GB2241941A - Charging containers with liquid - Google Patents

Abstract

A method of charging containers, especially thin-walled cans, with a lowly-carbonated liquid such a beer comprises dissolving carbon dioxide in the liquid, and dissolving nitrogen in the liquid with the liquid under a first pressure; holding the liquid containing dissolved carbon dioxide and nitrogen for at least ten minutes under a second pressure loss than the fret pressure with the liquid in a supersaturated state; and then closing the containers gas-tightly, whereby after closure dissolved gas comes out of solution to create a super-atmospheric internal pressure that resists deformation of the walls of the container. In the preferred embodiment beer in a tank 6 saturated with nitrogen from a source 10 is supersaturated by being passed through a venturi 26 supplied with a mixture of carbon dioxide and nitrogen, held in tank 6 for between 30 minutes and 24 hours, and then passed to a filler bowl 38 via a buffer tank 34. Preferably a cooler 30 is provided. <IMAGE>

Description

DISSOLVING A GAS IN A LIQUID This invention relates to dissolving a gas in a liquid as part of the process in which flexible containers such as thin walled cans, typically formed of aluminium or steel, and plastics bottles are charged with the liquid.

In the canning and bottling industries there has been a trend in recent years to substitute containers having flexible walls for the traditional rigid steel can and rigid glass bottle when canning or bottling an artificially carbonated beverage. Typically, the beverage is saturated with carbon dioxide under pressure. The beverage is then discharged under pressure into open containers to be filled. The containers are then closed and sealed. The open containers are exposed to the atmosphere and are hence at atmospheric pressure.

Accordingly, since the containers are filled with beverage which has been saturated with carbon dioxide at elevated pressure, some of the carbon dioxide comes out of solution after the containers are sealed. An elevated pressure is thereby created in the head space of each sealed container. By dissolving sufficient carbon dioxide in the beverage, this elevated pressure may be sufficient to prevent externally applied pressure deforming the container during normal handling. Typically, more than 2.5 volumes of carbon dioxide are dissolved in eaoh volume of liquid (when measured at 15 0C) in order to create the necessary super-atmospheric pressure in the head space of each container.In some beverages, particularly soft drinks, such a level of carbonation is deemed not to have an adverse effect on the quality of the beverage, and is frequently believed to be beneficial. There are however some drinks, particularly ales and other beers, which it is believed are adversely affected by such a high level of carbonation. For example, some traditional ales would be rendered too fizzy for some people's taste with such high levels of carbonation. Moreover, the acidic nature of carbon dioxide may also adversely affect the taste.

There is therefore a demand from brewers for a method of canning or bottling a beverage such as a beer which does not require such high levels of carbonation as are used in the soft drinks industry but which at the same time enables modern flexible containers be they thin-walled cans or plastics bottles to be used successfully.

Most attempts to solve the above-described problem have been based on the use of the so-called liquid nitrogen droplet dispenser. This is a device which delivers a small metered quantity of liquid nitrogen to each filled container.

The liquid nitrogen vaporises almost instantaneously and is thereby able to create a superatmospheric pressure in the head space of the vessel. Since modern canning lines can operate at speeds up to 2,000 cans per minute, there have been considerable problems in designing such a droplet dispenser so as to be able to deliver up to 2,000 equal unit quantities of liquid nitrogen per minute. To date, these problems have not been fully solved and there tends to be a noticeable variation in the head space pressure of the sealed cans even at moderate canning line speeds.Another difficulty associated with the operation of liquid nitrogen droplet dispensers is that whereas it is conventional in canning to blow a non-oxidising gas such as nitrogen or carbon dioxide over the mouth of the open container once it has been filled and up to the time when it is sealed, the rates of flow of non-oxidising gas that are the optimum for this purpose tend to draw nitrogen vapour out of the head space of the can and give rise to undue variations in the internal pressure of the sealed cans. Accordingly, lower than optimum flows of non-oxidising gas across the mouth of the open container tend to be used with the result that the oxygen content of the head space of each sealed container is higher than is ideal. Thus, an alternative to the liquid nitrogen droplet dispenser is needed.

There are indeed a number of alternative proposals in the art. For example, US patent specification 4 347 695 discloses a beverage bottling or canning method for non-carbonated beverages. An inert gas, other than carbon dioxide, such as nitrogen is injected into a non-carbonated beverage prior to filling a container. Inert gas is permitted to escape from the beverage in the filled container before sealing the container. The amount of gas released is sufficient to strip dissolved oxygen from the beverage and then purge air from the head space of the container. Sufficient gas is retained in the beverage to exert a super-atmospheric pressure after the container is sealed.The reduction in oxygen content of the head space is stated to be superior to that achieved when passing a stream of nitrogen purging gas into the head space, while dissolved oxygen is said to be substantially reduced and internal container is said to be increased, the latter being described as a distinct advantage in containers made of flexible material such as sheet metal and plastics. Table II in US patent specification 4 347 695 discloses that when filled at a pressure of 30 psig an internal sealed can pressure at 680F (200C) of 10.2 (psig) was obtained, i.e. well under 2 atmospheres absolute.

GB-A-2 134 496 also relates to filling thin-walled cans with non-fizzy or substantially non-carbonated drinks. In the processes described in GB-A-2 134 496A it is permitted to use carbon dioxide in addition to nitrogen to create the internal can pressure provided that the carbon dioxide level is not greater than 15 parts in 10,000 by weight. Nitrogen gas and carbon dioxide gas are dissolved under pressure in a non-carbonated drink in a saturator. Open cans are then charged with this drink in a filling machine at the same temperature and pressure as that at which the saturator operates.

Nitrogen or carbon dioxide is sprayed upon the upper surface of the drink in the cans while the drink is exposed to the atmosphere. The cans are then seamed in a seaming machine. It can be seen from Figure 2 that at a filling machine pressure of 3 atmospheres absolute a head space pressure of even 2 atmospheres absolute cannot be achieved (if measured at 200C).

GB-A-2 203 417A also relates to charging a flexible container such as a can or plastics bottle with non-carbonated liquid. Argon is dissolved in the liquid.

The containers are then filled from a bowl filler. In view of the greater solubility of argon than nitrogen, relatively higher head space pressures can be created. Unfortunately, argon is not an approved food additive in the United Kingdom and other countries, and this drawback has led to a delay in the commercial exploitation and method described in GB-A-2 203 417.

GB-A2 089 191 also discloses creating a super atmospheric pressure in a sealed container by pre-dissolving an inert gas in a liquid food before the container is filled with the food. In one example, an internal can pressure of 1.1 Kg 0 per square cm gauge (15.9 psig) at 20 C was created when nitrogen was dissolved in a coffee beverage at 4 atmospheres.

In, for example, the production and canning of beer, it is conventional practice to hold the carbonated beer in a so-called bright beer tank for a prolonged period of time while quality control checks are made on the beer or ale. The carbonated beer is then used to fill cans. The maximum pressure obtainable in the bright beer tank is normally 3 atmospheres absolute. A particularly popular size of can in the UK is 440 ml. With the kind of thin-walled can in use today, it is generally believed desirable to have a minimum internal can pressure of 20 psig at ambient temperature, say 200C.

There is thus a need for charging a flexible container with liquid such that the sealed container has an adequate superatmospheric pressure when the liquid contains some carbon dioxide and when it is required to hold the gas-charged liquid for a period of time at a relatively low pressure of, say, about 3 atmospheres absolute.

We have surprisingly discovered that when nitrogen is dissolved in a carbonated liquid such that the liquid is supersaturated in nitrogen at the pressure at which the liquid is held, the liquid is able to retain nitrogen in concentrations in excess of the saturation level over a prolonged period of time. We have utilised this discovery to provide a process which enables the above-described need to be met.

Accordingly, the present invention provides a method of charging containers with a moderately carbonated liquid (as hereinafter defined), comprising the steps of dissolving carbon dioxide in the liquid, dissolving nitrogen in the liquid with said liquid under a first pressure, holding for a period of at least 10 minutes the liquid containing dissolved carbon dioxide and dissolved nitrogen under a second pressure less than the first pressure, said liquid being in a state of supersaturation with respect to nitrogen at said second pressure, charging the containers with the supersaturated liquid, and then closing the containers gas tight, whereby after such closure dissolved gas comes out of solution in each container to create therein a super-atmospheric internal pressure that resists deformation of the walls of the container during normal handling.

By the term "lowly-carbonated liquid" as used herein is meant a liquid which 0 contains up to 2 volumes per volume of carbon dioxide (at STP (i.e. 15 C, 1 atmosphere absolute)). Typically, the liquid contains from 1.3 to 1.8 volumes per volume of carbon dioxide. These carbon dioxide concentrations are those in the liquid immediately prior to its being charged into the containers.

The term "beer" as used herein encompasses ales, lagers and stouts.

The supersaturated liquid is typically held for at least 30 minutes, during which period of time quality control checks may be performed on it. While it is not generally desirable to hold the liquid for prolonged periods of time we believe that adequate dissolved nitrogen levels may be maintained over a period of many hours, say, up to 12 or 24 hours or longer.

The method according to the invention is particularly suited for use in canning lowly carbonated beers and ales. Vhen canning a lowly carbonated ale, we have been able to obtain an internal can pressure (at 200C) in excess of the pressure at which the ale is held prior to filling even though the ale is held for a period of 2 hours. In particular, when holding the ale at a pressure of 3 atmospheres absolute and dissolving the nitrogen at a pressure of 4.5 atmospheres absolute, we were able to obtain an internal can pressure of 35 psig at ambient temperature (200C).

Preferably, the liquid is saturated with nitrogen at the first pressure.

Preferably, the first pressure is at least 15 psi greater than the second pressure. Typically, the first pressure is in the range of 4 to 5 atmospheres absolute and the second pressure is in the range of 2 to 3.5 atmospheres absolute. The amount of nitrogen that is introduced depends on the chosen internal pressure of the containers (at equilibrium). Preferably, the internal pressure (at equilibrium) is in the range 30 to 40 psig.

Preferably the nitrogen is introduced into the liquid in a gaseous mixture with carbon dioxide. The proportion of carbon dioxide in the mixture is preferably such as to obtain or maintain a desired dissolved carbon dioxide concentration in the liquid.

Preferably, dissolution of nitrogen and carbon dioxide in the liquid is effected by withdrawing a stream of the liquid from a tank in which the liquid is received raising the pressure of the stream to said first pressure, creating turbulence in the thus pressurised stream and introducing a mixture of carbon dioxide and nitrogen into the pressurised stream. The stream is then returned to the volume of liquid from which it was taken. If desired, the mixture of carbon dioxide and nitrogen may be introduced into the stream through a venturi. The shape of the venturi naturally creates turbulence in the stream which helps to dissolve the carbon dioxide and nitrogen so introduced. Nonetheless, not all the nitrogen and carbon dioxide is dissolved, and bubbles of undissolved gas are carried with the stream into the volume of liquid being held.The undissolved gas passes into the head space of the vessel in which the liquid is held. If desired, the stream may be chilled. The passage of the stream is continued for sufficient time for the liquid to be supersaturated at the second pressure in nitrogen. If desired, rather than withdraw a stream from the volume being held in order to dissolve the carbon dioxide and nitrogen in the liquid, such dissolution may take place as the liquid is flowing from the source thereof to the holding vessel or from one holding vessel to another holding vessel. It is also possible to introduce the nitrogen and carbon dioxide independently of one another into the stream.

The method according to the present invention will now be described by way of example with reference to the accompanying drawing which is a schematic diagram of an apparatus for filling cans with beer.

Referring to the drawing, freshly brewed ale is passed by pump 4 from a fermentation vessel 2 into a bright beer tank 6. The tank is filled to a chosen level 8 with the ale. Nitrogen gas is passed from a source 10 thereof into the head or ullage space 12 of the vessel 6 through an inlet 14. (If desired, the tank 6 may be purged with nitrogen prior to the introduction of the ale so as to flush air from the tank 6.) The tank 6 has a vent pipe 18 for gas having a vent valve 20 disposed therein. Typically, the vent valve is set to open if the pressure in the tank rises above 3 atmospheres absolute.

We prefer to hold the ale in the tank under a non-oxidising gas at a pressure of about 3 atmospheres absolute.

The tank 6 has a first outlet for liquid 22 communicating with the suction side of a pump 24. The outlet of the pump 24 communicates with a venturi 26 to the throat 28 of which a pressurised mixture of carbon dioxide and nitrogen is supplied. The outlet of the venturi 26 communicates with a chiller 30 of conventional kind. The outlet of the chiller 30 communicates with the interior of the tank 6.

In operation, the pump 24 withdraws a stream of beer or ale from the tank 6 and raises its pressure to at least one atmosphere in excess of that at which the ale is held in the tank 6. As the thus pressurised stream flows through the throat 28 of the venturi 26, so it is rendered turbulent by virtue of the narrowing of the venturi 26 from its inlet end to its throat 28. The mixture of carbon dioxide and nitrogen flows into the stream at the throat 28 and encounters the turbulent liquid flow. The turbulence helps to break up the gas into bubbles which dissolve more readily in the ale. Nonetheless, not all the gas is dissolved. Undissolved bubbles of nitrogen and carbon dioxide are carried with the stream into the volume of ale being held in the tank 6 as the stream returns to the tank 6 through an inlet 32 at a level beneath that of the the surface 8 of the ale in the tank 6.The re-introduction of the stream of ale into the tank 6 is performed so as to create relatively little turbulence and, accordingly, the inlet 32 is unrestricted.

The mixture of carbon dioxide and nitrogen is preferably supplied at a pressure which is above that to which the stream of ale withdrawn from the tank 6 is raised by the pump 24 and which gives a desired flow rate of gas into the ale. The relative proportions of carbon dioxide and nitrogen in the gas mixture are preferably determined so as to maintain or obtain a chosen dissolved carbon dioxide concentration in the ale. Typically, the beer or ale entering the tank 6 already has a dissolved carbon dioxide concentration at the desired level. The partial pressure of carbon dioxide is then selected to be substantially that which according to Henry's law is at equilibrium at the storage temperature with the dissolved carbon dioxide concentration. The dissolved carbon dioxide concentration is thus maintained at the desired level.It is quite usual for the dissolved carbon dioxide concentration to be that which is at equilibrium with a carbon dioxide partial pressure of about 1 atmosphere absolute. The carbon dioxide partial pressure in the gas mixture is thus selected to be about 1 atmosphere absolute. Bence, if the mixture of nitrogen and carbon dioxide is supplied at a pressure of 4.5 atmospheres absolute, it preferably contains 77.78Z by volume of nitrogen and 22.22% by volume of carbon dioxide. The undissolved gas which enters the tank 6 with the returning stream of beer will enter the ullage space 10 of the tank 6 displacing the atmosphere from that tank 6, excess gas being vented through the vent valve 20. Accordingly, an atmosphere similar in composition to the mixed gas is created in the ullage space of the tank 6.If desired, such a mixture rather than pure nitrogen may be used to purge the tank 6 before it is charged with beer so as to reduce the tendency for carbon dioxide to come out of solution from the beer while held in the tank 6.

The duration of the period in which the stream of beer is withdrawn from the tank 6 through the outlet 22 and the rate of withdrawal are selected so as to give the required degree of supersaturation in the beer held in the tank 6 at the end of such period. Preferably, the rate of flow of the stream through the venturi 26 and the rate of introduction of the gas mixture into the venturi are selected so as to saturate the stream in nitrogen at the pressure to which the stream is raised by the pump 24. The duration of the circulation of the stream is preferably such that at the end of the period in which gas is introduced into the stream at the throat 28 of the venturi 26, the degree of supersaturation at the prevailing pressure in the tank 6 is sufficient to create a pressure of at least 22 psig and preferably from 30 to 40 psig in an equilibrated can at a temperature of 200C.We have found that when the pressure in the tank 6 is 3 atmospheres absolute, dissolving 50% more nitrogen than the quantity required to saturate the volume of ale in the tank 6 at that pressure is adequate for the purposes of creating a suitable pressure in the head space of the cans.

Typically, the stream withdrawn from the tank 6 through the outlet 22 is chilled to a suitable sub-ambient temperature. For this purpose the chiller 30 is used. It is not essential that the chiller be located in this position.

If desired, it may be located intermediate of the pump 24 and the venturi 26.

In an alternative embodiment of the apparatus according to the invention, dissolution of the mixture of carbon dioxide and nitrogen in the beer may be effected as the beer or ale flows from the fermentation vessel 2 to the tank 6. If desired, the beer or ale may also be chilled as it flows from the vessel 2 to the tank 6.

Once the ale has attained the desired degree of supersaturation, the introduction of the mixture of carbon dioxide and nitrogen into it is stopped and then the beer is held before a sufficient period of time (at least 15 minutes, and typically at least an hour) for the normal quality control measurements to be made. We have surprisingly found that when held over a considerable period of time, for example 2 hours, there is no substantial loss of dissolved nitrogen from the ale in the tank 6 even though the beer is appreciably supersaturated. This is particularly surprising since one would expect that there would be a tendency even in a short period of time for nitrogen coming out of the solution to 'seed' carbon dioxide bubbles which in turn would promote the coming out of solution of further nitrogen gas.

Once the quality control checks have been satisfactorily completed, the beer may be employed to fill cans or other containers. The ale is typically then transferred to a buffer tank 34 having an ullage space 36 in which a gas pressure of 3 atmospheres absolute is maintained by means of nitrogen supplied from the source 10 or by carbon dioxide from a source (not shown) thereof.

The ale is resident in the buffer tank 34 for only a relatively short period of time, being transferred to a filler bowl 38 once the tank 34 has been filled to a chosen level with the beer. An ullage space 40 is maintained in the filler 38 and a pressure of 8 atmospheres absolute is created in the ullage space 40 by passage of nitrogen into the filler 38 from the source 10 or by passage of carbon dioxide into the ullage space 40. The filler 38 may be of a conventional kind. Flexible thin walled cans (not shown) are advanced under the filler 38 and are filled to a chosen level with the ale. As they are filled so a flow of nitrogen is blown over the open mouths of the cans so as to minimise the amount of air that enters into the head space of the cans.

The mouth of each can is subjected to this flow thereacross of nitrogen until a lid has been placed on to the top of the can and sealed thereto by means of a conventional seaming machine.

Once the cans have been seamed they are passed to a pasteuriser (not shown) in which the ale is pasteurised by conventional methods. This pasteurisation process involves creating a temperature of at least 65 0C. At such high temperatures, the amount of nitrogen that it is maintained in the solution is less than at ambient temperatures. Thus, in selecting the degree of supersaturation for the ale, care should be taken so as to avoid creating an excessive pressure in the head space of the can during pasteurisation.

In a practical example of the process according to the invention, the tank 6 was maintained at a pressure of 3 atmospheres absolute and the stream of beer withdrawn therefrom was pressurised to a pressure of 4.5 atmospheres absolute so as to create a level of dissolved nitrogen in the beer about 150% of that which saturates the beer at 3 atmospheres absolute. The beer was then held in the tank for 2 hours and then used to fill a number of cans. After the steps of filling, seaming and pasteurisation, the cans were allowed to return to ambient temperature. It was found that the gas pressure in the head space of each can was in the order of 35 psig at ambient temperature. It was also observed during the filling of the cans that there was remarkably little foaming and no clouding of the beer. Moreover on opening the can and pouring the beer into a glass, good head retention properties are obtained.

It will be appreciated that the method according to the invention may be performed using conventional bright beer tanks, a conventional filler, and a conventional seaming machine. Moreover, the mixture of carbon dioxide and nitrogen may be formed using conventional gas mixing apparatus. Accordingly, the method according to the invention is particularly simple to perform. The nitrogen and carbon dioxide coming out of solution in the sealed can are able to create a suitable internal pressure to enable the can to withstand the kind of external pressure to which it is subjected during normal handling.

Claims (15)

1) A method of charging containers with a lowly carbonated liquid containing upto 2 volumes per volume of carbon dioxide (when measured at 150C and 1 atmosphere absolute) comprising the steps of dissolving carbon dioxide in the liquid, dissolving nitrogen in the liquid with said liquid under a first pressure, holding for a period of at least 10 minutes the liquid containing dissolved carbon dioxide and dissolved nitrogen under a second pressure less than the first pressure, said liquid being in a state of supersaturation with respect to nitrogen at said second pressure, charging the containers with the supersaturated liquid, and then closing the containers gas tight, whereby after such closure dissolved gas comes out of solution in each container to create therein a super-ateospherie internal pressure that resists deformation of the walls of the container during normal handling.

2) A method as claimed in Claim 1, in which the liquid contains from 1.3 to 1.8 volumes by volume of carbon dioxide.

3) A method as claimed in Claim 1 or Claim 2, in which the supersaturated liquid is'held for a period of from 30 minutes to 24 hours.

4) A method as claimed in any one of the preceding claims, in which the liquid is saturated with nitrogen at the first pressure.

5) A method as claimed in any one of the preceding claims, which the first pressure is at least 15 psi greater than the second pressure.

6) A method as claimed in any one of the preceding claims, in which the first pressure is in the range of 4 to 5 atmospheres absolute.

7) A method as claimed in any one of the preceding claims, in which the second pressure is in the range of 2 to 3.5 atmospheres absolute.

8) A method as claimed in any one of the preceding claims, in which the pressure in each container at equilibrium at 200C is in the range of 30 to 40 psig.

9) A method as claimed in any one of the preceding claims, in which the nitrogen is introduced into the liquid in a gaseous mixture with carbon dioxide.

10) A method as claimed in Claim 9, in which dissolution of nitrogen and carbon dioxide in the liquid is affected by withdrawing a stream of the liquid from a tank in which the liquid is received, raising the pressure of the stream to said first pressure, creating turbulence in the thus pressurised stream and introducing a mixture of carbon dioxide into the pressurised stream, and returning the pressurised stream to the tank or another holding tank.

11) A method as claimed in Claim 10, in which the mixture of carbon dioxide and nitrogen is introduced into the stream through a venturi.

12) A method as claimed in any one of the preceding claims, in which the liquid is a beer or ale.

13) A method as claimed in any one of the preceding claims, in which the container is a flexible can or flexible bottle.

14) A method of charging containers with a lowly carbonated liquid substantially as herein described with reference to the accompanying drawing.

15) A container charged by a method as claimed in any preceding claim.