GB2170396A - For processing method and apparatus - Google Patents

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 along the cooking path substantially conforms to a curve having at least one change in sign of slope. The apparatus includes means for withdrawing high-moisture oil from the cooking tank and mixing it with oil heated by a heat exchanger and then returning the mixture to the cooking tank. The relative amounts of the high- moisture oil and the oil heated by the heat exchanger are controlled to give the required time-temperature profile to the oil in the cooking tank. <IMAGE>

Description

SPECIFICATION Food processing method and apparatus 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 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 so 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 cooking 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 conveyors. In such a cooker, the slices are continuously 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in the oil at one end of the cooker and advanced under control through the cooker where potato chips are continuously withdrawn from the other end.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 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 have a fat content in the range of about 3240% 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 circulation. The chip is immersed initially into hot oil at a temperature of about 360" to 3900F 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 temperature of about 320 to 35O0F. There is usually a 30 to 45" drop in temperature during the course of continuous cooking of conventional potato chips. In some instances, multi-zone cookers are used wherein the temperature drops along the cooking path in one zone, then rises as the next zone is entered, resulting in a "sawtooth" temperature profile along the cooking path.

Other continuous cooking 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 is 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 unnecessarily contain much more cooking oil than required to 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 fact affecting cooking oil quality is the film temperature 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.

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 of chips are recognized and preferred by some consumers. These preferences for certain variations of chips may be related to ethnic or regional habits, to fat or to the consumer's desire to reduce fat intake.

One of these variations of chips is the low fat potato chip, which has 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 350"F. 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 2224% by weight or lower, compared to the usual 3240% 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 365"F 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 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 cooking oil temperature and particular timetemperature curve allow the water to be renaoved 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 entry into the cells.

There are at least two types of potato chipsiwhich have been recognized by the consumer as besng neither a low fat chip nor a conventional potato chip.

One of these types is usually characterized byFthe descriptive terms "home style" or"open kettle" chips. Ratherthan being cooked buy a continuous process which is generally used for conventional chips, the "home style" chips are cooked in a batch process and are usually crisper and heavierthan a conventional chip. Also, whereas conventional chips are normaily cooked in oil "home style" chips are sometimes cooked in iard, which is a solid 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 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 speciality chip which has been recognized by the consumer is the so-called "Mauistyle" chip. This chip is recognizable in that it is normally of heavier thickness than a conventional chip, has more color variation and is characterized by a harder bite. The "Maui-style" chip is processed differently than a conventional chip in that the uncooked potato slices are usualy unwashed or only lightly washed prior to being immersed in oil. For conventional chips, the uncooked slices are usually washed prior to being immersed in the oil in order to remove the surface starch. Furthermore, "Mauistyle" chips are usually made by batch processing, although continuous processes exist.The timetemperature profile of a batch cooking process for a "Maui-style" chip is unlike the conventional chip or low fat chip 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 chip, usually in the range of 72 to 9 minutes. While 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 "Maui-style" chip.Typically, to process "Mauistyle" chips, the unwashed or lightly washed uncooked slices are initially immersed into the hot oil at a temperature of about 290 to 330"F. Over a period of approximately 29 minutes temperature of the oil drops by approximately 30 , depending on the cooker size, oil volume, batch size and surface water. After thins period, the cooking will continue during which there is a gradual rise in temperature, usually of about 20 to 30"F. Partially due to the fact that a "Maui-style" chip requires a longer cooking time and also because of its unusual timetemperature cooking profile, the chips are usually made by batch processing since conventional continuous cookers produce linear, saw-tooth, or gradually decreasing time-temperature cooking profiles which are inappropriate for cooking "Mauistyle" chips.

Itwould thus be desirable to provide an apparatus which is readily adaptable for continuous cooking of various types of chips, including chips which have 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 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 is thus advantageous to provide an apparatus whereby 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 time-temperature relationship. It is thus desirable to be able to readily vary the cooking oil temperature profile in a cooking apparatus, since cooking 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.

It is therefore an object of the present invention to provide an apparatus for continuous processing of cooked food products which is adaptable to provide a wide variety oftime-temperature profiles.

It is another object of the present invention to provide an apparatus which provides an adjustable time-temperature cooking profile to accommodate variations in the solids content, sugarlstarch content and other characteristics in raw potatoes in order to achieve a uniform and/or improved product.

These and other objects of the present invention will be apparent from the following description of the preferred embodiment: 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 exchanging 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 withdrawn from the container through a plurality of inlet means disposed along the path wherein the inlet means comprise means for mixing the recirculated highmoisture oil with oil in communication with the heat exchanging means, and means for proportioning the 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 highmoisture oil. 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 its 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 to 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 steam which is a poor conductor of heat; as compared with water.

This steam blanket further reduces the heat transfer from the oil to the water droplet. If, however, the oil is sufficiently agitated so 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 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 capitation of the pump occurs, resulting in dama'ge to the pump and, since most pumps operate on a volumetric 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. lisa schematic illustration of a preferred cooking apparatus according to the present invention.

FIG. 1A is a detailed view of the mixing apparatus 31A and 32B in 1.

FIG. 2 is a schematic drawing of a second preferred apparatus according to the present invention.

FIG. 2A is a detailed view of the mixing apparatus 56A 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.

The cooking apparatus according to the present invention may be utilized as the continuous cooking component in a food processing system. Thus, the cooking apparatus according to the present invention may be used in conjuction with a slicer or combination of 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 appropriate means and deposited into the entrance end of the cooker. Alternatively, the slicer may be disposed 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 be optionally used, to provide the versatility of cooking washed raw slices 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 equipment.

Downstream from the cooker there may be used a defatter 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 conventional 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 is adapted for 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 cooked, they will usually float and eventually come into contact with conveyor 12 which with oil velocity in zone A 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 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 flighted submergerconveyor 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 15A and excess surface oil is drained at the same time from 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 container 10 and the temperature profile within the container is determined by the temperature gradient, if any, along the cooking path in container 10.

Fitted inside the transfer conveyors 12 and 14 are adjustable heightweirs 12Aand 14a, respectively, that control the oil level in zones A and B, respectively. Since the oil entering a zone must equal the amount of oil leaving the same zone, this weir maintains 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 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. The reaction of water with oil (hydrolysis) shortens the useful life 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 various points along the cooking path so that thetime4emperature profile along the cooking path may be made to substantially conform to a pedetermined time-temperature curve, and particularly to a time-temperature curve having at least one change in slope. A change in slope in a curve means there is at least one point in the timetemperature profile where the temperature changes.

from decreasing to increasing or from increasing to decreasing.

Referring again to FIG. 1, container 10 is adapted with oil discharge lines 17A, 17B and 17C. The oil which discharges through line 17A during the cooking process will contain a substantial amount of water, with somewhat less water being present in the oil discharging through line 17B. The oil discharge through line 17Cwill usually contain a relatively small amount of water, if any, since the cooked chips, at the end of the cooking process, contain little water. The oil through line 17C is pumped via pump 18 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 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 containing oil from lines 178 and 17A, 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 17A controlled respectively through valves 27 and 28.

Appropriate pumps 29 and optional filter30 are provided. The apparatus for mixing the high water containing oil and the hot oil comprises components 31A, 318, 32A and 32B.

The detail of 31 A, 318, 32A and 32B is shown in FIG. The high water containing oil is forced through a distribution manifold and through a plurality of jets 32A. 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 concentric to jet 32A. The rapid contact and intimate mixing of the highmoisture 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 re-enters tank 10. As shown, jets 32A and 32B may be disposed at an angle with respect to the oil flow within the tank 10.Alternatively, high water containing oil may be forced through jets 32B and hot heat exchanger oil may be forced through jets 32A, thereby reversing the roles of the jets.

The relative flow rates of hot oil through jet 32B and cooler oil through jet 32A will control the average temperature of the oil within the vicinity of each inlet 32B into container 10. Thus, by disposing a 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 temperature monitoring means, such as thermocouples, may be disposed at advantageous points to monitor the temperature characteristics of the oil. Exemplary temperature 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, bot of which drain into sump 40 and 50 in the tank comprising sections 41A and 41 B.

The sliced raw food products are dispensed from conveyor belt 42 and dropped into the hot oil into tank 41A. Chips are conveyed through cook zone A by a combination of forward oil velocity and the speed of submerged conveyor43. Conveyor 43 also serves to seperate the chips from the oil exiting through oil outlets 46 and sumps 40 and 50. This positive means of separating the chips from the oil exiting the fryer provides greater flexibility in adjusting oil flow rates through intermediate inlets and outlets 56A, 56B and 46 which as necessary provide the desired time-temperature curve. As the chips leave zone A, they are engaged by the initial portion of conveyor 44 which positively conveys the chips through both zone Band zone C by a plurality of suspended positioning flights 44A.Since the chips in zone B may still 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 onlythe positioning flights are used to control the chip movement. When the chips reach zone C, the conveyor belt 44 is offset downwardly to reduce the product space and then submerges the chips underthe surface of the oil where cooking is completed.

Positioning flights 44A also serve as wipers to prevent build-up of starch or product fines on the tank bottom. This application flights 44A 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.

The cooked chips are conveyed onto take-out conveyor 45 and discharged from the cooker. The oil in tank 418 flows downwardly into sump 50 to the left whereas the oil in tank 41 A flows downwardly into sump 40 to the right in FIG. 2 as shown The high water containing oil in zone A is confined substantially to tan k 41 A and is discharged through a network of lines 46 and pumped by pump 47 for recirculating into tank 41A and 41B through lines 48 and 49. The substantially moisture-free oil from zone B and C draining into sump 50 from the tank 41B is separated from oil in the sump 40 draining from 41A by baffle 50. This substantially moisturefree oil is withdrawn through line 51 by pump 52 into heat exchanger 53 where the oil is reheated to an appropriate temperature. The reheated oil is then recirculated into tank 41A through the network of lines 54 and into tank 418 through line 55. The hot oil in lines 54 is mixed with the high water containing 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 56A and 56B, shown in greater detail in FIG. 2A.

Referring to FIG. 2A,the hot oil from the heat exchanger is passed through a distribution manifold and through jets 57B. The high water containing cooler oil is passed through the distribution manifold and through jets 57A which are concentric with jets 578. The rapid contact of the hot oil and the cooler high water containing oil causes intimate mixing and 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 41A and 41 B.

The localized temperature along sections of tank 41B may be controlled by disposing along the cooking path within tank 418 inlet jet 58 which contain reheated oil from heat exchanger 53 and which flash off moisture in oil before it reaches sump 40 and pump 52. Various temperature control means such as thermocouples, not shown, may be appropriately located along various lines and locations in thetankto control the localized temperature within each tank 41A and 418. 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 timetemperature curve. In addition, the aparatus shown in FIGS. 1 and 2 remove the dispersed water droplets 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 for cooking a food productwhich requiresatime- temperature profile having a temperature drop followed by a temperature rise. For example, referring to FIG. 3, there is 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 using a continuous cooker as shown in FIGS. 1 or 2. As may be seen in FIG. 3, the time-temperature profile for cooking "Maui-style"' chips shows an initial cooking temperature of about 330"F which gradually decreases for approximately 3 to 31 minutes to about 304"F. After 3 to 32 minutes, the temperature then increases and gradually increases over the next 4l minutes to a final temperature of about 324"F, at which time the cooked chips are removed from the oil and the oil temperature is allowed to increase to 330"F before the next batch is started.

It will be readily apparent that various modifications may be made to be within the scope of the present invention. In particular, in a particularly preferred embodiment, a defatting unit may be provided downstream from cookers shown in FIGS. 1 or 2 produce a food product having a substantially decreased fat content.

Claims (9)

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 withdrawn from said containerthrough 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 communication with said heat exchanging means; and means for proportioning the relative amounts of said high-moisture oil and said oil and communication 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 highmoisture 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 timetemperature 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.

7. Apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

8. A process substantially as hereinbefore described with reference to the accompanying drawings.

9. A product obtained by a process as claimed in Claim 5, 6 or 8.