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.
Benchmarking of canned commercial wines
Samples of 16 commercial canned products were monitored over a five-month period for concentrations of aluminium, SO2 and volatile sulfur compounds (VSCs). Data were also collected on ullage (headspace) volumes and some of the products were subjected to oxygen transmission rate measurements, as well as imaging and elemental analysis, using scanning electron microscopy (SEM).
Results showed that most commercial canned wines experience a significant increase in aluminium concentration post-packaging (Figure 21) and many show elevated levels of VSCs (especially H2S) during storage (Figure 22). Sensory evaluation showed that several products exhibited ‘reductive’ attributes and were rated as faulty by the AWRI technical quality panel. Scanning electron microscopy images and subsequent x-ray analysis highlighted that there was direct contact between the aluminium body of cans and the wine inside, with evidence of pitting on the surface of the can interior.
Monitoring the development of ‘reductive’ compounds and assessing the impact of key wine characteristics
A series of benchtop experiments investigated the relative impacts of aluminium (metal) addition, pH increase, oxygen, SO2 and copper on H2S and methanethiol (MeSH) levels in a commercial wine at elevated temperature (35oC). This work showed that the impact of aluminium on H2S formation is lower with higher pH, higher oxygen concentration, decreased SO2 and lower copper concentration. Minimal effects of these characteristics were seen on MeSH concentration.
Assessing the effectiveness of mitigation strategies for decreasing metals content in wines
Initial attempts to mitigate the development of H2S in canned wines focused on the use of two commercially available cross-linked polymers (CLPs) to sequester copper and minimise the impact of any aluminium transfer during storage. Results to date show that these CLPs are effective in drastically decreasing copper levels in white and red wines. A more detailed investigation of the forms of copper removed during this process was carried out in conjunction with collaborators at the National Wine and Grape Industry Centre. This showed that these CLPs tend to remove sulfide-bound forms of copper, thereby decreasing the residual concentration of VSC precursor compounds in wines and delaying the onset or decreasing the subsequent concentrations of H2S.