WO1997041737A1

WO1997041737A1 - Reconstitution of a stable grain product

Info

Publication number: WO1997041737A1
Application number: PCT/US1997/007361
Authority: WO
Inventors: James C. Breslin; Stephen J. Kalchik; Gloria Cagampang; Kenneth O. Weil; Elizabeth C. Garcia; Brian F. Jacob
Original assignee: Kellogg Co
Current assignee: Kellanova
Priority date: 1996-05-06
Filing date: 1997-05-02
Publication date: 1997-11-13
Anticipated expiration: 1998-11-06
Also published as: AU2822497A

Abstract

Disclosed is a process for reconstituting a stable grain product. In the invention, a stable, at least partially cooked grain, having a water activity of no more than about 0.65 is exposed to thermal energy whereby the surface of the grain is at a temperature of from about 140 to 200 °F. The heat treated grain is thereafter milled, flaked or puffed within a set period. The process has particular application for the manufacture of R-T-E cereals.

Description

RECONSTITUTION OF A STABLE GRAIN PRODUCT

Background Of Invention

The present invention is in a process for reconstituting a stable, at least partial¬ ly gelatinized, grain product.

It is conventional practice in the manufacturing of pelletized cereal product to utilize the product moisture content to provide the required texture of the grain to mill the pellets into flakes. In such procedures, the unit operations such as cooking, pelletizing, drying, flaking and toasting, are performed in a sequential, uninterrupted sequence of steps so as to be linked together in a continuous flow process. The conventional wisdom is that any separation or delays between sequential process steps or unit operations results in physical and/or chemical changes in the properties of the product. These changes are undesirable because they result in inconsistent product characteristics which impact on the consumer's purchasing decisions.

Important steps in the conventional art practice include flaking, milling or puffing. The presence of moisture in the product renders the product soft and pliable so the flaking or milling operation can change the shape of the pellets or grits from three dimensions to two dimensions. If the pellets are not soft and pliable, they will be shattered during the flaking or milling. As such, in prior art processes, partially gelatinized grains could not be flaked or milled if the grain had a water activity of

below about 0.5 to 0.6. Water activity is the relative humidity of the air in the voids between the particles. However, it is sometimes required or preferable that the unit operations be conducted separately or at separate locations. The ability to separate the steps can allow for the most economic and advantageous use of commodities and facilities, especially in view of sources of supply, finishing operations and markets. However, as discussed above, such a separation of the stages using conventional practice can result in undesirable product variations and product deterioration such as in the

formation of mold on the product.

It has been found that the sequence of steps can be performed in such a man¬ ner that they may be interrupted and the product can be stored or transported, as desired, and then reconstituted to a useable form with the surprising result that the product does not undergo noticeable changes.

In particular, it has been found that a partially cooked product can be dried to a safe storage condition, stored, and then reconstituted to a useable product without sacrificing product characteristics rendering the product non-millable.

Summary Of The Invention

The present invention is in a process for reconstituting a stable grain product, and more specifically in a process of returning dry glassy pellets or grits into a pliable and millable and/or puffable product without moisture addition.

In another aspect, the invention is in a pelletized or natural shaped particle cereal process wherein the processing sequence is interrupted but allows for the subsequent processing of the grain to form a useable product such as a ready-to-eat (R-T-E). cereal. In the process of the invention, a grain which is at least partially cooked, i.e. , one which contains some amount of ungelatinized starch, and preferably a grain which is more than partially cooked, and which has been stabilized so that it has a water activity of below about 0.65 is used. Partially cooked grain products having a water

activity below about 0.65 do not exhibit molding or other forms of biological growth. In this state, the physical structure of the grain is an amorphous glass. Grains in such a state, under proper conditions, can be stored and transported with no change in the grain characteristics. The stable product is exposed to thermal energy for a

predetermined period. During the period of exposure, the temperature of the grain particle surface is raised. Also, the bulk temperature, that is the temperature of the mass of the grain particles as a whole, is also raised. The thermal energy is supplied by a heat source and is at a high temperature.

In the practice of the invention, the stable grain is exposed to thermal energy under otherwise normal atmospheric conditions for no more than a predetermined period. Within a short period after the heat treatment, and while still at a temperature above the grain's glass transition temperature, the grain grits are flaked or milled

and/or puffed.

An advantage of the process of the invention is that the grain products can be cooked, pelletized (if required), dried, and cooled at one location and then can be transported and/or stored. Subsequently, the grain product can be heat treated and the heat treated grain products can now be flaked, milled or puffed without shattering, whereas the transported and/or stored products could not have been so processed without the heat treatment. If the milling, flaking or puffing is not performed promptly after the heat treatment, the grits would shatter to an unusable or undesired condition.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

Brief Description Of The Drawings The Figure 1 shows in block diagram form a sequence of steps which include the process of the invention; and

Figure 2 shows a representative phase diagram for a grain product.

Description Of Preferred Embodiment

Figure 1 shows in block diagram format a sequence of steps which includes the

process of the invention.

Grain is provided in its usual form for making the particular product. The

grain can be any of the commonly used grains such as corn, wheat, barley, oats, sorghum, brans, short, medium and long-grained rices, including brown rices and

mixtures of such common grains but is not limited to the above list. If the intended product is, for instance, an R-T-E cereal, the grain is provided in the usual process form for that product through line 10 to a cooker 12. The grain is at least partially, and preferably is more than partially, cooked in cooker 12 to provide an intermediate

product 14. Typically, the grain is cooked under conditions to give a product 14 temperature of about 200-220 °F and a moisture content of 30-40 wt.-%. Under such cooking conditions, the intermediate product 14 will have a softened texture and at least some of the starch content will be gelatinized with no prominent DSC

(differential scanning calorimeter) gelatinization peak detectable. The texture of prod¬ uct 14 is sufficiently pliable such that a grit could be deformed by hand squeezing. Intermediate product 14 is discharged to a surge bin 16. In bin 16, through radiant heat losses and evaporation, the intermediate product will cool such that the product temperature will decrease by about 50 to 75 °F. The product will also experience some water loss by evaporation so that the moisture content may also fall by, for instance, about 1 to 5%. Under these conditions, the product maintains a soft

texture.

The surge bin 16 allows for the controlled feed of the cooked product 18 to, if required, a pelletizer 20 which is of the conventional type used in the food processing industry, when the intermediate product 14 is already in a suitable form, i.e. , such as a grit, pelletizer 20 need not be included. In pelletizer 20, the partially cooked grain now is formed into pellet-like bodies of a preselected size and/or weight. The grain is discharged from the pelletizer 20 in the form of pellets or bodies 22 at a temperature approaching, or slightly above, room temperature and in the range of 80 to 130°F

with a remaining moisture content of from about 20 to 30 wt.-% . The bodies 22 still have a relatively soft texture. In the process of the invention, the grain or pellets or bodies of grain are then introduced into a belt-type dryer 24. In the dryer, the pellets 22 or grits lose both moisture and enthalpy The dried product 26 is optionally cooled to about room temperature but has a significantly reduced moisture content so that the water activity is below about 0.65., is typically in the range of 0 45 to 0.63, and is preferably about 0.6 to 0.63. The texture of the pellets or grits has also changed such that the

surfaces of the pellets or grits are no longer soft or deformable but now are hard to glassy with an amoφhous physical structure.

In conventional practice, the grain 22, if dried, would have a water activity of in excess of 0 7, a product temperature of 90 to 130°F, and would then be immediately further processed or processed within a period of no more than six (6) hours to avoid mold growth on the product. However, the invention enables one the option to store or ship 28, the partially cooked stable product for extended periods of up to in excess of six months under normal grain product storage or shipping

conditions

In the invention, the stable product, i.e. product 26, which optionally has been stored and/or transported, can now be processed to a useable form without compromising the physical, chemical or organoleptic characteristics of the gram

product Again referring to Figure 1, the stable product 30 which optionally has been

stored or transported is subjected to a heat treatment 32 In the heat treatment of the stabilized product which has a water activity not exceeding about 0 65, preferably about 0.5 to 0.63, and most preferably about 0 6 to 0 63, the product is exposed to thermal energy. The thermal energy can be provided in radiant, convective or conductive form or a combination of such thermal mechanisms. In a preferred embodiment, the thermal energy is supplied in radiant form by at least one infrared heating element. In that embodiment, the product 30 is exposed to the radiant heat for a period of about 20 to 65, and preferably 30 to 45, seconds. The radiant heat is preferably supplied by one or more infra-red heating elements which radiate at a

temperature of about 1300-1500°F. The energy wavelength is from about 0.5 to 0.7 microns. The stable product is irradiated such that the surface temperature of the product is in the range of about 140 to 200°F, preferably about 160 to 185°F, and most preferably in the range of about 165 to 180°F. Under these conditions, the

stable product has both a surface temperature and an average internal temperature no lower than the glass transition temperature and essentially maintains its moisture content or loses relatively little moisture. The heat treated product now has a pliable surface texture. That is to say, the grain particle has now transformed from an amorphous rigid structure to an amoφhous plastic or rubbery consistency.

In the preferred embodiment, the heat treatment of the stable product can be performed by conveying the product on a vibratory conveyor through an enclosure or housing in which the one or more infra-red heating elements are mounted. The conveyor and housing should be of sanitary construction and of appropriate materials such as stainless steel or other materials permitted by regulating authorities. The product preferably is on the conveyor in a thickness of about 1 " and preferably about 1/2". The enclosure may have an inner polished surface for assisting in the radiation. In one embodiment, the enclosure may be hemispherical in cross section so as to focus the radiation onto the product but other geometrical arrangements can be employed.

It has been found useful to agitate the product so as to expose any underlying product and underside surfaces to the radiation, especially when the product is deposited or placed on the conveyor in thicker layers. The agitation also assists in obtaining the desired temperature in the above-stated range.

In a preferred embodiment, the heat treatment is conducted in an apparatus having a reciprocating or mixing movement such as an apparatus which has a lower section which is a shaker pan and which can be reciprocated to obtain a mixing or shaking and an upper section covering the shaker pan. The upper section can be in the form of a housing and the one or more infra-red elements optionally are mounted on, or supported from, the inside of the housing. Preferably, the lower surface of the reciprocating or vibrating apparatus has a slight slope so that when shaken, the product is both agitated and tumbled. The slope is a negative incline from the feed end of the shaker 32 to the discharge end. In a still more advantageous arrangement, the lower section is formed with a bottom having a series of descending steps. This arrangement provides an improved tumbling action so that particle undersides are exposed to the radiant energy as the particles move along the lower section bottom. Other mechanical arrangements or systems which cause agitation and/or tumbling can be used in the invention so as to meet the above discussed temperature and exposure criteria. In another preferred aspect of the invention, the infra-red heating elements are quartz heaters. Preferably the heating elements are less than 12 inches above the product surface and most preferably are about 4 to 8 inches above the product top¬ most surface.

Since it is important that the above mentioned temperature ranges and time periods be substantially maintained to obtain the benefits of the invention, in a preferred embodiment the heat treated product 34 is sampled or subjected to a temperature sensing 36 at, or near, the discharge from shaker 32. If the product temperature measurements do not substantially comply with the above criteria, the power input to the heaters can be adjusted so as to bring the product temperature into the desired ranges by the use of a feedback control loop. Of course, feed forward systems can be employed if, for instance, temperature sensing shows a pattern of temperature decrease. A combination of feed back and feed forward control loops can be used.

The product 34 should be discharged from heat treatment 32 at a temperature of approximately 160 to 180°F with a water activity essentially the same or slightly less than product 30 but with a pliable surface. The change from hard, glassy and amoφhous to pliable is not limited to a surface condition but is present within the particle extending inward from the surface. Preferably substantially the entire particle is pliable throughout. That is to say, the heat treatment has caused a change in the pellet or particle and the surface and at least some portion of the particle's internal structure. Immediately after, and preferably within a period t greater than 0 but less than or equal to about 30 seconds (0 < t < = 30 seconds) following the radiant heat treatment, and while the grain is still at an elevated temperature, the product is then flaked, milled and/or puffed, 38. The flaking and/or milling and/or puffing operations are conventional in the manufacture of cereal products. The ground or flaked product 40 is at a temperature of about 140 to 160°F, has a water activity essentially the same as, or slightly less than product 34, but has an elastic or deform- able texture. The ground or flaked product 40 can then be further processed, i.e., further toasting or roasting, coating, etc., collectively represented in Figure 1 as 42 to make an end product 44 such as an R-T-E cereal optionally ready for sale, consumption or decoration.

In the above described preferred embodiment, the thermal energy is provided

to the grain primarily by radiation. In another embodiment, the thermal energy is added to the particle by means of contacting the pellet or grit with heated air so that the thermal energy is supplied, in part, by convection. In a preferred embodiment, this contact is carried out in a fluidized bed and most preferably a horizontally- or substantially horizontally-oriented jet zone fluidized bed. The heat-treated pellets or grits are discharged from the fluidized bed and are optionally recycled depending on the bed length and period of contact so as to obtain the desired temperature and structural characteristics described above. In the fluidized bed, the contacting air

which is also the fluidizing air is at a temperature in excess of 400 °F and preferably is at a temperature of 400 °F to 500°F. Care must be taken that the temperature is not so high and/or the contact period not so long as to cause a burning of the pellets or grits. Preferably, the period of contact is no more than about 30 seconds. It is recommended that the heated fluidizing air have some degree of humidity so that particles or grits do not experience a significant loss of moisture content or reduction of water activity. Preferably, the fluidizing air contains about 0.075 to 0. 125 pounds of water per pound of dry air. The velocity of the air in the fluidized bed is in the conventional range for jet zone fluidized beds. The ratio of pellets or grits to the fluidizing air is about 1.5 to 2.5 pounds of the grain to about 1 pound (dry basis) of

the fluidizing air. The fluidizing air can be discharged along with the pellets and passed through a separating means such as a cyclone and the pellets can be recycled to the fluidized bed. However, care should be taken that the velocity in the fluidized bed or the separating device is not so high as to cause shattering of the pellets prior to their reaching the desired temperature range. With recycling, the pellet has an average dwell or residence time within the fluidized bed of up to about 30 seconds and

preferably about 8 to 12 seconds.

In another embodiment, the thermal energy can be supplied to the grain primarily by conduction. In this embodiment, the grain is contacted with a surface having a temperature of about 700-1200°F, preferably 800-1000°F, for a short period

of time of less than about 90 seconds, i.e. for about 50 to 90 seconds, and preferably about 65 to 80 seconds. The contact may be, for instance, in a pan or screw conveyor with provisions for moving the grain from the inlet to the outlet. Preferably the conveyor is sloped downwardly from inlet to outlet. Optionally, air with humidity as described above may be blown in to assist the screw in moving the grain. Figure 2 shows a representative phase diagram for a grain product. The phase

diagram shows, for grain products with different moisture contents and temperatures above room temperature (RT), the glass transition temperatures (A). Area B is the area of conventional milling as defined by moisture contents and temperatures. Area

11 SUBSTITUTE SHEET (RULE 28) C shows, in a relative sense, the relative moisture content and temperature for reconstitution of the stabilized product. Line D shows, in a relative sense, the demarcation between product conditions which provide a biologically stable (Area E) and biologically unstable (Area F - subject to molding, etc.) product. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, it being recognized that various modifications are possible within the scope of the invention.

Claims

1. A process for reconstituting a stable grain product, comprising:

a) providing a stable at least partially cooked grain having a water activity of no more than about 0.65; b) exposing the grain to thermal energy whereby the surface of the grain is at a temperature of from about 140 to 200 ^CF; and c) milling and/or flaking and/or puffing the grain within a period t defined as

0 < t ≤ 30 seconds after the thermal energy exposure.

2. The process of claim 1 wherein the thermal energy is radiant heat from a radiant heat source which radiates at a temperature of about 1300 to 1500°F.

3. The process of claim 2 wherein the grain is exposed to the radiant heat for a

period of about 20 to 65 seconds.

4. The process of claim 1 wherein in step (c) the period t is about 5 to 10 seconds .

5. The process of claim 2 wherein the grain is exposed to the radiant heat for a period of about 30 to 45 seconds.

6. The process of claim 1 wherein the grain is milled or flaked within a period t of about 5 to 10 seconds after the exposure to the energy.

7. The process of claim 1 wherein the grain is selected from the group consisting

of rice, wheat, oats, barley, sorghum, corn, brans, and mixtures thereof.

8. The process of claim 1 wherein the grain is corn.

9. The process of claim 1 wherein the grain is agitated and/or tumbled during the exposure period.

10. The process of claim 1 wherein the surface and/or bulk temperature of the

grain is controlled.

11. The process of claim 1 wherein the grain is short, medium, or long-grained

rice.

12. The process of claim 1 wherein the stable partially cooked grain is stored and/or transported.

13. The process of claim 1 further comprising additional toasting of the milled or flaked grain.

14. The process of claim 1 further comprising coating the milled or flaked grain.

15. The process of claim 1 wherein the grain is brown rice.

16. The process of claim 1 wherein the grain is flaked and then puffed.

17. The process of claim 1 further comprising: d) processing the grain to make an R-T-E cereal.

18. The process of claim 16 further comprising processing the puffed grain to

make an R-T-E cereal.

19. The process of claim 1 wherein the grain is exposed to thermal energy by contacting the grain with heated fluidizing air at a temperature in excess of about 400°F for a period t,, defined as 0< t, <> 30 seconds.

20. The process of claim 19 wherein the contact is in a fluidized bed.

21. The process of claim 20 wherein the heated fluidizing air has about 0.075 to 0.125 pounds of water per pound of dry air.

22. The process of claim 20 wherein the fluidizing air is at a temperature in the range of about 400 °F to 500 °F .

23. The process of claim 20 wherein the fluidized grain has a ratio to the fluidizing air of about (1.5 to 2.5): 1.

24. The process of claim 23 wherein the grain particles exit the fluidized bed and are recycled to the fluidized bed.

25. The process of claim 23 wherein the fluidized bed is a horizontal fluidized bed.

26. The process of claim 20 wherein the grain is exposed to the thermal energy by the grain contacting a heated surface whereby thermal energy is transferred to the grain primarily by conduction.

27. The process of claim 26 wherein the contact period t₂ is 0 < t₂ < 90 seconds and is preferably about 65 to 80 seconds.

28. The process of claim 27 wherein the heated surface is at a temperature of from 700 to 1200°F and preferably 800-1000°F.