Canning soft drinks

Abstract

 A process of pressurising a container which is to be part­ially filled with a still drink comprising the steps of:

a) Dissolving CO₂ into the drink either before or after the drink has been placed in container;

b) Ensuring that there is substantially no froth present on the surface of the drink;

c) Removing substantially all of any gaseous CO₂ present in the headspace of the container whilst maintaining a pressure in the headspace of not less than 0.7 bar; and

d) Sealing the container.

Description

Field of the Invention

[0001] The invention relates to a process for reinforcing containers of drinks, and is specifically concerned with a process for pressurising containers of still drinks.

Review of Prior Art

[0002] It is common for carbonated drinks to be supplied in thin-­walled aluminium or steel cans. These cans are usually very flimsy until they are filled with the carbonated (or fizzy) drink and sealed. The process of carbonating a drink involves dissolving carbon dioxide under pressure into the drink.

[0003] The can is then filled, usually under pressure, with the drink. When inside a can, some of this CO₂ comes out of this solution into the headspace above the surface of the drink and exerts its partial pressure on the inner walls of the can.

[0004] This extra internal pressure serves to reinforce the can, making it more rigid.

[0005] This pressurisation would not occur if the can were to be filled with a still , non-carbonated drink. Since it is the process of dissolving relatively large quantities of CO₂ into the drink that makes the drink fizzy, cans of still drinks cannot be pressurised in this way.

Summary of the Invention

[0006] According to the invention, a process of pressurising a contain­er which is to be partially filled with a still drink comprises the steps of:

1. Dissolving carbon dioxide into the drink either before or after the drink has been placed in the container.

2. Ensuring that there is substantially no froth present on the surface of the drink.

3. Removing substantially all of any gaseous CO₂ present in the headspace of the container whilst maintaining a pressre in the headspace of not less than 0.7 bar and preferably approximately one atmosphere.

4. Sealing the container.

[0007] Preferably CO₂ is dissolved into the drink before it is placed in the container.

[0008] With most of the gaseous carbon dioxide removed from the headspace, the dissolved carbon dioxide in the drink will no longer be in equilibrium with the gaseous carbon dioxide content of the headspace. As a result, dissolved carbon dioxide passes out of solution, becoming gaseous carbon dioxide in the headspace of the container.

[0009] The partial pressure of this gaseous carbon dioxide adds to the pressure already being exerted by the other gases in the headspace, and thus pressurises the container.

[0010] The filling of a container with a drink almost inevitably results in froth being formed on the surface of the drink.

[0011] If too much froth is present when the container is sealed,the carbon dioxide in the froth tends to dissolve back into the liquid, causing a drop in pressure and often the collapse of the container. It is, therefore, necessary to remove any excess froth which has formed.

[0012] The carbon dioxide in the headspace could preferably be removed by a process known as under cover nitrogen flushing. This involves passing gaseous nitrogen into the headspace so that the other gases present are displaced from the contain­er.

[0013] The skilled addressee of this specification already knows of the process of undercover nitrogen flushing as a way of removing oxygen from the headspace of drinks containers, and thus of inhibiting oxidation of the drink.

[0014] Preferably any excess froth is removed from the surface of the drink by passing the surface of the drink under a gas flame.

[0015] There are other ways of removing the froth, for example by exposing it to the radiant heat produced by an electrical infra red heater. The advantage of using a gas flame is that it rapidly removes the froth and can, therefore, be used without causing any substantial increase in the temperature of the drink.

[0016] Under current United Kingdom fruit juices and nectares reg­ulations, these are "carbonated" if the concentration of dissolved CO₂ in the drink exceeds the concentration of 2000mg/l which is approximately nineteen hundred ppm (parts per million by weight). However, we have discover­ed by experiment that the flavour of the drink is noticeably affected if the concentration of dissolved CO₂ exceeds 700 ppm.

[0017] We have also discovered that no useful pressure increase is obtained if the concentration of dissolved CO₂ is less that 300 ppm.

[0018] It is, therefore, preferable that the concentration of CO₂ dissolved into the drink lies within the range 300-700 ppm.

[0019] Furthermore, in the case of fruit juices, drink containing dissolved CO₂ within this range shows a significant taste preference over juice without dissolved CO₂ in taste panel tests.

Description of Possible Embodiment

[0020] A process embodying the invention will now be described by way of example only with reference to the accompanying drawing which shows an apparatus for removing froth from liquid orange juice in a can.

[0021] This liquid has already had CO₂ dissolved into it in a mixing vessel. The CO₂ is dissolved into the liquid using dry ice or CO₂ gas which is passed into the liquid through a diffuser. The temperature of the liquid in the mixing vessel is no more than 10°C,preferably under 6°C since CO₂ is very soluble at these temperatures.

[0022] Once an adequate amount of CO₂ has been dissolved into the liquid in the mixing vessel, the liquid is transferred to a number of relatively tall thin-walled open-topped cans ident­ical to the can 1 of the drawing. These cans then pass along the conveyor 2 and under the opposing gas flames 3 and 4 which are directed towards the centre of the surface of the liquid 5 in each can. The gas flames remove most or all of the froth, which is generated by the process of filling the cans. This froth cannot easily be removed by simple undercover nitrogen flushing.

[0023] It is possible to remove the froth by exposing it to the radiant heat produced by an electrical heater, and directing a stream of fan-blown air over the froth. But, when compared with the gas flame technique, this method is slow and results in an appreciable heating of the liquid in the can.

[0024] The headspace of each can is then flushed with gaseous nit­rogen at one atmosphere of pressure,and the can is then sealed and pasteurised.

[0025] By the time the can has been through the pasteurising process, CO₂ distribution inside should have reached equilibrium.

[0026] The nitrogen in the headspace, which on its own is providing one atmosphere of pressure will be reinforced by CO₂ which has come out of solution. This extra pressure contribution will provide rigidity in the can.

[0027] The following table gives theoretical internal pressures in psi achievable with different concentrations of CO₂ in solution and in the headspace. The actual figures are based on sim­plified theory and assumptions. However, the dividing line between net positive pressure (rigid cans) and negative press­ure (collapsing) is hopefully clear.

[0028] Flushing the headspace of each can with nitrogen, whilst displacing gaseous oxygen from the headspace, does not remove any useful amount of the oxygen which has dissolved into the juice. However, dissolving CO₂ into the juice removes much of the dissolved oxygen in the juice, thus increasing the shelf life of the juice by reducing the total content of oxygen in the can.

[0029] Filling at 6°C or below greatly reduces frothing of the juice. Whilst defoaming, as already described, is still necessary to ensure pressurisation of the can, maintaining a temperature below 6°C allows an increased filling rate of, typically, one hundred and fifty to two hundred and twenty cans per minute on a ten head filler, compared with seventy to one hundred and twenty cans per minute at higher temperatures.

[0030] Although the process was designed to work at atmospheric pressure, a pressurised carbonated drinks filling machine may be used in the process. In this case, the juice with carbon dioxide already dissolved in it, is pumped to the filling machine which is pressurized with nitrogen.

[0031] The process, although having been described in relation to cans, may also be applied to other containers such as bottles made from a suitable plastics material. In this case, the plas­tics material of the containers may not be able to withstand the temperatures involved in the pasturising process. A poss­ible way of overcoming this problem may be to pasturise the juice before it undergoes the pressurising process.

Methods of introducing CO₂into the juice

[0032] Using dry ice allows the direct weighing of the amount of CO₂ to be introduced into the juice. However, only approximately 20% of the CO₂ so introduced actually dissolves. The probable reason for this is that the relatively large pellets of dry ice produce large bubbles of gaseous CO₂ in the juice. Dry ice can also cause the juice in the outlet pipe of mixing vessel to freeze, and cannot easily be stored.

[0033] The preferred method of introducing CO₂ into the juice is by injecting gaseous CO₂ into the mixing vessel through a sintered metal diffuser. The amount of gaseous CO₂ introduced can be sufficiently accurately deduced by measuring the length of time over which the gas is injected.

[0034] An example of a sintered metal diffuser which may be used in this method is that sold under the trading style sintercom (grade 2) by Accumatic Engineering Limited of Wrexham, North Wales. This diffuser basically consists of a pair of sintered stainless steel tubes, each of which is sealed at one end and connected to the source of gaseous CO₂ at the other end. Each tube is ten inches long, has a diameter of seven inches and a pore size of 5-10 microns.

[0035] Alternatively, carbonated water may be added to concentrated juice. Since only low concentrations of dissolved CO₂ are required in this process, the gas can in this case be dissolved at atmospheric pressure.

[0036] Some CO₂ may be introduced into the juice by adding de­alkalised water to concentrated juice. Hard water to be used in reconstitution of concentrated juice must first be softened or demineralised to prevent precipitation of calcium salts in the reconstituted juice. Treatment with de- alkalising resin produces water with a significant content of dissolved CO₂ 300 - 700 ppm of dissolved CO₂ are required in the juice at the time of filling into the cans. About 150 ppm of dissolved CO₂ are available from the dealkalisation of typical Norfolk water with about 400 ppm of hardness as CaCO₃ .

INTERNAL PRESSURES IN 250ml BEVERAGE/JUICE CAN
(PRESSURES IN P.S.I AT VARIOUS DISSOLVED HEADSPACE CO₂ CONCENTRATIONS)

Headspace - % of CO₂
Dissolved CO₂ % of saturation	0	10	20	30	40	50	60	70	80	90	100
0	0	-1.3	-2.6	-3.9	-5.2	-6.5	-7.8	-9.1	-10.4	-11.7	-13.0
10	1.3	0	-1.3	-2.6	-3.9	-5.2	-6.5	-7.8	-9.1	-10.4	-11.7
20	2.6	1.3	0	-1.3	-2.6	-3.9	-5.2	-6.5	-7.8	-9.1	-10.4
30	3.9	2.6	1.3	0	-1.3	-2.6	-3.9	-5.2	-6.5	-7.8	-9.1
40	5.2	3.9	2.6	1.3	0	-1.3	-2.6	-3.9	-5.2	-6.5	-7.8
50	6.5	5.2	3.9	2.6	1.3	0	-1.3	-2.6	-3.9	-5.2	-6.5
60	7.8	6.5	5.2	3.9	2.6	1.3	0	-1.3	-2.6	-3.9	-5.2
70	9.1	7.8	6.5	5.2	3.9	2.6	1.3	0	-1.3	-2.6	-3.9
80	10.4	9.1	7.8	6.5	5.2	3.9	2.6	1.3	0	-1.3	-2.6
90	11.7	10.4	9.1	7.8	6.5	5.2	3.9	2.6	1.3	0	-1.3
100	13.0	11.7	10.4	9.1	7.8	6.5	5.2	3.9	2.6	1.3	0

Claims

1. A process of pressurising a container which is to be partially filled with a still drink comprising the steps of:

a. Dissolving CO₂ into the drink either before or after the drink has been placed in container;

b. Ensuring that there is substantially no froth present on the surface of the drink;

c. Removing substantially all of any gaseous CO₂ present in the headspace of the container whilst maintaining a press­ure in the headspace of not less than 0.7 bar; and

d. Sealing the container.

2. A process of pressurising a container which is to be partially filled with a still drink comprising the steps of:

a. Dissolving CO₂ into the drink either before or after the drink has been placed in the container;

b. Ensuring that there is substantially no froth present on the surface of the drink;

c. Removing substantially all of any gaseous CO₂ present in the headspace of the container whilst maintaining a press­ure in the headspace of not less than approximately 1 atmos­phere; and

d. Sealing the container

3. A process of pressurising a container which is to be partially filled with a still drink comprising the steps of:

a. Dissolving CO₂ into the drink either before or after the drink has been placed in the container;

b. Ensuring that there is substantially no froth present on the surface of the drink.

c. Removing substantially all of any gaseous CO₂ present in the headspace of the container whilst maintaining a press­ure in the headspace in the range of 0.7 bar to approximately 1 atmosphere.

d. Sealing the container.

4. A process according to any of the preceding claims in which the CO₂ is dissolved into the drink before it is placed in the container.

5. A process according to any of the preceding claims in which the gaseous CO₂ in the headspace is removed by pass­ing gaseous nitrogen into the headspace so that the other gases previously present in the headspace are displaced from the headspace.

6. A process according to any of the preceding claims in which froth is removed from the surface of the drink by passing the surface of the drink under a gas flame.

7. A process according to any of the preceding claims in which the concentration of CO₂ dissolved into the drink lies within the range of 300 ppm - 700 ppm.

8. A process substantially as described herein with reference to the accompanying drawing.

Drawing