AU2006230815A1 - Packaging wine in a metallic container with an internal coating - Google Patents

Description

WO 2006/105610 PCT/AU2006/000467 PACKAGING WINE IN A METALLIC CONTAINER WITH AN INTERNAL COATING. BACKGROUND 5 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 10 containers made from aluminum and steel, and includes, by way 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. 15 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 20 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. 25 The term "wine" is understood herein to include still wines, sparkling wines, fortified wines, and wines blended with mineral waters and fruit juices. 30 The present invention relates particularly to the impact of sulphur dioxide (SO 2 ) on packaging wine in metallic containers. Wine is produced by the yeast fermentation of the 35 juice of grapes and occasionally other fruits. As part of the control processes for the fermentation and handling of wine, S02 and/or analogues such as metabisulphite is often WO 2006/105610 PCT/AU2006/000467 -2 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 5 sulphite with peroxide, the binding of aldehydes and anthocyanin pigments and the delay of brown pigment development". In addition, SO 2 can also be advantageous at the time of packaging wine as a means of allowing winemakers to quickly stabilise wine so that it is 10 suitable for packaging. One accepted method for measuring SO2 found in wine is the so-called Aspiration method (Iland, 2004) which allows total S02 and free SO 2 to be determined. The 15 total SO 2 of any measured wine system is the sum of the free SO2 and the bound SO 2 . The first step of the Aspiration method is to remove free SO 2 by passing a stream of air through an acidified sample. Free SO 2 is collected in hydrogen peroxide/mixed indicator solution. The 20 indicator changes from green to purple when free S02 is collected, indicating sulfuric acid has formed from the reaction of hydrogen peroxide and S02. The sulfuric acid is back titrated with standardized sodium hydroxide to the end point (green color returns). The acidic sample is 25 then heated which releases the bound SO 2 which is subsequently collected and analysed in the previously described manner. Some types of wine are packaged under pressure, 30 with the pressure being caused either by the gases produced during the natural fermentation process or by gases added during packaging, especially carbon dioxide. Boulton, R. B., V. L. Singleton, L. F. Bisson, R. E. Kunkee. 1999 Principles and practices of winemaking. Springer Science+Business Media Inc. pg 448 2 1land, P., Bruer, N., Edwards, G. Weeks, S. and Wilkes, E. 2004 Chemical analysis of grapes and wine: techniques and concepts. Patrick Iland Wine Promotions Pty Ltd. pp 55.

WO 2006/105610 PCT/AU2006/000467 -3 Australian patent application 2002304976 in the name of Barokes Pty Ltd describes and claims a process for packaging wine in aluminium cans. 5 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: 10 (a) preparing wine characterized in that the wine has less than 35 ppm of free S02, less than 300 ppm of chlorides and less than 800 ppm of sulfates; 15 (b) filling a two-piece aluminium can body with the wine; and (c) sealing the can with an aluminium closure 20 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 S02, chlorides, and 25 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 30 confirmed, that the reaction of free SO 2 with metal is the key reaction causing adverse reaction in packaging wine in metal containers. This is a redox reaction where SO 2 is reduced to hydrogen sulphide, which taints wine, and the metal is oxidized to metal ions in solution and thereby 35 corrodes the container. This reaction is known to occur with aluminium and its alloys, steel and tin, which are the conmon metals used in the packaging. It is likely that WO 2006/105610 PCT/AU2006/000467 -4 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 5 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 10 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 15 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 20 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 25 one of the constituents free SO 2 , 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 30 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 SO 2 in wine that are above the 35 limits that are generally regarded as acceptable from the viewpoints of corrosion and wine tainting in metallic WO 2006/105610 PCT/AU2006/000467 -5 containers that have the above-mentioned particular coating. The applicant has determined that the coating is 5 an inhibitor of the Al/SO 2 reaction discussed above and thereby minimizes the reaction. STATEMENT OF INVENTION 10 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 SO 2 in the wine that result in container corrosion and wine 15 tainting, which method includes the steps of: (a) preparing wine that has a concentration of free SO 2 that is greater than 35 ppm; 20 (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 25 predetermined limit at a relevant temperature. According to the present invention there is also provided a process of packaging wine in a metallic 30 container having an internal coating that includes the steps of: (a) preparing wine that has a concentration of free S02 that is greater than a limit that 35 is generally regarded as acceptable from the viewpoints of container corrosion and wine tainting; WO 2006/105610 PCT/AU2006/000467 -6 (b) filling a metallic container, as described herein, with the wine; 5 (c) sealing the container such that the pressure within the container is at least a predetermined limit at a relevant temperature; and 10 (d) treating the wine after the container has been filled and sealed and reducing the concentration of free S02 to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and 15 wine tainting. The coating may be any suitable coating that inhibits and thereby minimises reactions between free S02 and the metal of the container that result in container 20 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. 25 The upper limit for free S02 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 30 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 SO 2 to 35 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 WO 2006/105610 PCT/AU2006/000467 -7 containers. More specifically, Metal Box plc 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 SO 2 of between 25 and 50 ppm. In 5 particular, as a consequence of this work, it was thought that 25 ppm is the upper limit for S02 for aluminium cans. Preferably step (d) comprises treating the wine after the container has been filled and sealed and 10 reducing the concentration of free S02 to be less than 35 ppm. There are a number of options for treatment step (d). 15 Preferably treatment step (d) includes selecting the coating of the container so that it can absorb free S02 from the wine into the coating or can react with the wine to reduce the free S02 concentration to be below the limit generally regarded as acceptable from the viewpoints of 20 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. 25 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. 30 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 35 nitrogen in still wine, by the addition or retention CO 2 in sparkling wine, by a combination of the two gases, or by any other suitable means of providing mechanical pressure.

WO 2006/105610 PCT/AU2006/000467 -8 The wine may be prepared in step (a) by any suitable process. 5 Preferably step (a) includes preparing wine that has at least 40 ppm free S02. More preferably step (a) includes preparing wine that has at least 45 ppm free SO2 10 According to the present invention there is also provided a wine container that has been packaged in accordance with the above-described process. 15 EXAMPLES The present invention is described further in the following Examples. 20 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 25 conditions were used unless stated otherwise: * 250 ml 'slim line' aluminium beverage cans, normally used for the packaging of soft drinks and having an internal coating manufactured by 30 Valspar Corporation and marketed under the trade mark Ecodex. * Manual filling to a nominal volume of around 250 ml (+/-) 10 mLs, adjusted by eye. * The temperature of filling was ambient. 35 * Cans were pressurized with liquid nitrogen after filling the cans with wine and immediately prior to sealing the cans to an uncontrolled pressure WO 2006/105610 PCT/AU2006/000467 -9 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 5 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 10 oxygen found in the air. e The wine used was a SE Australian dry white wine blend (Tahbilk "Everyday drinking" Chairmans Dry White). e The free S02 in the wine was adjusted to 60 ppm 15 +/- 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 SO 2 levels. 20 e 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. o Chemical analysis of SO 2 was done using the above 25 described Aspiration method 2 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 30 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). 35 A sample of the headspace gas was injected into a gas chromatography unit fitted with a pulsed flame photometric detector (PFPD). The limit of WO 2006/105610 PCT/AU2006/000467 - 10 detection was 2 pg/L and the system was calibrated to the 40 pg/L level. Samples which had higher levels of hydrogen sulfide than 40pg/L were diluted until results were within 5 calibration range. It is thought that hydrogen sulphide can produce an unpleasant odour if dissolved at a concentration greater than 50 pg/L. e 24 cans were packed in each experiment. 10 FIRST EXPERIMENT In order to confirm the importance of the aluminium/S02 reaction, the wine was poured into aluminium 15 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 20 sulphide. The cans were sealed within one minute of pouring, and analyzed after 2 weeks, 1 month, 2 months and 3 months. 25 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 30 to 96 ppm during the three months of the experiment. " A reduction in free S02 from 56 ppm down to 2.4 ppm during the first two weeks. " A reduction in total S02 from 177 ppm down 35 to 65 ppm during the first two weeks. " Very high levels of hydrogen sulphide in the wine.

WO 2006/105610 PCT/AU2006/000467 - 11 In sumary, the results indicate that there was corrosion of the aluminium can as a result of S02 reaction and probably wine tainting as a result of the increase in 5 H 2 S concentration. Table 1 - Results of chemical analysis on Experiment 1 samples. SO 2 and hydrogen sulphide levels in the wine were not measured after two weeks and one month 10 respectively as the strong smell of hydrogen sulphide suggested that the wine was commercially unacceptable. Initial 2 weeks 1 month 2 months 3 months Dissolved 27 86 97 92 96 aluminium, ppm Free S02, 56 2.4 ppm Total SO 2 , 177 65 ppm Hydrogen 2.5 100 350 Sulphide, pg/L pH 3.18 Headspace 2.6 oxygen, % I I III SECOND EXPERIMENT 15 Wine was packaged into cans lined with a commercial amine epoxy coating applied in a standard commercial manner to minimize metal exposure. 20 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 WO 2006/105610 PCT/AU2006/000467 - 12 three months after filling. Odour threshold is typically 5 ppb 2 , but this can range significantly between individuals. The results of the experiment are set out below 5 in Table 2. The results in Table 2 showed: e No consistent change in dissolved aluminium content. " Reduction in free SO 2 from 60 ppm down to 30 10 ppm during the three months of the experiment. * No consistent change in total S02. " An increase in hydrogen sulphide content from 2.5 to 28 pg/L during the first month 15 of this experiment, after which it reduced to 11 pg/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 20 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 SO 2 from 60 ppm down to 30 ppm indicates that there was some reaction 25 occurring that reduced the concentration of S02. Thus, the results indicate that the coating formed a chemical and a physical barrier to S02 contacting the aluminium can. Table 2 - Results of chemical analysis on 30 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.

WO 2006/105610 PCT/AU2006/000467 - 13 Initial 2 weeks 1 month 2 months 3 months Dissolved 1.2 1 1.5 1.9 1.1 Aluminium, (27)* (86)* (97)* (92)* (96)* ppm Free SO 2 , 60 52 38 43 30 ppm (56) (2.4)* Total S02, 183 179 164 171 157 ppm (177) (65)* Hydrogen 2.5 7 28 17 11 Sulphide, (100)* (350*) pg/L THIRD EXPERIMENT To investigate whether the protective ability of 5 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 10 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 15 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 mA, 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 20 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. 25 Analysis of the hydrogen sulphide content showed levels below the odour threshold at the time of filling, WO 2006/105610 PCT/AU2006/000467 - 14 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. 5 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 10 the experiment. " A reduction in free SO 2 from 60 ppm down to 42 ppm during the three months. * No consistent change in total SO 2 * An increase in hydrogen sulphide content 15 from 2.5 to 31 pg/L during the first month of this experiment, after which it reduced to 11 pg/L by the third month. These results are all very similar to the result 20 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 25 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 30 Experiment 3 samples. Comparable results from the unscratched cans (Experiment two) are shown in brackets, with statistically significant differences noted with a *. Initial 2 weeks 1 month 2 months 3 months Dissolved 1.2 1 1.3 1.8 1.3 Aluminium, (1.2) (1) (1.5) (1.9) (1.1)

PPMI

WO 2006/105610 PCT/AU2006/000467 - 15 Free SO 2 , 60 48 35 34 42 ppm (60) (52) (38) (43)* (30)* Total S02, 182 173 162 160 173 ppm (182) (179) (188.) (171) (157)* Hydrogen 2.5 3 31 19 11 Sulphide, (2.5) (7) (28) (17) (11) ptg/L IIII1 FOURTH EXPERIMENT This experiment investigated the effect of gas 5 flushing. In particular, the applicant wished to investigate whether the oxygen in the standard environment would reduce the level of S02 in the canned wine. 10 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% 15 (flushed) to 15.6% (unflushed). The results of the experiment are set out below in Table 4. The results in Table 4 show: 20 * 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 25 completely statistically different (however note that only three cans were tested in each experiment). * A reduction in free S02 from 60 ppm down to 2.4 ppm during the first two weeks of this 30 experiment. After two weeks the S02 content WO 2006/105610 PCT/AU2006/000467 - 16 of these cans was significantly lower than the SO 2 content of the gas flushed can. " Reduction in total S02 from 177 ppm down to 65 ppm during the first two weeks. Again 5 these values were significantly lower than for the gas flushed can. * An increase in hydrogen sulphide content from 2.5 to 250 pg/L during the first month of this experiment, which was significantly 10 lower than the S02 content of the gas flushed cans. In summary, this experiment indicates that the following effects of gas flushing uncoated cans: 15 * Increase the dissolved aluminium in the wine. * Accelerate the loss of free and total SO 2 in the wine. 20 Increase the production of hydrogen sulphide in the wine. The explanation for this is that S02 is both an 25 oxidant and reductant. In the presence of oxygen, the SO 2 is oxidized to SO 4 , thus removing the oxygen and reducing free S02. The reduction in free S02 due to reaction of S02 to form sulfate is the reason for the lower corrosion rate. 30 The effect of the oxygen in the headspace on the flavour of the wine was not tested in this experiment. Table 4 - Results of chemical analysis on 35 Experiment 4 samples. SO 2 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 WO 2006/105610 PCT/AU2006/000467 - 17 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 ). 5 Initial 2 weeks 1 month 2 months 3 months Dissolved 28 39 58 41 77 Aluminium, (27) (86)* (97) (92)* (96) ppm Free SO 2 , 17 4.8 ppm (56)* (2.4)* Total SO 2 , 118 90 ppm (177)* (65)* Hydrogen 2.5 -320 250 Sulphide, (2.5) (~100)* (350)* pjg/L Ph 3.18 (3.18) Headspace 15.6 oxygen, % (2.2)* Many modifications may be made to the invention described above without departing from the spirit and scope of the invention. 10

Claims (13)

1. A process of packaging wine in a metallic container 5 having an internal coating that inhibits reactions between the metal of the container and free S02 in the wine that result in container corrosion and wine tainting, which method includes the steps of: 10 (a) preparing wine that has a concentration of free S02 that is greater than 35 ppm; (b) filling a metallic container, as described herein, with the wine; and 15 b (c) sealing the metallic container such that the pressure within the container is at least a predetermined limit at a relevant temperature. 20

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 S02 that is greater than a limit that is 25 generally regarded as acceptable from the viewpoints of container corrosion and wine tainting; (b) filling a metallic container, as described 30 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 35 (d) treating the wine after the container has been filled and sealed and reducing the concentration WO 2006/105610 PCT/AU2006/000467 - 19 of free SO 2 to be below the limit generally regarded as acceptable from the viewpoints of container corrosion and wine tainting. 5

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 S02 to be less than 35 ppm. 10

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 S02 from the wine into the coating or can react with the wine to reduce the free S02 concentration to be below the limit generally regarded 15 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. 20

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. 25

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 30 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 35 sufficient to provide the mechanical stiffness required for handling of the container in a supply chain. WO 2006/105610 PCT/AU2006/000467 - 20

10. The process defined in any one of the preceding claims wherein step (a) includes preparing wine that has at least 40 ppm free SO 2 . 5

11. The process defined in claim 10 wherein step (a) includes preparing wine that has at least 45 ppm free SO 2 .

12. A wine container that has been packaged in accordance with the process defined in any one of the preceding 10 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 15 making process.