GB2060851A

GB2060851A - Method of and apparatus for keeping fresh and preserving perishable products, in particular foodstuffs

Info

Publication number: GB2060851A
Application number: GB8026368A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-09-21
Filing date: 1980-08-13
Publication date: 1981-05-07
Also published as: AU6243180A; FR2465973A1; LU82776A1; FI802939A; NL8005253A; GR70256B; IT1133608B; DE3035460A1; PT71817A; RO80895A; ES8105852A1; IL61066A0; HU178900B; PT71817B; ES495211A0; BR8005994A; RO80895B; DK397580A; SE8006565L; BE885314A

Abstract

For keeping fresh and preserving perishable products the perishable products are introduced into a closable thermally insulated container (1) and thereafter the atmosphere within the container (1) is controlled by injecting liquefied gas from a battery of gas bottles (3) thereinto through spray nozzles (7). To regulate the temperature and the composition of the gas mixture within the container temperature sensors (8) are arranged close to the top and bottom of the container as well as gas concentration regulators (9). <IMAGE>

Description

SPECIFICATION Method of and apparatus for keeping fresh and preserving perishable products, in particular foodstuffs The invention relates to a method of and apparatus for keeping fresh and preserving perishable products, in particular foodstuffs, by using liquefied gases as coolant. The method is suitable in particular for keeping fresh and preserving fruit, vegetables, meat, poultry, dairy products, plants, flowers, chocolate wares and like products which can spoil under the influence of atmospheric oxygen, the prevailing ambient temperature and/or microorganisms contained in the products or in the surrounding medium respectively.

Moreover the invention relates to apparatus for the performance of the method as well as a gas lock installation cooperating with this apparatus.

It is known that the chemical processes which take place in easily perishable foodstuffs and which appear in the case of parts of living plants, for example, as changes in metabolism, are the more slowed down, the more the temperature is lowered. Since the optimum temperature for the growth of most microorganisms lies between + 25 and + 35"C, by lowering the temperature during transport and storage of foodstuffs the growth of the microorganisms can be largely or completely prevented (this usually done by cold storage, freeze-storage). By means of an atmosphere controlled or regulated in a suitable way, in particular in the case of a greatly reduced content of oxygen, fruit or other perishable foodstuffs can be stored in cool rooms over a fairly long period, for example, over several months.In the case of fruit such as apples it is known that the living functions are maintained even after the harvest, in which oxygen is consumed and carbon dioxide is formed. The more rapidly these breathing processes proceed, the quicker the fruit ages. The intensity of the breathing can be reduced and thereby the keeping quality can be increased if the concentration of oxygen in the atmosphere of the store is lowered and the concentration of carbon dioxide is raised.

Use is made of these known facts in the case, for example, of so-called gas cold storage which for kinds of applies sensitive to cold has proved particularly advantageous.

But the hitherto known methods of keeping fresh and preserving perishable foodstuffs and other perishable products exhibit serious disadvantages. The transport and storage of perishable products demand the use of cold or freeze units which involve very high initial investment costs and must be continuously carefully maintained. In the case of the failure of a cold unit, for example, in the case of a cold transport vehicle, the whole load is frequently impaired in its quality so far that it becomes unsaleable. Stationary cold stores, in particular C02-stores can only be charged or respectively emptied all at one go, so that no possibility exists of removing certain different goods from storage at different times.

An object of the present invention is the overcoming of the disadvantages of these known methods, that is, by the use of liquefied gases as coolant. It has been found that by an, as far as possible, uninterrupted maintenance of an atmosphere which is regulated as regards temperature and composition, the products stored and/or transported in it, which are normally easily perishable, preserve their optimum state in a surprising way practically unaltered over fairly long periods of time.

According to the invention in a method of keeping fresh and preserving perishable products, in particular foodstuffs, the perishable products are introduced into a closable thermally insulated container and thereafter the atmosphere within the container is controlled by injecting liquified gas there into to regulate the temperature and the composition of the gas mixture with in the container By means of the invention, as far as possible, uninterrupted maintenance of the regulated atmosphere and of the temperature practically from the harvest or placing in storage, and during the whole of the transport procedures until removal from storage, and therefore until directly before consumption of the goods by consumers can be achieved.It proves particularly advantageous to inject liquefied gases into the close container to control and maintain both the optimum temperature for the goods in the container and also the composition of the gas mixture which is an optimum for the goods in question.

The invention also includes apparatus for use in keeping fresh and preserving perishable products, the apparatus comprising a closable thermally insulated container which has a compartment for a battery of bottles of liquefied gas, a separate storage space for the perishable products, and lines from the gas bottles to spray nozzles in the storage space close to the roof of the container, control valves in these lines being controlled by temperature sensors arranged close to the roof of the container and close to the floor of the container and by concentration sensors arranged close to the roof of the container.The temperature of the products introduced into the container and the surrounding storage atmosphere can in that way be set in a simple manner at any desired value in a range of preferably - 10 up to + 20"C. The use of liquefied carbon dioxide gas is particularly advantageous because in this case the desired temperature and a regulated atmosphere which counteracts the breathing process of the products introduced may be set deliber ately.

Depending upon the product which is to be introduced into the container, the temperature and the gas composition in the space in the container is regulated in a different way. It has moreover proved advantageous in addition to the regulation of the temperature and the percentage composition of the storage atmosphere, to keep the relative humidity in the space in the container at the respective optimum values too in order to keep as small as possible any eventual loss of weight and the risk of withering or shrinking.

By means of the invention fruit and vegetables in particular, for example, apples, pears, strawberries, cherries, peaches, tropical fruits, and bananas; potatoes, lettuces, tomatoes, beans, onions, cucumbers; raw meat, fish and poultry, as well as other perishable agricultural products, for example, eggs, and flowers, can be kept fresh over unexpectedly long periods of time.

For the maintenance of a regulated atmosphere during transfer to or from storage for transportation, a gas lock may be provided in which the controlled atmosphere is maintained. This has proved particularly advantageous.

Such a lock has a gastight closable inlet opening for the container specified above, which if necessary is arranged on a travelling bogie, a likewise gastight closable charging opening leading into an adjoining storage space having a controlled atmosphere, gas bottles, fittings and measuring and regulating elements necessary to the setting of the controlled atmosphere in the lock. The additional arrangement of a weighing platform in the lock is particularly advantageous in order to check the weight of the charge of product introduced or removed.

An example of the method and apparatus according to the invention will now be described in greater detail below with reference to the accompanying drawings, in which: Figure 1 shows a section through a container according to the invention; and, Figure 2 illustrates in outline a gas lock in accordance with the invention.

Fig. 1 shows a closed fully insulated enclosure or container 1 having a K-value of about 0.4 and a special compartment 2 in which there is a battery of insulated gas bottles 3 which are filled with, for example, liquefied nitrogen or carbon dioxide. Behind a partition 4 which forms a wall of the compartment 2 is a storage space 5 of, for example, 60m3 volume, in which easily perishable products such as fruit, vegetables or meat can be stored. Conduits 6 provided with the necessary fittings lead from the gas bottles 3 to spray nozzles 7 arranged in the storage space 5 close to the roof of the container.Temperature sensors 8 are arranged both close to the roof of the container and close to the floor of the container and, together with suitable control apparatus (not shown in the drawing) and a source of electric current (indicated diagrammatically) e.g., a vehicle battery, regulate an electromagnetic supply valve 1 0. In parallel therewith in a further line 6 a second valve 10 is arranged, actuated by a %-regulator (or gas concentration regulator) 9.

Alternatively, if desired, a construction may be chosen in which the bottles and load are accommodated in the container without a partition or else the bottles may be arranged outside the insulated container, e.g., as a separate battery of insulated bottles.

The method of operation is as follows: When the goods which are to be stored or transported are introduced into the storage space 5, the container is closed and the blowing out process of, for example, liquid carbon dioxide via the electromagnetic valve 10 is controlled via an integrated temperaturecontrolled system which lowers the temperature in the storage space via the temperature sensors 8, in such a way as to achieve the required temperature in the loading space 5.

The %-regulator 9 comes into action in parallel connection with this temperature regulation, and by making use of the gaseous phase of the liquefied gas, the desired storage atmosphere, for example, a certain CO2 content is achieved in the storage atmosphere.

The gas lock shown in Fig. 2 has a gastight closable run-in opening 11 for the container 1 which may be arranged on a travelling bogie.

If the container 1 is made as a "container" or semitrailer for a tractor unit, then, if necessary, the whole lorry train may be run into the lock. A likewise gastight closable charging opening 1 3 leads out of the lock into a connected storage space 12, for example, a stationary CO2 store. For checking the charging and unloading a weighbridge 14 may be provided in the gas lock.

The gas lock illustrated serves for the charging and unloading of the container constructed in accordance with the invention, whilst maintaining the regulated storage atmosphere, in particular for the transfer of, for example, perishable products transported in a demountable container into a stationary store with a correspondingly regulated storage atmosphere. After running the container into the lock the controlled atmospheric necessary conditions in the storage space 1 2 are produced in it, for which purpose gas storage bottles, fittings and measuring and regulating members (not shown in the drawing) are provided.

After reaching the same controlled atmosphere in the lock as in the adjoining storage space the container maybe filled or emptied through the opening 1 3 whereupon after completion of the loading process the charging opening 1 3 is closed, the normal atmosphere in the lock is restored and the container is run out of the lock through the opening 11.

In the case of an arrangement of four insulated 40 litre gas storage bottles, filled with liquefied CO2, a fully insulated storage space of about 60m3 capacity can be kept for about 14 days at an inside temperature of O to 3"C and a C02-concentration in the storage atmosphere of about 5%.

Example 1: Into a "standard container" which has, in a special compartment, a battery of insulated storage bottles filled with liquefied nitrogen or carbon dioxide, freshly harvested apples are introduced. After the closing of the "container", via an integrated temperature-controlled system which picks up the temperature at the roof and at the floor of the "container", nitrogen in the liquid phase is injected into the storage space via spray nozzles arranged at the roof of the container.

The temperature in the storage space is thereby lowered to just above 0 C, for example, + 0.5,C, and afterwards kept continuously within a range of up to + 4"C by further controlled injection of CO2. In parallel with the temperature regulation is an 02 concentration measuring apparatus which by making use of the gaseous phase of the liquefied carbon dioxide regulated the proportion of CO2 in the storage atmosphere continuously to about 5% by volume. In the case of a relative humidity of 90-95% the apples upon removal from the container after a storage time of 1 2 months exhibit outstanding quality, particularly as regards colour, firmness, vitamin content and taste.

Example 2: The measures specified in Example 1 were repeated with pears. The temperature was kept at + 0.5"C, the concentration of CO2 in the storage atmosphere was set at about 5% by volume. After 1 2 months storage at a relative humidity of 85-90% the fruit exhibited an unaltered good quality.

Example 3: Peaches were stored by adhering to the measures specified in Example 1.

The temperature was kept in a range from + 0.5 to + 4"C and the concentration of CO2 in the storage atmosphere was set at about 5% by volume. By maintenance of a humidity in the air of about 90-95% this fruit was stored without depreciation of its quality over a period of from 2 to 4 months.

Example 4: Potatoes are introduced into a container according to the method specified in Example 1. The temperature in the storage space is lowered by injecting liquid nitrogen to + 4 to + 7"C and afterwards kept continuously in this range. The concentration of CO2 in the storage atmosphere is set at about 5% by volume. With a relative humidity of about 90% a storage term of 10 to 20 months can readily be achieved.

Claims

1. A method of keeping fresh and preserving perishable products in which the perishable products are introduced into a closable thermally insulated container and thereafter the atmosphere within the container is controlled by injecting liquified gas thereinto to regulate the temperature and the composition of the gas mixture within the container.

2. A method according to claim 1, wherein the products are transferred from or to the container to or from a store, for subsequent or prior storage, in such a way that the atmospheric conditions within the container are maintained externally of the container as well during transfer.

3, A method according to claim 1, or claim 2, in which the injection of the liquified gas is controlled by means of temperature sensors arranged close to the roof of the container and to the floor of the container and by means of apparatus which measures the content of oxygen and/or gas within the container.

4. A method according to any of claims 1 to 3, in which the temperature is kept within a range from - 10 to 20"C.

5. A method according to any of claims 1 to 4, in which a liquefied industrial gas is used for the cooling and carbon dioxide, oxygen or other protective gases are used for regulating the composition of the controlled atmosphere.

6. A method according to any of claims 1 to 5, in which the humidity of the atmosphere in the container is also regulated.

7. A method according to any of claims 1 to 6, wherein the perishable products are fruit, vegetables, meat, fish, poultry, plants or flowers.

8. A method according to claim 1, substantially as described with reference to the accompanying drawings.

9. Apparatus for use in keeping fresh and preserving perishable products, the apparatus comprising a closable thermally insulated container which has a compartment for a battery of bottles of liquefied gas, a separate storage space for the perishable products, and lines from the gas bottles to spray nozzles in the storage space close to the roof of the container, control valves in these lines being controlled by temperature sensors arranged close to the roof of the container and close to the floor of the container and by concentration sensors arranged close to the roof of the container.

10. Apparatus according to claim 9, substantially as described with reference to the accompanying drawings.

11. A gas lock for use in the method of claim 2, the lock having a gastight closable inlet opening for a container according to claim 9, a gastight closable charging opening leading into an adjoining storage space and gas bottles, fittings, and measuring and regulating elements necessary to the setting of a controlled atmosphere in the lock.

1 2. A lock according to claim 11, which includes a weighing mechanism for checking the charging of the container.