Abstract:
A method for making an expandable half-product or pellet suitable for cooking by microwave oven (or other method such as frying) that results in a non-uniform, random design, while having a distinct pattern or style. The half product design is achieved by inducing stress cracks in the half product. The stress cracks are created by a controlled drying process whereby extruded half-products are first case hardened to create an outer skin that requires an internal build-up of pressure to penetrate. After creation of the outer skin, by drying in an oven or in ambient air, the half-product is heated to permit the vapor pressure of the moisture inside the half-product to break through the outer skin and escape. Such escape points induce stress cracks in random places in the half-product. The general pattern of the stress cracks can be varied by manipulation of the time-temperature profile of the case hardening and stress cracking steps.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to expandable food products and more specifically to a process for drying a pellet or half-product to induce stress cracks and non-uniformity in size and shape in microwave snacks. 
     2. Description of Related Art 
     Microwave ovens have become common devices used to cook and reheat food products and 95% of all households in the United States own at least one microwave oven. Consequently, there is a large market for microwaveable foods including microwaveable snack foods. One such product is microwave popcorn. Generally, such popcorn products comprise an expandable paper bag containing a charge or matrix of popcorn, fat and salt. A wide variety of products have been developed, including improvements in bag design and variations in salt and fat levels. Flavored fat popcorn products have even been developed, e.g., butter flavored. 
     The widespread household use of microwave ovens has inspired efforts to provide snack foods suitable for microwave ovens. To this end, the art includes products which comprise pellets which puff upon microwave heating, in substitution for popcorn. Such puffable pieces are generally referred to as “half products” in the puffed snack food art. In particular, U.S. Pat. No. 4,251,551 disclosed such a food product. The product therein described comprises a plurality of puffable pellets matrixed in a flavored fat coating. Upon microwave heating, the pellet gradually expands to form puffed pieces which are covered with a flavored coating. According to the &#39;551 patent, the half products can be made by extruding a dough into small pellets and drying the pellets to a 5% to 15% moisture range. Like many half-product patents, the &#39;551 patent teaches that the drying process must be controlled and warns that if the moisture loss occurs only from the outer surface of the pellets while the inner portion of the pellets retains moisture, then the total moisture of the pellets may be within the required 5% to 15% range, but will not puff or expand properly during puffing. The patent indicates that such poor puffing results from the starch material in the outer portions of the pellets having little or no moisture with which to expand during the microwave puffing step. Hence, the &#39;551 patent teaches that a convection drying operation, carried out at about 70° F. to about 200° F. with a relative humidity of 35% can dry the pellets and the moisture distribution within the pellets will be proper. Similarly, U.S. Pat. No. 4,844,937 teaches that a drying step can be used to remove the surface moisture from the formed pieces so that the pieces are non-sticky, but cautions against case hardening. 
     While the various microwave popcorn and half products are popular, it would be desirable to have even greater variety in texture, flavors and to have flavored textured products that correspond to specific flavors. Yet it would be desirable to mimic the controlled randomness look of popcorn. For example, while each piece of popcorn has a different shape, there is a clear pattern or style to the look of popcorn. However, there are variables such as size constraints that limit or control the amount of randomness imparted. Yet, other than color, there is no way for a consumer to differentiate a butter flavored piece of popcorn firm a cheese flavored piece of popcorn. 
     One problem in using microwave half-products to mimic popcorn is that because microwave half-products are typically extruded from a die, the expanded or puffed half-products are typically uniform in shape and therefore do not have any such “controlled randomness” aspects. Half-products, therefore fail to provide a satisfactory alternative to microwave popcorn. Consequently, a need exists for a microwaveable half-product snack food having non-uniform shapes, yet a distinct style. Further, a need exists for a process to induce stress cracks in such snack food to induce random shapes in the snack food. 
     SUMMARY OF THE INVENTION 
     Dry ingredients comprising starches, oils, and/or flavorings are mixed together in a hopper. In an optional pre-conditioning step, steam and/or liquid water is added to the dry mix. The mixture is extruded and the extrudate is cut into pellets upon exiting the extruder. The pellets are case hardened to create an outside skin layer. Next, the pellets are heated such that portions of the outer skin layer are breached by the expanding vapors inside the pellet and thereby stress cracks the pellet. The pellets can then be dried to a moisture content of between about 5% and about 15%. Additional topical seasoning, topical oil, and salt can be added to the dried pellets, and the finished half-product is packaged. The packaged, finished half-product is designed to puff and expand non-uniformly upon application of heat from hot oil, a microwave, or hot air. The above as well as additional features and advantages of the present invention will become apparent in the following written description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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, farther 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: 
         FIG. 1  is a schematic representation of the overall steps of the new process; 
         FIG. 2  is a schematic representation depicting two separate embodiments of the present invention; 
         FIG. 3   a  is a perspective view of an unexpanded half-product having stress cracks induced by a method in accordance with one embodiment of the present invention; and 
         FIG. 3   b  is a perspective view of an expanded half-product having stress cracks induced by a method in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the innovative invention will now be described with reference to  FIG. 1 . Dry ingredients comprising native potato starch, native tapioca starch, potato flakes, pre-gelatinized, waxy maize starch, flour salt, fully hydrogenated soybean oil, and flavoring are mixed together in a hopper. Other dough compositions can be used including those disclosed in U.S. Pat. No. 4,409,250 and references to dough compositions disclosed therein. In an optional pre-conditioning step, steam at a pressure of at least 10 psig, and liquid water is added to the dry mix. The mixture is extruded  110  at temperatures between about 130° F. to about 190° F. and pressures between about 300 and about 1,500 psig. The extrudate comprises a moisture content of between about 25% and about 35% and more preferably between about 28% and about 32% upon exit from the extruder. The extrudate is cut into pellets upon exiting the extruder and the pellets are then case hardened  120 . As used herein, case hardened refers to a hardening of the outer peripheral surface or outer skin of the pellet such that a build-up of internal pressure is required for moisture to escape. When such moisture is released, a crack in the pellet is formed. 
     The purpose of the case hardening  120  is to form an outer skin layer and raise the vapor pressure required to penetrate and crack the skin layer. Any case hardening time-temperature profile that can achieve this objective can be used including drying in ambient or heated air for the requisite amount of time. Next, the pellets are heated and thereby stress cracked  130  in a manner such that portions of the outer skin layer are breached by the expanding vapors inside the pellet. The pellets are then dried  140  to an overall moisture content of between about 5% to about 15% and more preferably about 11% to about 14%. Additional topical seasoning, topical oil, and salt  160  can be added to the dried pellets, and the finished half-product is packaged. The packaged, finished half-product is designed to puff and expand upon application of heat from hot oil, a microwave, or hot air. 
       FIG. 2  is a schematic representation depicting two separate embodiments of the present invention. In both embodiments, dough is first extruded in a multi-zone barrel twin screw extruder  210  at temperatures between about 130° F. to about 190° F. and pressures between about 300 and about 1,500 psig and cut into pellets. These pellets are then case hardened with a case hardening time-temperature profile. As used herein, a case hardening time-temperature profile is any time-temperature profile which results in a case-hardened pellet. The case hardened pellet comprises a moisture gradient between the outer skin of the pellet and the inside of the pellet. In one embodiment, the outer skin comprises a moisture content of less than about 4% by weight. 
     In one embodiment, the pellets are case hardened  220  by ambient air  222 . This can occur by moving the pellets along a conveyor belt. The time and temperature required for the requisite case hardening will be dependent upon several factors including, but not limited to the ambient air temperature, the amount of the time the pellets are exposed to the ambient air, the surface area to volume ratio of the pellet, the relative humidity of the ambient air, and shape of the pellet. Consequently, some trial and error may be required to determine the optimum amount of time required for case hardening. 
     In one embodiment, sufficient case hardening was achieved for a relatively spherically shaped pellet extruded from a temperature of between about 170° F. and about 200° F. having a diameter of about ⅛″ exposed to ambient air from about 60° F. to about 100° F. and more preferably from about 70° F. to about 80° F. for between about 5 and about 15 minutes. In one embodiment, the overall moisture content dropped from about 30% to about 26% by weight after the case hardening  220  step. 
     Once the pellets are case-hardened, or have an outer skin, the outer skin can be penetrated by stress cracking  230  with a stress cracking time-temperature profile. As used herein, a stress cracking time-temperature profile is any time-temperature profile which results in a crack in a portion of the case hardened pellet, but remains an expandable half-product. In one embodiment, stress cracking  230  can be achieved in a pre-heater  232 . A single pass pre-heater such as the Enersyst M970101, available from Enersyst Corporation in Dallas, Tex. can be used. In an alternative embodiment, a low temperature tumbler such as the Cantrell Modular Rotary Oven, Model MRO-18-2A, available from A.C. Horn Inc. in Dallas, Tex. can be used. In one embodiment, the pellets are placed in the single pass pre-heater having a relative humidity of between about 5% and about 15% for between about 2 to about 30 minutes, at a temperature of between about 150° F. to about 300° F. Such ranges are provided for purposes of illustration and not limitation. Any stress cracking time-temperature profile can be used in the pre-heater  232  that provides the requisite stress cracking  230 . Because of the outer skin layer, when the pellets are exposed to the pre-heater  232 , the outer skin prevents the moisture within the pellet from escaping throughout the periphery of the outer surface of the pellet. Consequently, internal pressure within the pellet builds until the pressure is sufficient to breach one or more weak points on the outer skin. Steam and/or moisture can then escape through each weak point thereby creating a stress crack. The pellets can then be dried in one or more multi-stage dryers. In one embodiment, the pellets are routed to a multi-pass pre-dryer  240  having a relative humidity of about 5% to about 15% for about 30 to about 60 minutes at a temperature of about 150° F. to about 200° F. A multi-pass pre-heater such as the APV Enerjet Oven, Model 5400/24/1, available from Invensys APV in Getzville, N.Y. can be used. The pellets can then be routed to a multi-pass finish dryer  250  having a relative humidity of about 10% to about 40% for about 30 to about 90 minutes at a temperature of about 125° F. to about 210° F. A multi-pass finish dryer  250 , such as the Proctor K95135, available from Proctor &amp; Schwartz, Inc. in Horsham, Pa. can be used. 
     It should be pointed out that the case-hardening time-temperature profile and stress cracking time-temperature profile can be varied to achieve the goals of the invention. For example, in one embodiment, the pellets can be case hardened  220  by ambient air  222  and further case hardened by a pre-heater  232  by operating the pre-heater at relatively lower temperatures and/or placing the pellet in the pre-heater for a relatively shorter dwell time, as illustrated by Example 4 below. In such scenario, the stress cracking can then occur concurrently with the drying step and in the unit operations defined as the pre-dryer  240  and finish dryer  250  by using relatively higher temperatures and/or relatively higher dwell times in the pre-dryer  240  and/or finish dryer  250 . For example, in one embodiment, the pellets are case hardened  220  by ambient air for about 10 to about 15 minutes, further case hardened in a pre-heater having a relative humidity of between about 5% and about 15% for between about 5 to about 30 minutes, at a temperature of between about 150° F. to about 200° F., and then stress cracked in a multi-pass pre-dryer  240  operating at about 200° F. to about 300° F. for about 10 to about 60 minutes and then dried in a finish dryer  250  having a relative humidity of about 10% to about 40% for about 30 to about 90 minutes at a temperature of about 125° F. to about 210° F. Consequently, although specific unit operations are shown in the block diagram in  FIG. 2 , those skilled in the art will recognize that such operations can be manipulated and the objective of providing a case hardened pellet that is then stress cracked can still be achieved. For example, although a pre-dryer  240  and a finish dryer  250  are depicted, a single multi-pass dryer can be used. 
     Topical seasoning, topical oil, and salt  260  can be added to the dried pellets, and the finished half-product can be packaged for consumer use. The packaged, finished half-product having stress cracks is designed to puff and expand in a non-uniform way upon application of heat from hot oil, a microwave, or hot air. 
       FIG. 3   a  is a perspective view of an unexpanded half-product or pellet having stress cracks in accordance with one embodiment of the present invention. The unexpanded half-products  312  comprise induced stress cracks  352  produced by a method in accordance with one embodiment of the present invention. It should be noted that the stress cracking time-temperature profile can be manipulated to achieve the level of stress cracking desired. For example, if a greater number of smaller stress cracks are desired, then less case hardening can be provided by utilizing relatively shorter case hardening dwell times and/or lower temperatures. Conversely, if a fewer number of larger stress cracks are desired, then relatively more case hardening can be provided by utilizing relatively longer case hardening dwell times and/or higher temperatures. 
       FIG. 3   b  is a perspective view of an expanded half-product or pellet having stress cracks in accordance with one embodiment of the present invention. The expansion from exposure to heat causes the half-product  370  and its stress cracks  372  to concomitantly expand, but at different rates. The stress cracks  372  expand at a different rate than the rest of the half-product because moisture within the half-product has a preferred pathway of escape, namely through the existing stress cracks  372 . Stated differently, in areas where the case hardened outside skin is intact, the moisture cannot escape as rapidly as moisture can escape in areas near the stress cracks  372 . Consequently, there is relatively more expansion in the portion of the pellet where the outside skin is intact. Where there is easy escape of moisture in areas, such as through the un-cooked stress cracks, there is less expansion as moisture can easily escape through the stress crack resulting in less build-up of pressure. The stress cracks therefore allow the pellet to expand non-uniformly as the intact surfaces and stress crack surfaces expand independently of each other. 
     Referring back to  FIG. 2 , in an alternative embodiment, after the dough is extruded, it is case hardened  220  by a pre-heater  226 . In one embodiment, the pre-heater  226  has a relative humidity of between about 5% and about 15% for between about 5 to about 30 minutes, at a temperature of between about 150° F. to about 200° F. Such ranges are provided for purposes of illustration and not limitation. As stated above, any set of variables can be used in the pre-heater  226  that provides the requisite case hardening  220 . The same pre-heater  226  as described above referenced with numeral  232  for the stress cracking can be used. It should be pointed out that case hardening  220  may occur at a faster rate in the lower temperature ambient air dry  222  embodiment, described above, than in the elevated temperature of a pre-heater  226  embodiment because of the greater temperature differential that exists between the pellet leaving the extruder and the ambient air. The pellet can cool quicker in ambient air permitting excess moisture to flash from the surface. 
     Next, the pellets are routed to a high temperature, short dwell time (HTSD) oven  236  having a temperature of about 200° F. to about 400° F. for a dwell time of between about 30 seconds and about 5 minutes. Such ranges are provided for purposes of illustration and not limitation. The above range is merely provided as an example of a time-temperature profile that can be used. For example, if the pellets placed in the oven  236  have a dwell time of less than about 30 seconds in an oven having a temperature of less than about 200° F., the internal pressure may not raise enough to sufficiently channel moisture through the case hardened outer skin. Similarly, if the pellets placed in the oven  236  have a dwell time of more than about 5 minutes in an oven having a temperature of more than about 400° F., the pellets can begin to expand, which can limit the expansion experienced by the half-product when later heated by a consumer. 
     The pellets can then be dried in one or more multi-stage dryers. In one embodiment, the pellets are routed to a multi-pass pre-dryer  240  having a relative humidity of about 5% to about 15% for about 30 to about 60 minutes at a temperature of about 150° F. to about 200° F. In that embodiment, the pellets are then routed to a multi-pass finish dryer  250  having a relative humidity of about 20% to about 30% for about 30 to about 60 minutes at a temperature of about 175° F. to about 210° F. The pellets are dried to an overall moisture content of between about 11% to about 14% by weight. The pellets can then be seasoned  260  and packaged for consumer use. Additional topical seasoning, topical oil, and salt can be added to the dried pellets, and the finished half-product is packaged. The packaged, finished half-product or pellet having stress cracks is designed to puff and expand in a non-uniform way upon application of heat from hot oil, a microwave, or hot air. 
     The following Examples are presented to further illustrate making and using the compositions of this invention. These Examples are not to be construed as limiting. 
     EXAMPLE 1 
     A dough was extruded and face cut into ⅛-inch diameter pellets. The pellets were case hardened in ambient air having a relatively humidity of about 20% to about 35% and at about 70° F. to about 80° F. for about 10 minutes. The air dried and case hardened pellets were then stress-cracked by a pre-heater and exposed for 6 minutes to oven air having a temperature of about 170° F. and a relative humidity of about 20% to about 40%. The pellets were again air dried in ambient air having a relatively humidity of about 20% to about 35% and at about 70° F. to about 80° F. for about 10 minutes. Next the pellets were dried in a multi-pass pre-dryer/finish dryer. The dryer operated in 3 zones—a first zone had an oven temperature of about 150° F. and a relative humidity of about 10% to about 15%. The second zone had an oven temperature of about 135° F. and a relative humidity of about 25% and the third zone had an oven temperature of about 125° F. and had a relatively humidity of about 40%. The pellets were in the multi-zone oven for a total of about 90 minutes. 
     EXAMPLE 2 
     A dough was extruded and face cut into ⅛-inch diameter pellets. The pellets were case hardened in a pre-heater having a relatively humidity of about 20% to about 40% and an oven temperature of about 170° F. about 6 minutes. The pellets were then stress cracked in HTSD oven operating at an oven temperature of about 300° F. for about 3 minutes. Next the pellets were dried in a multi-pass pre-dryer/finish dryer. The dryer operated in 3 zones—a first zone had an oven temperature of about 150° F. and a relative humidity of about 10% to about 15%. The second zone had an oven temperature of about 135° F. and a relative humidity of about 25% and the third zone had an oven temperature of about 125° F. and had a relatively humidity of about 40%. The pellets were in the multi-zone oven for a total of about 90 minutes. 
     EXAMPLE 3 
     A dough was extruded and face cut into ⅛-inch diameter pellets. The pellets were case hardened in a pre-heater having a relatively humidity of 20% to about 40% and an oven temperature of about 200° F. about 6 minutes. The pellets were then stress cracked in an HTSD oven operating at an oven temperature of about 300° F. for about 3 minutes. The pellets were again air dried in ambient air having a relatively humidity of about 20% to about 35% and at about 70° F. to about 80° F. for about 10 minutes. Next the pellets were dried in a multi-pass pre-dryer/finish dryer. The dryer operated in 3 zones—a first zone had an oven temperature of about 150° F. and a relative humidity of about 10% to about 15%. The second zone had an oven temperature of about 135° F. and a relative humidity of about 25% and the third zone had an oven temperature of about 125° F. and had a relatively humidity of about 40%. The pellets were in the multi-zone oven for a total of about 90 minutes. 
     EXAMPLE 4 
     A dough was extruded and face cut into ⅛-inch diameter pellets. The pellets were case hardened in a HTSD oven operating at an oven temperature of 400° F. for about 1 minute. Next the pellets were stress cracked and dried in a multi-pass pre-dryer/finish dryer. The dryer operated in 3 zones—a first zone had an oven temperature of about 150° F. and a relative humidity of about 10% to about 15%. The second zone had an oven temperature of about 135° F. and a relative humidity of about 25% and the third zone had an oven temperature of about 125° F. and had a relatively humidity of about 40%. The pellets were in the multi-zone oven for a total of about 90 minutes. 
     The instant invention provides several advantages over the prior art. First, a pellet or half-product having stress cracks is provided. Thus, when the half product is heated in a microwave by a consumer, the half-product expands non-uniformly and thereby resembles a controlled randomness, in a way reminiscent of microwave popcorn, more than a non-stressed cracked half product. Second, the invention provides a way for a line of snack food half products having a distinct style that corresponds to a specific flavor. For example, a butter flavored half product can be extruded from a die having a first shape and can have induced stress cracking from a first case-hardening and/or stress cracking time-temperature profile and a cheese flavored half product can be extruded from a die having a second shape and a can have induced stress cracking from a second case hardening and/or stress cracking time-temperature profile. Further, although each of the butter flavored half products will be non-uniform, they will have a first distinct pattern or style and the cheese flavored half products will have a second distinct pattern or style. The present invention can thereby provide a consumer with a variety of flavors and distinct patterns that consumers can come to identify with those flavors. Such products are desirable because they provide excellent product recognition. Hence, the present invention provides a way for a new product line that can not only compete with microwave popcorn as a snack food, but can provide a greater variety of distinct patterns or styles. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.