WO2006105610A1

WO2006105610A1 - Packaging wine in a metallic container with an internal coating

Info

Publication number: WO2006105610A1
Application number: PCT/AU2006/000467
Authority: WO
Inventors: David Carew; John Lovett
Original assignee: Amcor Limited
Priority date: 2005-04-07
Filing date: 2006-04-07
Publication date: 2006-10-12
Also published as: NZ590675A

Abstract

A process of packaging wine in a metallic container or aluminium can that has an internal coating that provides a physical and chemical barrier to reactions between the metal of the container and free sulphur dioxide (SO2) in the wine that result in container corrosion and wine tainting. A redox reaction where SO2 is reduced to hydrogen sulphid taints the wine and metal is oxidized to metal ions in solution. The internal coating can be an amine epoxy coating which is sprayed onto the interior of the can, or metallic plate used to make cans coated with a polymer to form polymer coated steel (PCS). The wine to be packaged has a concentration of free SO2 of greater than 35 ppm, and even at least 45 ppm of free SO2. The container is gas flushed with an inert gas such as nitrogen, or an oxygen containing gas such as oxygen.

Description

PACKAGING WINE IN A METALLIC CONTAINER WITH AN INTERNAL COATING.

BACKGROUND

The present invention relates to a process for packaging wine in metallic containers.

The term "metallic containers" is understood herein to mean any metallic container, including containers made from aluminum and steel, and includes, byway of example, one-piece cans, two-piece cans, and "bottles" with screw or other closures. The screw or other closures may be made from aluminium or any other suitable material.

The term "can making" is understood herein to include the making of both cans and metallic bottles with screw caps, as while metallic bottles are not cans, a similar manufacturing process is used, that only significantly differs from a can making process in the way the shoulder and neck of the metallic bottle is formed. The differences between can and metallic bottle making processes do not affect the working of the invention as disclosed hereafter.

The term "wine" is understood herein to include still wines, sparkling wines, fortified wines, and wines blended with mineral waters and fruit juices.

The present invention relates particularly to the impact of sulphur dioxide (SO₂) on packaging wine in metallic containers .

Wine is produced by the yeast fermentation of the juice of grapes and occasionally other fruits. As part of the control processes for the fermentation and handling of wine, SO₂ and/or analogues such as metabisulphite is often added to wine for reasons including "the killing and growth inhibition of unwanted bacteria and yeast/ the inhibition of phenoloxidase activity, the interaction with wine phenols in the competitive oxidation, the reaction of sulphite with peroxide, the binding of aldehydes and anthocyanin pigments and the delay of brown pigment development"¹. In addition, SO₂ can also be advantageous at the time of packaging wine as a means of allowing winemakers to quickly stabilise wine so that it is suitable for packaging.

One accepted method for measuring SO₂ found in wine is the so-called Aspiration method (Hand, 2004) which allows total SO₂ and free SO₂ to be determined. The total SO₂ of any measured wine system is the sum of the free SO₂ and the bound SO₂. The first step of the Aspiration method is to remove free SO₂ by passing a stream of air through an acidified sample. Free SO₂ is collected in hydrogen peroxide/mixed indicator solution. The indicator changes from green to purple when free SO₂ is collected, indicating sulfuric acid has formed from the reaction of hydrogen peroxide and SO₂. The sulfuric acid is back titrated with standardized sodium hydroxide to the end point (green color returns) . The acidic sample is then heated which releases the bound SO₂ which is subsequently collected and analysed in the previously described manner.

Some types of wine are packaged under pressure, with the pressure being caused either by the gases produced during the natural fermentation process or by gases added during packaging, especially carbon dioxide.

¹ Boulton, R. B., V. L. Singleton, L. P. Bisson, R. Ξ. Kunkee. 1999 Principles and practices of winemaking. Springer Science+Business Media Inc. pg 448

²Iland, P., Bruer, N., Edwards, G. Weeks, S. and Wilkes, E. 2004 Chemical analysis of grapes and wine: techniques and concepts. Patrick Hand Wine Promotions Pty Ltd. pp 55. Australian patent application 2002304976 in the name of Barokes Pty Ltd describes and claims a process for packaging wine in aluminium cans .

Claim 1 of the Barokes patent application defines a process of packaging wine in a two-piece aluminium can having an internal corrosion resistant coating. The claimed process comprises the steps of:

(a) preparing wine characterized in that the wine has less than 35 ppm of free SO₂, less than 300 ppm of chlorides and less than 800 ppm of sulfates;

(b) filling a two-piece aluminium can body with the wine; and

(c) sealing the can with an aluminium closure such that the pressure within the can is at least 25 psi.

The Barokes patent application describes that the above-mentioned maximum levels of free SO₂, chlorides, and sulfates are necessary in order to minimise corrosion of the packaged cans and minimize tainting of the packaged wine in aluminium containers .

It is well known, and the applicant has confirmed, that the reaction of free SO₂ with metal is the key reaction causing adverse reaction in packaging wine in metal containers . This is a redox reaction where SO₂ is reduced to hydrogen sulphide, which taints wine, and the metal is oxidized to metal ions in solution and thereby corrodes the container. This reaction is known to occur with aluminium and its alloys, steel and tin, which are the common metals used in the packaging. It is likely that the reaction occurs with other metals, but this has not been specifically investigated by the applicant.

Cans are commonly used to package a range of beverages . In recent years it has become common to coat the inside of beverage cans with an amine epoxy coating which is sprayed onto the interior of the can during can making. The particular coating used by the applicant is manufactured by Valspar Corporation and marketed under the trade mark Ecodex.

An alternative method of making cans is to coat the metallic plate used to make the cans with a polymer such as polyethylene terephthalate (PET) or other polyesters, and then form the metallic container from the coated metal plate, known as the Polymer Coated Steel (PCS) . No further polymer coating is applied during the can making process. It should be understood that the present invention is intended to cover metallic containers made from PCS as well as metallic containers coated during the can making process.

The applicant has found, surprisingly, that it is possible to package wine that has concentrations of any one of the constituents free SO2, chlorides, and sulfates that is above the above-mentioned maximum concentrations in metallic containers that have the above-mentioned amine apoxy coating on an internal surface of the containers without creating issues with respect to corrosion of the containers and tainting of wine in the containers.

More particularly, the applicant has found, surprisingly, that it is possible to package wine that has concentrations of free SO₂ in wine that are above the limits that are generally regarded as acceptable from the viewpoints of corrosion and wine tainting in metallic containers that have the above-mentioned particular coating.

The applicant has determined that the coating is an inhibitor of the AI/SO₂ reaction discussed above and thereby minimizes the reaction.

STATEMENT OF INVENTION

According to the present invention there is provided a process of packaging wine in a metallic container having an internal coating that inhibits reactions between the metal of the container and free SO₂ in the wine that result in container corrosion and wine tainting, which method includes the steps of:

(a) preparing wine that has a concentration of free SO₂ that is greater than 35 ppm;

(b) filling a metallic container, as described herein, with the wine; and

(c) sealing the metallic container such that the pressure within the container is at least a predetermined limit at a relevant temperature .

According to the present invention there is also provided a process of packaging wine in a metallic container having an internal coating that includes the steps of:

(a) preparing wine that has a concentration of free SO₂ that is greater than a limit that is generally regarded as acceptable from the viewpoints of container corrosion and wine tainting; (b) filling a metallic container, as described herein, with the wine;

(c) sealing the container such that the pressure within the container is at least a predetermined limit at a relevant temperature; and

(d) treating the wine after the container has been filled and sealed and reducing the concentration of free SO₂ to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and wine tainting.

The coating may be any suitable coating that inhibits and thereby minimises reactions between free SO₂ and the metal of the container that result in container corrosion and wine tainting.

By way of example, the coating is an amine epoxy coating, such as the coating manufactured by Valspar Corporation and marketed under the trade mark Ecodex.

The upper limit for free SO₂ that is generally regarded as acceptable from the viewpoints of container corrosion and wine tainting will vary from container to container and is a function of a number of factors including, by way of example, the metals from which the containers are formed and the compositions of the internal coatings .

In general terms, the upper limit for free SO₂ to avoid corrosion and tainting of the wine is thought to be around 50 ppm, more preferably 35 ppm_# for metallic containers, such as aluminium containers and steel containers. More specifically, Metal Box pic and others in the 1960's and 1970' s showed that steel cans did not corrode appreciably when containing wine having upper limits of free SO2 of between 25 and 50 ppm. In particular, as a consequence of this work, it was thought that 25 ppm is the upper limit for SO₂ for aluminium cans.

Preferably step (d) comprises treating the wine after the container has been filled and sealed and reducing the concentration of free SO₂ to be less than 35 ppm.

There are a number of options for treatment step (d).

Preferably treatment step (d) includes selecting the coating of the container so that it can absorb free SO₂ from the wine into the coating or can react with the wine to reduce the free SO₂ concentration to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and wine tainting.

Preferably the process further includes a step of gas flushing the container with an inert gas, such as nitrogen, after step (b) of filling the container.

A further embodiment of the invention is gas flushing the wine with a gas that contains an elevated oxygen content, or even pure oxygen to oxidize free SO to sulfate.

The pressure in the container can be any pressure sufficient to provide the mechanical stiffness required for the handling of the container in the supply chain. This pressure may be provided by the addition of liquid nitrogen in still wine, by the addition or retention CO₂ in sparkling wine, by a combination of the two gases, or by any other suitable means of providing mechanical pressure. The wine may be prepared in step (a) by any suitable process.

Preferably step (a) includes preparing wine that has at least 40 ppm free SO2.

More preferably step (a) includes preparing wine that has at least 45 ppm free SO2.

According to the present invention there is also provided a wine container that has been packaged in accordance with the above-described process.

EXAMPLES

The present invention is described further in the following Examples .

The importance of the use of the internal coating on metallic containers was confirmed in the following set of experiments.

In these experiments, the following standard conditions were used unless stated otherwise:

• 250 ml ¹SUm line' aluminium beverage cans, normally used for the packaging of soft drinks and having an internal coating manufactured by Valspar Corporation and marketed under the trade mark Ecodex.

• Manual filling to a nominal volume of around 250 ml (+/-) 10 itiLs, adjusted by eye.

• The temperature of filling was ambient. • Cans were pressurized with liquid nitrogen after filling the cans with wine and immediately prior to sealing the cans to an uncontrolled pressure thought to be between 5 and 30 psi for the purpose of providing mechanical stability to the can.

• Except for one specific trial that is discussed below, the air in the headspace of the cans was removed by undercover gassing (flowing an inert gas between can and end) immediately before sealing to remove the oxygen containing area. The purpose of undercover gassing is to remove the oxygen found in the air.

• The wine used was a SE Australian dry white wine blend (Tahbilk "Everyday drinking" Chairmans Dry White) .

• The free SO₂ in the wine was adjusted to 60 ppm +/- 10 ppm by a stock solution of sodium metasulphite prior to filling the cans with wine and measured by three independent laboratories experienced in the testing of wine for free SO₂ levels . • Wine was stored for up to 3 months at 30 degrees Celsius. This is an accelerated test pack in the sense that it is equivalent to storing the wine for 6 months at 24 degrees Celsius.

• Chemical analysis of SO₂ was done using the above described Aspiration method² test.

• The dissolved aluminium content in the wine during the experiments was measured using Inductively Coupled Plasma (ICP) analysis.

• The hydrogen sulphide content in the wine was measured using the following procedure - 5 ml of sample was incubated in a 20 ml headspace vial until an equilibrium was achieved in the headspace (optimal conditions for incubation time and temperature were determined experimentally) . A sample of the headspace gas was injected into a gas chromatography unit fitted with a pulsed flame photometric detector (PFPD) . The limit of detection was 2 μg/L and the system was calibrated to the 40 μg/L level. Samples which had higher levels of hydrogen sulfide than 40μg/L were diluted until results were within calibration range. It is thought that hydrogen sulphide can produce an unpleasant odour if dissolved at a concentration greater than 50 μg/L.

• 24 cans were packed in each experiment.

FIRST EXPERIMENT

In order to confirm the importance of the aluminium/SO₂ reaction, the wine was poured into aluminium cans that had the standard aluminium coating removed.

Less than 30 seconds after this pouring a strong odour described as 'rotten eggs' was detected. The smell of rotten eggs is a common descriptor of hydrogen sulphide .

The cans were sealed within one minute of pouring, and analyzed after 2 weeks, 1 month, 2 months and 3 months .

The results of the experiment are set out below in Table 1. The results in Table 1 showed:

• An increase in dissolved aluminium from 27 to 96 ppm during the three months of the experiment .

• A reduction in free SO₂ from 56 ppm down to 2.4 ppm during the first two weeks.

• A reduction in total SO₂ from 177 ppm down to 65 ppm during the first two weeks.

• Very high levels of hydrogen sulphide in the wine. In summary, the results indicate that there was corrosion of the aluminium, can as a result of SO₂ reaction and probably wine tainting as a result of the increase in H₂S concentration.

Table 1 - Results of chemical analysis on

Experiment 1 samples. SO₂ and hydrogen sulphide levels in the wine were not measured after two weeks and one month respectively as the strong smell of hydrogen sulphide suggested that the wine was commercially unacceptable.

SECOND EXPERIMENT

Wine was packaged into cans lined with a commercial amine epoxy coating applied in a standard commercial manner to minimize metal exposure.

Analysis of the hydrogen sulphide content showed levels below the odor threshold at the time of filling, and this was also seen when the cans were opened up to three months after filling. Odour threshold is typically 5 ppb², but this can range significantly between individuals.

The results of the experiment are set out below in Table 2. The results in Table 2 showed:

• No consistent change in dissolved aluminium content .

• Reduction in free SO₂ from 60 ppm down to 30 ppm during the three months of the experiment .

• No consistent change in total SO₂.

• An increase in hydrogen sulphide content from 2.5 to 28 μg/L during the first month of this experiment, after which it reduced to 11 μg/L by the third month.

A comparison of the results in Tables 1 and 2 indicates that the effect of the lining on the chemistry of the wine was dramatic in a very positive way.

Specifically, the results indicate that there was no corrosion and probably a very small increase in the risk of wine tainting. In adition, the decrease in SO₂ from 60 ppm down to 30 ppm indicates that there was some reaction occurring that reduced the concentration of SO₂. Thus, the results indicate that the coating formed a chemical and a physical barrier to SO₂ contacting the aluminium can.

Table 2 - Results of chemical analysis on Experiment 2 samples. Comparable results from the unlined cans (Experiment 1) are shown in brackets, with statistically significant differences noted with a * .

² Non-Dust Atmospheric Emissions From Minerals Processing, Environment Australia, Austrlaian Government Department of the Environment and Heritage,

<http://www.deh.gov.au/settlements/industry/minerals/booklets/atmosphe re/common . html> , at 25 October 2005.

THIRD EXPERIMENT

To investigate whether the protective ability of the coating was dependent on complete coverage of the aluminum surface of the cans, cans were scratched with a sharp implement exposing the metal surface. Each scratch was around 10 mm in length and the approximate width of the scratching implement. The area of the metal exposed by the scratch was deliberately chosen to be much greater than the level of metal exposure acceptable in quality testing in a beverage package.

Loss of coating is not normally measured directly in can production, but instead the current is measured when a given voltage is applied across the coating. If the current is higher than about 5 m&, there is a defect in the can. This test is extremely sensitive and can detect and reject cans with gaps in the coating smaller than the eye can see, or smaller than a pinhole. Hence, it will be apparent that the scratch made in the third experiment will be much greater than would passable in normal can production.

Analysis of the hydrogen sulphide content showed levels below the odour threshold at the time of filling, and this was also seen when the cans were opened up to three months after filling. Odour threshold is 5 ppb, but this can range significantly between individuals.

The results of the experiment are set out below in Table 3. The results in Table 3 show:

• There was no consistent change in dissolved aluminium content during the three months of the experiment.

• A reduction in free SO₂ from 60 ppm down to 42 ppm during the three months .

• No consistent change in total SO₂.

• An increase in hydrogen sulphide content from 2.5 to 31 μg/L during the first month of this experiment, after which it reduced to 11 μg/L by the third month.

These results are all very similar to the result of Experiment 2, with no consistent differences between the scratched and un-scratched cans having the coating. This suggests the coating does not merely act as a physical barrier between the aluminium can and the wine, but also by possibly directly reacting with the SO₂ in the wine, possibly absorbing or adsorbing with it. Chemical analysis of the coating is required to confirm this mechanism.

Table 3 - Results of chemical analysis on Experiment 3 samples. Comparable results from the unscratched cans (Experiment two) are shown in brackets, with statistically significant differences noted with a *

FOURTH EXPERIMENT

This experiment investigated the effect of gas flushing.

In particular, the applicant wished to investigate whether the oxygen in the standard environment would reduce the level of SO₂ in the canned wine.

An unlined can as per the First Experiment was used. No gas flushing was used. Hence there was a small amount of air left in the can's headspace. This led to a increase in the oxygen content of the headspace from 2.2% (flushed) to 15.6% (unflushed) .

The results of the experiment are set out below in Table 4. The results in Table 4 show:

• An increase in dissolved aluminium from 28 to 77 ppm over the three months of this experiment . These values were lower than those seen with the gas flushed cans, although these differences were not completely statistically different (however note that only three cans were tested in each experiment) .

• A reduction in free SO₂ from 60 ppm down to 2.4 ppm during the first two weeks of this experiment. After two weeks the SO₂ content of these cans was significantly lower than the SO₂ content of the gas flushed can.

• Reduction in total SO₂ from 177 ppm down to 65 ppm during the first two weeks. Again these values were significantly lower than for the gas flushed can.

• An increase in hydrogen sulphide content from 2.5 to 250 μg/L during the first month of this experiment, which was significantly lower than the SO₂ content of the gas flushed cans.

In summary, this experiment indicates that the following effects of gas flushing uncoated cans:

• Increase the dissolved aluminium in the wine.

• Accelerate the loss of free and total S0₂in the wine .

Increase the production of hydrogen sulphide in the wine .

The explanation for this is that SO₂ is both an oxidant and reductant. In the presence of oxygen, the SO₂ is oxidized to SO₄, thus removing the oxygen and reducing free SO₂. The reduction in free SO₂ due to reaction of SO₂ to form sulfate is the reason for the lower corrosion rate.

The effect of the oxygen in the headspaσe on the flavour of the wine was not tested in this experiment.

Table 4 - Results of chemical analysis on Experiment 4 samples. SO₂ and hydrogen sulphide levels in the wine were not measured after two weeks and one month respectively as it was apparent by then that the wine was commercially unacceptable. The comparable values for the gas flushed samples are given in brackets, with a * next to this value indicating a statistically significant difference (p=0.05).

Many modifications may be made to the invention described above without departing from the spirit and scope of the invention.

Claims

1. A process of packaging wine in a metallic container having an internal coating that inhibits reactions between the metal of the container and free SO₂ in the wine that result in container corrosion and wine tainting, which method includes the steps of:

(b) filling a metallic container, as described herein, with the wine; and b

(c) sealing the metallic container such that the pressure within the container is at least a predetermined limit at a relevant temperature.

2. A process of packaging wine in a metallic container having an internal coating that includes the steps of:

(a) preparing wine that has a concentration of free SO₂ that is greater than a limit that is generally regarded as acceptable from the viewpoints of container corrosion and wine tainting;

(b) filling a metallic container, as described herein, with the wine;

(d) treating the wine after the container has been filled and sealed and reducing the concentration of free SO2 to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and wine tainting.

3. The process defined in claim 2 comprises treating the wine after the container has been filled and sealed and reducing the concentration of free SO₂ to be less than 35 ppm.

4. The process defined in claim 2 or claim 3 wherein treatment step (d) includes selecting the coating of the container so that it can absorb free SO₂ from the wine into the coating or can react with the wine to reduce the free SO₂ concentration to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and wine tainting.

5. The process defined in any one of the preceding claims wherein the coating is an amine epoxy coating.

6. The process defined in any one of the preceding claims further includes a step of gas flushing the container with an inert gas, such as nitrogen, after step (b) of filling the container.

7. The process defined in claim 6 includes gas flushing the wine with a gas that contains oxygen content.

8. The process defined in claim 7 wherein the oxygen- containing gas is oxygen.

9. The process defined in any one of the preceding claims wherein step (c) includes sealing the metallic container such that the pressure within the container is sufficient to provide the mechanical stiffness required for handling of the container in a supply chain.

10. The process defined in any one of the preceding claims wherein step (a) includes preparing wine that has at least 40 ppm free SO₂.

11. The process defined in claim 10 wherein step (a) includes preparing wine that has at least 45 ppm free SO₂.

12. A wine container that has been packaged in accordance with the process defined in any one of the preceding claims.

13. The process defined in any of claims 1 to 4 where a polymer coated steel is used to form the wine container, without an additional polymer coating step during the can making process.