Abstract:
A continuous process for frying potato chips to produce a darker crunchy chip having the characteristics of batch type frying, said process using substantially isothermal frying zones.

Description:
BACKGROUND OF THE INVENTION 
     Conventionally potato chips are fried in a large kettle in a batch process. 
     Kettle frying of potato chips results in a firm texture high crunch chip. Commercial kettle frying of potato chips results in U-shaped oil temperature curve. After dropping potato slices into the oil, the oil temperature drops rapidly as the heat required to evaporate the high amount of water in the potatoes is consumed, generally faster than the burner can restore heat to the oil. After much of the water is evaporated, the heat load declines and the oil temperature moves higher. Frying is usually completed at an oil temperature near to, but somewhat below, the starting temperature. 
     Some typical commercial kettle frying conditions for 0.072&#34; thick potato slices are as follows: 
     
                       TABLE NO. 1______________________________________Type PotatoStarting Temp. (°F.)            Russet Burbank                        Norchip______________________________________Starting Oil Temp. (°F.)            300-325     300-335Lowest Oil Temp. (°F.)            240-270     260-280Final Oil Temp. (°F.)            275-300     300-315Frying Time (min.)             7-10        8-12______________________________________ 
    
     Specific frying curves for commercial batches of Russet Burbank potatoes and for Norchip potatoes are as follows: 
     
         ______________________________________Run No. I. Russet Burbank PotatoesLoading 55 Lbs. Potatoes/238 Gal. Oil (Cottonseed)Slice Thickness = 0.072&#34;; Potato H.sub.2 O = 78.2%Time (Min.)   Oil Temp. (°F.)______________________________________0             3051             2662             2663             2674             2705             2736             283  7.5         284______________________________________ 
    
     
         ______________________________________Run No. II. Norchip PotatoesLoading 55 Lbs. Potatoes/215 Gal. Oil (Cottonseed)Slice Thickness = 0.075&#34;; Potato H.sub.2 O = 78.8%Time (Min.)   Oil Temp. (°F.)______________________________________0             3251             2722             2783             2824             2815             2866             2947             299  8.5         307______________________________________ 
    
     Russet Burbank potatoes contain higher sugar content and thus produce a darker, sweeter chip. These potatoes are used to make a dark Maui style chip, and when kettle fried, produce a dark, sweeter crunchy chip. Norchips, when kettle fried, produce a lighter colored, less sweet crunchy chip. 
     Some of the general characteristics of batch kettle frying are: 
     (a) produces a good firm texture (high crunch) chip, 
     (b) longer frying time than a standard continuous process, 
     (c) a U-shaped oil temperature curve during frying, 
     (d) is labor intensive, i.e., one kettle fryer normally requires 1 man and will produce about 75-150 Lbs./hour of chips, whereas a large continuous fryer may produce 4000 Lbs./hour of chips and require only 2 people to operate it, 
     (e) produces a darker chip having more hardness than a chip fried in a continuous process. 
     Accordingly, it is a principal object of this invention to provide a continuous frying process that will produce chips having the quality, texture, color and hardness of chips produced by the batch kettle process. 
     A further object is to provide a chip frying process which provides higher throughput, plus lower labor costs, than a batch system. 
     Still another object is to provide a continuous process for producing Maui type potato chips. 
     These and other objects and advantages will become apparent hereinafter. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a continuous chip frying process involving isothermal temperature zones for producing potato chips in a fast efficient rate with the chips having the desirable characteristics of chips made by a conventional batch process. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic flow diagram of a two-stage continuous chip frying process; and 
     FIG. 2 is a schematic flow diagram of a three-stage continuous chip frying process. 
    
    
     DETAILED DESCRIPTION 
     I have found that using a two or three-stage isothermal frying process will produce good appearing potato chips with good crunch with both Russet Burbank and Norchip potatoes and will work as well with other varieties having similar characteristics. The essential steps in the process are a slow fry at lower temperatures to remove water without darkening chips, and a finish fry at higher temperature and for a short time to remove the last amounts of water, darken the chips, and produce a firm chip texture (crunch). 
     In the three-stage process, an initial very short high temperature fry is added. 
     It is preferred to use a series of fryers, each having a separate isothermal temperature with the temperature drop in each fryer (zone) being less than 10° F. This will require that the oil in each vessel be circulated and that there be suitable heat recovery capabilities in each fryer, particularly in the early stages of the process. In other words, water is being evaporated from the individual potato slices and as the water is evaporated, the oil is cooled because of the heat (BTU) loss from the oil to boil the water away. Thus, the initial heat input must be high, followed by declining heat input sufficient to maintain substantially constant oil temperature across the isothermal temperature zone. 
     An alternative construction is to use a multizone fryer, but it is difficult to maintain two or three significantly different isothermal temperature zones in the same body of oil while moving chips continuously through the body of oil without any temperature gradient between the zones. 
     FIG. 1 shows a two-stage fryer with two kettles 10 and 11, each with a circulating pump 12 combined with a heat exchanger 13 for hot vegetable frying oil, preferable cottonseed oil. The heat source 13 is located at each kettle 10 and 11 to maintain the temperature in the kettles at predetermined levels. It is critical that the temperature drop in each of the kettles 10 and 11 is less than 16° F., and preferably less than 10° F. at any time. The potatoes are moved through each kettle by the movement of the hot oil from the pump 12 and heat exchanger 13. The potatoes are moved between the kettles 10 and 11 and into the storage area by conventional conveyors. 
     Following are typical two-stage processes for Russet and for Norchip potatoes: 
     
                       TABLE NO. 2______________________________________Slice Thickness - 0.065&#34;-0.080&#34; Range 0.070&#34;-0.075&#34; Preferred  Russets       Norchip  Oil Temp.           Time     Oil Temp.  Time  (°F.)           (Min.)   (°F.)                               (Min.)______________________________________First StageRange    240-270    4-8      260-305   3-10Preferred    260        5-7      250-280   6-10Second StageRange    330-340    0.25-2.0 305-350  0.5-3.0Preferred    340        0.5-1.0  340      0.5-1.0______________________________________ 
    
     Following are typical ranges of temperatures and fry times for three-stage processes with Russet and Norchip potatoes: 
     
                       TABLE NO. 3______________________________________  Russets       Norchip  Oil Temp.           Time     Oil Temp.  Time  (°F.)           (Min.)   (°F.)                               (Min.)______________________________________First StageRange    290-310    0.1-1.0  290-310  0.5-1.5Preferred    305        0.5      305      1.0Second StageRange    250-270    4-7      240-280  3-8Preferred    260        5-6      260      4-7Third StageRange    325-340    1-3      300-350  0.1-3.0Preferred    330-340    1-2      305      1.5                        340      0.5______________________________________ 
    
     Following in Table No. 4 are specific runs in three-stage and two-stage processes using Russet Burbank potato slices of 0.072&#34; in thickness. 
     
                                           TABLE NO. 4__________________________________________________________________________Stage 1              Stage 2         Stage 3         ColorRun No.Fry Time (Min.)         Temp. (°F.)                Fry Time (Min.)                         Temp. (°F.)                                Fry Time (Min.)                                         Temp. (°F.)                                                Texture__________________________________________________________________________67   1.0      305°                3.0      260°                                1.5      305°                                                Agtron 3-4                                                Good Crunch68   1.5      305°                3.0      260°                                1.0      305°                                                Agtron 3                                                Good Crunch69   1.5      305°                5.0      260°                                1.5      330°                                                Agtron 3                                                Good Crunch70   .5       305°                3.0      260°                                2.0      330°                                                Agtron 4-5                                                Bitter No Crunch71   .5       8° drop                5.0      260°                                1.5      6° drop                                                Agtron 3         305°                     330°                                                Good Crunch72   .5       305°                6.0      260°                                1.5      340°                                                Agtron 4-3                                                Slightly Bitter                                                Good Crunch73   .5       305°                5.0      260°                                2.0      330°                                                Agtron 3-4                                                Very Good Crunch74   6.0      260°                2.0      330°                                --       --     Agtron 4-3                                                Slightly Bitter                                                Very Good Crunch75   6.0      260°                1.5      340°                                --       --     Agtron 3-4                                                Excellent Crunch76   5.0      305°                --       --     --       --     Control Run                                                Agtron 3                                                Not Crunchy77   .5       305°                5.0      260°                                2.0      330°                                                Agtron 4-3                                                Very Good Crunch78   6.0      260°                1-11/4   340°                                --       --     Agtron 3-4                                                Excellent Crunch79   7        260°                1        340°                                --       --     Agtron 3-4                                                Very Good Crunch80   8        260°                1        340°                                --       --     Agtron 4-3                                                Very Good Crunch81   5        270°                 1.15    340°                                --       --     Agtron 3-4                                                Not Crunchy82   4        270°                 1.15    340°                                --       --     Agtron 3                                                Good Crunch83   15.      260°                --       --     --       --     Agtron 3                                                Very Good Crunch84   12.      270°                --       --     --       --     Agtron 3                                                Not Crunchy85   10.      280°                --       --     --       --     Agtron 3                                                Not Crunchy86   4.0      280°                3.0      340°                                --       --     Agtron 4-3                                                Not Crunchy__________________________________________________________________________                                                Blister 
    
     From the point of view of economics of operation including equipment costs, maintenance, and efficiency, the two-stage process is preferred. 
     The combination of temperature drop limitation, frying retention time per stage, and heat recovery capabilities of the fryer will determine loading levels. 
     Slice thickness can vary for different type products, such as lattice chips, but frying retention time also will then need to be varied. This invention is applicable to chips of 0.04&#34; to 0.25&#34; in thickness. A lattice chip typically is 0.15&#34;-0.20&#34; in thickness. 
     Following are specific runs in three-stage and two-stage processes using Norchip potatoes of 0.072&#34; in thickness. 
     
                                           TABLE NO. 5__________________________________________________________________________Stage 1             Stage 2        Stage 3        ColorRun No.Fry Time (Min.)         Temp. (°F.)               Fry Time (Min.)                        Temp. (°F.)                              Fry Time (Min.)                                       Temp. (°F.)                                             Texture__________________________________________________________________________1    1        305°               3        260°                              1.5      305°                                             Agtron 1                                             Soft-Chewy2    1        305°               5        260°                              1.5      305°                                             Agtron 1                                             Very Good3    8        260°               1        340°                              --       --    Agtron 1-2                                             Very Good4    7        260°               1        340°                              --       --    Agtron 2                                             Good5    6        305°               --       --    --       --    Agtron 1                                             Good6    7        305°               --       --    --       --    Agtron 2-1                                             Good7    9        260°               1        340°                              --       --    Agtron 2-1                                             Very Good8    10       260°               1        340°                              --       --    Agtron 2                                             Good9    9        260°               2        305°                              --       --    Agtron 2                                             Good10   6        260°               3        305°                              --       --    Agtron 1-2                                             Good11   7        260°               1        305°                              --       --    Agtron 1                                             Soft__________________________________________________________________________ 
    
     The data in Tables Nos. 4 and 5 support the ranges of time and temperature shown in Tables Nos. 2 and 3 respectively. 
     In Runs Nos. 83, 84 and 85, a long fry at low temperatures was tried. It is noted that 15 minutes at 260° F. produced a satisfactory chip, but shorter times, even at higher temperatures were not satisfactory. The use of a 15 minute or longer run would require additional capital cost and larger, longer fryers. Thus, the cost/pound of product is higher. 
     The present invention is intended to include all changes and modifications of the examples of the invention herein chosen for purposes of disclosure, which do not constitute departures from the spirit and scope of the invention.