Title: Inert gas-filled cooking system
Abstract: An inert gas-filled cooking process is disclosed which provides for quick sterilization of food in inert gas-filled packages in a manner that prevents deterioration of food quality as well as assures a long taste guaranteed period by raising the temperature of hot water to be applied onto the food packages in a sterilization tank so as to satisfy the retort sterilization requirements.The sterilization tank is pressurized at a predetermined value by control of an analog pressure regulating valve. The temperature of the hot water flowing from a heat exchanger into the sterilization tank is varied in a multi-staged fashion to follow a predetermined sterilization temperature-time curve by control of an analog steam regulating valve and a steam superheater. The hot water is applied onto the packaged food for sterilization.
Patent Number: 7,008,659 Issued on 03/07/2006 to Ono
| Inventors:
|
Ono; Takuji (Okayama, JP)
|
| Assignee:
|
Ono Foods Industrial Co., Ltd. (Okayama, JP)
|
| Appl. No.:
|
700365 |
| Filed:
|
March 6, 1995 |
| PCT Filed:
|
March 6, 1995
|
| PCT NO:
|
PCT/JP95/00359
|
| 371 Date:
|
November 12, 1996
|
| 102(e) Date:
|
November 12, 1996
|
| PCT PUB.NO.:
|
WO95/23526 |
| PCT PUB. Date:
|
September 8, 1995 |
Foreign Application Priority Data
| Current U.S. Class: |
426/412; 426/521 |
| Current Intern'l Class: |
B65B 55/00 (20060101) |
| Field of Search: |
426/412,407,521
436/407,412
|
References Cited [Referenced By]
U.S. Patent Documents
| 3892058 | Jul., 1975 | Komatsu et al.
| |
| 5277923 | Jan., 1994 | Mignogna et al.
| |
| 5395634 | Mar., 1995 | Humphreys.
| |
| 5562938 | Oct., 1996 | Lee et al.
| |
| Foreign Patent Documents |
| 59-210879 | Nov., 1984 | JP.
| |
Other References
Wayne Gisslen, Professional Cooking, 2nd Edition, John Wiley & Sons Inc., 1989,
pp. 58 and 111.
|
Primary Examiner: Becker; Drew
Attorney, Agent or Firm: Bacon & Thomas
Claims
What is claimed is:
1. An inert gas-filled cooking method for sterilizing food at a food sterilization
temperature, comprising the steps of:
preliminarily processing food by heating which does not cook the food;
filling the preliminarily processed food which is prepared but not cooked into
retort pouches and hermetically sealing the retort pouches under an inert gas atmosphere;
loading the food retort pouches into a sterilization tank;
pressurizing the sterilization tank having the food retort pouches loaded therein
at a predetermined pressure value by means of a pneumatic conduit and an analog
pressure regulating valve;
raising the temperature of the food in the food retort pouches to a first predetermined
temperature value below the sterilization temperature of the food in the food retort
pouches by reheating a heated steam supplied to the primary of a heat exchanger
by means of a steam superheater causing a rapid increase in the temperature of
heated water flowing in the secondary of the heat exchanger and subsequently into
the sterilization tank where the heated water is applied to the food retort pouches;
maintaining the temperature of the food in the food retort pouches at said first
predetermined temperature value by continuing the application of the heated water
to the food retort pouches;
raising the temperature of the food in the food retort pouches from said first
predetermined temperature value to a second predetermined temperature value which
corresponds to the sterilization temperature of the food in the food retort pouches,
by increasing the temperature of the heated water supplied to the sterilization
tank where the heated water is applied to the food retort pouches;
maintaining the second predetermined food sterilization temperature on the food
in the food retort pouches for a predetermined time by continuing the application
of heated water at said second predetermined temperature value which is less than
the time at which the first predetermined temperature is maintained; wherein said
predetermined pressure value is maintained during the maintenance of said first
and second predetermined temperature values; and
cooling the food retort pouches from said second predetermined food sterilization
temperature by applying cooling water instead of hot water on the food retort pouches.
2. The method as defined in claim 1 wherein said preliminary processed food is
prepared by blanching in oil.
Description
FIELD OF THE INVENTION
The present invention relates to the sterilization of foods in inert gas-filled
packages and, more particularly, to an inert gas-filled cooking method.
BACKGROUND OF THE INVENTION
Conventionally, in a sterilization process for food in inert gas-filled
packages, food which has been cooked up to a certain stage is put into a bag ("retort
pouch") formed of highly gas-impermeable laminated sheet material; the bag is hermetically
sealed as by heat sealing after replacing the air in the bag with an inert gas;
the bag thus sealed is loaded into a sterilization tank; and a hot water or heated
steam is fed into the sterilization tank to sterilize the food in the bag.
To enhance the sterilization effect as well as to maintain the taste, shape and
quality of the food, it is desirable that the sterilization be performed at a higher
temperature and for a short period of time. According to a certain heat sterilization
standard, the temperature of 120° C. is generally maintained for four minutes
at the heart of the food (F value-4).
In a conventional sterilization tank, the food in inert gas-filled packages is
immersed in hot water for a certain period of time, or otherwise, the food is subjected
to sprays of hot water or heated steam for a certain period of time in a certain
pressurized condition. However, as shown in FIG. 9, these methods cannot raise
the core temperature of the food in inert gas-filled packages readily to a predetermined
sterilization temperature. Also, temperature control tends to be inaccurate. Accordingly,
it is necessary to increase the heating time equivalently if it is desired to enhance
the sterilization effect. As a matter of fact, the sterilization is performed in
the neighborhood of 120° C. for about 60 minutes.
This can provide for adequate sterilization of a major portion of bacteria which
cause food poisoning; however, some bacteria can survive the treatment. Accordingly,
in order to enhance the sterilization effect 3-percent hydrogen peroxide sorbic
acid or the like are used additionally, or packages are sealed under a vacuum or
an inert gas atmosphere.
During the sterilization process, the food is kept under a heated condition
for an extended period of time so that the food sometimes acquires the smell characteristic
of the retort pouch with its organoleptic properties deteriorating. Some foods,
which need to be shipped in a semi-cooked condition, tend to be cooked over beyond
that condition. These provide limitations on quality control of foods in inert
gas-filled packages.
The present invention overcomes the above-stated problems of the prior art by
providing an inert gas-filled cooking process which can sterilize foods in inert
gas-filled packages rapidly and effectively without deteriorating food quality
by raising the temperature of the hot water to be applied onto the food packages
in the sterilization tank.
SUMMARY OF THE INVENTION
The present invention achieves the above-stated object by providing an inert
gas-filled cooking process which comprises: a food filling step of filling a preliminarily
processed food into packages and hermetically sealing the packages under inert
gas atmosphere; a food package loading step of loading the food packages into a
sterilization tank; a pressurization step of pressurizing the sterilization tank
having the food packages loaded therein at a predetermined pressure value; a primary
temperature raising step of raising the temperature of the packaged food to a first
predetermined value by reheating a heated steam supplied to the primary of a heat
exchanger by means of a steam superheater to cause a rapid increase in the temperature
of a hot water flowing in the secondary of the heat exchanger into the sterilization
tank for application onto the food package; a temperature maintaining step of maintaining
the temperature of the packaged food at the first predetermined value by continuing
with the supply of the hot water; a secondary temperature raising step of raising
the temperature of the packaged food to a second predetermined food sterilization
temperature by increasing the temperature of the hot water supplied to the sterilization
tank; a sterilization step of maintaining the second predetermined food sterilization
temperature for a predetermined time; and a cooling step of rapidly cooling the
packaged food from the second predetermined food sterilization temperature by applying
a cooling water instead of the hot water on the food package.
Food is put into a retort pouch by means of a tube or other food filling means;
the air in the pouch is replaced with an inert gas by a replacing means in a continuous
process; the pouch is stretched in its both ends by a stretching means; the pouch
thus stretched is heat sealed by a heat sealing means to provide the food in inert
gas-filled and hermetically sealed packages; and the packages are placed on a transport
rack having a plurality of shelves for loading into the sterilization tank.
In this condition, the pressure in the sterilization tank is raised to, and maintained
at, the predetermined value, by means of a pressure sensor provided within the
sterilization tank and the analog pressure regulating valve provided in the pneumatic
conduit; the temperature of the hot water flowing in the secondary of the heat
exchanger is raised by increasing the temperature of the heated steam flowing in
the primary of the heat exchanger; and the hot water is applied onto the food packages
in the sterilization tank by means of the circulating pump.
Provided in the conduit leading from a boiler to the heat exchanger are
an analog steam regulating valve and a steam superheater which generates superheated
steam by reheating the heated steam from the boiler. The heat exchanger raises
the temperature of the hot water to the predetermined value so that its application
onto the packaged food will raise the food temperature to the predetermined value
to provide for rapid sterilization of the food.
Immediately after commencement of an operation, the opening of the analog
steam regulating valve is increased to increase the flow rate and the temperature
of the heated steam flowing into the heat exchanger. Simultaneously therewith,
the heated steam to be supplied to the primary of the heat exchanger is reheated
by the steam superheater so as to rapidly raise the temperature of the hot water
flowing from the heat exchanger to the sterilization tank for application onto
the packaged food therein. Thus, the temperature of the food in inert gas-filled
packages is raised to approximately 100° C. as the primary temperature-raising
step. In this condition, the temperature is maintained for a certain period of
time by controlling the steam superheater. After a predetermined time has elapsed,
the steam superheater is controlled so as to raise the temperature of the hot water
to the predetermined sterilization temperature of approximately 120° C. as
the secondary temperature-raising step. This temperature is maintained for a predetermined
period of time (four to six minutes) for sterilization. A predetermined time thereafter,
the steam superheater is shutdown; a two-way change-over valve is operated to stop
the application of the hot water; the hot water remaining in the sterilization
tank is recovered to a hot water recovery tank. Simultaneously therewith, the food
in inert gas-filled packages is cooled to a temperature suitable for shipment by
supplying a cooling water from a first and a second cooling water tank to water
application assemblies.
For the packaged foods to be shipped in a cooked condition, a partially cooked
food is filled into a retort pouch together with liquid-state seasonings; the air
remaining in the pouch is replaced with an inert gas; the pouch is hermetically
sealed; and the pouch is then loaded into the sterilization tank. Hot water to
be applied is heated to the predetermined temperature as the primary temperature-raising
step; this temperature is maintained for a predetermined time necessary to complete
cooking; the hot water is further heated to the predetermined temperature for sterilization
as the secondary temperature-raising step. Both cooking and sterilization are performed
in this single step. In this manner, the temperature of the food in inert gas-filled
packages and the temperature of the hot water are varied to conform to the sterilization
temperature-time curve suitable for sterilization.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the system configuration of an embodiment
of the present invention;
FIG. 2 is a plot showing a sterilization temperature-time curve according to
the present invention for use with foods in inert gas-filled packages;
FIG. 3 is a table showing an embodiment of the sterilization temperature-time
curves for foods in inert gas-filled packages;
FIG. 4 is a block diagram showing the control arrangement of the embodiment
of the present invention;
FIG. 5 is a sectional view of a water application assembly provided in a sterilization tank;
FIG. 6 is a front view of a nozzle of the water application assembly shown in
FIG. 5;
FIG. 7 is a flow chart showing how a packaged food, "beef and burdock sliced
thin and cooked lightly with seasonings", is cooked and sterilized;
FIG. 8 is a flow chart showing how another packaged food, "yellowtail broiled
with soy", is cooked and sterilized;
FIG. 9 is a plot showing a sterilization temperature-time curve for foods in
inert gas-filled packages as prepared in a conventional manner; and
FIG. 10 is a table showing an embodiment of the sterilization temperature-time
curves according to a conventional retorting method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with respect to embodiments as shown
in the accompanying drawings.
Referring to FIG. 1 which shows, in block form, the configuration of an
embodiment of the present invention, heated steam generated by a boiler (not shown)
flows via an analog steam regulating valve
18 and a steam superheater
19
into the primary of a heat exchanger
9 for heat exchange with hot water
flowing in the secondary of the heat exchanger. The hot water flows via a two-way
change-over valve
10a to a circulating pump
11 which feeds
the water via a conduit
12 to water application assemblies
3 to apply
it onto the food packages placed in a sterilization tank
1 so as to heat
the food. After heat exchange with the food, the hot water is collected in the
bottom portion of the sterilization tank
1 for recirculation via a drain
valve
35 and a return conduit
13 to the secondary of the heat exchanger
9.
After the food packages have been heated by the hot water for a predetermined
time for complete sterilization, the two-way change-over valve
10a is
operated to stop the flow of the hot water. The hot water remaining in the sterilization
tank
1 is then recovered into a hot water recovery tank
14 via a
two-way change-over valve
10b and an ON-OFF valve
36a.
After completion of the recovery process, the ON-OFF valve
36a is
closed and an ON-OFF valve
36b is opened and the circulating pump
11 is operated to feed a cooling water from a first cooling water tank
20
via the two-way change-over valve
10a to the water application assemblies
3 so that the cooling water is applied onto the food packages in the sterilization
tank
1. The cooling water, after having been warmed through contact with
the food packages, is recovered by the first cooling water tank
20. Then,
the ON-OFF valve
36b is closed and an ON-OFF valve
36c
is opened, allowing cooling water to flow from a second cooling water tank
21. In this manner, the first and second cooling water tanks
20 and
21 are used alternately, lowering the temperature of the cooling water for
resupply until the food packages have been cooled enough for removal from the tank.
The sterilization tank
1 includes a pressure-resistant housing provided
with an air-tight door (not shown) through which a transport rack
2 having
numerous shelves for receiving food packages thereon can be brought into or from
the housing. Provided within the sterilization tank are a pair of opposed water
application assemblies
3 each including a plurality of nozzles
4
for applying the hot or cooling water onto the food packages placed on the transport rack.
Referring to FIG. 5, the water application assembly
3 as depicted
has connected to one side thereof, the conduit
12 leading from the circulating
pump
11 and includes, on the other side, a plurality of the nozzles
4
disposed in spaced relationship. Provided within the water application assembly
3 is a pressure equalizing plate
33 which is disposed between the
conduit
12 and nozzles
4 spacedly therefrom to act as a baffle for
the incoming hot (or cooling) water under pressure by the circulating pump
11
so that the water may spread evenly within the water application assembly
3.
As shown in FIG. 6, the nozzle
4 has a rectangular opening
37 for
applying a progressively increasing strip of hot or cooling water evenly throughout
the food packages.
Further, a pneumatic conduit
7 is provided on the ceiling of the
sterilization tank
1 to regulate the pressure in the tank. A compressor
5 is used together with an analog pressure regulating valve
6 to
increase the pressure in the tank. A pressure sensor
8 provided within the
sterilization tank is used to sense the pressure in the tank. The analog pressure
regulating valve
6 and the drain valve
34 are operated to maintain
the pressure in the tank at a predetermined pressure value corresponding to the
temperature of the hot water.
The steam superheater
19 reheats the heated steam flowing therethrough
and converts it into a superheated steam by a separate heat source such as, for
example, an electric heater with a heat exchange mechanism. The steam superheater
feeds such a superheated steam to the primary of the heat exchanger
9 and
generates high temperature water at the secondary thereof.
A hot water temperature sensor
15 is provided in the secondary of the
heat
exchanger
9 and also a tank inside temperature sensor
16 is provided
within the sterilization tank
1. They sense the hot water temperature and
the tank inside temperature, respectively, and feed information on sensed temperatures
to a control panel
17 which controls the operation of the steam superheater
19 and the opening of the analog steam regulating valve
18 so as
to vary the hot water temperature and the tank inside temperature to follow the
predetermined sterilization temperature-time curve.
FIG. 2 is a plot of such sterilization temperature-time curve for the food packages
placed in the sterilization tank, showing the time T on an abscissa and the tank
inside temperature t° C. on an ordinate.
To begin the sterilization process, food in inert gas-filled packages is loaded
into the sterilization tank
1; and the temperature of the heated steam is
raised by means of the analog steam regulating valve
18 and the steam superheater
19 so as to increase the temperature of the hot water circulating from the
heat exchanger
9 into the sterilization tank for application onto the food
packages. In this manner, the tank inside temperature t is increased rapidly to
a predetermined value (about 100° C.) (the primary temperature-raising section
a); the predetermined temperature is maintained for a certain period of time (the
temperature maintaining section b); the steam superheater
19 is then controlled
to reheat the heated steam so as to increase further the temperature of the hot
water flowing from the heat exchanger
9 (the secondary temperature-raising
section c); sterilization is performed by maintaining a predetermined sterilization
condition F04 (120° C., four minutes); and the food packages are cooled by
switching into application of the cooling water upon completion of the sterilization
process. It is to be noted that the broken lines in FIG. 2 show the food core temperature.
The control panel
17 operates to sequentially compare the temperature
information from the tank inside temperature sensor
16 with a preset reference
value from the sterilization temperature-time curve for each food in inert gas-filled
packages, and if the preset temperature is not exceeded, to increase the opening
of the analog steam regulating valve
18 to cause an increase in the temperature
of the hot water circulating in the secondary of the heat exchanger
9. If
the temperature information from the tank inside temperature sensor
16 is
higher than the preset temperature value on the sterilization temperature-time
curve, the opening of the analog steam regulating valve
18 is reduced to
decrease the flow of the heated steam. Simultaneously therewith, the steam superheater
19 is operated based on the temperature information from the hot water temperature
sensor
15 to cause a decrease in the temperature of the hot water and accordingly
the tank inside temperature t so that the preset temperature from the sterilization
temperature-time curve is followed.
FIG. 3 is a table showing exemplary sterilization temperature-time curves for
various foods in inert gas-filled packages, wherein a, b, c and d in the top row
represent the primary temperature-raising step, the primary sterilization (temperature
maintaining) step, the secondary temperature-raising step and the cooling step,
respectively. Except for "vegetables boiled with soy (small packages)", cooking
and sterilization are performed during the primary sterilization (temperature maintaining)
step. For those packaged foods which do not require cooking, the temperature-maintaining
step (b section) can be shortened prior to shifting into the secondary sterilization
and the cooling steps.
FIG. 10 shows the time required to perform sterilization of the same retorted
foods using a conventional sterilization tank. Comparison of FIGS. 3 and 10 indicates
that the overall processing time is reduced substantially for all the foods under
test and that the shortening of the sterilization time with a high temperature
of 110 to 120° C. (d and D of the respective tables) removes the problem that
food acquires smell characteristic of a retort pouch with the smell and taste of
the food deteriorating and that some foods, which need to be shipped in a semi-cooked
condition, tend to be cooked over beyond that condition.
FIG. 4 is a block diagram of the control arrangement according to the present
invention. The control panel
17 comprises an input setting circuit
23
for inputting the sterilization temperature-time curve preset for a food in inert
gas-filled packages, a sequencing circuit
24 for controlling the process
according to a predetermined timing, a control value computing circuit
25
for computing control data such as set values for the heated steam temperature,
the heated water temperature, the tank inside temperature, and the tank inside
pressure, and adjusted values for the analog steam regulating valve
18 and
the analog pressure regulating valve
6, by following the sterilization temperature-time
curve using the elapsed time as a reference parameter, a first data memory
26
for storing the control data computed by the control value computing circuit
25
according to the timing selected by the sequencing circuit
24, a second
data memory
27 for storing the hot water temperature information from the
hot water temperature sensor
15 and the information from the tank inside
temperature sensor
16 and the pressure sensor
8 both provided in
the sterilization tank
1 according to the timing selected by the sequencing
circuit
24 after subjecting them to A/D conversion, a comparator circuit
24 for comparing the hot water temperature, the tank inside temperature
and the tank inside pressure retrieved from the first and second data memories
26 and
27 to provide deviations thereof, and a control signal generating
circuit
29 for generating control signals based on the deviations and the
control date stored in the first data memory
26, wherein control signals
from the control signal generating circuit
29 are subjected to A/D conversion
to control the analog steam regulating valve
18, the analog pressure regulating
valve
6 and the steam superheater
19 on a real time basis.
The conditions previously set by the input setting circuit
23 can be stored
in storage media such as floppy discs, card memories and the like by operation
of a personal computer
31 via an external interface circuit
30. Such
storage media permits direct inputting of the set conditions when the same type
of foods in inert gas-filled packages are processed.
In this arrangement, the sterilization tank
1 having foods in inert gas-filled
packages loaded in a hermetically sealed condition is pressurized to a predetermined
pressure by a compressor
5. The heated steam flowing through the analog
steam regulating valve
18 is further heated by the steam superheater
19
and flows into the heat exchanger
9. The hot water, after having been heated
due to heat exchange, is fed into the sterilization tank in jet form. By controlling
the analog steam regulating valve
18 and the steam superheater
19
based on the tank inside temperature and the hot water temperature, the tank inside
temperature is raised until it reaches approximately 100° C. whereupon that
temperature is maintained for a predetermined time (for example, 30 minutes) to
perform the primary sterilization and cooking. Thereafter, the steam superheater
19 is again operated so that the hot water supplied to the sterilization
tank
1 will increase the inside temperature t to 120° C. and that the
particular temperature is maintained for a predetermined time (for example, 5 to
10 minutes). Then, the two-way change-over valve
10a is operated
to stop the inflow of circulating hot water and instead to supply cooling water
to lower the temperature of the packaged food. In this manner, it is possible to
rapidly increase the temperature of the hot water to be applied to the packaged
food until it reaches approximately 100° C. whereupon that temperature is
maintained to perform cooking and pasteurisation. The temperature of the hot water
is further raised to approximately 120° C. and that temperature is maintained
for a predetermined time (5 to 10 minutes) to satisfy the F04 sterilization requirements.
FIG. 7 is a flow chart showing how the packaged food, "beef and burdock sliced
thin and cooked lightly with seasonings", is cooked and sterilized. Burdock is
washed and cut into pieces of a predetermined size and, as a preliminary cooking
step, it is subjected to a 60° C. weak acid bath for thirty minutes and then
is blanched in a 160° C. oil for ten seconds. Beef is sliced to a predetermined
thickness and is blanched in a 180° C. oil for five to ten seconds as a preliminary
cooking step. The burdock and beef thus cooked preliminarily are mixed and metered
and then filled into a bag of gas-impermeable material and sealed under inert gas
atmosphere. This packaged food is then subjected to a multi-stage sterilization
process in which the temperature is maintained at 102° C. for 20 minutes,
at 110° C. for 10 minutes and finally at 120° C. for 5 minutes for shipment
as the final product.
By cooking the beef and burdock in this manner, it is possible to sterilize them
completely without losing the beef's taste and glutinous mouthfeel and the burdock's crispness.
Further, the preliminary cooking of both beef and burdock before filling
into the bag alleviates the sterilization requirements in that complete sterilization
is possible in the multi-stage heat steriliztion process at lower than conventionally
used temperatures.
FIG. 8 is a flow chart for explaining the cooking/sterilization process for
"yellowtail broiled with soy". Frozen yellowtail is partially defrozen and sliced
and is subjected to an aqueous solution of 0.5% non-ionic surface active agent
(such as cane sugar-fatty acid ester) for 30 minutes. After washing with water,
it is blanched in a 150 to 160° C. oil for two to three minutes. It is then
deoiled and filled into a bag of gas-impermeable material and sealed under inert
gas atmosphere. Thereafter, it is subjected to the multi-stage heat sterilization
process which maintains the food at 100° C. for five minutes, at 110°
C. for twenty minutes and at 113° C. for ten minutes for shipment as the final products.
By cooking the yellowtail in this manner, it is possible to provide it as originally
broiled with sauce or gravy while keeping it tender as well as preventing pieces
from sticking to each other.
Also, by cooking the yellowtail in the manner as described above, it is possible
to perform complete sterilization at lower than conventionally used temperatures
in the multi-stage heat sterilization procedure while keeping the fish tender and
preventing pieces from sticking to each other.
As described above, the present invention provides completely sterilized foods
in inert gas-filled packages with a reduced sterilization temperature as well as
a shortened heat sterilization time by preliminarily processing the foods under
a predetermined condition followed by using the multi-stage heat sterilization
procedure with the inert gas-filled cooking system.
As described above, the present invention provides for complete and quick sterilization
of foods in inert gas-filled packages without losing the food's taste and mouthfeel
in a manner that satisfies the F04 sterilization requirements for foods by loading
preliminarily processed foods in inert gas-filled packages into sterilization tank
and following the predetermined sterilization temperature-time curve, i.e., applying
a hot water to the food packages in the tank so as to raise the food core temperature
rapidly to approximately 100° C., to maintain the temperature for a certain
period of time for cooking, and to raise the hot water temperature to 120°
C. rapidly.
*
