CA1238203A - Food processing method and apparatus - Google Patents

Abstract

ABSTRACT

Cooking apparatus is provided for cooking food products in a continuous manner whereby the moisture formed during the process of cooking is purged from the cooking oil and the time-temperature profile within the cooker along the cooking path may be adapted to substantially conform to a linear or non-linear curve. In particular, the apparatus provides a continuous cooking method whereby the time-temperature profile along the cooking path substan-tially conforms to a curve having at least one change in sign of slope. The apparatus provides a novel process for cooking specialty potato chips.

Description

~L~3~2(~3 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 , :.

8'~3 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in the oil at one end of the cooker and advanced under control through the cooker where potato chips are continuously withdrawn from the other end.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 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 .

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 aye 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 ~Z3~

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 .; .

~82~3 -7-- 61051-]872 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.

Jo ~3~2~3 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.

aye ~Z3~ 33 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 I;, ,, ~q~3~2~3 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 'I :`
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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 ;

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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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for cooking food products comprising a container adapted to accommodate hot oil;
conveying means for transporting food products along a predetermined path within said container;
heat exchanger means external to said container adapted for heat exchange with oil communicating with said container;
means for withdrawing high-moisture oil from said container;
distributing means for recirculating oil with-drawn from said container through a plurality of inlet means disposed along said path;
wherein said inlet means further comprises means for mixing said high-moisture oil with oil in commu-nication with said heat exchanging means;
and means for proportioning the relative amounts of said high-moisture oil and said oil in communica-tion with said heat exchanger means flowing into said mixing means.

2. An apparatus according to Claim 1 wherein said mixing means comprises two concentric jets, each respectively accommodating the flow of said high-moisture oil and said oil in communication with said heat exchanging means.

3. An apparatus according to Claim 2 wherein the flow of oil within said container is parallel to the longitudinal direction of said path.

4. An apparatus according to Claim 2 wherein said container accommodates two separate streams of flowing oil, wherein the direction of flow of each of said streams is opposite to one another and are both parallel to the longitudinal direction of said path.

5. 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.

6. A process according to Claim 5 wherein said food product comprises potato chips.