Wine in a can – rapid determination of a wine’s suitability for canning

Introduction

Screening and compatibility tests are important to confirm the suitability of a specific wine for packaging in aluminium cans.¹ Incompatibilities can lead to the formation of off-odours (hydrogen sulphide) due to the interaction between wine components and aluminium. Before a wine is canned for commercial sale, can providers usually conduct compatibility tests to evaluate pack performance and wine quality over time. This ensures that the final product meets the minimum quality requirements and that no negative interaction occurs between the packaging and its contents.

Usually, compatibility tests are conducted by storing packs for four months at 37°C. The elevated storage temperature accelerates the ageing process and enhances wine-packaging interactions (if any). If the wine quality and package integrity are acceptable after the storage period, then packaging for commercial sale can commence. This method of compatibility testing has its advantages; however, it is time-consuming and perhaps not practically possible to perform for every wine destined for canning.

A research group from Cornell University investigated and published a feasible method to determine the compatibility between a wine and a lined aluminium can in a test that can deliver results in as little as two weeks.² In this rapid compatibility test, wine is exposed to lined aluminium coupons for 14 days at an elevated temperature to evaluate possible metal-solution interactions. The use of coupons for corrosion testing is common in industrial settings as they allow convenient and reproducible evaluations. The coupons used for the rapid compatibility test are lined with the same coating to be used in the end product. After 14 days at 50°C, the hydrogen sulphide concentration in the wine is measured to determine if the liner has been breached and, therefore, if the wine and the liner are compatible.

Materials and methods

Aluminium coupons (1cm x 4.5 cm) (obtained from the packaging company) were cut from coated aluminium sheets using shears. The coating composition of the sheet must be the same as the coating composition of the intended packaging. The exposed and uncoated edges of the coupons were sealed with an inert ethyl vinyl acetate hot melt glue (B-2001 pellets; Surebonder) and allowed to air dry for about 30 seconds.

The coupons were placed in a clear glass crimp-top vial (30 mm x 60 mm, 27 mL headspace vial; Supelco). The vial was then purged with two to three drops of liquid nitrogen, after which 25 mL of wine was added. Vials were first lightly capped with 20 mm butyl rubber septa (10 to 15 seconds) to allow excess nitrogen to dissipate, preventing the vials’ cracking due to increased pressure. Vials were then sealed with a 20 mm crimp cap. Vials were stored at 50°C for 14 days, after which the hydrogen sulphide was measured using gas detection tubes.³

Results

Results showed that the concentration of hydrogen sulphide formed in the vials after 14 days at 50°C was a good predictor of the hydrogen sulphide formation in the same wine packaged and sealed in a can (with the same liner as the coupons) and stored upright in the dark for eight months at 20°C. This prediction was considered relatively accurate for epoxy-based liners (BPA and BPA NI) predominantly used for wine. Negligible hydrogen sulphide was formed in the control vials that contained no coupons.

Oxygen exclusion

A drawback of this method is the difficulty in managing oxygen exposure when working with small volumes of wine. The dissolution of oxygen in the wine during the test preparation can affect the results due to oxidative losses of the formed hydrogen sulphide.⁴ Therefore, avoiding oxygen exposure and ensuring the vial is adequately sealed is critical. The use of inert gas and liquid nitrogen can be used to protect the wine from oxygen exposure.

Conclusion

The development of a rapid method to predict the hydrogen sulphide formation during long-term storage of a canned wine provides a more convenient and feasible option to determine the compatibility between a wine and the intended aluminium packaging. The rapid method has significant time-saving advantages, while minimising material and operational costs by bypassing the canning procedure. It also minimises variations that can occur during filling and avoids sealing issues that may arise due to extended time spent at elevated temperatures. However, great care should be taken to prevent oxygen exposure when working with smaller volumes, as the dissolution of oxygen molecules during the preparation of the vials may affect the results.

Abstract

A rapid compatibility test has been developed as a useful tool to test the suitability of a wine for canning and long-term storage.

References

1. Coetzee, C., 2021. The Winemaker’s Guide to Wine in a Can, Winetech.
2. Montgomery, A., Allison, R.B., Goddard, J.M. & Sacks, G.L., 2023. Hydrogen sulfide formation in canned wines under long-term and accelerated conditions. American Journal of Enology and Viticulture 74(1), 0740011. https://doi.org/10.5344/ajev.2022.22051.
3. Allison, R.B., Montgomery, A. & Sacks, G.L., 2022. Analysis of free hydrogen sulfide in wines using gas detection tubes. Catalyst: Discovery into Practice 6(1): 1 – 8. https://doi.org/10.5344/catalyst.2021.21003.
4. Kreitman, G.Y., Elias, R.J., Jeffery, D.W. & Sacks, G.L., 2019. Loss and formation of malodorous volatile sulfhydryl compounds during wine storage. Critical Reviews in Food Science and Nutrition 59(11): 1728 – 1752. https://doi.org/10.1080/10408398.2018.1427043.

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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