Abstract:
A continuous oil fryer used to fry food slices, such as potato chips, having an internal oil stripping capability. The fryer accumulates the steam produced by the frying process in a hood and utilizes such steam, after superheating the steam by passing it through a heat exchanger, to strip oil from product immediately upon removal from the hot oil bath by passing the superheated steam through a product bed while on an output conveyor. The superheated steam removes oil from the product on the output conveyor without increasing the moisture level of the product. The fryer therefore accomplishes the same function as a low-oil stripper without increasing the footprint of the frying unit and with less energy.

Description:
PRIORITY CLAIM 
       [0001]    This application is a divisional of co-pending U.S. patent application Ser. No. 12/263,861, filed Nov. 3, 2008, entitled “Oil Stripping Fryer Unit,” the technical disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Technical Field 
         [0006]    The present invention relates to a fryer assembly having an oil stripping capability integral to the unit. More particularly, the invention relates to the extension of the steam collection hood on a chip frying unit and the incorporation of oil stripping features in such extended hood, thereby eliminating the need for a separate low-fat stripping unit. 
         [0007]    2. Description of Related Art 
         [0008]    Food pieces, such as potato chips, are commonly cooked in hot oil in a fryer, such as a Heat and Control PC-50 fryer. A simplified schematic illustration of such a continuous fryer is shown in  FIG. 1 . 
         [0009]    Referring to  FIG. 1 , the food pieces, such as potato slices, are inserted into the fryer unit by means of a infeed conveyor  102 . The slices then float in the hot oil  104  until removed from the fryer unit by an output conveyor  106 . Agitation paddles (not shown) and a submerger  105  can be used to keep the slices from clumping together and floating to the surface of the oil  104 . The fried food pieces on the output conveyor  106  are in a bed arrangement, as opposed to single chips in a monolayer arrangement, and are therefore referred to as a product bed  120  on the conveyor  106 . 
         [0010]    The food pieces are dehydrated during the frying process and, therefore, release moisture in the form of steam. This steam is collected by a hood  108  located above the oil  104 . As shown in  FIG. 1 , it is common to exhaust the steam collected by such hood by one or more large exhaust fans  110  associated with one or more exhaust ports  112 , as illustrated by the arrows within the hood  108 . The steam temperature within such hood is typically in the range of 220° F. to 260° F., or normally about 240° F. The collected steam from the exhaust ports  112  is typically condensed, collected, and discarded or used in other unrelated processes. Thus, in most prior art applications the latent heat of the steam is essentially lost in the process. 
         [0011]    Absent further processing to reduce the amount of oil in the chips produced by the fryer illustrated in  FIG. 1 , typically potato chips exit such fryer ready for seasoning and packaging with a total oil content by weight of approximately 36% and preferably a moisture level of about 1.1-1.5% by weight. In order to reduce the oil level of such chips, however, the chips can be routed directly from the frying unit illustrated in  FIG. 1  by means of the output conveyor  106  to a low-fat stripping unit as illustrated in  FIG. 2 . This output conveyor  106  remains enclosed such that the fryer of  FIG. 1  and the low-fat stripper of  FIG. 2  are in communication with each other and each is a part of a single enclosed system. 
         [0012]      FIG. 2  is a simplified schematic illustration of a prior art low-fat stripping system or unit, also referred to as a low-fat stripper, such as the model LFSS manufactured by Heat &amp; Controls of Hayward, California. Product, such as potato chips, enters the low-fat stripper by means of an infeed conveyor  206 , which has received the product from the output conveyor  106  of  FIG. 1  or is simply a continuation of said output conveyor  106 . The conveyor belt on such infeed conveyor  206  is porous, thereby allowing fluids, such as oil dripping off the product bed  220 , to easily pass through the belt. Superheated steam is forced at high velocity through the product bed  220  while the product is on the infeed conveyor  206 . This steam strips oil from the surface of the chips. The stripped oil drops to the base of the low-fat stripper or is carried with the steam as it exits the product bed  220 . 
         [0013]    The steam then flows through an oil separator  222  before being blown through a heat exchanger  224  to be reused again for stripping of the product bed  220 . The heat exchanger  224  adds heat to the steam to keep it in a super-heated state. Steam is also constantly generated and added to the low-fat stripper to replace steam vented back to the fryer and lost elsewhere in the system. The steam is circulated throughout the entire unit (as illustrated by the arrows) by a high-volume fan  226 . The stripped product exits the unit via an output conveyor  228 . 
         [0014]    The low-fat stripper recycles some of the steam it uses and removes some of the oil from the product. Potato chips made using a low-fat stripper typically have a finished oil content by weight of between 20% and 28% and a finished moisture level of about less than 2%. 
         [0015]    The steam in the low-fat stripper is superheated to typically in the range of 290° F. to 320° F. The pressure in the low-fat stripper unit is maintained at approximately ambient conditions. The velocity of the steam as it blows onto the product bed is in the range of 1,500 ft./min. to 2,500 ft./min. The use of superheated steam in the stripper is important, because if steam at lower temperatures is used the product tends to absorb moisture from the steam. Adding moisture back into the product at this stage is generally undesirable, as it is preferred that the product exit the stripper at or below 2% moisture by weight for, among other reasons, longer shelf stability. 
         [0016]    The low-fat stripper, as noted previously, is a separate unit from the fryer illustrated in  FIG. 1 . As a consequence, a product line that incorporates a low-fat stripper requires a larger plant footprint. In addition, the low-fat stripper is a capital expenditure above and beyond the cost of the fryer itself. There are energy costs as well when steam produced by the fryer is discarded while steam is constantly added and heated in the stripper. 
         [0017]    Low-fat strippers such as the one described above require the use of large amounts of steam at very high velocities to effectively strip the product of a meaningful amount of oil. It is now understood that the reason for this high-energy requirement relates to the amount of time that it takes to get the product from the cooking oil  104  of  FIG. 1  into the low-oil stripper of  FIG. 2 . During the transit time from the oil to the stripper, the product cools and continues to absorb oil. One of the mechanisms for reducing the oil in the chip is to heat the chip outside of the oil environment so that the dehydration of the chip drives the expulsion of oil from within the chip and off of its surface. In other words, the continued release of water vapor or steam from within the chip provides a mechanism for removing oil from the chip. When the chip is allowed to cool prior to exposure to superheated steam, much more energy or work is required to remove any substantial amount of oil from the chip. Unfortunately, since the oil stripper and the fryer are two separate units, the transit times between removal from the oil until entrance into the stripper can be in the range of 40 seconds to a minute or more. During that time, the chips cool considerably, making it that much more difficult to remove the oil from the chips. 
         [0018]    Consequently, a need exists for combining the low-fat stripper capabilities of reducing the oil content of the finished fried chips with the basic equipment of existing fryers. This new apparatus should minimally affect the equipment footprint of a stand-alone fryer while utilizing the steam produced in situ. Such unit should amount to a decrease in energy usage, decrease in plant footprint, decrease in capital outlay per line, and yet provide finished product chips with a reduced fat content and low moisture content similar to chips produced when an oil stripper unit is used. 
       SUMMARY OF THE INVENTION 
       [0019]    The present invention involves a modification to existing hooded fryer design in order to combine the functionality of a low-oil stripper with the fryer unit. In one embodiment of the present invention, the steam vents in the fryer hood over the hot oil are blocked off or restricted so that the steam accumulates in the hood as opposed to immediately venting. The steam is then drawn towards what is normally the exit end of the fryer by one or more fans positioned inside the hood or in an exhaust port at the exit end of the fryer. The steam is then passed through a heat exchanger, thereby pre-heating the steam to a superheated state, typically in the range of 300° F. to 310° F. This superheated steam is then passed through the product bed as the product is exiting the fryer on the output conveyor. Thus, the steam generated by frying the product is used to strip the product of excess oil all in the same unit. 
         [0020]    The present invention is an improvement over the prior art in that combining the functionality of a low-oil stripper within a fryer hood reduces the overall equipment footprint and takes advantage of the steam produced in the fryer for use as the stripping steam. Applicants&#39; invention decreases the overall energy use on a low-fat product line, decreases the plant footprint for such product line, and decreases the capital outlay required to set up such product line. Yet, Applicants&#39; invention produces low-fat chips with the requisite low moisture levels. 
         [0021]    These as well as additional features and advantages of the present invention will become apparent in the following written description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
           [0023]      FIG. 1  is a schematic illustration of a prior art fryer; 
           [0024]      FIG. 2  is a schematic illustration of a prior art low-fat stripping unit; and 
           [0025]      FIG. 3  is a schematic illustration of a fryer with built-in stripping capabilities of one embodiment of Applicants&#39; invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]      FIG. 3  is a simplified schematic representation of one embodiment of Applicants&#39; invention. As with a prior art fryer, Applicants&#39; continuous fryer comprises a steam hood  308  which collects the steam produced in situ by product being fried in the hot oil  304 . The product is likewise introduced into the fryer by an infeed conveyor  302 . However, the hood  308  of Applicants&#39; invention does not necessarily exhaust the produced steam through exhaust ports  340  located above the frying product, as is illustrated by the exhaust ports  112  in  FIG. 1 . In fact, a prior art frying unit can be modified by simply closing off or restricting any such exhaust ports  112  or can maintain one or more such ports  340  ( FIG. 3 ) with an adjustable door or closing means  338  that can restrict the flow of steam through the port  340 . 
         [0027]    As illustrated in  FIG. 3 , Applicants&#39; fryer comprises one or more flow inducing devices  310 ,  311 , such as a fan  310 , for the purpose of flowing the steam through the hood from an upstream position near the slice infeed  302  to a downstream position near the output conveyor  306 . Such one or more fans  310 ,  311  can be located in any number of areas in the hood, such as before or after the heat exchanger  324 , provided that the fans induce the flow as will be described herein. For example, and without limitation, a single exhaust fan  311  can be located in the exhaust port  312  at the downstream end of the unit. This exhaust fan  311  can operate alone or in conjunction with one or more other fans  310  located within the hood  308 . Likewise, one or more fans  310  located in the hood  308  can drive the steam flow with or without the benefit of an exhaust fan  311 . The location, number and type of fans  310 ,  311  used with Applicants&#39; invention is dependent on the desired flow characteristics, velocities, and product applications. 
         [0028]    Applicants&#39; invention further consists of a heat exchanger  324  located within the hood. This heat exchanger is located in close proximity to the output conveyor  306 . The heat exchanger  324  is upstream from a flow diversion component  330  that is used to direct steam after it has passed through the heat exchanger  324  towards the product bed located on the output conveyor  306 . The area on the output conveyor  306  that is exposed to the steam flowing through the product bed is referred to by Applicants as an oil stripping zone  332 . This oil stripping zone  332  is necessarily located between the heat exchanger  324  and the flow diversion device  330 . The output conveyor  306  is constructed of a porous material or design that allows for the free flow of the steam through the product bed found on the output conveyor  306  and through the output conveyor  306  itself. Once the steam is blown through the product bed on the output conveyor  306  the steam is directed out of the fryer by way of the exhaust port  312  which is accessed from an opening  344  downstream of the oil stripping zone. Product is removed from the output conveyor by way of a rotary air lock  336 . Because of the rotary air lock  336 , steam cannot exit the hood  308  after flowing through the stripping zone  324  by any means other than the exhaust port  312  by way of an opening  344  into said port  312 . 
         [0029]    The steam flow through the hood  308  from upstream to downstream is illustrated by the flow arrows shown in the hood  308 . In a preferred embodiment, steam is collected in the hood  308  in the temperature range of about 212° F. to about 300° F. The steam is then passed through the heat exchanger  324  in order to raise the temperature of the steam to preferably in the range of about 280° F. to about 320° F. or more preferably in the range of about 300° F. to about 310° F. Steam pressure within the unit is maintained at approximately ambient levels. The steam is next directed through the product bed and the output conveyor  306  at the oil stripping zone  332 . The velocity of this steam as it is blown through the oil stripping zone  332  (passes through the food pieces) is, in a preferred embodiment, less than 1,000 ft./min., and more preferably about 250 ft./min. to about 500 ft./min. This flow rate corresponds to a product production rate of about 2,000 lbs./hr. to 40,000 lbs./hr. and a steam production rate within the hood of about 500 lbs./hr. to about 10,000 lbs./hr. 
         [0030]    Applicants have found that much lower velocities can be used for the stripping steam than has been used in the past in low-oil strippers. This is believed to be a result of not allowing the product to cool prior to stripping. The product bed is subjected to super heated steam as soon as possible after removal from the oil  304 . Because the steam is super-heated as it passes through the oil stripping zone  332 , the food pieces on the output conveyor  306  continue to cook, thereby driving moisture out of the food piece. This continuous cooking, without a cool down while the product is in transit to the stripper as occurs in the prior art, inhibits the absorption of further moisture by the food pieces from the contact with the steam and more efficiently drives oil out of the chip, which is then more easily stripped by the steam. Importantly, the prior art methods involve an elapsed time of typically 30 to 60 seconds, between the time product is removed from the oil  304  and when it is subject to steam stripping. Applicants&#39; invention reduces this elapsed time to 10 seconds or less, because the product is stripped immediately after leaving the oil  304 . In fact, it is preferred that stripping occur within  5  seconds of removal of the product or food pieces from the hot oil  304  by the output conveyor  306 . In order to accomplish this timely stripping, the oil stripping zone  332  must start within a close proximity to the oil  304 , preferably within three feet thereof, and more preferably within two feet thereof. Thus, the oil stripping zone  332  starts within three feet of the point where the output conveyor  306  is in communication with the oil  304 . 
         [0031]    After passing through the oil stripping zone  332 , the steam can be further blown through an oil separator  322  before being exhausted from the frying unit. The recovered oil from the steam is then returned to the frying oil via an oil collection point  334  for further use. Alternatively, since virgin steam is being constantly produced in the hood  308 , the steam can be exhausted without passing through an oil separator  332 . 
         [0032]    The steam temperature and flow rates can be adjusted as well as the product throughput in order to obtain the desired reduction in oil content of a food piece fried with Applicants&#39; fryer. The volume of the steam can also be adjusted by a door  338  on an exhaust or relief port  340  (with its exhaust fan  342 ) located upstream of the heat exchanger. When excess steam collects in the hood  308 , the door  338  is opened on the relief port  340  in order to vent the excess steam prior to the steam passing through the heat exchanger  324 . If necessary, a fan  342  can be activated to draw the excess steam out of the hood  308 . The size of the opening obtained by opening the door  338  and/or the fan  342  speed can be adjusted to ensure the desired amount of steam is removed. 
         [0033]    In a preferred embodiment, Applicants&#39; modified fryer produces potato chips having a finished oil content of about 28% to about 31% by weight. These potato chips also have a low moisture level, typically about 1.1% to about 1.5% by weight due to the use of the super-heated steam as previously described. Yet, Applicants&#39; invention uses less energy to accomplish this stripping. 
         [0034]    One embodiment of Applicants&#39; modified fryer is constructed by modifying existing hooded continuous fryers by sealing off the exhaust ports located above the frying oil, adding an internal heat exchanger and flow inducing device, and constructing the downstream portion of the fryer such that it directs the steam through the oil stripping zone and out an added exhaust port that defines the furthest downstream point of steam within the fryer. In an alternative embodiment of Applicants&#39; invention, a hooded continuous fryer is constructed of a hood having no or closeable/adjustable exhaust ports above the frying oil and the same configuration of the downstream heat exchanger, diversion device, and exhaust port as previously described. 
         [0035]    The foregoing is merely illustrative of the principles of this invention, and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, while the invention has been described in the context of a potato chip frying line, it should be understood that the invention and principles involved therein are applicable to the cooking and stripping of any fried food piece, such as fried fruit chips, fried vegetable chips, other fried tuber slices such as sliced sweet potatoes, and fabricated food slices made from sheeted dough as well such as fabricated potato chips, tortilla chips, and corn chips, and other fabricated vegetable and/or fruit based chips. Thus, the starting material can be either a raw food piece or a fabricated food piece made from sheeting a dough, any of which results in an end product generically referred to by Applicants as a “chip.” Applicants&#39; invention is applicable to all hooded continuous fryers used to cook food pieces of any type.