IE48731B1 - Process for continuously heat treating bulk,unwrapped,pre-packed or packed products - Google Patents

Description

The present invention relates to a process for continuously heat treating, in particular for the sterilization, pasteurization or the siitple heating, of a product which is followed or not followed by an immediate cooling, these operations occurring in the sane sealed container precluding any outside contamination.

It is kixwn that for the deep freezing of most vegetables, a prior blanching thereof is necessary. It reduces the enzymatic activity and sterilizes the product. This operation is usually carried out in blanching apparatus enplcying hot water or steam. A pre-cooling is then carried out either in air or with water during the conveyance of the products to the cooling systems.

It is moreover known that for meat (quarters, cut-up muscles, chickens, minced meat, etc.), there is practically no sterilization or pasteurization apart frcm rincing with water or wiping. The standards of a good preservation are only achieved by a very rapid cooling, whence the use of disproportionate freezing powers.

It is also known that for the plucking of chickens, the products must be hrought to a tarperature of the order of 50 to 55°c which facilitates the plucking of the feathers in mechanical means.

This heating is achieved by plunging the product in a bath of hot water which is a veritable culture medium which produces a large amount of highly polluted water and results in the transmission of microbial germs from one fowl to another, A sterilization process in an autoclave is known from French Patent No. 1,370,360, This process consists in putting the autoclave under pressure and vapourising therein a quantity of water introduced into the autoclave, then releasing the pressure frcm the autoclave by evacuating the water, the steam and the greater part of the air being again placed under pressure in the autoclave for sterilization by the vapourisation of a certain quantity of water.

A preservation process for food products is also known frcm French Patent No. 1,550,070 in which a material in the form of a gas or vapour under vacuim is brought into contact with the product to be treated.

Nevertheless, these processes do not allcw one to achieve a satisfactory heat treatment of products which may be wrapped.

An object of the invention is to overcome these various drawbacks and relates for this purpose to a process for obtaining continuously and without transferring the heating, the pasteurization, the sterilization and the blanching, which may or may not be followed by a cooling of the product with no bacterial or fungal contamination.

Preferably, the pressure in the interior of the container is maintained below atmospheric pressure for a sufficient period of thus to obtain the taiperatuxe necessary for the desired treatment, especially for 30-40 minutes.

Further, preferably, by releasing the vacuum a final 5 pressure of atmospheric pressure (approximately 10 Pa) is again reached.

According to another embodiment of the Invention, cooling is carried out subsequent to the desired treatment by producing a vacuum a second time in the container in order to obtain a pressure between approximately 13.3 and 133.3 Pa (0.1 and 1 mtrtig) and a tenperature preferably between -20 and 15°C.

The weight loss of the products due to evaporation of the water as a result of cooling under vacuum at a tenperature lower than 0°C, may be oaipensated by water condensation of the vapour if the product has to be removed at the same tenperature as its introduction tenperature, or by fine atomisation of distilled water, if the tenperature to be obtained is lower than the introduction tenperature.

The invention therefore provides a process for continuously heat treating, in particular for pre-cooking, pasteurization, sterilization or blanching products which are in bulk, unwrapped, pre-packed or packed, such as vegetables, meat, poultry or other food products, which process ccnprises enplcylng a sealed treating container, introducing the products into said container, producing a vacuum in the container at a pressure of 1 to 30 imHg partial air pressure and heating the products, wherein, before introducing the products into the container, the walls of the container are brought to a tenperature of between 30 and 150°C and which is higher than the temperature which must be reached an the products, and, after having oreated a vacuum, superheated steam is introduced into the container under a partial pressure which is lower than atmospheric pressure and said pressure is maintained until the required treatment of the product has been achieved, which temperature is lower than the taiperature of the walls of the container.

According to one feature of the invention steam or a vapour of alcohols or ethers is employed for the heating, cooking or sterilization operation.

The essential aim of the invention is to condense on the 10 food products contained in the sealed and heatable container superheated steam which beocnes fixed on the products owing to the fact that the walls of the container are brought to a taiperature which is at least equal to that to be reached on the products.

The process is characterized by the following steps: 1 - The products are therefore placed in a sealed container whose walls may be brought to a taiperature of between 30 and 150°C.

The thickness and the strength of these walls are so calculated as to withstand high internal or external pressures.

- The cycle of pressures may be as follows: - Producing a vacuun until a pressure of 1 to 30 itnHg of the air partial pressure is reached without maintaining this pressure; - Re-pressurizing to between 3,999 to 0.98 χ 108 Pa (30 irenHg and 1 kg/cm ) by the introduction of steam or other vapours (alcohols, ethers); - The exit of the product if only a heating thereof is required; - Producing a vacuum again in accordance wri.th a given programs and maintaining the final pressure until the required taiperature is obtained if the product must be cooled.

- The cycle of taiperature will be a function of the cycle of pressures, thus: - First stage: no notable change in taiperature, - Second stage; elevation of taiperature by condensation of the steam on the products (no condensation on the walls since they are maintained hot), the temperature being maintained by regulating the pressure, - Third stage: lowering of temperature by producing again a vacuum in the container at the final required pressure; the pressure is also, for this operation, the main magnitude for regulating the temperature.

- The products issuing from the vessel are maintained in an aseptic medium by the use of a semi-permeable membrane or other conventional means.

The carrying out of the process of the invention may naturally involve the use of variations corresponding to a more convenient use. These are of the field of those skilled in the art and in no way affect the scope of the invention as defined in the appended claims.

Advantageously, the following main devices will be employed: The container or vessel may be constructed according to two modes of construction, depending on whether the pressure programme 5 2 is lower or higher than 0.98 x 10 Pa (1 kg/αη ) which corresponds to the obtainment of tsiperatures higher or lower than 1ΟΟ°Ο.

Higher than 100eC: construction in accordance with the method employed for the construction of high-pressure ovens but provided with sealing means enabling a vacuum to be produced in the oven.

Lower than 100°C: construction in accordance with the method employed for vacuum vessels the walls of which are heated.

In both cases, the walls are heated. The heating systems are within the knowledge of those skilled in the art; it is well to employ hot water coils since all means for obtaining vacuum or freezing supply large quantities of water at moderate temperature. The energy balance sheet of the installations would in this way be improved.

The device for creating the vacuum may be constructed in two different ways: - mechanical pumps for the extraction of the incondensable elements and the pumping of vapour onto cold walls which are maintained at the required temperature by conventional systems; - Pumping of the vapour and the incondensable elements by vapour ejectors.

These two types of installation are commonly employed in vacuum cooling installations.

The measurement of the pressure is of great importance. It is well to employ apparatus for measuring the total and absolute pressure. This type of gauge is often constructed with pressostat membranes comprising a reference pressure and a measurement of displacement by a differential linear transformer.

The measurement of the air partial pressure is achieved with a similar apparatus, but the pipe connecting it to the vessel is provided with a valve. A cold surface at a temperature of -20°C enables the pressure of condensable vapours to be neglected and therefore enables the partial pressure of the incondensable element to be determined at this temperature.

Several pressure programmes are possible. In order to achieve a good rate of drop of temperature, it is well to employ the following method: in order to bring the product to 0°C, there 2 ο must be a stage of pressure of between 6.13 x 10 and 6.66 x 10 pa (4.6 and 5 mmHg); if idle product must be brought to a temperature lower than 0°C, it is well to effect a stage at 0°G since, when the evaporating surface is in the state of ice, the cooling rate is lower.

EXAMPLES 1. Pre-cooked potatoes.

A ton (metric) of pre-cooked potatoes which have been peeled and cut into pieces for sale or direct use by the public, are put into the machine. The air partial pressure is brought to (3 mrHg) by using the vapour ejectors. Choking is achieved by introducing the vapour up to a pressure of 9.86 x IO4 Pa (740 rtnHg), The walls were previously brought to a tenperature of 11O°C. For small pieces (10 to ran), the cooking tine is 20 minutes. The introduction of vapour is stopped and the vacuum pumps are brought back into operation, ftor more convenience, the vessel is returned to a temperature in the neighbourhood 2 2 of roan tenperature. Pressure is regulated at 6.13 x 10 to 6.66 x 10 Pa (4.6 to 5 mrHg); after a stage at this pressure for 30 minutes, the taiperature of the potatoes is 1?C within the mass. The weight balance sheet is particularly interesting: as the cooking is achieved by condensation of vapour, the cooling only evaporates the amount of water added during the heating stage. To within 1 to 2 %, the same weight of the product is found as it issues frcm the tunnel. 2. Blanching of peas.

After having carefully removed dust and other impurities from the peas, they are introduced in the tunnel. The cycle is identical to that for potatoes, solely the output temperature may be different, 1°C if the product is intended to be deep frozen in conventional tunnels, to 30°C if the product is intended for preserving. 3. Blanching followed by the deep freezing of the peas, green beans, fried potatoes, cauliflowers cut into pieces, corn (seeds), spinach, artichokes (hearts), egg-plants, carrots in pieces, cherries, marrows, pieces of fruit, chestnuts.

The products are introduced into the vessel after having been prepared in such manner as to require no further modification in their presentation for subsequent use. If the packing withstands the blanching temperature, and if it is sufficiently open or perforated during the operation, the products may be packed or pre-packed. The operations are carried out in the same way as in Example 1. After the blanching cycle, identical to that carried out for potatoes, when the products are at a taiperature of 1°C, the pressure is lowered to between 13.3 and 66.6 Pa (0.1 and 0.5 rrmHg) and the deep freezing of the product is carried out.

The temperature of the product will be between -20 and -15°C after a maintenance time of the order of 40 minutes for fried potatoes and green beans. The maintenance time required varies between 30 and 90 minutes, depending on the structure of the product and the sizes of the pieces. The weight balance sheet is of particular interest, since the departure of supplementary water due to cooling to a temperature below O’C may be compensated for by the washing water of by a spraying carried out in the container. 4. Blanching of poultry before plucking.

The container is maintained at a temperature of 6O°C.

The fowls are introduced immediately after slaughter. The 2 air partial pressure is lowered to around 3.99 x 10 Pa (3 imHg), it is measured with a precision of the order of 1,33 x 10 Pa (1 nnfig). Steam is supplied to the vessel until a pressure of 4 between 1,33 x 10 and 1.99 x 10 Pa (100 and 150 itmHg) is reached, depending on the optimum tocperature to be reached on the bodies.

The fowls are then discharged and conveyed to the plucking machines.

A passage way having hot surfaces is placed between the container and the plucking machine in order to avoid an excessive cooling of the bodies.

The use of this process avoids bacterial contamination of one fowl by another. There is no large amount of polluted water produced and the feathers retain substantially dry.

. Surface sterilization of meat and preservation frcm exterior contamination.

The process is essentially applicable to boned meats and fowls after evisceration, but nay also be applicable to whole carcasses of large animals. As a rule, in order to ensure a good preservation of the meat, the surface must be as sterile as possible before it is placed in the freezer; the process according to the invention permits this result to be achieved. Its application is according to the following mode of operation; the walls of the container are maintained at a minimum temperature of 1CO°C, the meats to be treated are introduced therein, an 2 3 air partial pressure of between 3.99 x 10 and 3.99 x 10 Pa (3 and 30 imHg) 4 is produced, the steam is introduced until a pressure between 5.33 x 10 and 105 Pa (400 and 750 nnHg) has been reached, with a possibility of a high rate of flow since the temperature of the surface must be raised rapidly without producing cooking phenanena, the pressure of the container is then lowered and a pressure is maintained at a stage for a duration which is a function of the tsiperature required to be obtained.

For certain applications, the steam must be replaced by vapours, which ensure, at the same time as the heating, a chanical sterilization, for exanple vapours of alcohols or ethers. In order to ensure that no exterior contaminations (fungal or bacterial contaminations) are possible, it is well to proceed as follows: at the exit or better still, within the container, after having broken the vacuum with a carefully sterilized gas, the meats are enclosed in sealed flexible or rigid vessels whose internal atmosphere will be that of the air but will be ensured to a sanr-permeable membrane of silicone elastomer identical to that anplcyed in French Patent No 1 567 996 the surfaces of the maiibranes o being in this utilization of the order of 2 to 5 dm per 100 kg.

The latter process is of particular interest if the quality of the disinfections of transporting equipment cannot be relied upon. 8 7 31 It must be understood that the invention is not intended to be limited to the examples described hereinbefore.

Claims (9)

CLAIMS;

1. A process for continuously heat treating, in particular for pre-cooking, pasteurization, sterilization or blanching products which are in bulk, unwrapped, pre-packed

2. A process according to Claim 1, wherein the pressure in the interior of the container is maintained below atmospheric pressure for a sufficient period of time to obtain the temperature necessary for the desired treatment. 25

3. A process according to Claim 2, wherein the period of time is 30 - 40 minutes.

4. A process according to any one of Claims 1 to 3, wherein by releasing the vacuum a final pressure of approximately 10^ Pa is again reached. 30 5. A process according to any one of Claims 1 to 4, wherein cooling is carried out subsequent to the desired treatment by producing a vacuum a second time in the container in order to obtain a pressure between approximately 0.1 and 1 mmHg and a temperature between -20 35 and 15°C.

5. Vapour if the product has to be removed at the same temperature as its introduction temperature, or by fine atomisation of distilled water, if the temperature to be obtained is lower than the introduction temperature. 5 or packed, such as vegetables, meat, poultry or other food products, which process comprises employing a sealed treating container, introducing the products into said container, producing a vacuum in the container at a pressure of 1 to 30 mmHg partial air pressure and heating the 10 products, wherein, before introducing the products into the container, the walls of the container are brought to a temperature of between 30 and 150°C and which is higher than the temperature which must be reached on the products, and, after having created a vacuum, superheated steam is 15 introduced into the container under a partial pressure which is lower than atmospheric pressure and said pressure is maintained until the required treatment of the product has been achieved, which temperature is lower than the temperature of the walls of the container. 20

6. A process according to any one of Claims 1 to 5, wherein steam or alcohols or ethers in the form of vapour are used.

7. A process according to Claim 5, wherein the weight loss of the products due to evaporation of the water as a result of cooling under vacuum at a temperature lower than 0°C is compensated by water condensation of the

8. A process according to any one of Claims 1 to 7, 10 wherein the products are enclosed, after releasing the vacuum in tight casings whose inner atmosphere consists of air which has been previously filtered through a window made of a silicone elastomer.

9. A process according to Claim 1 for continuously 15 heat treating products, substantially as hereinbefore described with particular reference to the accompanying Examples.