Understanding and mitigating the development of reductive characters in canned wine
The project aims to develop a detailed understanding of the main drivers behind the formation of reductive characters in canned commercial wines and identify ways to mitigate the risk of their formation post-packaging. This will be delivered through a consortium-based trial that includes financial contributions from major wine producers, based both in Australia and in the USA. It is also supported by a Food Innovation Australia Ltd (FIAL) grant through the Enterprise Solution Centre Programme (ESCP), which provides funding for activities up to and including FY20-21.
The key elements of this trial will be:
- to trial the use of wine remediation methods and/or can modifications that can mitigate the risk of formation of reductive characters in canned wines post-packaging.
- to validate the performance of commercial wines in achieving extended shelf life.
Evaluating the impact of wine attributes on aluminium cans
Previous benchmarking studies showed that, unlike most other canned carbonated beverages, most commercially canned wines experience a significant increase in aluminium concentration after packaging. This can lead to the development of ‘reductive’ attributes in the wines, especially H2S (‘rotten egg’), in a relatively short timeframe (Figure 19).
The corrosion chemistry of aluminium dictates that elevated concentrations of SO2, copper and chloride can lead to pitting in the can surface and migration of aluminium into the wine. There is potential for this to be more significant across the surface of the can lid, as the application process for the protective barrier film (epoxy-based polymer) is different from that applied to the inner surface of the can body.
Understanding the development of ‘reductive’ compounds
In order to better understand the role of individual wine attributes in the development of H2S in canned wines, bench-scale experiments were set up using a commercially available wine with varying pH and varying concentrations of copper, aluminium, SO2 and oxygen. These experiments showed that:
- transition metals, such as copper, can speed up the formation of H2S in canned wines, especially in a low-oxygen concentration environment
- the presence of aluminium (metal) accelerates the formation of H2S, both with and without copper present
- the onset of H2S formation can be delayed if the copper concentration is significantly decreased, even when aluminium (metal) is present
- the impact of aluminium on H2S formation appears to be lower when pH is higher, oxygen concentration (total package oxygen) is higher and SO2 concentration is lower.
Assessing the effectiveness of strategies to decrease H2S formation
Poly-vinyl imidazole/poly-vinylpyrrolidone (PVI/PVP) co-polymers have been shown to be effective in scavenging copper species from wines and therefore decreasing the transfer of aluminium into wine after canning and the subsequent H2S generation. To date, this appears to be the most effective method for delaying the onset of H2S production in canned wines. A small-scale canning experiment demonstrated that the migration of aluminium into wine, and the resulting H2S formation, is faster when SO2 levels are elevated and when cans are stored with a greater surface area of the lid contacting the wine (inverted storage in Figure 20). The use of a commercial PVI/PVP product (Claril HM, Enartis Pacific) to remove copper from the wine prior to canning was effective in preventing the migration of aluminium into the wine. The data in Figure 20 were generated for a lightly carbonated (~2 g/L CO2) Chardonnay wine after three months in can. Samples were subjected to elevated temperature (35oC) to accelerate the reactions occurring in the wine. Half of the wine was treated with the PVI/PVP scavenging agent to remove copper prior to canning and half of the canned samples were stored inverted.
A commercial canning production run will be carried out to directly compare the performance of PVI/PVP-treated wines to untreated (control) wines. If this proves successful, it will be an important step towards eliminating negative attributes associated with canned wines and will help contribute to the ongoing success of this product category for Australian wine producers.