% by
5 weight or lower, compared to the usual 32-40% of a
conventional chip.
A problem with conventional deep-fried cooking is that
when the potato slices come into contact with the fat,
the temperature of the fat is about 365F which will
decrease during the stay of the slices in the cooker.
On account of the high temperature of the fat, an
explosive boiling takes place in the first part of the
cooker, as a result of which the vapor pressure in the
slices causes some of the cell walls to burst. these
15 ruptured cells will at least partially fill with fat
when the water contained in the slices is nearly all
gone. For this reason, a conventional potato chip
will contain a large proportion of fat.
However, in the cooking of low fat chips, the low
20 cooking oil temperature and particular time-tempera-
lure curve allow the water to be removed from the
potato cells at a slower rate than with conventional
chips, thus minimizing rupture of the cells while
maintaining sufficient vapor pressure to minimize oil
25 entry into the cells.
There are at least two types of potato chips which
have been recognized by the consumer as being neither
a low fat chip nor a conventional potato chip. One of
these types is usually characterized by the descrip-
30 live terms "home style" or nope kettle chips Rather than being cooked by a continuous process which
is generally used for conventional chips, the "home
style" chips are cooked in a watch process and are
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usually crisper and heavier than a conventional chip.
Also, whereas conventional chips are normally cooked
in oil, "home twill chips are sometimes cooked in
lard, which is idea at room temperature. Since
they are batch processed, "home style" chips not only
are highly labor intensive to produce, but the product
uniformity is difficult to control and the energy
efficiency of the process is lower than what is
achievable by a continuous process. Moreover, in
10 limited regional markets a certain degree of non
uniformity and variation in finished food product
color, fat and moisture content may be acceptable to
the consumer, but in the large national market, such
variation is less readily accepted.
Another type of specialty chip which has been recog-
sized by the consumer is the so-called "Maui-style"
chip. This chip is recognizable in that it is
normally of heavier thickness than a conventional
chip, ha more color variation and is characterized by
20 a harder bite. The "Maui-style" chip is processed
differently than a conventional chip in that the
uncooked potato slices are usually unwashed or only
lightly washed prior to being immersed in the oil.
For conventional chips, the uncooked slices are
25 usually washed prior to being immersed in oil in order
to remove the surface starch. Furthermore, "Maui-
style" chips are usually made by batch processing,
although continuous processes exist. The time-
temperature profile of a batch cooking process for a
30 "Maui-style" chip is unlike the conventional chip or
low fat whip in that the oil temperature decreases
during the initial portion of the cooking period, then
increases during the later portion of the cooking
period. Its cooking time is longer than a normal
35 chip, usually in the range of I to 9 minutes. While
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not intending to be bound by any particular theory, it
is believed that the characteristic time-temperature
profile the particular potato used and the surface
starch on the slices are at least required to produce
a mustily" chip. Typically, to process Maui-
style" chips, the unwashed or lightly washed uncooked
slices are initially immersed into the hot oil at a
temperature of about 290~ to 330F. Over a period of
approximately 2-4 minutes temperature of the oil drops
10 by approximately 30, depending on the cooker size,
oil volume, batch size and surface water. After this
period, the cooking will continue during which there
is a gradual rise in temperature, usually of about 20
to 30F. Partially due to the fact that a "Maui-
15 style" chip requires a longer cooking time and also because of its unusual time-temperature cooking
profile, the chips are usually made by batch process-
in since conventional continuous cookers produce
linear, saw-tooth, or gradually decreasing time-
20 temperature cooking profiles which are inappropriate for cooking mustily" chips.
It would thus be desirable to provide an apparatus
which is readily adaptable for continuous cooking of
various types of chips, including chips which have
25 heretofore primarily been cooked by batch processing.
It is also desirable to provide a method and apparatus
for improving the quality of conventional potato
chips, whereby potatoes of lesser chipping quality may
30 be used to produce commercially acceptable chips. For
example, dark or varied colored chips are a result of
presence of reducing sugars which have been converted
from starch due to improper storage conditions, growth
condition and the particular variety of potatoes. It
35 is thus advantageous to provide an apparatus whereby
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the cooking conditions are readily varied in the cooker to adapt
to the characteristics (such as, sugar content) of a particular
supply of potatoes in order to produce the constant and lighter
chip color.
It is also desirable to be able to vary the oil content of the
potato chip. For example, low fat potato chips require a
specialized process, but oil content may also be varied by the oil
temperature which, in part, is governed by the time-temperature
relationship. I-t is -thus desirable to be able to readily vary the
cooking oil temperature profile in a cooking apparatus, since cook-
in -time may be readily varied.
It is therefore most desirable to provide one apparatus which may
be adjusted or programmed to cook all types of potato chips as
well as deal with variations in the raw potatoes and which is
adaptable to provide a wide variety of time-temperature profiles.
The invention provides a process for continuous cooking of food
products comprising the steps of continuously introducing uncooked
food products at one end of the cooking zone containing hot oil;
continuously conveying said food product along a path through said
hot oil; and continuously withdrawing said cooked food product from
said oil after traversal of said path; said path through said oil
characterized by a -time-temperature profile which substantially
conforms to a predetermined curve having at least one change in
sign of slope.
An adjustable time-temperature cooking profile accommodates vane-
lions in the solids content, sugar/starch content and other kirk-
teristics in raw potatoes in order to achieve a uniform and/or
improved product.
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The present invention provides an apparatus for
continuous processing of food products comprising a
container adapted to accommodate hot oil a conveying
means for controlled advance of food products along a
predetermined path within the container, heat exchange
in means external to the container adapted for heat
exchange with oil communicating with the container,
means for withdrawing high-moisture oil from the
container, distributing means for recirculating oil
10 withdrawn from the container through a plurality of
inlet means disposed along the path wherein the inlet
means comprise means for mixing the recirculated
high-moisture oil with oil in communication with the
heat exchanging means, and means for proportioning the
15 relative amounts, such as a valve, of the recirculated
high-moisture oil and the oil communicating with the
heat exchanging means flowing into the mixing means.
One of the advantages of the present invention is that
it efficiently deals with the problem of high-moisture
oily. Cooking oils at 275~ and higher can contain
water in droplet form. The water enters the oil from
both the food product's surface and the water being
driven out of the food product. The mechanism of
water being contained in oil at a temperature above
it's boiling point is a result of several phenomena. A
droplet of water, spherical in shape, has little
surface area compared to its volume. As heat is
transferred from the hot oil to the colder water the
surface of the water droplet changes state from liquid
Tao vapor. In doing so, a large quantity of heat is
required, specifically 970 BTU/pound of water at
atmospheric pressure As this change of state occurs
the surface of the water droplet becomes enveloped by
team which it a poor conductor of heat, as compared
I
with water. This steam blanket further reduces the
heat transfer from the oil to the water droplet. If,
however, the oil is sufficiently agitated Jo as to
remove the steam blanket from the water droplet, or
more important if the water droplet is divided into
smaller particles, then the heat transfer rate is
greatly increased and rapid change of state from water
to steam occurs.
It is essential that most of the water be removed from
10 the oil before leaving the cooker and entering the
suction of a circulating oil pump as the reduced
pressure and turbulence that occur in the pump suction
accelerate the process of steam removal from the oil
and cavitation of the pump occurs, resulting in damage
15 to the pump and, since most pumps operate on a volt-
metric basis the mass flow of the oil is reduced since
much of the volume being pumped is replaced by vapor.
This situation has added serious effects in the heat
exchange system due to reduced oil flow rates and
local hot spots on the heat transfer surface due to
the presence of vapor instead of oil. The cavitation
may at times become so severe that oil circulation
ceases completely.
Since a minimum system oil volume is of primary
importance in maintaining low free fatty acid in the
oil, systems which remove water from oil but require
large volumes of cooking oil, are not practical.
In the accompanying drawings, FIG. 1 it a schematic
illustration of a preferred cooking apparatus accord-
in to the present invention.
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FIG. lo is a detailed view of the mixing apparatus Andy 32B in FIG. 1.
FIG. 2 is a schematic drawing of a second preferred
apparatus according to the present invention.
FIG. PA is a detailed view of the mixing apparatus AYE
and 56B in FIG 2.
FIG. 3 is a plot of a typical time-temperature curve
and time-Btu required curve for the cooking of Maui-
style" potato chips.
10 The cooking apparatus according to the present inane-
lion may be utilized as the continuous cooking combo-
next in a food processing system. Thus, the cooking
apparatus according to the present invention may be
used in conjunction with a slicer or combination of
15 slicer and washer located upstream of the cooker. The
slicer may be located upstream of the cooker whereby
the sliced raw food products are conveyed by appear
private means and deposited into the entrance end of
the cooker. Alternatively, the slicer may ye disposed
20 above the entrance end of the cooker whereby the
slices of raw food are dropped directly into the hot
oil It is preferred that the slicer be adapted with
a washing apparatus which may ye optionally used, to
provide the versatility of cooking washed raw slices
25 of potatoes for conventional potato chips, or unwashed
raw potato slices for "Maui-style" chips. washing
apparatus is commercially available whereby a washing
step may be used or omitted without changing equip-
mint.
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Downstream from the cooker there may key used a
defter apparatus, such as that described in Swedish
Patent 833,714 or U.S. Patent No. 3,627,535~ whereby
the cooking system will make low fat potato chips.
Also located downstream from the cooker may be convent
tonal seasoning and packaging apparatus.
Referring to Figure 1, there is shown a schematic
diagram of a preferred cooking apparatus according to
the present invention. Container 10 it adapted for
10 accommodating hot cooking oil. The raw food product
is introduced into the container in the area indicated
by arrow 11. As the food products are rooked, they
will usually float and eventually come into contact
with conveyor 12 which with oil velocity in zone A
15 controls residence time. Conveyor 12 also transfers
the chips into zone B where a plurality of rotating
paddles 13 dunk, separate, agitate and control the
advance of the chips. The forward velocity of the
cooking oil is usually faster than the paddle speed so
20 the paddles 13 hold the chips back to provide uniform
cook time. After the chips pass through the agitated
zone B they will contact a conveyor 14 which transfers
them into the final zone C where they are conveyed
through the hot oil by means of a frighted submerge
25 conveyor belt 15 which holds the chips below the
surface of the oil while controlling their advance
through the cooker. The cooked chips are then removed
from the cooker by means of take-out conveyor AYE and
excess surface oil is drained at the tame time from
30 the product. It may be seen that the total cooking
time is determined by the period it takes for a
particular chip to traverse the length of the con-
trainer 10 and the temperature profile within the
container is determined by the temperature gradient
35 if any, along the cooking path in container 10.
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Fitted inside the transfer conveyors 12 and 14 are
adjustable height whirs AYE and AYE, respectively,
that control the oil level in zones A and B, respect
timely Since the oil entering a zone must equal the
amount of oil leaving the same zone, this whir main-
twins zone oil level while allowing the excess oil
volume to flow from zone A to zone B, and zone B to
zone C. This feature allows much greater flexibility
in setting the oil circulation rates in each zone to
lo accomplish the desired temperature profile.
During the process of cooking potato chips, the
initial zone within the cooker produces a high level
of water in the oil as a result of raw product surface
water removed from the product in the cooking process.
15 The reaction of water with oil (hydrolysis) shortens
the useful fife of the oil, so water should be removed
as rapidly as possible from the oil.
The apparatus shown in figure 1 is equipped with means
for varying the localized cooking oil temperature at
20 various points along the cooking path so that the
time-temperature profile along the cooking path may be
made to substantially conform to a predetermined
time-temperature curve, and particularly to a time-
temperature curve having at least one change in slope.
25 A change in slope in a curve means there is at least
one point in the time-temperature profile where the
temperature changes from decreasing to increasing or
from increasing to decreasing.
Referring again to FIG. 1, container lo is adapted
30 with oil discharge lines AYE, 17B and 17C. The oil
which discharges through line AYE during the cooking
process will contain a substantial amount of water,
with somewhat less water being present in the oil
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discharging through line 17B. The oil discharge
through line 17C will usually contain a relatively
small amount of water, if any, since the cooked chips,
at the end of the corking process, contain little
water. The oil through line 17C is pumped via pump 1 8
into heat exchanger 19 where the oil is reheated for
recirculating into the container 10. The heat
exchanger 19 may be fuel-fired burner or use any other
heat transfer means conventional in the art. The
10 reheated oil exiting from heat exchanger 19 through
line 20 is then distributed through a network of lines
21, 22, 23 and 24 into container 10. However, before
entering container 10 the recirculated hot oil in
lines 22 and 23 is first mixed with high water con-
15 twining oil from lines 17B and AYE, respectively. The proportioning of the mixtures of the oil from lines 22
and 17B is controlled respectively through valves 25
and 26 and the proportioning of oil from lines 23 and
AYE controlled respectively through valves 27 and 28.
20 Appropriate pumps 29 and optional filter 30 are
provided. The apparatus for mixing the high water
containing oil and the hot oil comprises components
AYE, 31B, AYE and 32B.
The detail of AYE, 31B, AYE and 32B is shown in FIG.
25 lay The high water containing oil is forced through a
distribution manifold and through a plurality of jets
AYE. The hot oil from the heat exchanger 19 is also
forced through a distribution manifold and through a
plurality of jets 32B which is larger in diameter and
30 concentric to jet AYE. The rapid contact and intimate
mixing of the high-moisture containing oil with the
hot oil will cause the dispersed water droplets to
vaporize and flash from the oil, thereby lowering the
moisture content of the oil as it reenters tank 10.
35 As shown, jets AYE and 32B may be disposed at an angle
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with respect to the oil flow within the tank loo
Alternatively, high water containing oil may be forced
through jets 3~B and hot heat exchanger oil may be
forced through jets AYE, thereby reversing the roles
5 of the jets.
The relative flow rates of hot oil through jet 32B and
cooler oil through jet AYE will control the average
temperature of the oil within the vicinity of each
inlet 32B into container 10. Thus, my disposing a
10 plurality of inlets 32B along the cooking path within
container 10 the time temperature profile along the
cooking path may be controlled to substantially
conform to any predetermined curve. Various tempera-
15 lure monitoring means, such as thermocouples, may redisposed at advantageous points to monitor the temper-
azure characteristics of the oil. Exemplary tempera-
lure monitoring units 33 are shown in FIG. 1,
FIG. 2 shows another preferred apparatus according to
the present invention. A difference is that in FIG.
2, there are two streams of oil flowing in opposite
directions, both of which drain into sup 40 and 50 in
the tank comprising sections AYE and 41B. The sliced
raw food products are dispensed from conveyor belt 42
and dropped into the hot oil into tank AYE. Chips are
conveyed through cook zone A by a combination of
forward oil velocity and the speed of submerged
conveyor 43. Conveyor 43 also serves to separate the
chips from the oil exiting through oil outlets 46 and
jumps 40 and 50. This positive means of Separating
the chips from the oil exiting the fryer provides
greater flexibility in adjusting oil slow rates
through intermediate inlet and outlet AYE, 56B and
46 which as necessary provide the desired time-temper-
azure curve. As the chip leave zone A, they are
engaged by the initial portion of conveyor 44 which
positively conveys the chips through both zone B and
zone C by a plurality of suspended positioning flights
AYE. Since the chips in zone B may till contain
sufficient moisture that confinement in a restricted
area would result in the formation of clumps of chips
that are cooked together, the belt portion of conveyor
44 is kept above the oil level and only the position-
in flights are used to control the chip movement.
10 When the chips reach zone C, the conveyor belt 44 is
offset downwardly to reduce the product space and then
submerges the chips under the surface of the oil where
cooking is completed.
Positioning flights AYE also serve as wipers to
15 prevent build-up of starch or product fines on the
tank bottom. This application flights AYE is similar
to that shown in Patent No. 3,472,155. Flights may
also be attached to belt 43 to provide similar wiping
action in Zone A.
20 The cooked chips are conveyed onto take-out conveyor
45 and discharged from the cooker. The oil in tank
41B flows downwardly into sup 50 to the left whereas
the oil in tank ala flows downwardly into sup 40 to
the right in FIG. 2 as shown. The high water contain-
25 in oil in zone A is confined substantially to Tenneco and is discharged through a network of lines 46
and pumped by pump 47 for recirculating into tank AYE
and 41B through lines 48 and 49. The substantially
moisture-free oil from zone B and C draining into sup
30 50 from tank 41B is separated from the oil on the sup
40 draining from AYE by baffle 50. This substantially
moisture-free oil it withdrawn through line 51 by pump
So into heat exchanger 53 where the oil is reheated to
an appropriate temperature. The reheated oil is then
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recirculated into tank AYE through the network of
lines 54 and into tank 4lB trough line 55. The hot
oil in lines 54 is mixed with the high water contain-
in oil from lines 48 and the hot oil from line 55 is
mixed with high water containing oil from line 49 by
the mixing apparatus AYE and 56B, shown in greater
detail in FIG. PA.
Referring to FIG. PA, the hot oil from the heat
exchanger is passed through a distribution manifold
10 and through jets 57B. The high water containing
cooler oil is passed through the distribution manifold
and through jets AYE which are concentric with jets
57B. The rapid contact of the hot oil and the cooler
high water containing oil causes intimate mixing and
1 sudden expansion of the water droplets and flashing
off the water vapor. As shown, the inlet jet 57B is
orthogonal to the flow of oil within tanks AYE and
41B.
The localized temperature along sections of tank 41B
may be controlled by disposing along the cooking path
within tank 41B inlet jets 58 which contain reheated
oil from heat exchanger 53 and which flash off moist
lure in oil before it reaches jump 40 and pump 52.
Various temperature control means such as thermos
couples, not shown, may be appropriately located along
various lines and locations in the tank to control the
localized temperature within each tank AYE and 41B.
The relative flow of hot and cold oil through the
various lines may be controlled by various valves 60.
Both the apparatus shown in FIGS 1 and 2 may be
utilized in a continuous cooking process whereby the
cooking path through the oil is characterized by a
time-temperature profile which may be controlled to
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substantially conform to a predetermined time-tempera-
lure curve. In addition, the apparatus shown in FIGS.
l and 2 remove the dispersed water droplet from the
oil without adding excessive oil volume to the system.
.
The apparatus in FIGS. 1 and 2 are particularly
adapted to provide a continuous process fox cooking a
food product which requires a time-temperature profile
having a temperature drop followed by a temperature
rise. For example, referring to FIG. 3, there is
lo shown a plot of a typical time-temperature profile and
time-Btu required profile for the cooking of "Maui-
style potato chips. Although these curves were
determined from a batch style cooker, these time-
temperature profiles may be substantially reproduced
15 using a continuous cooker as shown in FIGS. l or 2.
As may be seen in FIG. 3, the time-temperature profile
for cooking mustily" chips shows an initial
cooking temperature of about 330F which gradually
decreases or approximately 3 to I minutes to about
20 304F. After 3 to I minutes, the temperature then
increases, and gradually increases over the next I
minutes to a final temperature of about 324F, at
which time the cooked chips are removed from the oil
and the oil temperature is allowed to increase to
25 330F before the next batch is started.
It will be readily apparent that various modifications
may be made to ye within the scope of the present
invention. In particular, in a particularly preferred
embodiment, a defeating unit may be provided down-
30 Bream from cookers shown in FIGS. l or 2 produce Audi product having a substantially decreased fat
content.
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