Apparatus for incorporating additives in extruded foods

A method and apparatus for incorporating one or more additives throughout an expanded food product. An expandable mixture of moistened farinaceous and/or proteinaceous materials is extruded at elevated temperatures and pressures through the die orifice of an expander-cooker into the cylindrical bore of a tubular extrusion die which is secured to the external face of the extruder die plate. The cylindrical bore of the tubular die has the same cross-sectional area and shaped as the die orifice of the extruder, so that as the mixture passes longitudinally through the tubular die it is still radially confined and is maintained at the same high pressure and temperature as when extruded through the die orifice. One or more liquid additives are injected under pressure into the body of the farinaceous and/or proteinaceous mixture as it is passed through the tubular die, through a nozzle mounted concentrically within the cylindrical bore of the tubular die. As the material is extruded from the tubular die into the atmosphere, it expands to form a porous structure. Simultaneously with the expansion of the mixture, the liquid additive diffuses throughout the porous structure, from the center to the exterior surfaces thereof, to thereby provide a porous expanded product in which the additive is incorporated throughout the product.

BACKGROUND OF THE INVENTION 
This invention relates to the production of an expanded food product. More 
particularly, the invention relates to a method and apparatus for 
incorporating an additive uniformly throughout an extrusion-expanded food 
product. 
The production of extrusion-expanded food products, both those intended for 
human consumption and those for use as pet foods, is well known in the 
food industry. Typically such products are produced in an extrusion cooker 
of the general type disclosed in U.S. Pat. Nos. 3,117,006 and 3,385,709, 
in which a moistened mixture of farinaceous and/or proteinaceous materials 
is introduced into the extruder in which the mixture is subject to 
mechanical working at elevated temperatures and pressures and is extruded 
through an extrusion die into the atmosphere. As the material issues from 
the die, it expands into a porous expanded product due to the pressure 
drop across the die and the flashing off of water as steam. The extrudate 
is then cut into pieces of a desired length and dried. Examples of food 
products for human consumption which can be prepared by such procedures 
are disclosed in U.S. Pat. Nos. 3,104,975 to Bowman, 3,117,006 to Wenger 
and 3,385,709 to Wenger et al, and examples of the production of expanded 
animal food products are disclosed in U.S. Pat. Nos. 3,119,691 to 
Ludington et al, 3,447,929 to Hale, and 3,891,774 to Baker et al. 
While the expanded food products produced by such procedures are 
nutritious, it is frequently desired to incorporate one or more additives 
such as flavoring materials, palatability enhancers, coloring agents, and 
the like in the expanded product to improve the flavor of the product, or 
provide the expanded product with the appearance of meat, and the like. 
Melted fat, usually tallow, is commonly coated onto the product to improve 
its palatability, particularly when pet food products are being produced. 
For example, U.S. Pat. No. 3,119,691 to Ludington et al discloses coating 
the expanded particles with fat and a liquid meat extract. U.S. Pat. No. 
4,104,407 to Stringer et al discloses coating the expanded particles with 
a dextrin material and fat. U.S. Pat. No. 4,215,149 to Majlinger discloses 
coating the expanded particles with fat and a salt of phosphoric acid. 
U.S. Pat. No. 3,745,023 discloses coating the expanded particles with a 
composition containing modified animal fat extracts, vegetable oil and 
fish oil. U.S. Pat. No. 4,211,797 to Cante et al discloses coating 
expanded particles with a blend of lipolyzed beef tallow and digest of 
beef. In each of these disclosures, the fat and other additives are 
incorporated by coating the material on the surface of the expanded 
pieces, such as by spraying, tumbling, dipping, and the like. While such 
an application of the additive is effective to enhance the palatability or 
other characteristics of the expanded food, it is subject to certain 
disadvantages. For example, an additional processing step is required in 
the production of the product. Moreover, when fat is applied to the 
surface of the expanded pieces, the fat-coated surface is greasy and 
requires packagers to sell the product in grease-resistant lined 
containers, since paper containers absorb the fat, resulting in an 
unsightly package. Also, the fat coating on the product is exposed to the 
oxygen of the air and is thus subject to oxidative rancidity. 
Prior attempts to include such additives, particularly fat, directly into 
the matrix of the expanded product have not been entirely successful. 
Thus, when fat is added to the farinaceous and/or proteinaceous mix in the 
expander, the fat has a tendency to be expressed from the ingredient mix 
during the extrusion process. Attempts to add substantial amounts of fat 
directly to the ingredient mixture prior to extrusion have reduced product 
expansion to such an extent that the products become undesirably dense. In 
order to avert these difficulties, a number of procedures have been 
suggested heretofore in order to incorporate fat or other additives in the 
matrix of the expanded product by the addition of fat and other additive 
to the ingredient mixture prior to extrusion, such as disclosed in U.S. 
Pat. Nos. 3,908,025 to Miller et al, 4,020,187 to McCulloch et al, and 
4,225,630 to Pitchon. 
SUMMARY OF THE INVENTION 
The present invention is directed to an apparatus for producing an expanded 
food product in which an additive is incorporated substantially uniformly 
throughout the matrix of the expanded product. An expandable mixture of 
moistened farinaceous and/or proteinaceous materials is introduced into a 
conventional extrusion cooker in which the mixture is subjected to 
mechanical working sufficient to raise the temperature of the mixture to 
substantially above 212.degree. F. and the mixture is compressed to a 
relatively high pressure, and the mixture is thereafter extruded through a 
die orifice in which the mixture is further compressed. The material is 
extruded through the die orifice into an elongated tubular extrusion die, 
mounted adjacent the die orifice, in which the material remains under 
elevated pressure and temperature. One or more additives, such as fat, 
coloring agents, flavoring material, etc., in liquid form, are injected 
into the center of the hot, pressurized mix as it passes through the 
tubular extrusion die, through an injection nozzle mounted concentrically 
within the tubular die, so that the additives are deposited within the 
pressurized material. As the material is extruded from the tubular die 
into atmospheric conditions, the superheated moisture partially flashes 
off to cause the material to expand, with the expanded product having a 
porous structure. As the material expands, the liquid additive permeates 
throughout the porous structure, from the center to the surface thereof. 
The expanded extrudate is then cut into pieces of a desired size upon 
exiting the tubular die, and may be dried to further reduce the moisture 
content of the pieces.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be described in detail hereinafter in connection 
with the production of an expanded pet food product. It will be 
understood, however, that the method and apparatus of this invention are 
equally suitable to the production of expanded products intended for human 
consumption. 
In accordance with the present invention, an expandable mixture of 
moistened farinaceous and/or proteinaceous materials is introduced into a 
conventional extrusion cooker, such as a commercially available Wenger 
cooker-extruder or Anderson expander, in which the mixture is subjected to 
mechanical working under elevated heat and pressure, and forced through a 
die orifice. Farinaceous ingredients which may be used include wheat, 
corn, barley, oats, and the like, and their derivatives such as corn meal, 
hominy, wheat middlings, wheat germ, etc. Typically the amount of 
farinaceous ingredients in the expandable mixture comprises between about 
30% to 70% by weight of the mix. 
The mixture may also include one or more proteinaceous ingredients of 
vegetable, animal or fish origin, such as soy bean meal, soy grits, meat 
meal, bone meal, poultry meal, fish scrap and combinations thereof. 
Typically, the proteinaceous ingredients comprise between about 20% to 50% 
by weight of the mix. 
The balance of the mixture may comprise salts, flavorings, colorings, 
vitamin supplements, minerals, and other like ingredients to form a 
nutritionally balanced pet food product. In general, the mixture 
introduced into the extrusion cooker has a moisture content of about 10% 
to 15%. 
The ingredients are blended and introduced into a conventional 
extruder-cooker where the mixture is subjected to mechanical working under 
elevated temperatures and pressures to rapidly cook the mixture, and is 
extruded through a die orifice. The temperatures in the extrusion zone are 
substantially above 212.degree. F., preferably between about 250.degree. 
F.-350.degree. F. Steam and/or water may be injected to control moisture 
and temperature of the mixture. The pressures developed within the 
extruder at the die plate should be above the vapor pressure of water at 
its extrusion temperature, typically between about 25-600 psi. 
As the material is extruded through the die orifice, it passes directly 
into an elongated tubular extrusion die which is mounted on the exterior 
face of the die plate of the extrusion cooker. Thus, the cooked mixture is 
forced under pressure through the die orifice of the extruder into the 
tubular extrusion die having a cylindrical bore which is axially aligned 
and in communication with the die orifice, with the cylindrical bore 
having an internal diameter substantially the same cross-sectional area 
and shape as the die orifice. The cooked material remains under elevated 
pressure and temperature as it is forced through the tubular die since the 
cylindrical bore prevents expansion of the material. 
As the material passes along the length of the tube, an additive, in liquid 
form, is injected into the cooked material. Thus, the liquid additive is 
pumped through an injection nozzle which is coaxially mounted within the 
cylindrical bore of the tubular die under a pressure sufficient to deposit 
the additive in the interior of the hot pressurized cooked material. 
The type of additive deposited in the cooked material is not critical to 
the process of the present invention, as long as it is sufficiently fluid 
to be pumpable. Any of the numerous additives usually coated onto expanded 
pet food products may be used, including fats or oils such as tallow, 
lard, vegetable oils and the like; flavor or palatability enhancers such 
as hydrolyzed protein, animal or poultry digest, hydrolyzed protein, 
dextrins, spices, coloring materials, and the like. When a fat is to be 
incorporated as the additive, it is heated to liquify the fat prior to 
being pumped into the pressurized cooked material. If desired, the 
additive may be mixed in a water base to provide a liquid solution or 
suspension of the additive which is injected into the cooked material. The 
amount of additive deposited in the cooked material is regulated in 
relation to the quantity of the cooker material being forced through the 
tubular extrusion die and the desired effect of the additive, and may 
range from about 2% to 20% or more of the product. For example, when fat 
is used as the additive, the rate of fat addition is controlled so that 
the amount of fat deposited in the cooked material constitutes between 
about 4% to 10% or more, based on the dry weight of the expanded product. 
Preferably, the injection nozzle is mounted concentrically within the 
cylindrical bore of the tubular extrusion die, at or near the upstream end 
of the tubular die, adjacent the die orifice of the expander. As the 
pressurized cooked material is forced through the elongated tubular die 
beyond the injection nozzle, the additive begins to migrate outwardly from 
the interior of the confined material. When the cooked material exits the 
tubular extrusion die into the atmosphere, it expands into a porous 
expanded product due to the pressure drop across the die opening and the 
flashing off the water contained in the extruded product as steam. The 
expansion of the cooked material causes the additive to diffuse 
substantially uniformly throughout the porous structure, from the center 
to the surface thereof. In this manner, a desired additive is incorporated 
in the expanded product during the expansion of the product, thereby 
eliminating the need for separately coating the expanded product. The 
extrudate, which typically has a moisture content of about 20% to 35% by 
weight, is then cut into small chunk-like pieces by a rotating knife, and 
is passed through a conventional dryer to reduce the moisture content of 
the expanded pieces to about 7% to 15%. 
One embodiment of the apparatus of the present invention will be described 
by reference to FIGS. 1 and 2, in which a food product extruder of the 
type disclosed in U.S. Pat. Nos. 3,117,006 to Wenger and 3,358,709 to 
Wenger et al is broadly designated by the numeral 10, and includes a 
housing 11 and an extruder screw 12. Screw 12 is provided with flights 14 
which force a mass of moistened farinaceous and/or proteinaceous material, 
capable of expanding after extrusion, toward die plate 15. Die plate 15 is 
provided with a die orifice 20 through which the material is forced at an 
elevated temperature and pressure. Housing 11 may be provided with an 
annular jacket 16 having inlet and outlet connections 17 to facilitate 
circulation of a heating fluid through chamber 18 for heating the material 
as it is moved toward die plate 15 by flights 14. However, in many cases, 
a sufficient product forming temperature is developed in the material by 
friction as it is compressed and forced toward die plate 15. 
Alternatively, cooling fluids may be circulated through chamber 18 to 
control the temperature of the food material if it becomes excessively 
high. If desired, steam may be injected into the material in the extruder 
to increase the temperature and/or moisture content of the material. 
Generally, the farinaceous and/or proteinaceous mixture being processed 
should have a moisture content at the time of extrusion of about 10% to 
35% by weight. Additionally, the temperature of the material as it is 
forced through orifice 20 in die plate 15 should preferably be in the 
range of between about 250.degree. F.-350.degree. F., while temperature 
in the range of about 225.degree. F.-400.degree. F. are acceptable. Also, 
the pressure developed at die plate 15 should be above the vapor pressure 
of water at its extrusion temperature, generally between about 25-600 psi. 
Tubular extrusion die 21, comprising an elongated tube 22 mounted on base 
plate 23, is secured by any suitable means to the exterior face of die 
plate 15. A cylindrical bore 24, which is axially aligned with die orifice 
20, extends through tubular extrusion die 21, with the inner end of bore 
21 being contiguous with and in communication with the die orifice 20. The 
internal diameter of bore 24 has substantially the same cross-sectional 
area and configuration as that of die orifice 20, so that as the 
farinaceous and/or proteinaceous mixture is extruded at elevated pressure 
through orifice 21, it passes directly into cylindrical bore 24 in which 
the material is maintained under the same elevated pressure as when it 
passes through the die orifice. Thus, as the mixture is longitudinally 
forced through the cylindrical bore of the tubular die, it is radially 
restricted along the length of the tube and maintained under high pressure 
and elevated temperature. The length of tubular extrusion die 21 is not 
critical, and may have a length of about 2 to 15 times its internal 
diameter. 
Injection nozzle 24 having a discharge opening 30 is mounted concentrically 
within cylindrical bore 24 of the tubular extrusion die 21, adjacent die 
orifice 20, to deliver a liquid additive, under pressure, to the interior 
of the mixture being carried through the tubular die member. The injection 
nozzle 25 is fed by a line 26 from a supply tank 27 in which the additive 
is maintained in liquid form. A suitable pump 28 is provided in feed line 
26 to deliver the liquid additive to the injection nozzle under sufficient 
pressure to deposit the additive in the pressurized mixture in the tubular 
die. A check value 29 or other similar device is preferably provided in 
line 26 to prevent backflow of the additive through the feed line 26. If 
tallow, which is not normally a liquid at ambient temperature, is used as 
the additive, it is heated to about 90.degree. F. or higher to liquify the 
tallow prior to being pumped to the injection nozzle. For example, supply 
tank 27 may be provided with heating coils to maintain the tallow in a 
liquid state. 
As the mixture emerges from the tubular extrusion die under the high 
internal pressure, into atmospheric conditions, the superheated 
equilibrium moisture partially flashes off by evaporation to cause product 
expansion. Simultaneously, the liquid additive is diffused throughout the 
expanded material, from the center to the outer surfaces. The extruded 
rope of material is cut into pieces of a desired length by a rotating 
knife (not shown) rotatably mounted adjacent the discharge end of the 
tubular extrusion die. 
Another embodiment of the invention is illustrated in FIG. 3 in which the 
tubular extrusion die is adapted to be used in conjunction with an 
extruder die plate have a plurality of circumferentially spaced die 
orifices therein. As shown in FIG. 3, the tubular extrusion die 31 is 
provided with a plurality of elongated tubes 32 extending from base plate 
33, with each of the tubes 32 having a cylindrical bore 34 which is in 
axial alignment with a die opening in the extruder die plate. An injection 
nozzle 35 is mounted within each of the cylindrical bores, with the 
injection nozzles being fed by lines 36 and 37 from the same or different 
liquid additive supply tanks. For example, a liquid solution or suspension 
of a dye of one particular color may be pumped through line 36, while a 
different color dye may be pumped through line 37. Alternatively, a 
different liquid additive may be fed to each injection nozzle, so that an 
expanded product having a variety of colors and/or flavors may be produced 
simultaneously utilizing a single extruder. 
The invention is further illustrated by the following examples. 
EXAMPLE I 
A dry, expanded pet food product was produced from the following 
ingredients: 
______________________________________ 
Ingredient Percent 
______________________________________ 
Ground corn 65.4 
Corn gluten 11.5 
Meat and bone meal 
11.0 
Soy meal 11.0 
Salt 1.0 
Vitamins and minerals 
.1 
______________________________________ 
The ingredients were mixed together and ground through a 3/64" hammermill. 
The mixture was introduced into a Wenger X-25 extruder in which the 
material was subjected to temperatures and pressures averaging about 
250.degree. F. and 300 psi, respectively, at the die plate. The mixture 
was extruded through a 7/16" circular die opening directly into a tubular 
extrusion die as shown in FIGS. 1 and 2, in which the tubular die had a 
cylindrical bore 7/16" in diameter and about 5 inches in length. An 
injection nozzle was mounted concentrically within the cylindrical bore, 
with the discharge end of the nozzle being situated about 1.5 inch from 
the outer face of the die orifice. Hot liquified tallow, at about 
150.degree. F., to which has been added a small amount of a dye, was 
pumped from a supply tank through the injection nozzle into the body of 
material being forced through the cylindrical bore, at a rate sufficient 
to provide the product with a fat level of about 6%. The mixture was 
extruded from the tubular die into the atmosphere in the form of an 
expanded rope which was cut into pieces about 1" in length and dried at 
280.degree. F. The resulting product had a porous expanded structure with 
the fat and dye being uniformly distributed throughout the product from 
the center to the outer surfaces. 
EXAMPLE II 
The process of Example I was repeated except that a liquid additive 
containing equal parts by weight of tallow and chicken digest together 
with a small amount of dye, was pumped at a temperature of 150.degree. F. 
through the injection nozzle into the body of the farinaceous and 
proteinaceous mixture confined in the tubular extrusion die, at a rate 
sufficent to obtain an additive level of about 6% by weight of the 
finished product. Examination of the dried product showed that the tallow, 
digest and dye had permeated throughout the porous expanded pieces, even 
to the exterior surfaces of the pieces. 
While the invention has been particularly described in connection with the 
production of expanded pet food products, it will be understood that the 
present invention is equally well suited for incorporating an additive in 
the production of expanded farinaceous and/or proteinaceous products 
intended for human consumption, such as, for example, expanded breakfast 
cereal products having coconut oil incorporated therein as a palatability 
enhancing additive. 
It is recognized that various modifications of the invention as described 
herein may be made by those skilled in the art without departing from the 
scope of the appended claims.