METHOD FOR COOKING AND STERILIZATION

Abstract

There is provided a method of cooking and sterilization of food arranged in a sealed package comprising a one-way valve that opens at a supra-atmospheric pressure of 20-200 mbar, said method comprising the steps of: a) heating the sealed package to cook the food; b) subjecting the sealed package from step a) to a sub-atmospheric pressure such that gas leaves the sealed package through the valve; and c) autoclaving the sealed package from step b) at a supra-atmospheric pressure.

Claims

1. A method of cooking and sterilization or high-degree pasteurization of food arranged in a sealed package comprising a one-way valve that opens at a pressure difference of 20-200 mbar, said method comprising the steps of: a) heating the sealed package to cook the food; b) subjecting the sealed package from step a) to a sub-atmospheric pressure such that gas leaves the sealed package through the valve; and c) autoclaving the sealed package from step b) at a supra-atmospheric pressure.

2. The method according to claim 1, wherein steps b) and c) are carried out in an autoclave capable of generating and maintaining the sub-atmospheric pressure of step b).

3. The method according to claim 2, wherein step a) is also carried out in the autoclave.

4. The method according to claim 1, further comprising the step of: d) releasing the pressure to obtain flash cooling of the food in the package from step c) and such that gas leave the sealed package from step c) through the valve.

5. The method according to claim 4, wherein step d) is carried out in an autoclave used for step c).

6. The method according to claim 4, further comprising the step of: e) further cooling the package from step d) such that the food in the package reaches a temperature of 50 C. or lower.

7. The method according to claim 6, wherein step e) is carried out at approximately atmospheric pressure.

8. The method according to claim 1, wherein the food reaches a temperature of 50-110 C. in step a).

9. The method according to claim 1, wherein the temperature is at least 110 C., such as at least 120 C., in step c).

10. The method according to claim 1, wherein the sub-atmospheric pressure of step b) is at least 200 mbar below atmospheric pressure.

11. The method according to claim 1, wherein the sealed package is heated for a time period of 5-180 min in step a).

12. The method according to claim 1, wherein step a) is carried out at approximately atmospheric pressure.

13. The method according to claim 1, wherein the food comprises vegetables, fish and/or transformed meat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above, as well as additional, objects, features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, with reference to the appended drawings, wherein:

[0039] FIG. 1 illustrates a flow chart representation of a method in accordance with an embodiment of the present invention.

[0040] FIG. 2 illustrates a non-limiting embodiment of a vacuum autoclave.

[0041] FIG. 3 illustrates another non-limiting embodiment of a vacuum autoclave.

DETAILED DESCRIPTION

[0042] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout the description.

[0043] FIG. 1 shows a flow chart representation of a method of cooking and sterilization (or high-degree pasteurization) of food according to one exemplary embodiment of the invention. The food is arranged in a sealed package having a one-way valve that opens at a pressure difference of 20-200 mbar. The food in the sealed package may for example comprise vegetables, fish and/or transformed meat, such as pt. The package in the method may thus be prepared by arranging food in a package and then sealing the package. For example, the food may be placed in a tray, such as a plastic tray, that is then sealed with a plastic film. The method can for example be performed in an autoclave as will be described in more detail with reference to FIGS. 2-3.

[0044] The method comprises the step of heating a) the sealed package in order to cook the food within the sealed package. The heating step a) may comprise dry heating, moist heating or a combination thereof. Consequently, steam may be applied during at least part of the first period (i.e. at least a part of the duration of the heating step a)).

[0045] Further, a step of subjecting b) the sealed package that has been heated to a sub-atmospheric pressure such that gas leaves the sealed package through the one-way valve is performed. During step b) the ambient pressure of the sealed packages may be decreased gradually. This may for example be the case if a vacuum autoclave is used and the gas outlet is coupled directly to a running vacuum pump. For example, the pressure may decrease continuously from atmospheric pressure to a target sub-atmospheric pressure, such as 500 mbar below atmospheric pressure. A benefit of a slower decrease of the pressure is that vigorous boiling in the package may be prevented. A problem of vigorous boiling is that the valve may be contaminated and lose its function. Accordingly, in one embodiment, the rate of pressure reduction after the first period never exceeds 500 mbar/min. For example, it may never exceed 250 mbar/min. In some embodiments, it never exceeds 100 mbar/min or 50 mbar/min.

[0046] Alternatively, the pressure may be pulsated during step b) to drive more gas out of the package. For example the pressure may be varied between a small sub-atmospheric pressure, such as less than 100 mbar below atmospheric pressure, and a pressure that is at least 400 mbar below atmospheric pressure.

[0047] When the sealed package is subjected to the sub-atmospheric pressure in step b), the valve opens and the food in the package is flash cooled, which may prevent over cooking.

[0048] Still further, the method comprises the step of autoclaving c) the sealed package that was subjected to a sub-atmospheric pressure in step b), at a supra-atmospheric pressure. To ensure an efficient sterilization, the ambient temperature of the package in step c) is above 100 C., such as at least 110 C., such as at least 120 C. A typical autoclaving temperature is 121 C. For example, the ambient temperature may be maintained above 100, 110 or 120 C. for at least 10 minutes. During step c), the ambient temperature corresponds to the ambient pressure as saturated steam is used as the heating medium. In one embodiment, the pressure is pulsated during step c) to further force gases out through the one-way valve. For example, the pressure may be varied between a small supra-atmospheric pressure of at least 0.5 bar, such as at least 1 bar above atmospheric pressure.

[0049] Furthermore, the method may include an additional step of releasing d) the pressure in order to obtain flash cooling of the food in the package from step c), by gas leaving the sealed package through the valve (one-way valve).

[0050] Next, the method may further comprise a step of further cooling e) the package from step d) such that the food in the package reaches a temperature of 50 C. or lower, such as 40 C. or lower.

[0051] FIG. 2 shows a non-limiting embodiment of a vacuum autoclave 100. The vacuum autoclave 100 is suitable for cooking and sterilization of food arranged in a sealed package 101 comprising a one-way valve 102 that opens at a pressure difference, normally at a pressure of 20-200 mbar, in accordance with the inventive method.

[0052] The vacuum autoclave 100 comprises a housing 103 that defines a cavity 104 capable of receiving the sealed food package 101. The housing 103 is openable, such that objects, e.g. the sealed food package 101, can be placed in the cavity 104 and taken out of it. The housing 103 is designed to maintain, in a closed configuration, a sub-atmospheric pressure, which is often somewhat inaccurately referred to as vacuum, in the cavity 104. The housing 103 is thus provided with seals to prevent substantial amounts of air from leaking in when the sub-atmospheric pressure is provided in the cavity 104. The housing 103 is also designed to maintain, in a closed configuration, the supra-atmospheric (i.e. above atmospheric) pressure in the cavity 104 that is necessary for autoclaving, such as in step c) of the method of the present disclosure. Again, the seals prevent leakages.

[0053] The vacuum autoclave 100 further comprises a steam generating device 105 for providing steam in the cavity 104. In the present embodiment, the steam generating device comprises a heating element 105b in contact with liquid water 105a at the bottom of the cavity 104. When the heating element 105b is turned on, it boils the water 105a and provides steam in the cavity 104. As the cavity 104 is sealed, a supra-atmospheric pressure and thus temperatures above 100 C. can be provided.

[0054] The vacuum autoclave further comprises heating elements 106 arranged in the cavity. These heating elements 106 are not in contact with the liquid water 105a at the bottom of the cavity 104. The purpose of the heating elements 106 is thus not to generate steam (they are not part of the steam generating device 105), but to provide heat for a cooking step, such as step a) of the method of the present disclosure. To facilitate the heat transfer during such a cooking step, the vacuum autoclave further comprises a fan arrangement 107 for circulating gas in the cavity. The fan arrangement 107 may significantly shorten the cooking time. An alternative or complementary way of facilitating heat transfer and thereby shorten the cooking time is to increase the humidity of the air inside the cavity 104 during cooking.

[0055] To provide the sub-atmospheric pressure in the cavity 104, such as in step b) of the method of the present disclosure, the housing is provided with a gas outlet 108. Further, the vacuum autoclave 100 comprises a vacuum pump 109 connected to the gas outlet 108. The other end of the vacuum pump 109 is connected to a drain (not shown) via an outlet line 109b. The vacuum autoclave 100 may further comprise an interface 110, such as a screen, e.g. a touch screen, providing information about the operation of vacuum autoclave 100. The interface 110 may also allow the user to program the operation in the steam autoclave 100. For example, the user may set a temperature profile and/or a pressure profile for the operation. Such (a) profile(s) may depend on the type and the thickness of the packaged food.

[0056] FIG. 2 shows another non-limiting embodiment of a vacuum autoclave 200. The vacuum autoclave 200 is suitable for cooking and sterilization of food arranged in a sealed package 101 comprising a one-way valve 102 that opens at a pressure difference, which is normally a pressure difference of 20-200 mbar, in accordance with the inventive method.

[0057] The vacuum autoclave 200 comprises a housing 103 that defines a cavity 104 capable of receiving the sealed food package 101. The housing 103 is openable, such that objects, e.g. the sealed food package 101, can be placed in the cavity 104 and taken out of it. The housing 103 is designed to maintain, in a closed configuration, a sub-atmospheric pressure, which is often somewhat inaccurately referred to as vacuum, in the cavity 104. The housing 103 is thus provided with seals to prevent substantial amounts of air from leaking in when the sub-atmospheric pressure is provided in the cavity 104. The housing 103 is also designed to maintain, in a closed configuration, the supra-atmospheric pressure in the cavity 104 that is necessary for autoclaving, such as in step c) of the method of the present disclosure. Again, the seals prevent leakages.

[0058] The vacuum autoclave 200 further comprises a steam generator 205 for providing steam. The steam generator 205 comprises a water inlet and a boiler. The steam generator 205, which in the present embodiment is arranged outside the housing 104, is connected to a steam inlet 205b in the housing, such that the generated steam may be provided in the cavity. As the cavity 104 is sealed, a supra-atmospheric pressure and thus temperatures above 100 C. can be provided.

[0059] The vacuum autoclave further comprises heating elements 106 arranged in the cavity. These heating elements 106 are not part of the steam generator 205. The purpose of the heating elements 106 is thus not to generate steam, but to provide heat for a cooking step, such as step a) of the method of the present disclosure. To facilitate the heat transfer during such a cooking step, the vacuum autoclave 200 further comprises a fan arrangement 107 for circulating gas in the cavity. The fan arrangement 107 may significantly shorten the cooking time. An alternative or complementary way of facilitating heat transfer and thereby shorten the cooking time is to increase the humidity of the air inside the cavity 104 during cooking.

[0060] To provide the sub-atmospheric pressure in the cavity 104, such as in step b) of the method of the present disclosure, the housing is provided with a gas outlet 108. Further, the vacuum autoclave 200 comprises a vacuum pump 109 connected to the gas outlet 108 via a vacuum line 108b. A heat exchanger 208 may be arranged on the vacuum line 108b. The other end of the vacuum pump 109 is connected to a drain (not shown) via an outlet line 109b.

[0061] The vacuum autoclave 200 may further comprise an interface 110, such as a screen, e.g. a touch screen, providing information about the operation of vacuum autoclave 200. The interface 110 may also allow the user to program the operation in the steam autoclave 200. For example, the user may set a temperature profile and/or a pressure profile for the operation. Such (a) profile(s) may depend on the type and the thickness of the packaged food.